7 Rice Starch Diversity - Effects on Structural, Morphological, Thermal, And Physicochemical...

Rice Starch Diversity: Effects on Structural,Morphological, Thermal, and PhysicochemicalPropertiesA ReviewAli Abas Wani, Preeti Singh, Manzoor Ahmad Shah, Ute Schweiggert-Weisz, Khalid Gul, and Idrees Ahmed Wani

Abstract: Rice starch is one of the major cereal starches with novel functional properties. Significant progress hasbeen made in recent years on the characterization of rice starches separated from different rice cultivars. Studies haverevealed that the molecular structure and functional properties are affected by rice germplasm, isolation procedure,climate, agronomic conditions, and grain development. Morphological studies (microscopy and particle size analysis)have reflected significant differences among rice starch granule shapes (polyhedral, irregular) and in granule size (2 to7 m). Nonwaxy and long-grain rice starches show greater variation in granular size than the waxy starches. Rice starchgranules are smaller than other cereal starches with amylose contents varying from virtually amylose-free in waxy toabout 35% in nonwaxy and long-grain rice starches. Amylose content appears to be the major factor controlling almostall physicochemical properties of rice starch due to its influence on pasting, gelatinization, retrogradation, syneresis,and other functional properties. Waxy rice starches have high swelling and solubility parameters, and larger relativecrystallinity values than nonwaxy and long-grain starches. However, nonwaxy rice starches have a higher gelatinizationtemperature than the waxy and long-grain starches. The bland taste, nonallergenicity, and smooth, creamy, and spreadablecharacteristics of rice starch make it unique and valuable in food and pharmaceutical applications. This review providesrecent information on the variation in the molecular structure and functional properties of different rice starches.

IntroductionRice (Oryza sativa L.) is a major cereal crop and the staple

food source for half of the world population. Starch is the ma-jor component of rice and accounts for more than 80% of thetotal constituents. The global rice (paddy) production for theyear 2010 reached 609642285.84 metric tons (FAOSTAT 2012).Larger rice starch diversity than other cereal grains (maize andwheat) is important as it allows isolation of rice starch with dif-ferent functionalities (Vandeputte and Delcour 2004). Increase inrice production and demand for polished rice has significantly in-creased the amount of broken rice. Moreover, new rice cultivarsare continuously being released and the total number has exceededmore than 2000 cultivars around the world (Deepa and others2008). Diversity in rice cultivars in different regions of the worldis shown in Figure 1. Rice starch is reported as unique, with bland

MS 20120093 Submitted 1/17/2012, Accepted 4/20/2012. Authors Ali AbasWani, Shah, and Idrees Ahmed Wani are with Dept. of Food Technology, IslamicUniv. of Science and Technology, Awantipora, Jammu and Kashmir 192122, India.Authors Ali Abas Wani, Singh, and Schweiggert-Weisz are with Fraunhofer Inst. ofProcess Engineering and Packaging IVV, Freising 85354, Germany. Author Ali AbasWani and Singh are also with Chair of Food Packaging Technology, Technical Univ.of Munich, Freising, Weinstephan 85354, Germany. Author Gul is with Dept. ofFood Engineering and Technology, Sant Longowal Inst. of Engineering and Technology,Longowal, Punjab 148106, India. Direct inquiries to author Ali Abas Wani/PreetiSingh (E-mail: [email protected] or preeti [email protected])

taste, creamy, spreadable, and smooth in texture. These character-istics include hypoallergenicity, digestibility, consumer acceptance,bland flavor, small granules, white color, increased freeze thawstability of pastes, greater acid resistance, and a wide range of amy-lose:amylopectin ratios (Mitchell 2009; Lawal and others 2011).These unique properties have increased rice starch demand in thefood and pharmaceutical industries.Starch occurs naturally as discrete particles, called granules. Rice

starch granules are the smallest known to exist in cereal grains,with the size reported in the range of 2 to 7 m (Vandeputte andDelcour 2004). These granules have smooth surface but angularand polygonal shapes. Starch properties depend on the physicaland chemical characteristics such as mean granule size, granulesize distribution, amylose/amylopectin ratio, and mineral con-tent (Madsen and Christensen 1996; Wani and others 2010). Thecomplexity of starch biosynthesis results in natural variability inamylose and amylopectin molecules, which is reflected in the di-versity of granule morphology. The variation, notably in granularsize and shape is associated with various functional properties indifferent food systems and the possibility of relating granule mor-phology to manufacturing processes or nutritional qualities (Pe-terson and Fulcher 2001). The role of amylose and amylopectinin the gelatinization and pasting properties of rice starch has beenwidely studied (Noda and others 2003; Vandeputte and others2003a, 2003b; Li and others 2008a, 2008b; Wang and others2010).

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Rice starch diversity . . .

Figure 1Biodiversity of world rice production (adapted and modified from Zhao and others 2011).

Amylose is the major factor influencing the physicochemicalproperties of rice starch. Upon heating in aqueous solutions, starchswells irreversibly and its crystalline structure collapses, a phe-nomenon known as gelatinization. Starch swelling is a propertyof amylopectin, whereas amylose has been known to restrict it(Tester and Morrison 1990a). Gelatinization converts starch intoa physical form that is desirable in many food systems. Starch gelsare, however, thermodynamically unstable and undergo changesaffecting their technological suitability (Lapasin and Pricl 1995).Upon cooling, starch molecules reassociate in a complex recrys-tallization process known as retrogradation, which is often associ-ated with water separation from the gel (syneresis) (Yeh and Yeh1993; Hoover and Manuel 1995). These changes may result intextural and visual gel deterioration (Thomas and Atwell 1999;Fredriksson and others 2000). The pasting properties are used inassessing the suitability of starch as a functional ingredient in foodand other industrial products.The minor components in starch, which are either at the

surface or inside the starch granules, are lipids and proteins.Cereal starches contain about 1% lipids and 0.25% proteins(Baldwin 2001). Nonwaxy rice starches (12.2% to 28.6% amy-lose) contain 0.9% to 1.3% lipids comprised of 29% to 45%fatty acids and 48% phospholipids (Azudin and Morrison 1986).Waxy rice starches (1.0% to 2.3% amylose) contain negligibleamounts of lipids (Azudin and Morrison 1986). Starch proteinsare mostly either storage proteins or biosynthetic or degrada-tive enzymes (Baldwin 2001). Rice storage proteins exist mainlyas protein bodies (PB), such as PB I (mainly prolamin) orPB II (mainly glutelin) (Resurreccion and others 1993). Biosyn-thetic or degradative enzymes are most probably entrapped withinthe starch granules following starch synthesis (Denyer and oth-ers 1995). Besides lipids and proteins, phosphorus is an importantcomponent of rice starch and plays an important role in starchfunctional properties, such as paste clarity, viscosity, consistency,and paste stability. Phosphorus in starch is mainly present in 2forms, phosphate-monoesters and phospholipids. In nonwaxy ricestarch, phosphorus is primarily in the form of the phospholipids(0.013% dry basis of phosphate-monoesters and 0.048% for phos-pholipids), whereas in waxy rice starch, phosphorus is present asstarch phosphate-monoesters (0.003% for phosphate-monoestersand nondetectable for phospholipids) (Lim and others 1994; Janeand others 1996). Starch phosphate-monoesters in native starchesare primarily found in amylopectin, and only a trace is found in

amylose. About 80% to 90% phosphate-monoester in waxy ricestarch is on the C6 of glucose units (Jane and others 1996). Othermineral components of starch which occur in their ionic form,are calcium, potassium, magnesium, and sodium.

Rice Starch IsolationRice starch isolation is different from other starches because

of its unique protein composition. The isolation process consistsmainly of the separation of starch from protein, fiber, and lipid.Important considerations thereby are avoidance of amylolytic ormechanical damage to the starch granules, effective deproteiniza-tion of the starch, minimization of loss of small granules, andavoidance of starch gelatinization (Schulman and Kammiovirta1991). Rice starch isolation is also associated with the entrapmentof small granules in the protein and fine fiber sediments gener-ated during centrifugation (McDonald and others 1991; Schul-man and Kammiovirta 1991; Lim and others 1999; Anderssonand others 2001; Xie and Seib 2002). When these sediments arescraped off and discarded, which is common in laboratory purifi-cation methods and in some industrial processes, a severe loss ofsmall granules occurs (Szczodrak and Pomeranz 1991). To reducethe entrapment of small granules in the protein layer, researcherscan degrade the protein enzymatically, followed by separation ofthe peptides and starch using centrifugation (Radosavljevic andothers 1998; Wang and Wang 2001). These protein digestionmethods produce starches with higher or comparable yields andreduced starch damage. However, these processes require chro-matography to purify the protease and remove any amylase activity(Radosavljevic and others 1998). Enzymes like hemicellulase andxylanase have also been used to degrade the polysaccharides presentin the sediments entrapping the starch granules (Wilhelm and oth-ers 1998). Lawal and others (2011) reported starch yields of 70.0%to 73.77% for 5 newly released West African rice cultivars. Wideranges of variations in rice starch yield have been observed fromdifferent rice cultivars: 59% to 71.6% (Mohan and others 2005;Wang and Wang 2004).Rice protein consists of albumin (5%), globulin (12%), prolamin

(3%), and glutelin (80%), which dissolve in water, salt, ethanol, andalkali, respectively (Juliano 1985). These proteins are soluble in analkaline medium; therefore, alkaline steeping (using 0.2% to 0.5%NaOH, w/w) has been conventionally used for the isolation ofrice starch, with good recovery and low residual protein content(Landers and Hamaker 1994; Patindol and others 2003; Sasaki

418 Comprehensive Reviews in Food Science and Food Safety Vol. 11, 2012 c 2012 Institute of Food Technologists


Figure 2Morphology of rice starch as measured by scanning electron microscopy at 2000X (a: SKUAST-5) and at 6000X (SR-1).

and others 2009). It has been reported that the structure of thestarch granule can be damaged when the rice grains are steepedin 0.2 M aqueous ammonia solution (Chiou and others 2002).Furthermore, the use of alkali for steeping has been associatedwith effluent disposal problems. Environmental concerns and strictregulations have produced interest among food scientists to findalternate starch extraction procedures. A physical process, whichemploys high-pressure homogenization, was studied for recoveringrice starch and protein fractions by partial mechanical breaking ofthe starchprotein matrix (Guraya and James 2002). The residualprotein in the starch yield was 2.7%, which was greater than that ofan alkaline process. Increase in efficiency is preferred for rice starchisolation, while preserving the native structure of the rice starchgranules and limiting the waste products from the starch separationprocess. Alternatively the use of alkaline proteases for rice starchhas been studied by Lumdubwong and Seib (2000). However, thismethod has been associated with salt waste. The production of ricestarch by an enzymatic process has reduced the levels of mineralloads in effluents of rice starch plants (Puchongkavarin and others2005). Two food-grade enzyme preparations (an alkaline protease,Alcalase and a neutral protease, Protease N) were found to be moreeffective than other proteases for protein removal in the isolationof rice starch from wet-milled flour (Li and others 2008a, 2008b).Wang and Wang (2001) found that neutral protease was effectivein assisting rice starch isolation under neutral conditions. Thismethod was not associated with salt effluent, but the reactiontime was too long to achieve a high starch yield with low residualprotein content. In another study,Wang andWang (2004) reportedthat the use of high-intensity ultrasound, alone or combined withsurfactants (for example, sodium dodecyl sulfate), reduced not onlyrice starch isolation time but also was not associated with effluentdisposal problems. Further investigations are required to extractrice starch with improvements in the existing methods. Specificconcerns will be the minimization/recycling of water requiredduring the extraction process.

Starch MorphologyStarch occurs naturally as discrete particles, called granules

(Figure 2). Granule size and shape of starch are reported to be pri-marily affected by the germplasm from which the starch is isolated.The other factors affecting starch granule morphology include cli-matic conditions and agronomic practices. Generally, granule sizerefers to the average diameter of the starch granule. Granule sizecan be determined by various techniques like microscopy (lightmicroscopy, scanning electron microscopy [SEM]), sieving, elec-

trical resistance, laser light scattering, and field flow fractionation(Lindeboom and others 2004). However, SEM is frequently usedto determine granule size. It also provides a more detailed perspec-tive on granule surface characteristics and granule morphology(Chmelik 2001). Various studies, using x-ray photoelectron spec-troscopy and SEM have revealed that the starch granule surface ispredominantly (90% to 95%) carbohydrate in nature (Oostergetaland van Bruggen 1993; Calvert 1997).The granular structure of rice starches varies in shape and size

among different cultivars (Table 1). In rice, several polyhedral smallgranules are produced in 1 amyloplast. They form parts of com-pound granules. Scanning electron micrographs have shown thatstarch granules of all rice types are mainly polyhedral in shape.These granules may also be oval, irregular, angular, or smooth inshape. Rice starch granules are the smallest known to exist in ce-real grains, with a size in the range of 2 to 7 m (Vandeputte andDelcour 2004). The size of starch granules varies between non-waxy, waxy, and long-grain rice starches and it also varies fromcultivar to cultivar. Nonwaxy cultivars reportedly show greatervariation than the waxy cultivars. However, the starches extractedfrom long-grain rice cultivars show a wide range of granule size(2 to 7 m) (Hoover and others 1996). Light scattering studies ofstarch dispersions have shown that the size and density of an av-erage rice starch granule is 14 m and 1.530 g/cm3, respectively(Odeku and Itiola 2007). Starch granule size has been reportedto affect the composition, gelatinization, and pasting properties,enzyme susceptibility, crystallinity, swelling, and solubility. How-ever, several other factors, including amylose/amylopectin ratioand molecular weight and granule fine structure, are also influen-tial (Lindeboom and others 2004).

Starch StructureStarch granules are packed in the form of semicrystalline ar-

eas and amorphous regions in an alternating fashion (Figure 3)(Jenkins and Donald 1994). Treatment with -amylase demon-strates a ringed pattern analogous to tree growth rings (Hoseney1994). According to French (1984), the number and size of thegrowth rings depend on the botanical origin of the starch, andthe semicrystalline growth rings have a thickness in the rangeof 120 to 400 nm. Cameron and Donald (1992) suggested thatthe amorphous growth ring has the same thickness as that ofthe semicrystalline one. The growth rings are approximately 400nm apart in rice starch as measured by atomic force microscopy(Dang and Copeland 2003). Like other starches, rice starch is acopolymer of linear chain (amylose) and branched (amylopectin)

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Table 1Diversity in the morphological properties of rice starches.

Type/cultivar Shape Size (m) ReferenceNonwaxy

TNu67 Polyhedral 6.4 Li and Yeh 2001PR103, PR-106, PR113, Polyhedral, round 2.4 to 5.4 Sodhi and Singh 2003

PR-114, IR-8PR113, PR111, Basmati-370, Polyhedral, irregular 1.5 to 5.8 Singh and others 2006b

IET-16313, IR-64, PR103,IR08, Bas-386, RYT-2492

ZHONG9B Polyhedral, angular, oval 1.08 to 7.49 Yang and others 2006PUSA44, PR106, PR114 Polyhedral 3.11 to 7.78 Raina and others 2007Not specified Polyhedral, smooth 4.16 to 4.48 Zhang and others 2010Exiang No.1, Honglianyou No. 6, Liangyoupeijiu (Hunan), Angular, polygonal 3 to 8 Wang and others 2012

Zhongjian No 2, Liangyoupeijiu (Hubei), Heiyouzhan,98112jing, Tongjin611, Jiyujing, TianjinxiaozhanFARO 51, 52, 54, 32 NERICA Polyhedral with irregular shapes 1.5 to 6.1 Lawal and others 2011

WaxyNot specified Polyhedral, smooth 5.00 Zhang and others 2010TCW70 5 to 6 Lu and others 2008SMJ Polyhedral 5 to 6 Tatongjai and Lumdubwong 2010

Long-grain riceIR64 Polyhedral, angular 2 to 8 Hoover and others 1996

Figure 3Starch granular structure: (a) the whole granule, (b) the lamellae, and (c) the polymer chains. Adapted from Waigh and others (1996).

biopolymers. The other minor components in rice starch are lipidsand proteins, and calcium, potassium, magnesium, and sodium inthe ionic form (Vandeputte and Delcour 2004). Starch is classifiedas rapidly digestible starch (RDS), slowly digestible starch (SDS),or resistant starch (RS) (Zhu and others 2011). Variations in amy-lose and amylopectin ratio and molecular structure are reported tobe greatly affected by genetic, environmental, and agronomic con-ditions (Lawal and others 2011). These 2 principal componentsgreatly influence the functional properties of rice starches.

AmyloseAmylose, a linear polymer, is composed almost entirely of

-1,4-linked D-glucopyranosyl units; many amylose moleculeshave a few -1,6-linked D-glucopyranose branches, about 0.3%to 0.5% (Whistler and BeMiller 1997) and at times less than 0.1%(Ball and others 1996). The location of amylose in a starch gran-ule is still in dispute. Various possible locations have been listed:(1) amorphous lamellae, (2) amorphous growth ring, or (3) in-terspersed or cocrystallized with amylopectin molecules (Hooverand others 2010). Amylose is actually helical. The interior of thehelix contains hydrogen atoms and is therefore hydrophilic, allow-

ing amylose to form a type of clatherate (an inclusion complexwherein a host molecule entraps a 2nd molecular species as theguest) complex with free fatty acids, fatty acid components of glyc-erides, some alcohol, and iodine (Fennema 1985). It has an averagedegree of polymerization (DP) value of 800 to 4920, average chainlengths (CL) of 250 to 670, and -amylolysis limits of 73% to 95%(Morrison and Karkalas 1990). Rice starch amyloses have DP val-ues of 920 to 1110, CL of 250 to 370, and -amylolysis limitsof 73% to 84%. They are slightly branched with 2 to 5 chains onaverage (Takeda and others 1986). Takeda and others (1993) foundratios of branched to linear rice amylose molecules of 0.22:0.78 bymole and 0.32:0.68 by weight with DP values of 1180 and 740,respectively. The branched amylose molecule has been suggestedto have a structure intermediate between that of linear amyloseand amylopectin, frequently referred to as intermediate material(Takeda and others 1993).Amylose forms a complex with iodine, changing the color

of amylose to blue-black. This is the basis of commonly usedcolorimetric methods or determining the amylose content ina sample (Juliano and others 1981). Mahmood and others(2007) attribute the methods widespread use to its economic



advantage and greater throughput per day over other methodsavailable. The use of delicate reagents such as enzymes is alsonot required (Mahmood and others 2007). Yun and Mathe-son (1990), however, noted a major limitation of the colori-metric method, namely, relying on the color formation of thestarchiodine complex. The amylopectin portion of the starchalso produces a reddish-purple compound when complexed withiodine (BeMiller and Whistler 1996), which subjects the colormeasurements to uncertainties. Amylose standards obtained fromvarious sources may vary widely in terms of quality, the pres-ence of lipids that could interfere with the assay, and the pH ofthe final solution are other possible sources of error (Bhattacharya2009). Therefore, results from this method could either be loweror higher than the actual value (Singh and others 2003), and thevalue obtained should be termed apparent amylose or amy-lose equivalent (Bhattacharya 2009). Gibson and others (1997)developed a method that estimates the amount of the polysac-charide after precipitation with concanavalin-A (Con A), a lectinthat can selectively precipitate amylopectin from starch throughthe formation of a complex under defined conditions of pH, tem-perature, and ionic strength. Yun and Matheson (1990) refinedthis method by including an ethanol pretreatment of the starchsample to extract the lipids, which can also complex with amy-lose and interfere with colorimetric determinations. The amyloseis then either reacted using phenolsulfuric acid reagent or hy-drolyzed enzymatically. The use of phenolsulfuric acid reagent,however, could yield a higher amylose value, which may be dueto the presence of nonstarchy polysaccharide (Yun and Matheson1990). Megazyme Intl. Ireland Ltd. (Co. Wicklow, Ireland) hasdeveloped an amylose/amylopectin assay which is based primarilyon the method of Yun and Matheson (1990), but utilized only theenzymatic hydrolysis.The amylose content of starch has been reported to vary with

the botanical source of the starch and is affected by the climatic andsoil conditions during grain development (Morrison and others1984; Yano and others 1985). The variation in the amylose contentamong different rice cultivars is reported in Table 2. Typical levelsof amylose in starches are 15% to 25% (Manners 1979). However,waxy starches are reported to be virtually amylose-free. On thebasis of amylose content, rice starch may be classified as waxy(0% to 2% amylose), very low (5% to 12% amylose), low (12% to20% amylose), intermediate (20% to 25% amylose), or high (25%to 33% amylose) starch (Juliano and others 1981; Yu and others2012). Wang and others (2010) isolated starches from 10 differentnonwaxy rice cultivars and reported amylose content in the range18.1% to 31.6%. The amylose content of waxy rice starches rangedfrom 0.1% to 3.25% (Zuo and others 2009; Chang and others2010) and varied among different waxy rice cultivars. The amylosecontent of long-grain rice starches ranged from 17.0% to 35.7%(Puchongkavarin and others 2005; Patindol and others 2007).The differences in amylose content might be related to cultivar

differences, growing zone and environment. The compositionsof starches can be different, even when all the samples are fromthe same rice cultivar. Peisong and others (2004) reported thatthe amylose content was in the range of 13.2% to 26.5% for non-waxy rice starches. The difference might be caused by the differentgrowing zones and cultivars. On the contrary, rice mutants withhigh levels of amylose are known to have amylose content in arange of 35% to 40% (Juliano 1992). Morrison and others (1993)reported that in determining amylose contents, the existence ofboth lipid-complexed amylose (LAM) and free amylose (FAM)(major fraction) must be taken into account. LAM may be present

in the native starch (Morrison and others 1993), but is possiblyalso formed during hydrothermal treatment or gelatinization of thestarch (Biliaderis and others 1986). Amylose content appears to bethe major factor controlling almost all physicochemical proper-ties of rice starch such as turbidity, syneresis, freezethaw stability,pasting, gelatinization, and retrogradation properties (Wickramas-inghe and Noda 2008). Varavinit and others (2003) reported apositive correlation of gelatinization with amylose content. Theeffect of amylose on the rheological property of rice starch pastehas been investigated by Lii and others (1996). They explainedthat the amount of leach-out amylose was one of the major factorsinfluencing the rheological properties of starch during heating.

AmylopectinAmylopectin, consisting of -1,4-linked D-glucopyranosyl

chains, is highly branched (5% to 6%) with -1,6-bonds (Buleonand others 1998). It has a DP of 4700 to 12800, CL values of17 to 24, and -amylolysis limits of 55% to 60% (Morrison andKarkalas 1990). Individual chains may vary between 10 and 100glucose units (Manners 1979). Rice starch amylopectins have aDP of 8200 to 12800, CL of 19 to 23, -amylolysis limits be-tween 49% and 59% (Takeda and others 1987; Wang and others2010), average external chain lengths (ECL) of 11.3 to 15.8, andaverage internal chain lengths (ICL) of 3.2 to 5.7 (Lu and others1997). Waxy japonica rice starches have the lowest CL (17 to 19)(Morrison and Karkalas 1990). Takeda and others (2003) reportedthat the DP of amylopectins from starches of different botanicalorigins is in the range of 9600 to 15900. Moreover, they revealedthe presence of large (DP 13400 to 26500), medium (DP 4400 to8400), and small (DP 700 to 1200) species.Both semicrystalline and amorphous growth rings are subdi-

vided into large (20 to 500 nm in dia) and small (25 nm in dia)spherical blocklets, respectively (Gallant and others 1997). Thus,1 blocklet in a semicrystalline growth ring contains several amor-phous and crystalline lamellae. On average, 2 end-to-end blockletswould constitute a single semicrystalline growth ring. Accordingto Dang and Copeland (2003), cross-striations occur within thegrowth rings of rice starch which correspond to the blocklets ofamorphous and crystalline lamellae. These blocklets have an aver-age size of 100 nm in dia and are proposed to contain 280 amy-lopectin side chain clusters. Each semicrystalline growth ring (120to 400 nm thick) is composed of repeats of alternating amorphous(2 to 5 nm thick) and crystalline (5 to 6 nm thick) lamellae (French1984; Cameron and Donald 1992). Independent of the botanicalorigin of the starch, repeat distances of amorphous and crystallinelamellae are about 9 nm (Oostergetel and van Bruggen 1989;Jenkins and others 1993). Amorphous lamellae contain branchpoints of the amylopectin side chains and possibly some amylose,whereas semicrystalline lamellae are constituted of amylopectindouble helices. Amorphous growth rings contain amylose andprobably less ordered amylopectin (Morrison 1995).Amylopectin molecules are highly branched, of high molecular

weight and constitute the skeleton of the starch granule (Kossmannand Lloyd 2000). Peat and others (1956) defined the basic structureof amylopectin in terms of linear A, B, and C chains. A chains(outer chains) are attached through their potential reducing end toB chains. The latter are linked in the same way and carry one ormore A chains. The C chain contains the single reducing groupof the amylopectin molecule and carries other chains. Based onthe A-, B-, C-chain terminology of Peat and others (1956) andHizukuri (1986) the cluster model has been refined. Amylopectinhas a polymodal distribution with A (CL 12 to 16) and B chains,



Table 2Diversity in physicochemical properties of starches separated from different rice cultivars.

Type/cultivar Amylose (%) Swelling power (%) Solubility (%) Syneresis (%) ReferenceNonwaxy

PR103, PR-106, PR113,PR-114, IR-8

7.83 to 18.86 26.06 to 33.20 0.287 to 0.360 0.04 to 2.41 (48 hrs) Sodhi and Singh 2003

PR113, PR111,Basmati-370,IET-16313,IR-64, PR103, IR08,Bas-386, RYT-2492

4.10 to 16.40 17.2 to 38.8 0.00 to 1.81 (24 hrs) Singh and others 2006b

PUSA44, PR106, PR114 5.80 to 12.55 12.95 to 15.82 7.25 to 8.25 Raina and others 2006PR113, PR103, PR115,

Basmati370,Basmati386,IR64

9.7 to 28.3 Singh and others 2007b

Not specified 11.9 15.5 3.9 Techawipharat and others2008

AT405, AT306,BG450,Batapola wee, MartinSamba, Bandara, BataMawee, Heenati662

16.0 to 34.6 7.33 to 16.12 Wickramasinghe and Noda2008

Xing indica 24 28.5 Lin and others 2009Exiang No. 1, Honglianyou

No. 6, Heiyouzhan,98112jing, Jiyjing,Tianjinxiazhan

18.1 to 31.6 16.3 to 30.2 17.0 to 40.0 22.9 to 46.4 (22 hrs) Wang and others 2010

PUSA1121 19.2 18.3 10.8 Sandhu and others 2010SM, DH, TML 16.99 to 38.62 12.11 to 15.98 6.28 to 7.06 Yu and others 2012

WaxyCalmochi 101 0.80 Li and others 2008aNot specified 0.92 26.9 14.9 Techawipharat and others

2008Koganemochi,

Hakuchomochi,Kantomochi

1.1 to 1.7 Sasaki and others 2009

Not specified 3.25 Zuo and others 2009SMJ 2.07 Tatongjai and Lumdubwong

2010TKW1 0.10 0.6 to 8.5 Chang and others 2010RD6 2.08 Noosuk and others 2003SN2 1.50 13.08 69.16 Yu and others 2012Not specified 2.0 Shih and others 2007W4109, W4111 0.5 to 1.0 Iturriaga and others 2004Calmochi 101 1.0 Park and others 2007b

IR29, Malagkit S,RD4, Tapol

1.2 to 2.4 Nakamura and others 2006

Long-grainCocodrie, L205 17.6 to 20.8 Li and others 2008a, 2008bNot specified 35.7 Puchongkavarin and others

2005Not specified 20.0 Shih and others 2007Cocodrie, L205 17.1 to 19.9 Park and others 2007bBolivar, Cheniere, Dixiebelle,

L205, Wells17.0 to 21.6 Patindol and others 2007

Lebonnet 17.9 2.0 (2 wk) Matalanis and others 2009Doongara 27.0 Zhou and others 2007

namely B1 (CL 20 to 24), B2 (CL 42 to 48), B3 (CL 69 to 75), andB4 (CL 104 to 140) chains. A and B1 chains form a single cluster,whereas B2, B3 and, B4 chains extend into 2, 3, and more than 4clusters. Hanashiro and others (2002) suggested that C chains arevery similar among botanical sources and range in size from 10to 130 glucose units, with the majority being around 40 glucoseunits (Hanashiro and others 2002). The following compositionwas proposed for waxy rice amylopectin: A (CL 13), B1 (CL22), B2 (CL 42), B3 (CL 69), and B4 (CL 101) (Hizukuri 1986).Enevoldsen and Juliano (1988) reported waxy and nonwaxy (lowamylose) rice amylopectin to have similar molar ratios of A to Bchains (1.1 to 1.5).

Molecular WeightUnderstanding the relationship of starch functionality to its fun-

damental molecular properties, such as weight-averaged molecu-lar weight and structure, has long been a goal of food scientists.

The characteristics of foods containing starch are understood to belargely by the mass ratio of amylose:amylopectin and the molecularweight of amylose (Yoo and Jane 2002; El-Khayat and others 2003;Varavinit and others 2003). The pasting peak viscosity (PV) andbreakdown viscosity of rice and wheat starch were negatively cor-related with amylose content (El-Khayat and others 2003; Varavinitand others 2003). Long-chain-length branches of amylopectin andintermediate-size branches of amylose produced the greatest syn-ergistic effect on pasting viscosity of reconstituted starch (Jane andChen 1992). The role of amylopectin size in starch functionalityhas been difficult to determine because of its tendency to forminsoluble aggregates. A key part of the picture of starch function-ality includes sound data on the associated molecular structureof all starch polymers. The fundamental starting point is knowl-edge of the molecular weight and size of amylose and amylopectinstarch molecules. The molecular weight of polymers is commonlydetermined by size exclusion chromatography (SEC). However,



this measurement for starch is challenging because calibrationstandards are usually necessary. In recent years, high-performance(HP) SEC instrumentation equipped with both MALLS(multi-angle laser light scattering) instrumentation and differen-tial refractometer (refractive index, RI) has been used routinelyto determine the molecular weight of polymers without the useof standards. This technique makes starch molecular weight mea-surement possible (Aberle and others 1994; Bello-Perez and others1996). This system has been used to measure average molar massmolecular weight (Ong and others 1994; Yoo and Jane 2002),amylose molecular weight (Radosta and others 2001; Roger andothers 2001), and amylopectin molecular weight (Bello-Perez andothers 1998; Yoo and Jane 2002). But to obtain the accuratemolecular weight of amylopectin or amylose by this technique,the complete dissolution of amylopectin and amylose is necessary.Dissolving starch is a minimum requirement for the separation andmolecular weight determination of amylopectin and amylose byHPSEC. Soluble but entangled amylose and amylopectin will leadto molecular weight values higher than their true values. The lim-ited solubility of starch in neutral aqueous solutionmakes structuralanalysis of starch in aqueous media difficult (Han and Lim 2004).High temperatures and high pH increase the solubility of manycereal starches in aqueous solvents, but may result in molecular sizereduction resulting from degradation, depolymerization, or oxi-dation (Yokoyama and others 1998). Dimethyl sulfoxide (DMSO)is the most frequently used polar aprotic solvent for SEC analysis(Jackson 1991).According to Zhong and others (2006), the SEC analysis of

nonwaxy rice starches should have only 2 peaks, one for amy-lopectin and the other for amylose. But there was only 1 peakfollowed by an unresolved shoulder in the SEC profiles of ricestarch. The poor result could possibly be due to the branched struc-ture of amylopectin. Therefore, starch was physically fractionatedinto amylose and amylopectin and molecular weight of both thepolymers was determined separately by HPSEC-MALLS (Zhongand others 2006) and SEC-MALLS (Park and others 2007a). Themolecular weights of amylopectin and amylose determined byHPSEC equipped with MALLS and RI detectors showed molec-ular weights of amylopectin and amylose were 1.48 109 and3.85 105, respectively (Bao and others 2004). Zhong and others(2006) reported the molecular weight of amylopectins and amy-loses in the range (4.0 to 5.5) 107 and (3.1 to 3.4) 106,respectively, from different rice cultivars. According to Park andothers (2007a), the averagemolecular weight values of amylopectinwere 1.10 108 (long grain), 1.81 108 (short/medium grain),and 2.47 108 (waxy grain); and for amylose were 3.90 105(long grain) and 3.73 105 for starches extracted from short-/medium-grain rice cultivars. Park and others (2007a) comparedthe molecular weight of the starches and those of the fractionatedcomponents, the molecular weights of amylopectin and amylosemixtures, and they observed that the molecular weights of thestarches measured by HPSEC-MALLS were lower than the calcu-lated values corresponding to the amylopectin/amylose fractions.

X-Ray Diffraction StudiesStarch structure is described in terms of amorphous and

semicrystalline growth rings (Figure 4). The amorphous re-gion contains mainly amylose and less ordered amylopectin(Morrison 1995). Every semicrystalline region is composed ofrepeats of alternating amorphous and crystalline lamellae, whichconsist of branch points of amylopectin side chains and amy-lopectin double helices, respectively (French 1984). The amount

of crystallinity within starch granules can be determined by differ-ent techniques, but x-ray diffraction is most widely used to studystarch structure. The parallel chains occasionally have crystallinearrangements in the local regions of submicroscopic size that makesx-ray diffraction a suitable approach to study starch (Dunder andothers 2009). Wide-angle x-ray scattering and small-angle x-rayscattering are used in parallel to reveal the complex ultra-structureof the granule and quantification of crystallinity and polymorphicforms or crystalline laminates, respectively (Tester 1997).As mentioned earlier, starch crystallinity is primarily determined

with a wide-angled x-ray diffractometer. X-ray determinations ofcrystallinity include determinations of absolute and relativecrystallinity. The former differentiates between the amorphousand crystalline components (integrated area) of the x-ray diffrac-togram. The latter relies on calculating the proportion of crys-tallinity within starch granules, using as references materials with0% and 100% crystallinity. The 0% reference, representing fullyamorphous material (such as freeze-dried gelatinized material),and the 100% reference usually generated by extensive acid hy-drolysis of starch in which all the amorphous (but not crystalline)material has been eroded (Tester and others 2004). Starches canbe designated as A, B, and C type on the basis of x-ray diffrac-tion patterns. The differences between A-type and B-type starchesarise from water content and the manner in which these pairs arepacked in the crystals (Imberty and others 1991). The lattice ofB-type starch has a large void in which numerous water moleculescan be accommodated. This void is not present in A-type starch.Rice starch (cereal starch) exhibits the A-type pattern.Native rice starches (waxy and normal) displayed A-type diffrac-

tion patterns to Vandeputte and others (2003a). The x-ray diffrac-tograms of native nonwaxy rice starches showed typical A-typediffraction patterns with strong reflection at 15 and 23, andthe degree of crystallinity of the rice starch was 21.69% (Mohanand others 2005). The x-ray diffraction patterns of rice (japon-ica) starch also showed an A-type x-ray diffraction pattern with acrystallinity of 36.1% (Bao and others 2004). Waxy rice starcheshad larger relative crystallinity values than normal starches. Ab-solute and free amylose contents are reported to be negativelycorrelated with relative crystallinity. Crystallinity was also influ-enced by amylopectin CL distribution. According to Iturriagaand others (2004), the x-ray diffraction spectra of starch fromthe 7 rice cultivars studied showed an A-type pattern typical ofcereal starches. The relative crystallinity in waxy genotypes wasfound to be higher (48%) than that corresponding to the non-waxy ones (37% to 40%). It is widely accepted that the amy-lopectin is the predominant crystalline component in granules,with the short-branched chains forming local organizations com-patible with cluster models (Imberty and others 1991). However,no significant differences in crystallinity were found among thenonwaxy varieties with different amylose:amylopectin ratios. Ongand Blanshard (1995) reported similar relative crystallinities fordifferent nonwaxy rice starch varieties. The extent of crystallinityseemed to be closely related with the gelatinization temperatures(Yang and others 2006). The spectrum of rice starch shows defi-nite diffraction peaks that presumably reflect the crystalline regionin the starch. The A-type rice starch with characteristic diffractionpeaks at 14.0, 16.9, 17.6, and 22.9 is most susceptible to enzy-matic hydrolysis (Han and others 2007; Martinez and others 2007).According to Singh and others (2007a, 2007b), x-ray diffractionsof rice starches from various nonwaxy rice cultivars showed thetypical A-pattern. These rice starches showed strong reflectionsat 2 = 15.1, 17.2, 18.1, and 23.2. An additional peak at



Figure 4The range of elastic neutron scattering techniques, corresponding size range, and complementary methods shown in relation to thehierarchical structure of starch (adapted from Lopez-Rubio and Gilbert 2009).

2 = 20.0 was observed for Basmati-386, which was attributedto amyloselipid complexes by Zobel and others (1988). Higherpeak intensities indicate greater crystallinity, while the weakest x-ray patterns, as well as the lowest peak intensities, indicate lowgranule crystallinity. Yu and others (2012) reported that x-raydiffractions of rice starches showed typical A-pattern and strongreflections at 2 = 15, 17.5 (nonwaxy), and 23.16 (waxy).Amylose does not appear to have any significant effect on crys-

tallinity in normal and waxy starches (which may be virtually freeof amylose), both of which display strong birefringence (Morrisonand Karkalas 1990; Zobel 1992; Kent and Evers 1994; Hoover2001; Tester and Karkalas 2002). Singh and others (2007a, 2007b)attributed the differences in crystallinity in different rice starchesto differences in proportions of amylose, short side-chain and longside-chain amylopectin. Tester and others 2000 reported that inhigh-amylose starches, the amylose may contribute significantly tothe crystallinity. The exact nature of the crystalline polymorphsmay be different (Matveev and others 2001). However, in the caseof amylopectin-rich starches it is understood that the origin ofcrystallinity is due to the intertwining of the outer chains of amy-lopectin (exterior or external chains, representing A and B1 types)in the form of double helices. These associate together to formordered regions or crystalline lamellae. Adjacent double helicesgive rise to regular 3-dimensional geometrical patterns. Such anarray of atoms, molecules, or groups of molecules, according to therules of crystallography, will interact with electromagnetic wavesof short wavelength (x-rays) to give a characteristic diffractionpattern (Tester and others 2004).

Starch GelatinisationGelatinization, an endothermic process, results in the disrup-

tion of molecular order within the starch granules. Double he-lical and crystalline structures are disrupted in starches duringgelatinization. Increase in temperature causes the crystallites tobreak apart, and then to undergo hydration resulting in severalchanges such as granular swelling, native crystalline melting, loss ofbirefringence, and starch solubilization (Atwell and others 1988).Gelatinization, or molecular disordering, is not a simple granular

order-to-disorder transition; it is more complex. Understandingof the gelatinization mechanism has evolved simulatneously withthe knowledge of granular structure (Blazek and Gilbert 2011).Gelatinization is a 2-step process, first starch granules swell dueto breakage of hydrogen bonds in the amorphous portions of thestarch. In the next event, water acts as a plasticizer, which results inhydration and swelling of the amorphous regions. Slade and Levine(1988) reported that for gelatinization to occur, the amorphousregions of starch must first melt or undergo glass transition. Last,polymer molecules, particularly those of amylose, leach out of thegranules resulting in increased viscosity (Biliaderis 1991; Eerlingenand Delcour 1995; BeMiller 2007). Gelatinization is an importantfunctional property of starches that varies with respect to theircomposition (such as amylose-to-amylopectin ratio, phosphorus,lipids, proteins, and enzymes), the molecular structure of amy-lopectin (unit CL, extent of branching, molecular weight) granulearchitecture (crystalline-to-amorphous ratio), granule morphol-ogy, and granule size distribution (Tester 1997; Hoover and others2010).Although several analytical methods exist, differential scan-

ning calorimetry (DSC) has emerged as the preffered methodof choice for the measurement of starch gelatinization (Nakazawaand others 1984; Shiotsubo and Takahashi 1984; Wickramasingheand Noda 2008; Acquistucci and others 2009; Wani and oth-ers 2010). The other methods include x-ray diffraction (IAnsonand others 1988; Zobel and others 1988), nuclear magnetic res-onance (NMR) (Chinachoti and others 1991) and use of therapid visco-analyzer. Thermal properties typically reported usingDSC include gelatinization onset (To), peak (Tp), and conclu-sion (T c) temperatures, peak hight index (PHI), gentinizationrange (R), and enthalpy (Hg). It measures 1st-order (melting)and 2nd-order (glass transition) transition temperatures and heatflow changes in polymeric materials and gives information onorderdisorder phenomena of starch granules (Biliaderis and oth-ers 1986). In the DSC curve of starch at intermediate water levels,3 endothermic transitions are usually observed. The first 2 en-dotherms correspond to the disorganization of starch crystallites(Biliaderis and others 1986), or gelatinization, wherein glass



transitions of water-plasticized amorphous portions and thennonequilibrium melting of the microcrystallites of the partiallycrystalline amylopectin occur (Slade and others 1996). The 3rdendotherm, which occurs at higher temperature, relates to themelting of complexes formed by amylose and native lipids (Bili-aderis and others 1986). Crystallite quality and the overall crys-tallinity of the starch are measured by the peak temperature (Tp)and the enthalpy of gelatinization (Hg), respectively (Tester andMorrison 1990a). Onset temperature (To) and conclusion tem-perature (T c) determine the boundaries of the different phases ina semicrystalline material like starch (Biliaderis and others 1986).Noda and others (1996) postulated that DSC parameters (To,

Tp, T c, and Hg) are influenced by the molecular architectureof the crystalline region of starch, which corresponds to the dis-tribution of short-chain amylopectin (DP 6 to 11) and not bythe proportion of the crystalline region which corresponds to theamylose content. Cooke and Gidley (1992) have shown that theHg values of gelatinization primarily reflect more the loss ofdouble helices than the loss of crystallinity. However, Tester andMorrison (1990a) postulated that Hg reflects the overall crys-tallinity (quantity and amount of starch crystallites) of amylopectin.Tester (1997) suggested that the extent of the crystalline perfectionis reflected in the gelatinization temperature. Starch reportedly ex-hibits lower To, Tp, and T c, but higher Hg, compared to theflour prepared from the sample (Teo and others 2000; Wang andothers 2002). This reportedly is due to the heat-moisture treatmentduring starch preparation.DSC results of starches separated from different rice cultivars

are summarized in Table 3. The transition temperatures (To,Tp, and T c), enthalpies of gelatinization (Hg), temperaturerange (T ) among different rice cultivars varies significantly re-sulting in different physicochemical properties of these starches.For nonwaxy rice starches the values of To range from 53.3 C(Wang and others 2010) to 75.9 C (Wickramasinghe and Noda2008); Tp from 61.8 C (Wang and others 2010) to 80.0 C(Wickramasinghe and Noda 2008); T c from 70.9 C to 85.4 C(Wang and others 2010); Hg from 3.7 J/g (Singh and others2007a, 2007b) to 19.2 J/g (Vandeputtee and others 2003a); andT from 7.43 C (Sodhi and Singh 2003) to 21.1 C (Wang andothers 2010). In the case of waxy rice starches the values of Torange from 5.5 C (Lin and others 2008) to 63.0 C (Lin 2007);Tp from 1.6 C (Lin and others 2008) to 75.8 C (Sasaki andothers 2009); T c from 4.9 C (Lin and others 2008) to 88.3 C(Sasaki and others 2009); Hg from 3.4 J/g (Lin and others 2008)to 16.7 J/g (Sasaki and others 2009); and T from 1.6 C (Linand others 2008) to 24.0 C (Li and others 2009). For long-grainrice starches the values of To range from 50.9 C (Shih and others2007) to 77.0 C (Patindol and others 2007); Tp from 62.3 C(Shih and others 2007) to 80.8 C (Patindol and others 2007); T cfrom 72.1 C (Li and others 2009) to 89.6 C (Puchongkavarinand others 2005); Hg from 10.3 J/g (Zhou and others 2007)to 14.4 J/g (Patindol and others 2007); and T from 8.7 C(Li and others 2008a) to 21.6 C (Puchongkavarin and others2005). Vandeputte and others (2003a) reported that waxy ricestarches have lower Tp values than normal rice starches. Amy-lose content (absolute and free amylose content) did not affectthe transition temperatures of waxy rice starches. Higher levels oflong amylopectin chains delay gelatinization, whereas short amy-lopectin chains (DP 6 to 9) facilitate it (Vandeputte and others(2003a). The differences in To, Tp, T c, and Hg in starchesfrom different rice cultivars may be attributed to differences inamylose content, granular structure, molecular weight, and amy-

lose/amylopectin ratio (Chung and others 2011). The variationin To, Tp, T c, Hg, and T in starches from different culti-vars might be due to differences in amounts of longer chains inamylopectins. These longer chains require a higher temperatureto dissociate completely than that required for shorter double he-lices (Yamin and others 1999). Raina and others (2007) reportedthat a small variation in amylose contents has no significant effecton thermal properties as compared to the higher amylose con-tent. According to Singh and others (2007a, 2007b), Basmati-386exhibited 2 endotherms during heating, one for melting of crys-tallites and the other for melting of amylose-lipid complexes. Thecomplexes have been reported to be present in some native cerealstarches (Morrison and others 1993) and more are formed dur-ing heating (LeBail and others 1999). Double-helical and crys-talline structures are disrupted in starches during gelatinization.This orderdisorder phase transition is due to the melting of crys-tals, which has been illustrated by DSC endotherms in the rangeof 60 to 85 C for various native starches (Jacobs and others 1995).The variation in To, Hg, and T in starches from differentcultivars might be due to differences in proportion of amylose,fraction I, long sidechains, and short sidechains of amylopectin.Noda and others (1998) postulated that gelatinization temperatureis influenced by the molecular structure of the crystalline regionwhich corresponds to the distribution of amylopectin short chains(DP6 to 11). The variation in gelatinization temperatures mightbe due to differences in the amounts of longer chains in amy-lopectin. These longer chains require a higher temperature todissociate completely than that required for shorter double helices(Yamin and others 1999). The high To values of Liangyoupeijiu(Hubei) and Liangyoupeijiu (Hunan) starch suggests the presenceof crystallites of varying stability within the crystalline domains oftheir granules (Hoover and others 1997). Thermal properties arecontrolled in part by the molecular structure of amylopectin (unitCL, extent of branching, molecular weight, interaction and/or su-permolecular interaction of molecular chains, and polydispersity),starch composition (amylose content), and granule architecture(crystalline to amorphous content) (Tester 1997; Bao and others2004).

RetrogradationRetrogradation causes starch gels to become less soluble dur-

ing cooling due to recrystallization of starch molecules (BeMillerand Whistler 1996). It is basically a crystallization process aris-ing from a strong tendency for hydrogen bond formation betweenhydroxyl groups on adjacent starch molecules. In simple terms, ret-rogradation of gelatinized starch materials involves formation andsubsequent aggregation of double helices of amylose and amy-lopectin chains, thus governing elasticity, firmness, and texturalstaling of all starch-containing systems (Atwell and others 1988).The changes leading to retrogradation restrict starch functionalproperties making starch less desirable for various food products.Several factors have different responsible roles for starch ret-

rogradation. Amylose content plays a significant role. Amy-lose retrogradation occurs on cooling and very short-term-aging(Biliaderis and Zawistowiski 1990). As described, the retrograda-tion depends on the amylose content in the sample, the amountthat is free and uncomplexed with lipids, and its molecular weightdistribution. Amylose content bestows critical influences on theelastic property of freshly retrograded starch dispersions (Lii andothers 1996) and on hardness of freshly cooked rice (Champagneand others 1999). Retrogradation due to amylose is favored atlower starch concentration (Orford and others 1987) and results



Table 3Diversity in thermal properties of starches separated from different rice cultivars.

Type/cultivar To (C) Tp (C) Tc (C) Hg (J/g) R ReferenceNonwaxy

TNu67 57.7 65.1 11.5 Li and Yeh 2001IR42, IR48, IR24, IR5,

IR2071, Thaibonnet,Puntal, PSBRc18, Pelde,Century Patna231

56.6 to 75.6 62.8 to 78.5 71.0 to 83.3 7.7 to 19.2 16.8 to 19.8 Vandeputtee and others2003a

PR103, PR-106, PR113,PR-114, IR-8

66.0 to 67.3 69.74 to 71.94 74.08 to 78.04 8.16 to 11.80 7.43 to 10.78 Sodhi and Singh 2003

Not specified 73.45 77.77 83.52 15.07 10.07 Thirathumthavorn andCharoenrein 2005

PR113, PR111,Basmati-370,

IET-16313,IR-64, PR103, IR08,Bas-386, RYT-2492

61.1 to 74.47 66.6 to 79.21 71.93 to 84.49 8.09 to 13.81 7.85 to 10.89 Singh and others 2006b

PUSA44, PR106, PR114 65.17 to 68.92 70.15 to 71.84 73.66 to 76.86 13.24 to 14.98 Raina and others 2007PR113, PR103, PR115,

Basmati370,Basmati386,

IR64

60.8 to 71.8 65.7 to 75.9 72.2 to 82.4 3.7 to 5.1 8.2 to 9.8 Singh and others 2007b

Not specified 71.64 76.38 83.50 11.74 11.86 Deetae and others 2008AT405, AT306, BG450,

Batapola wee, MartinSamba, Bandara, BataMawee, Heenati662

64.1 to 75.9 69.4 to 80.0 12.0 to 17.3 Wickramasinghe and Noda2008

Basmati, Pachchaperumal,Selenio, Perla, Baldo,

Roma,Arborio

57.8 to 71.5 66.61 to 79.20 11.03 to 17.04 Acquistucci and others 2009

Not specified 72.3 76.4 80.2 12.5 7.9 Banchathanakij andSuphantharika 2009

Exiang No. 1, HonglianyouNo. 6, Heiyouzhan,98112jing, Jiyjing,Tianjinxiazhan

53.3 to 71.0 61.8 to 76.0 70.9 to 85.4 7.2 to 11.8 9.2 to 21.1 Wang and others 2010

Arborio, Calrose, Glutinous 58.5 to 60.0 68.2 to 68.9 79.4 to 80.5 13.1 to 15.4 19.4 to 22.0 Chung and others 2011Waxy

Thai glutinous I, Thaiglutinous II,

Sanpathong,Black rice, IR65

57.9 to 59.6 65.2 to 65.8 75.5 to 75.8 16.3 to 17.7 18.4 to 19.6 Vandeputtee and others2003a

Not specified 58.9 67.1 15.7 Jacquier and others 2006TCW70 63.0 70.7 82.5 14.5 19.5 Chang and Lin 2007TCW70 5.5 1.6 4.9 3.4 -1.6 Lin and others 2008Koganemochi,

Hakuchomochi,Kantomochi

41.6 to 61.6 56.9 to 75.8 76.7 to 88.3 12.6 to 16.7 Sasaki and others 2009

SMJ 61.58 67.72 74.26 16.53 Tatongjai and Lumdubwong2010

RD6 62.68 69.00 75.21 13.95 Noosuk and others 2003CM 101 56.2 63.5 80.2 13.2 24.0 Li and others 2009Not specified 59.9 66.6 84.1 10.1 Shih and others 2007Calmochi 101 56.25 62.6 83.95 12.8 Park and others 2007b

Long-grainLebonnet 70.0 74.7 81.1 13.7 11.1 Matalanis and others 2009Doongara 71.3 76.6 80.6 10.3 9.3 Zhou and others 2007RL-100 66.6 73.1 12.4 Wang and Wang 2004Not specified 68.0 79.3 89.6 13.2 21.6 Puchongkavarin and others

2005Cocodrie 63.4 67.2 72.1 11.7 8.7 Li and others 2009Not specified 50.9 62.3 76.8 10.4 Shih and others 2007Cocodrie, L205 61.8 to 67.7 67.9 to 71.9 75.4 to 83.4 10.9 to 13.7 Park and others 2007bBolivar, Cheniere,

Dixiebelle, L205, Wells73.4 to 77.0 78.0 to 80.8 83.1 to 86.1 13.3 to 14.4 Patindol and others 2007

Long grain 67.8 74.3 84.7 13.5 16.9 Chung and others 2011

To = Onset gelatinization temperature; Tp = Peak onset gelatinization temperature; Tc = conclusion gelatinization temperature; Hg = gelatinization enthalpy; R = gelatinization temperature range.

in a material very resistant to enzymatic hydrolysis. On the otherhand, amylopectin retrogradation occurs slowly during aging andrequires several weeks or months of storage for equilibrium (Bil-iaderis and Zawistowiski, 1990; Lai and others 2000), and thedegree of retrogradation depends on the CL distribution of amy-lopectin (Philpot and others 2006). Amylopectin tends to haveadditional effects on the extent of retrogradation of starches (Yaunand others 1993) or on the hardness of short-term staled cooked

rice through the proportion of extra long and long B chains(Ramesh and others 1999; Lai and others 2001). Recrystalliza-tion and retrogradation of amylopectin are dominant at a higherconcentration of solids (Orford and others 1987) and the polymerformed is more loosely bound than retrograded amylose (Englystand others 1992) and, hence, is highly susceptible to amylolysis.The retrogradation properties can be measured by DSC

(Qi and others 2003; Vandeputte and others 2003b; Lawal and



others 2011; Chung and others 2011), rheological properties,(Vandeputte and others 2003b), and NMR (Yao and others 2003;Qi and others 2003). Methods to study retrogradation of starchhave been reviewed by Karim and others (2000). Recrystallizationof amylopectin branched chains has been reported to occur in a lessordered manner in stored starch gels than in native starches. Thisexplains the occurrence of amylopectin retrogradation endothermsat a temperature range below that for gelatinization (Ward and oth-ers 1994). Enthalpy of retrogradation (HR) for starches separatedfrom different rice cultivars ranged from 2.61 to 3.71 J/g. Thedifferences in the HR among the various rice starches suggestdifferences in tendencies toward retrogradation. The retrograda-tion (percent) ranged from 61.9% to 86.6% (Lawal and others2011) The differences in H r of different starches may be dueto differences in amylose-amylopectin ratios, granular structures,and phosphate esters (Hizukuri and others 1983; Kasemsuwan andothers 1995; Hizukuri 1996). The amylopectin and intermediatematerials play a significant role in starch retrogradation during re-frigerated storage. The intermediate materials with longer chainsthan amylopectin may also form longer double helices during reas-sociation under refrigerated storage conditions (Yamin and others1999).

Pasting/Rheological PropertiesHeating of starch continuously in excess of water with stirring

causes the granules to swell and burst due to breakage of the nativestarch structure. Then the amylose leaches out and the granulesdisintegrate resulting in the formation of a viscous material calledpaste (BeMiller 2007). Pasting occurs after or simultaneously withgelatinization. Pasting properties of starch are important indicatorsof how the starch will behave during processing and, starch is gen-erally regarded as the most important constituent of rice in termsof cooking quality and functionality. The pasting properties ofstarch are used in determining the suitability of starch in differentfoods and other allied products. The most important pasting char-acteristic of granular starch dispersion is its viscosity. High pasteviscosity suggests suitability as a thickening agent in foods and as afinishing agent in the textile and paper industries.The pasting characteristics of starch are determined either us-

ing a Brabender Visco Amylograph or a Rapid Visco Analyzer(RVA) (Wickramasinghe and Noda 2008; Tukomane and Var-avinit 2008; Lin and others 2009). Rotational rheometers (Parkand others 2007b; Li and others 2008a, 2008b) or other viscome-ters, which record the viscosity continuously with respect to tem-perature changes, are also used to measure the pasting properties.RVA is used to determine pasting properties, namely PV, final vis-cosity, setback viscosity, breakdown viscosity, pasting temperature,and peak time. Figure 5 shows a typical pasting curve with pastingparameters as measured by RVA/Visco Amylograph. In the RVAtest, starch is mixed with water and allowed to rapidly hydrateon heating, held constant for a specific time, and then cooled tomeasure the pasting properties of the starch. As heating contin-ues, an increase in viscosity can be observed by swelling of starchgranules, which reflects the process of pasting. The temperatureat the onset of viscosity increase is termed pasting temperature.Viscosity increases with continued heating until the rate of gran-ule swelling equals the rate of granule collapse, which is referredto as the peak viscosity (PV). PV reflects the swelling extent orwater-binding capacity of starch and often correlates with finalproduct quality since the swollen and collapsed granules relate tothe texture of cooked starch. Once PV is achieved, a drop in vis-cosity, or breakdown, is observed as a result of disintegration of

Figure 5Typical starch pasting curve showing pasting parametersmeasured with Rapid Visco Analyzer or Visco amylograph.

granules. Breakdown is a measure of the ease of disrupting swollenstarch granules and suggests the degree of stability during cooking(Adebowale and Lawal 2003). Minimum viscosity, also called hotpaste viscosity, holding strength, or trough, marks the end of theholding stage at the maximum temperature of the RVA test. Thecooling stage begins and viscosity again rises (setback) which iscaused by retrogradation of starch, particularly amylose. Setback isan indicator of final product texture and is linked to syneresis orweeping during freezethaw cycles. Viscosity normally stabilizesat a final viscosity or cold paste viscosity, which is related to thecapacity of starch to form a viscous paste or gel after cooking andcooling (Newport Scientific 1998). Other components naturallypresent in the starchy material or additives interact with starchand influence pasting behavior (Newport Scientific 1998). Thepresence of proteins with disulfide linkages has been reported toconfer shear strength and gelatinized paste rigidity to rice starch(Hamaker and Griffin 1993; Xie and others 2008).Pasting parameters of rice starches are summarized in Table 4.

The pasting temperature for nonwaxy rice starches ranges from63.80 C (Raina and others 2007) to 95.10 C (Banchathanakijand Suphantharika 2009); PV from 45.8 RVU (Banchathanakijand Suphantharika 2009) to 5512.0 RVU (Raina and others2007); breakdown viscosity from 3.3 RVU (Banchathanakij andSuphantharika 2009) to 3187.0 RVU (Raina and others 2007);final viscosity from 55.9 RVU (Banchathanakij and Suphantharika2009) to 454.8 RVU (Lin and others 2009); and setback viscosityfrom 55.6 (Lin and others 2009) to 4999.0 RVU (Raina and oth-ers 2007). For waxy rice starch pasting temperature ranges from69.0 C (Lu and others 2008) to 69.1 C (Techawipharat and oth-ers 2008); PV from 76.0 RVU (Park and others 2007b) to 471.2RVU (Noosuk and others 2003); breakdown viscosity from 25.5RVU (Park and others 2007b) to 228.2 RVU (Noosuk and oth-ers 2003); final viscosity from 79.5 RVU (Park and others 2007b)to 182.5 RVU (Lu and others 2008); and setback viscosity from14.1 RVU (Techawipharat and others 2008) to 30.0 RVU (Noosukand others 2003). For long-grain rice starch PV ranges from 42.0RVU (Park and others 2007b) to 369.0 RVU (Wang and Wang2004); breakdown viscosity from 9.5RVU (Park and others 2007b)to 145.02 RVU (Wang and Wang 2004); final viscosity from 60.0RVU (Li and others 2008a, 2008b; Park and others 2007b) to



Table 4Diversity in pasting properties of starches separated from different rice cultivars.

Pasting Peak Breakdown Final SetbackType/cultivar temperature (C) viscosity (RVU) viscosity (RVU) viscosity (RVU) viscosity (RVU) ReferenceNonwaxy

PR113, PR111,Basmati-370,IET-16313,IR-64, PR103, IR08,Bas-386, RYT-2492

71.55 to 79.90 83.6 to 201.0 124.6 to 277.2 56.2 to 146.8 Singh and others 2006b

PUSA44, PR106, PR114 63.80 to 67.05 4994 to 5512 2918 to 3187 4128 to 4999 Raina and others 2007AT405, AT306, BG450,

Batapola wee, MartinSamba, Bandara, BataMawee, Heenati662

73.5 to 84.0 218 to 458 146 to 380 177 to 433 99 to 285 Wickramasinghe and Noda2008

Not specified 67.0 243.0 94.4 169.3 20.7 Techawipharat and others2008

Not specified 95.1 45.8 3.3 55.9 12.5 Banchathanakij andSuphantharika 2009

Xing indica 24 82.3 510.4 347.2 454.8 55.6 Lin and others 2009Arborio, Calrose, Glutinous 64.4 to 70.8 454 to 543.7 214.1 to 328.56 255 to 365.5 39.8 to 154.1 Chung and others 2011FARO 51, 52, 54, 32,

NERICA85.6 to 87.2 147.6 to 209.2 23.8 to 65.7 182.7 to 273.5 58.8 to 122.4 Lawal and others 2011

WaxyNot specified 69.1 141.4 66.0 89.5 14.1 Techawipharat and others

2008Calmochi 101 86.0 34.0 80.0 27.0 Li and others 2008aRD6 471.2 228.2 30.0 Noosuk and others 2003Calmochi 101 76.0 25.5 79.5 29.0 Park and others 2007bTCW70 69.0 70.92 182.5 16.67 Lu and others 2008

Long-grainCocodrie, L205 48.0 to 72.0 18.0 to 25.0 60.0 to 109.0 30.0 to 61.0 Li and others 2008aRL-100 369.0 145.0 304.0 80.0 Wang and Wang 2004Cocodrie, L205 42.0 to 64.0 9.0 to 14.0 60.0 to 103.0 30.0 to 54.0 Park and others 2007bDoongara 153.0 93.8 128.7 24.4 Zhou and others 2007Long grain 76.6 319.3 151.9 389.4 221.9 Chung and others 2011

RVU = rapid visco unit.

304.0 RVU (Wang and Wang 2004); and setback viscosity from30.0 RVU (Li and others 2008a, 2008b; Park and others 2007b)to 80.0 RVU (Wang and Wang 2004).The increase in viscosity with temperature may be attributed

to removal of water from the exuded amylose by the granulesas they swell (Ghiasi and others 1982). Final viscosity increasesupon cooling, which may be due to the aggregation of the amy-lose molecules (Miles and others 1985a,1985b). Setback value isthe recovery of viscosity during cooling the heated starch suspen-sion. High setback of starches may be due to the amount andthe molecular weight of the amylose leached from the granulesand the remnants of the gelatinized starch (Loh 1992). Pastingproperties of starch have been reported to be affected by amy-lose and lipid contents and by branch chainlength distribution ofamylopectin. The small variation in the amylose contents had nosignificant effect on pasting (Raina and others 2007). Han andHamaker (2000) observed that almost all amylose in the granuleis leached out at the level of PV. Thus, the influence of amyloseon the breakdown would be very low, even though the PV couldbe affected by both amylose and amylopectin (Han and Hamaker2001). Amylopectin contributes to swelling of starch granules andpasting, while amylose and lipids inhibit the swelling (Tester andMorrison 1990a). Also, the amylopectin chainlength and amylosemolecular size produce synergistic effects on the viscosity of starchpastes (Jane and Chen 1992).The other major techniques to measure starch rheology in-

clude rotational viscometers (viscosity) to modern stress-controlledrheometers (dynamic properties). The rheological measurementsfor rice starch include flow behavior, viscoelastic properties, me-chanical properties, recovery measurements, gel strength, gelatin-isation kinetics, and so on (Ahmed and others 2008; Lawal andothers 2011). The most frequently measured flow behavior in-

dex of rice starch dispersions in steady flow can be carried outduring gelatinization or on a gelatinized paste. Power law andHerschellBulkely models are frequently used to describe the flowbehavior of rice starches. These models give information on theflow behavior index (n) and the consistency coefficient (K) andYeild stress ( o) of starch suspensions. The values of n, K , and o are dependent on starch type, starch concentration, and tem-perature. The gelatinized starch pastes preheated to temperaturesof about 90 C are generally reported to exhibit shear-thinning(pseudoplastic) behavior with values of n considerably less than1.0. Lawal and others (2011) reported the shear thinning behav-ior of 5 different rice starches from West Africa. Differences inthe shear thinning behavior could be observed between differentrice starches. Amylose content was reported be the responsiblefactor for variation in the viscosity values. Other studies have re-vealed that the flow behavior is affected by temperature, starchconcentration, density, amylose CL, extraction conditions, gran-ule size, and so on (Karim and others 2008; Ahmed and others2008).Small amplitude oscillatory shear measurements have been used

for soft materials to elucidate their structural insight. Wang andothers 2010 reported that during earlier stages of heating rice starchsuspensions increases the storage modulus (G) while storage mod-ulus (G) was relatively slow. These values reached a maximumand then decreased with further heating. The initial increase in Ghas been attributed to the starch granule swelling and the forma-tion of a 3-dimensional gel network (Hsu and others 2000; Wangand others 2010). Singh and others (2011) reported that the ini-tial rise in the moduli for different rice starches separated Indianrice cultivars were in the range of 66.75 to 81.07 C. The de-crease in the values of storage and loss moduli (Gmax and Gmax)may be attributed to starch gel breakdown due to disentaglement



of the amylopectin molecules in the swollen particles. Wang andothers (2010) reported that the differences in dynamic propertiesof 10 rice starches are due to variation in amylose contents, va-riety, the branch CL, and distribution of amylopectin. Lawal andothers (2011) performed oscillatory shear tests of rice starches andreported that they have weak elastic behavior. Such behavior hasbeen classified as Type III by different researchers (Hyun and oth-ers 2002; Sim and others 2003). Type III behavior is exhibitedby disperse systems and weak polymeric gels where polymeric in-terchain association posses several constraints to incipient flow ofthe relevant structural units. The rheological data are increasinglybeing used to correlate the rheological properties with the molec-ular structure and the thermal properties of different starches. Therheological data provide information on the processing of starchinto different food products and starch based laminates and films.

Physicochemical Properties of Rice StarchPhysicochemical characteristics of rice starches largely depend

on the rice cultivar, environment, and agronomic and extrac-tion conditions. The physicochemical characteristics of differentrice starches are shown in Table 2. Most of the thermophysicalproperties are dictated by the amylose content. In turn, amylosecontent varies with growth and environment conditions of thestarch source.Studies have shown that there are significant changes in the

structural and thermophysical properties of various starches whensubjected to annealing. There is structural change within theamorphous and crystalline domains of starch granules (Tester andothers 2000; Lan and others 2008). The changes in amorphousand crystalline domains, in turn, influence granular swelling, amy-lose leaching, pasting properties, gelatinization, and susceptibilitytoward enzymes and acid. The changes to physicochemical prop-erties of normal, waxy, and high-amylose starches on annealing areinfluenced by changes to amylose conformation (helix to coil), en-hanced interaction between starch chains, increase in crystallineperfection, decrease in the proportion of small B-type granules,and by the native starch structure (crystalline defects, amylose con-centration, amylopectin CL, distribution degree of association be-tween starch chains within the amorphous, and crystalline domainsof the granule) (Lan and others 2008).Zhu and others (2011) investigated that there was a positive

corelation between amylose content and resistant starch (RS). Theportion of starch that is not digested in the small intestines is RS.Less of the starch is converted to glucose when RS is ingested.This has a potential impact on diabetes and energy intake, providesfermentable carbohydrates to colon bacteria, there is productionof short-chain fatty acids also that have direct health benefits tothe colon and also play other physiological roles (Bird and oth-ers 2009). With an increasing level of amylose, RS content alsoincreases, except for low-amylose rice (Zhu and others 2011).

Light Transmittance (Percent)Light transmittance provides the information on the behavior

of starch paste when the light passes through it (Sandhu and others2007). Higher light transmittance implies a more transparent paste.The light transmittance of starch paste is a function of the amountof swollen starch granules in the paste, which refract light (Singhand others 2006a, 2006b). Singh and others (2006a, 2006b) re-ported light transmittance by measuring the transmittance of starchpastes (1%) from different indica rice cultivars. Measurements car-ried out every 24 h by transmittance at 640 nm against a waterblank showed decrease in light transmittance during storage from

0 h (3.0% to 5.8%) of 1.6% to 4.2% after 144 h. The presenceof phospholipids produces opaque starch pastes and solutions withlow light transmittances (Jane and others 1996). The difference inthe light transmittance values may be due to the variation in theamount of swollen granule remnants in the starches that refractlight to different extent and thus give the distorted images (Craigand others 1989).

Swelling Power and SolubilityWhen starch is heated in excess water the crystalline struc-

ture is disrupted due to the breakage of hydrogen bonds, andwater molecules become linked by hydrogen bonding to the ex-posed hydroxyl groups of amylose and amylopectin. This causesan increase in granule swelling and solubility. Swelling power andsolubility can be used to assess the extent of interaction betweenstarch chains and within the amorphous and crystalline domainsof the starch granule (Ratnayake and others 2002). Starch swellingoccurs concomitantly with loss of birefringence and precedes sol-ubilization (Singh and others 2004). The extent of this inter-action is thought to be influenced by a samples amylose con-tent, amylose and amylopectin structure, degree of granulation,starch components, and other factors. According to Tester andMorrison (1990a), amyloselipid complexes inhibit swelling, andthe swelling behavior of cereal starch is primarily related to amy-lopectin structure and amylose acts as a diluent. Vandeputte andothers (2003a) have reported that swelling power is a function oftemperature for waxy and normal rice starches. The swelling ofnormal rice starch is a 2-step event. In the first swelling step, at atemperature between 55 and 85 C, amylose does not influencethe swelling of normal rice starches, whereas the relative amountsof short amylopectin chain (DP 6 to 9) increase swelling at 55and 65 C. Only in the 2nd swelling step (at temperatures be-tween 95 and 125 C), amylose decreases swelling power. In thefirst swelling step, granule swelling is influenced by the short amy-lopectin chains, whereas in the 2nd step, it is influenced by amyloseleaching. Lee and Osman (1991) reported that swelling power ofstarch depends on the capacity of starch molecules to hold waterby hydrogen bonding; when the hydrogen bonds between starchmolecules are broken after complete gelatinization they are re-placed by hydrogen bonds of water. The amylose content and theproportion of outside-chains of amylopectin were thought to bethe major factors stabilizing the gel structure to retain water (Tangand others 2005). The distribution of amylose in a starch granulewas shown not to be uniform (Seguchi and others 2003), whichalso affects the swelling power of starch. It was explained that thestarch granules mainly contained amylose and amylopectin andduring gelatinization some amylose molecules leaked out; how-ever, the quantity of amylose that leaked out was related to thechannels and molecule structure or to hydrogen bonding. Thedistribution of amylose and amylopectin in starch granules alsoinfluences the solubility of starch. Amylose played a role in themaintenance of the structure of starch granules and was concen-trated in the central region of the granules in a study by Seguchiand others (2003). Therefore, the higher the amylose content, themore compact the starch granule and the starch is more difficultto overflow outside the granules and thus lowers solubility values.The swelling power and solubility of rice starches from all

the 3 types of rice starches are shown in the Table 4. Theswelling power for nonwaxy rice starches ranged from 7.33%(Wickramasinghe and Noda 2008) to 38.8% (Singh and others2006a, 2006b). According to Sodhi and Singh (2003), the cultivarwith the lowest amylose content has the highest swelling power



and the lowest solubility, whereas the sample with the greatestamylose content has the lowest swelling power. Lii and others(1995) also reported a higher swelling power for rice with loweramylose content. The differences in swelling power and solubilityamong different cultivars may be attributed to the differences inamylose content, viscosity patterns, and weak internal organiza-tion resulting from negatively charged phosphate groups withinthe rice starch granules (Jane and others 1996). Techawipharat andothers (2008) determined the swelling power of different waxy andnormal rice starches and observed that swelling power of waxy ricestarch (26.9%) was higher than those of normal rice starch (15.5%).Lii and others (1996) observed that waxy rice starch granules wereless firm and tended to disintegrate easily when swollen and exten-sively overcrowded. In contrast, normal rice starch granules weremore rigid, with less swelling, and not easily ruptured. Gener-ally, the amount of exudate from normal rice starch granules wassmall, suggesting that the main component leached from the gran-ules was amylose (Mandala and Bayas 2004), whereas the amountof exudate from waxy rice starch granules was large and consistedof amylopectin molecules (Tester and Morrison 1990b). The sol-ubility of nonwaxy rice starches ranged from 0.287% (Sodhi andSingh 2003) to 40.0% (Wang and others 2010) and in the case ofwaxy rice starch solubility ranged from 0.6% (Chang and others2010) to 69.16% (Yu and others 2012).

SyneresisAs cooked, cooled starch gel ages it contracts causing water

loss and shrinkage. This is known as syneresis or weeping. Starchsuspensions (5%) were heated at 90 C for 30 min followed byrapid cooling to room temperature. The syneresis of gels preparedfrom starches separated from different rice cultivars was measuredas amount of water released from the gels during storage (up to168 h) at 4 C (Sodhi and Singh 2003; Singh and others 2006a,2006b). Syneresis increased with length in storage duration forvarious nonwaxy (indica) rice cultivars (Sodhi and Singh 2003).The increase in percentage syneresis during storage has been at-tributed to the interaction between leached amylose and amy-lopectin chains, which leads to the development of junction zones,which reflect or scatter a significant amount of light (Perera andHoover 1999). Amylose aggregation and crystallization have beenreported to be completed within the first few hours of storage,while amylopectin aggregation and crystallization occurs duringlater stages (Miles and others 1985a,1985b).Syneresis of starches is an undesired property for the use of

starch in both the food and nonfood industries. It is also an indexfor degree of starch retrogradation at low temperature. Singh andothers (2006a, 2006b) had reported low syneresis values in therange of 0.00% to 1.81% for various indica rice starches storedat 4 C for 24 h. According to Sodhi and Singh (2003), thesyneresis ranged from 0.04% to 2.41% for nonwaxy (indica) ricestarches stored at 4 C for 48 h. The syneresis values indicated thattemperatures below freezing point are against recommending thestorage of frozen starch paste (Wang and others 2010).

FreezeThaw StabilityFreezing a starch gel normally leads to the formation of ice

crystals and the concentration of starch in the unfrozen phase.Upon thawing, water is easily expressed from the network, givingrise to the phenomenon known as syneresis. The ability of a starchgel to withstand this phenomenon during freezethaw cycling(freezethaw stability) enhances its potential use in frozen foodproducts (Baker and Rayas-Duarte 1998). The level of syneresis

is inversely proportional to the freezethaw stability of a starchgel.Freezethaw stabilities of native rice was determined with 25 g

starch paste (8%) in centrifugal tubes, allowed to cool to 30 Cfollowed by freezing at 14 C for 22 h. They were subjected to5 freezethaw cycles, each time thawed at 30 C in a water bath for1 h. Rice starch showed the highest percent syneresis in the 1stcycle and then syneresis gradually decreased to the 5th cycle, de-creasing of percent syneresis from cycle 1 to cycle 5 of 28.86%,22.26%, 10.61%, 1.25%, and 1.31%, respectively (Deetae and oth-ers 2008). Rice starches showed decreases in percent syneresis fromcycle 1 to cycle 5, which was not the normal freezethaw sta-bility property. The water separation or percent syneresis of anystarch paste should increase with an increase of freezethaw cycling(Varavinit and others 2000). Native rice starch with rather highamylose showed a high percent syneresis for the first freezethawcycle, but surprisingly low syneresis after the 2nd cycle, where itappeared to have good freezethaw stability (Varavinit and oth-ers 2002). However, it was found that during these cycles theamylose rice starch gel had changed from a smooth gel to a rough-textured porous gel (rough surface) with a sponge-like structurethat allowed it to reabsorb the separated water; thus syneresis wasreduced, unless this rough-textured gel was pressed to squeeze outthe absorbed water. This retrogradation phenomenon occurredwhen the rice starch gel was frozen and ice crystals spread withinthe gel. Upon subsequent thawing at a lower temperature (30 C),the ice crystals melted and a rough-textured with relatively highporosity was obtained. In the 1st freezing cycle, only a small quan-tity of the rough porous gel was formed and it was not enough toform a spongy structure and a high syneresis value was observed.From the 2nd to the 5th cycle, the quantity of rough-textured gelaccumulated sufficiently to form a sponge-like structure (Deetaeand others 2008).

Rice Starch ApplicationsCommercial native rice starch finds applications as cosmetic

dusting powder, laundry stiffening agent, paper and photographicpaper powder, sugar coating in confectionary products, soups,noodles, and thickener and excipient for pharmaceutical tablets(Singh and others 2006a, 2006b). Rice starch granules being verysmall in size provide a texture perception similar to that of fatand have a low glycemic index (Champagne 1996). Rice starchacts as a carrier and offers time-release and protection of flavorsfrom oxidation (Zhao and Whistler 1994). Starch is an attrac-tive raw material for edible packaging because of its low cost,renewability, and biodegradability (Guilbert 2000). Furthermore,it is abundant, nonallergenic, and possesses good mechanical andbarrier properties that may allow for wider food applications (Gu-jska and others 1994; Rindlav-Westling and others 1998; Pagellaand others 2002). It is used in various fermentation processes toproduce different compounds with high specificity and purity.Lactic acid was synthesized by the fermentation of rice starch us-ing microorganisms, and it was found to be of high optical purity(Fukushima and others 2004). Starches as a group are the cheapestand most important polysaccharides and are therefore used in avariety of food and industrial applications (Ellis and others 1998).Starch is one of the most important and abundant food ingre-dients of staple foods such as in bread and noodle manufacture(Funami and others 2005), as well as adhesion, binding, clouding,dusting, film-formation, foam strengthening, antistaling, gelling,glazing, moisture retention, stabilizing, texturizing, and thickeningapplications (Whistler and BeMiller 1997).



Starches are generally regarded as the most important con-stituents of cereals in terms of pasting behavior, gelatinization,retrogradation, and other functional attributes which influenceproduct quality (Hagenimana and Ding 2005). In the worldwidemarket for industrial starches, corn accounts for over 90% of thetotal starch production, followed by potatoes and wheat. In theAsian market the most used starch as a food additive is rice starch.The availability of corn to the Indian starch industry is decreasing,day by day, because of its increased demand being involved in theproduction of breakfast cereals and snacks. Broken rice, whichis cheaper than corn and is available in abundance, can be usedin the production of starch (Sodhi and Singh 2003). Rice starchexhibits a number of unique characteristics and can be a bettersubstitute of corn starch in a number of food applications (Juliano1984). Rice starch, in its gelatinized form, has a bland taste andis smooth, creamy, and spreadable, which makes it a good custardstarch. Rice starch granules are of the same size as homogenizedfat globules, therefore, they provide a texture perception simi-lar to that of fat. Rice starch with high amylose content has alow glycemic index (Champagne 1996). It is the ratio of amy-lose to amylopectin and the fine structure of these polymers thatgive native starches its distinctive properties (Alberle and others1994). Starch granules are used as flavor carriers. Using appro-priate methods, small starch granules may be mixed with gelatinor water-soluble polysaccharides and then spray-dried forming aglobular mass. These spherical aggregates of starch granules con-tain open porous spaces that can be filled and used to transportmaterials such as flavors, essences, and other compounds. Spheri-cal aggregate carriers potentially offer time-release and protectionof these flavors from oxidation (Zhao and Whistler 1994).Interest in biodegradable packaging is increasing because it con-

sists of natural materials, which do not contribute to environmen-tal pollution (Ahvenainen and others 1997; Webb-Jenkins 2002).These films and coatings may be applied on a food or between het-erogeneous food components to prevent mass transfer phenom-ena that could deteriorate the quality of food (Guilbert 2000).Starch is an attractive raw material for edible packaging becauseof its low cost, renewability, and biodegradability (Guilbert 2000).Furthermore, it is abundant, nonallergenic, and possesses goodmechanical and barrier properties that may allow for wide foodapplications (Gujska and others 1994; Rindlav-Westling and others1998; Pagella and others 2002). High-amylose starch is a very use-ful film-forming material because of its strong gelation propertiesand helical linear polymer structure (Juliano 1985). Starch can beused as a starting material for the production of various chemicals;for example, D-lactic acid was synthesized by the fermentation ofrice starch using microorganisms (Lactobacillus delbrueckii and Sporo-lactobacillus inulinus) and it was found to be of high optical purity(Fukushima and others 2004).

Summary and ConclusionStarch is the major component of rice grain comprising about

90% of total weight of polished rice grains. Rice starch is com-monly isolated by alkaline extraction, but this method produces ahighly loaded alkaline effluent. Enzymes and other physical meth-ods can be used to isolate starch with high purity and without anyobjectionable effluent. Rice starch is composed mainly of amyloseand amylopectin. Starch occurs as discrete, semicrystalline gran-ules. The rice starch granule is one of the smallest starch granules(2 to 7 m). Starch is insoluble in cold water, but when heatedin the presence of water starch granules swell and soluble com-ponents leach out. The phase transition of starch granule i

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