Write Up Resistant Starch

8/3/2019 Write Up Resistant Starch

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Starch

Starch is one of the main forms of carbohydrate in the diet. Starches are polysaccharides,

they are made up of a number of glucose molecules which are linked together. They cantherefore be described as complex carbohydrates. Starches are found in plant sources

including potatoes and cereal products (e.g. bread, pasta). In general, digestible starches broken down by digestive enzymes in the small intestine into glucose molecules. The gluco

is then absorbed into the blood and used to provide energy for the body.

Resistant starch

Resistant starch is generally considered to be represented by the total amount of starch anthe products of starch degradation that are not digested in the small intestine, and pass in

the large intestine (or the colon). Therefore, resistant starch can be regarded as a componof dietary fibre.

Types of Resistant starch

Class Types

RS1 physically inaccessibleRS2 granular, ungelatinised

RS3 nongranular, indigestibleRS4 chemically changed starch

Resistant starch not digested

There are several reasons why resistant starch is not digested:* The starch may be physically inaccessible to the digestive enzymes such as in grains,

seeds or tubers.* The starch granules themselves are structured in a way which prevents the digestive

enzymes from breaking them down, e.g. raw potatoes and unripe bananas.* When starches are heated they gelatinise and become more easily digested. However,

if these starch gels are cooled, starch crystals form in the food that are resistant to enzym

digestion. This form of retrograded starch is found in foods such as cornflakes or cooked acooled potatoes.

* Starches that have been chemically treated (etherisation, esterisation, cross-bonding)cannot be broken down by digestive enzymes.

Sources of resistant starch in the dietResistant starch is found in a wide range of foods including intact wholegrains, legumes,

pasta, unripe bananas, raw potatoes, cooked and cooled potatoes, bread, cereals, some hi

fibre drinks and foods containing modified starches (some breads and cakes).

Properties of RS

Low water holding capacity.

Small particle size.

Bland flavour with no energy.

Stable suspension viscosity.

White colour.

High gelatinized temperature


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ctional Properties of RS in food

Functional fibre

Texture modifier

Crisping agent

Colour modifier

Reduction in hardness

Improved expansion

Reduction in dough rheology

Bulking agent

Thickner for health

Resistant starch in the gut

Resistant starch reaches the large intestine (or the colon) virtually unchanged. However, itthen fermented by the microbial flora naturally present in the colon, to produce low levels

the gases carbon dioxide, methane and hydrogen. Additional fermentation products includ

organic acids and short chain fatty acids.

Short chain fatty acidsShort chain fatty acids (SCFA) are formed when polysaccharides are fermented by the

anaerobic bacteria present in the large intestine. Many different forms of polysaccharides apresent in the large intestine, including resistant starch. The main SCFAs produced in the

human gut are butyrate, propionate and acetate. The concentrations of SCFAs in the large

intestine vary depending on the types of polysaccharides although generally acetate is themost abundant and butyrate is the least abundant. Concentrations also vary in the differen

regions of the large intestine with higher concentrations detected in the area nearest thejunction with the small intestine (70 140mM).

Effect of short chain fatty acids in the large intestineSCFAs lower the pH of the contents of the large intestine. This is of benefit to health becau

the reduced pH creates an environment that prevents the growth of harmful bacteria. A lopH also aids in the absorption of minerals such as calcium and magnesium. SCFAs increase

the blood flow to the colon and provide the cells in the wall of the intestine with a metabol

fuel (mainly in the form of butyrate). Additionally, butyrate has been shown to induceprogrammed cell death (apoptosis) and exert a level of control over the cell cycle. This

suggests that butyrate might play an important role in maintaining the integrity of the gutby preventing the uncontrolled proliferation of abnormal cells that occurs in the early stage

colorectal cancer.

Health benefits of resistant starch

Resistant starch contributes to the amount of fibre in the large bowel. Many health benefit

have been attributed to foods providing resistant starch in the context of a high fibre diet.These include: a slower, more controlled release of glucose from the food into the bloodstream (the glycaemic response see below); improved bowel health; improved blood lipi

profile; an increased feeling of satiety and increased micronutrient absorption (magnesium

calcium) in the colon. These factors may affect the risk of developing diseases such ascolorectal cancer, cardiovascular disease, osteoporosis and obesity and assist in the

management of diabetes, impaired glucose tolerance, inflammatory bowel diseases,diverticulosis and constipation

.

Resistant starch improve the glycaemic response after a


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meal?

When most carbohydrates are consumed, the levels of glucose in the blood are raised,

peaking 15 45 minutes after finishing your meal. Levels return to normal within two to thours. The concentration of the hormone insulin in the blood also increases in response to

elevated glucose concentration. High levels of insulin in the blood inhibit the use of storedbody fat, as well as modulating appetite and satiety signals. Rapidly digestible carbohydrat

such as those in white bread and confectionery, bring about a high glycaemic andinsulinaemic response. In some instances, for example when you are being very active, th

of benefit as the glucose is rapidly absorbed into your blood stream to give you a fast suga

boost. However, carbohydrates that are broken down slowly, for example those fromwholegrain foods or legumes, are generally better for keeping energy levels up throughout

day. This slower, more controlled glycaemic response is could be beneficial to all individuaas there is greater access to and use of stored fat, and hunger signals are suppressed. For

people with diabetes or impaired glucose tolerance, increasing the amounts of resistant

starch in the diet can help with the day-to-day management of blood glucose levels, as weas contributing to the bodys use of fat.

Resistant starch has been shown to improve bowel health and function.

How can this be assessed?There are several markers that can be used to assess the health and function of the bowelThe time it takes for food to pass through the entire gut is referred to as the transit time.

Healthy bowels process food quickly and gut cells absorb just enough water to produce firmstools. This, along with other factors, including the amount of fibre in the diet and

numbers

of bacterial cells in the gut, affects the faecal weight. Some compounds, such as ammoniaphenols or bile acids are produced in the gut which can be damaging to the cells lining the

large intestine. Low levels of these compounds in faeces suggest that the bowel is healthyand that their effects in the gut are lessened

.Improvements in bowel health

Resistant starch, like other forms of dietary fibre, helps to prevents constipation by provid

bulk to the faeces. Bulky faeces move through the gut faster and result in an increased stoweight. Diets high in resistant starch have been shown to reduce the luminal pH, limiting t

growth of harmful bacteria in the gut. They also decrease the amounts of secondary bile aand ammonia present in the large bowel. Secondary bile acids can be converted into active

compounds by the microbial flora and these can damage DNA. Ammonia has been shown t

increase the proliferation rate of the cells in the gut wall. It is therefore advantageous to lithe concentrations of these compounds in the colon to reduce the risk of developing

colorectal cancer. Additionally, the increased faecal bulk dilutes the effect of any genotox

agents in the large intestine, thereby reducing the extent of DNA damage to the cells liningthe colon.

Resistant starch can function as a prebiotic.

Prebiotics are non-digestible food ingredients that stimulate the growth and activity of bacin the colon. Approximately 100 trillion bacteria live in our large intestines and they are

essential for keeping our digestive system healthy. As resistant starch, along with other fo

of dietary fibre, arrives in the large intestine unchanged, it provides metabolic substr(fuel)

for these colonic bacteria and promotes the growth of the beneficial strains of bacteria (e.g


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Bifidobacteria). A healthy bacterial flora further improves bowel health and function.

Resistant starch used to prevent weight gainDue to its indigestible nature, resistant starch has a lower calorific value than that of

digestible starch (16kJ/g or 4kcal/g). Therefore, foods high in resistant starch may provideless energy weight for weight, although this will depend on the amounts of other nutrients

the food.

How much of a contribution should resistant starch make to the diet?

In the UK, resistant starch makes up a very small proportion of total daily starch intake. Oaverage, the intake of all starches is 130g per day whereas the average intake of resistant

starch is only around 4g per day. This is very low compared to countries in the developingworld where intakes of resistant starch are much higher (for example 10g per day in India

Intake of dietary fibre in the UK should increase in order to improve bowel health and

increasing consumption of foods rich in resistant starch is one way of achieving this.However, current intakes of dietary fibre in the UK are already well below recommendation

and it has been recognised that substantial dietary changes would need to be made to reathese targets

.Is resistant starch safe?Resistant starch is well tolerated in the diet. Minor effects of very high levels of resistant

starch consumption are consistent with those of high fibre intakes, such as flatulence,belching, bloating and stomach aches which can occur when large amounts of resistant

starch are fermented in the large intestine.

How can resistant starch be incorporated into meals?

You can up your intake of resistant starch, along with other forms of dietary fibre, byincreasing the amount of wholegrain foods in your diet, for example seeded or granary

breads, wholemeal pasta or high fibre cereals. There are also commercially producedresistant starches, for example Hi-maizeTM or NOVELOSE 330TM which are sometimes use

by food manufacturers to produce a food product that is high in fibre and which can also b

lower in calories.

Factors influencing the formation of RS.

Inherent properties of starch

Crystallinity of starch. One of the causes of resistance to enzymes is the crystallini

native type B starch granules as observed in the case of amylomaize starch and also

encapsulation of starch within plant cell or tissue structures. X-ray diffraction and differe

scanning calorimetry studies on crystalline residues from amylomaize starch samples suggested that chain fragments packed in a type B crystalline structure with a slienlarged crystal lattice contribute to formation of RS from amylomaize starch. Any treat

that eliminates starch crystallinity (that is, gelatinization) or the integrity of the plant ce

tissue structure (that is, milling) increases enzyme availability and reduces the content ofwhereas recrystallization and chemical modifications tend to increase the RS. The mod

food starches are partially resistant to enzymes as a result of chemical modifications indintentionally . Besides these, the cellular structure of plant foods influences the digestibili

starch in the small intestine as well as the intrinsic digestibility of a particular physical for

starch.


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Granular structure. A large variability in susceptibility to amylases shown by raw st

granules also influences RS formation. Potato starch and high amylose maize starch

known to be very resistant in vitro and incompletely absorbed in vivo, whereas most cestarches are slowly but virtually completely digested and absorbed in vivo . The sm

surface-to-volume ratio of the large potato granules is probably important. The nature ogranule surface also needs to be considered; an adsorbed layer of non-starch material w

effectively impede the action of the enzyme . Raw tepary starch is found to be more resisto hydrolysis than maize starch, perhaps due to differences in granule structure and amy

content .

Amylose:amylopectin ratio. A higher content of amylose lowers the digestibility of stdue to positive correlation between amylose content and formation of RS . The importanc

the amylose:amylopectin ratio in the postprandial glycaemic and insulinaemic response

corn was studied in commonly consumed corn products . The meals containing high amy(70%) corn flour had an RS of 20 g/100 g DM than that containing ordinary corn flour (

amylose) that had RS of 3 g /100 g DM.

Retrogradation of amylose. When heated to about 50 C, in the presence of wateramylose in the granule swells; the crystalline structure of the amylopectin disintegrates

the granule ruptures. The polysaccharide chains take up a random configuration, causwelling of the starch and thickening of the surrounding matrix such as, gelatinizatio

process that renders the starch easily digestible. On cooling/drying, recrystalliz

(retrogradation) occurs. This takes place very fast for the amylose moiety as the listructure facilitates cross linkages by means of hydrogen bonds. Figure 10 shows

formation of gel and micelle on cooling of a concentrated solution of amylose . The brannature of amylopectin inhibits its recrystallization to some extent and it takes place

several days. Retrograded amylose in peas, maize, wheat, and potatoes was found t

highly resistant to amylolysis . The rate and extent to which a starch may retrograde gelatinization essentially depends on the amount of amylose present. Repeated autoclavin

wheat starch may generate up to 10% RS. The level obtained appeared to be strongly reto the amylose content, and the retrogradation of amylose was identified as the

mechanism for the formation of RS that can be generated in larger amounts by repe

autoclaving . During storage, the dispersed polymers of gelatinized starch are said to undretrogradation to semicrystalline forms that resist digestion by pancreatic _-amylase. It fo

a major portion of RS in wheat bread and corn flakes , whereas only 25% of the RS in coocooled potatoes can be accounted for as retrograded amylose. The digestibility of leg

starch is much lower than that of cereal starch, which is attributable to higher contenamylose in the former. The digestibility of high amylose cereal starch is reported t

significantly lower.

Native high-amylose starch is known to be high in type II RS (RS2) , which is defined as starch in its native granular

state that is resistant to digestion in the small intestine. This after cooking and cooling g

high yields of type III RSor retrograded starch . Heating of RS preparation from amylomVII resulted in broad endothermic transition, which is ascribed to melting of amy

crystallites . Exothermic transitions during controlled cooling of isolated potato amyfractions have been attributed to amylose chain association. The formation of RS likewise

been attributed to the ordering of amylose chains . Based on previous studies of amy

behavior, it has been suggested that the exotherms observed during the cooling of eamylose or a thermally treated RS preparation reflect chain association, which may inv

amylose aggregation and gelation dominated by formation and subsequent lateral aggreg


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of type B double helices in crystalline array . Gelatinized waxy corn starch stored at var

temperatures from 6 C to 60 C for 1 to 29 d also showed reduced enzyme susceptibili

pancreatic _-amylase and amyloglucosidase .

Influence of amylose chain length. Influence of amylose chain

length on enzyme RS formation was studied by hydrolyzing potato starch amylose to va

degrees by incubation with barley _-amylase for different periods, and monitored

measuring the number of average chain lengths or degree of polymerization (DPn). The DRS varied between 19 and 26 and was independent of the chain length of the amylose (

40 to 610) from which it was formed. Results suggested that RS might be formeaggregation of amylose helices in a crystalline _-type structure over a particular region o

chain (about 24 glucose units).

Linearization of amylopectin. Linearization of amylopectin occurs during the long temperature baking process due to the prolonged activity of intrinsic amylases in the do

and is prominent in the presence of certain organic acids that is, in bread products baked added lactic acid . It has been reported to significantly increase RS formation during

autoclaving .

Heat and moisture

Water content is an important factor that affects formation of RS. Repeated heat/moitreatment is associated with a decrease in the hydrolysis limit of pancreatic _-amylase

increased formation of RS. Maximum RS yield was obtained at a starch:water ratio of 1(w/w) and a heat treatment at 18% moisture gave increased levels of the degre

crystallinity of normal and waxy starches and thus reduced enzyme susceptibility. Howe

at 27% moisture, starch degradation to some extent made areas of starch more accesto enzyme attack. Thus, proper heat treatment could be used as a method of preparati

RS . In addition, higher temperature and less water results in type A configuration, whelower temperature and high water content results in type B configuration .Some scie

determined solubility, water vapor sorption, and swelling characteristics for RS prepfromwheat starch and linterized wheat starch by autoclaving and cooling

and by cross-linking The experimental RS made from wheat

starch contained 10% to 73% RS versus 58% and 40% in commercial

sources, Novelose 240 and 330 respectively, produced

from high-amylose maize (corn) starch. In excess water, the experimental

RS starches (except for the cross-linked wheat starch)

gained 3 to 6 times more water than the commercial RS starches

at 25 C, and 2 to 4 times more at 95 C. All starches showed similar

water vapor sorption and desorption isotherms at 25 C and

aw < 0.8. At aw 0.84 to 0.97, the RS made from wheat starch (except

cross-linked wheat starch) showed approximately 10% higher water sorption thancommercial RS.


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RS determined in several selected cereals, legumes, and tubers subjected to dry and

heat treatment brought out higher RS contents in foods subjected to dry heat treatm

compared with wet processed ones. Sorghum, green gram dhal, and green plantain shohighest RS content (5.51%, 5.81%, and 10.7%, respectively) .

Interaction of starch with other components

Interactions of starch with different components present in the food system are know

influence the formation of RS as follows.

Protein. Starch-protein interaction has been believed to reduce RS contents as observe

case of potato starch and added albumin when autoclaved and subsequently cooled atC .

Dietary fiber. Insoluble dietary fiber constituents such as cellulose and lignin have shown to have minimal effects on RS yields compared with other constituents suc

potassium and calcium ions and catechin.

Enzyme inhibitors. Polyphenols, phytic acid, and lectins present mainly in legumiseeds, have been reported to inhibit in vitro starch hydrolysis and to lower the glyc

index. Tannic acid significantly inhibits both amylases and intestinal maltase activ

Indigestible residues from black beans (Phaseolus vulgaris cv. Tacari gua), green beanvulgaris), carrots (Daucus carota), and rice bran (Oryza sativa) are all reported to in

pancreatic _-amylase in vitro . Since amylolysis is inhibited by phytic acid, a decreasphytate content increases starch digestibility . Contradictory information exists in

literature on this aspect. The autoclaving and subsequent cooling of potato starch

catechin was found to significantly reduce the yields of RS, whereas the addition of phacid to potato starch reduced the RS contents to a minor extent compared with th

formed from potato starch with no added constituent. The reasons for the same are stilclear.

Ions. The yields of RS in potato starch gels decrease in the presence of calcium

potassium ions compared with those with no added constituent , presumably due toprevention of formation of hydrogen bonds between amylose and amylopectin chains ca

by adsorption of these ions.

Sugars. The addition of soluble sugars such as glucose, maltose, sucrose, and ribosebeen found to reduce the level of crystallization and subsequently reduce the yields of

The mechanism of retrogradation inhibition was considered as the interaction between s

molecules and the starch molecular chains, which change the matrix of gelatinized st

(the sugars act as anti-plasticizers and increase the glass transition temperature).

The role of sugars on the formation of RS in starch gels (RS type III) . Sugars influencedRS levels in starch gels only when added in high concentration (final starch-water-sugar

of 1:10:5 w/w). In wheat starch gels, the RS yields decreased from approximately 3.4

2.8% in the presence of sucrose or glucose, and to 2.5% in the presence of ribosmaltose. An increase in RS yield was observed with high-amylose corn starch.

experiments showed that the differences in gelatinization temperature, lipid content,apparent amylose content of the 2 starches were not the main causes of the different im

of sugars on RS yields.


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Lipids, emulsifiers. In a study, amylomaize VII starch, autoclaved

at 125 C, was reacted during cooling below 100 C with

lysophosphatidyl choline (LPC), sodium stearoyl lactylate (SSL),and hydroxylated lecithin (OHL) . Differential scanning calorimetry95 C to 110 C indic

formation of amylose-lipid complexes,and at about 155 C indicated the presence of enzyme-resistant

starch (RS). Yields of RS from complexed samples isolated by thermostable

bacterial _-amylase or amyloglucosidase were lower

than yields of RS from the autoclaved and cooled control. Formation

of complexes competes with amylose chains involved in generation

of RS. Amylose-lipid complexes are enzyme-degradable,

and an increase in complexed amylose reduced yields of RS.

Amylose recrystallization in RS formation is competitively affected

by complexation of amylose with LPC and SSL. Results of X-ray

diffraction powder crystallography were in agreement with DSCmeasurements. Complexes of amylose with LPC, SSL, and OHL

gave type V patterns; enzymic hydrolysis of the complexes yielded

type B RS structures. However, the viewpoint differs among scientists

working in this area. While some workers believe amyloselipid

complex to reduce the formation of RS, others believe the

amylose-lipid complex itself to be a form of RS.

Processing conditionsProcessing techniques may affect both the gelatinization and retrogradation

processes, influencing RS formation. This fact is of great

importance for the food industry since it offers the possibility of increasing

the RS content of processed foods and foodstuffs. Baking,

pasta production, extrusion cooking, autoclaving, and so forth are

known to influence the yield of RS in foods. Highly processed cereal

flours and foods made from the flours, such as pasta, contain much

lower levels of RS, averaging only about 1.5% to 8% RS on a dry

basis. Since the crystalline structure of starch in legumes (type C) is

more stable compared with the crystal structure in cereal grains

(type A), processing cereal grains results in a

large decrease in RS content, while legumes are excellent sources

of RS. Cooking under conditions of high moisture and temperature

can significantly lower the RS content by disrupting crystalline


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structure. Increasing the levels of RS can be done in other conditions,

such as extrusion followed by cooling to induce crystallization

The RS contents in various processed food

samples have been reported .

Thermal processing

Steam cooking. Steam cooking helps in production of RS. Starchesisolated from several steam-heated legumes were rich in indigestible

RS (19% to 31%, DM basis), which was not observed in

raw beans .Similarly, RS measured directly

in conventionally and high-pressure steamed beans were 3 to 5

times higher than in the raw pulses, suggesting retrogradation to be

mainly responsible for the reduction in digestibility. Prolonged

steaming as well as short dry pressure heating decreased the enzymically

assessed total starch content of whole beans by 2% to 3%

(DM basis), indicating that these treatments may induce formation

of other types of indigestible starch.

Autoclaving. Autoclaving results in increase in RS. Autoclaved

wheat starch has 9% RS compared with less than 1% in uncooked

wheat starch. Autoclaved

wheat starch contained 6.2% RS (of dm); this increased to 7.8%

after 3 further reboiling/cooling cycles .

In another study, white flour subjected

to repeated autoclaving and cooling cycles showed an increase in

total dietary fiber >3 times that of bread flours and 4 times that of

pastry flours . The increase was primarily

due to the formation of RS. Investigations on the formation

of enzyme-resistant starch (RS) during autoclaving and cooling showed highest

(21.3%) to be

obtained from amylomaize VII starch (70% amylose). Formation of

RS in amylomaize VII starch was affected by the starch/water ratio,

autoclaving temperature and number of autoclaving-cooling cycles.

The number of cycles exerted the most pronounced effect on

RS; increasing the number of cycles to 20 raised RS level to

>40%. Furthermore, the thermoanalytical data suggested that

amylose-lipid complexes were not involved in the formation of


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RS. Yields in excess of 20% RS can be obtained from autoclaved

amylomaize starch containing 70% amylose. They can be raised

to levels of 40% by increasing the number of autoclaving-cooling

cycles up to 20.

The extent of RS formation in commercially available autoclaved

corn, potato, and leguminous products and in autoclavedpurees intended for consumption by infants aged 3 to 8

Parboiling. Parboiling increases RS production. In studies on 5 rice varieties, differin

amylose content, the in vitro and in vivo RS levels were low and positively correlated amylose content Higher RS starch levels were found incooked and parboiled-cooked rice

in raw rice; waxy rice had very low values. Higher contents of RS have been reporteparboiled rice than raw white rice, which also increased by cooling

or freezing .

Baking. Baking increases RS content. In a study to evaluate the effect

of baking on RS formation, white bread was baked and divided

into 3 fractions (crumb, inner crust, and outer crust) .Starch levels were found to be higin dough

and lowest in outer crust after baking for 35 min. RS levels were

lowest in dough and highest in crumb after baking for 35 min. A

low-temperature, long-time baked product contained significantly

higher amounts of RS than bread baked under ordinary conditions

. Addition of lactic acid increased RS recovery

further whereas malt had no impact on RS yield. The highest

level of RS was noted in long-time baked bread based on highamylose

barley flour. RS isolated from wheat-based foods such as

chapatti and phulka was structurally characterized as a linear 1, 4-

linked _-D-glucan essentially derived from retrograded amylose

fraction, which was dependent on the severity of the processing

treatments as well as the levels of gluten and damaged starch in the

wheat flour .

Extrusion cooking. Effect of extrusion cooking, at different temperatures

(90, 100, 120, 140, or 160 C), moisture contents

(20%, 25%, 30%, 35%, or 40%) and screw speeds (60, 80, or

100 rpm), was investigated on the formation of RS of type 3 (RS3)

in hull-less barley flours from CDC-Candle (waxy) and Phoenix

(regular). The RS3 content of the native flours, in general, decreased


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by extrusion cooking, but not significantly. Storage of extruded

flour samples at 4 C for 24 h before oven drying slightly

increased RS3 content . With pearl barley

used as the primary material in tests designed to optimize the production

of RS by extrusion an extrusion temperature of 150 C

and a barley moisture content from 17.5% and 22.5% moisture,followed by cold storage at 18 C gave the best results .

Corn starches with and without guar gum [10% (w/w)] and 2%

(w/w) of diacetyl tartaric acid ester of monoglyceride, sodiumstearoyl-2-lactylate or citric acid, respectively, were extrusioncooked

in a twin-screw extruder at 18% moisture, 150 C, and 180rpm screw speed. The formation of RS in extruded

corn starch was found to be strongly affected by the addition of

gum and the different food additives. X-ray diffraction of the extruded

starches gave a V diffraction pattern indicating the effect of extrusion

cooking and amylose-lipid complexes. Enzymatic digestion

did not affect the V structure, which could apparently be attributed

to extrusion cooking. Purification of the isolated RS by size exclusion-

HPLC showed a dependence of molecular weight on the added

additives. Results of differential scanning calorimetry and X-ray

diffraction suggest that amylose-lipid complexes could also be involved

in the formation of RS in extruded cornstarch.

Pyroconversion. Pyroconversion of starch increases RS content.

Lima bean (Phaseolus lunatus) starch was modified using pyroconversion,

the optimum product being recovered from native

starch treated with a 160:1 starch/HCl ratio, at 90 C for 1 h, resulting

in starches containing 49.5% indigestible starch

. Starch pyrodextrinization decreased the

amount of enzymically available starch through formation of atypical

glycosidic bonds that are not digested by the amylases andmaltooligosaccharidases in the small intestine of humans.

Microwave irradiation. Microwave irradiation improves the digestibility

of tuber starches, which could be accompanied by

physicochemical and structure changes.

Microwave cooking of legumes such as chickpeas and common

beans produced a redistribution of the insoluble nonstarch


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polysaccharides to soluble fraction, although the total nonstarch

polysaccharides were not affected. This was evaluated by assessing

the physicochemical, nutritional, and microstructural modifications

in starch and nonstarch polysaccharides

. The RS level decreased from 32.5% of total starch in

raw chickpeas and beans, respectively, to about 10% in cookedsamples with a concomitant increase in the level of rapidly digestible

starch from 35.6% and 27.5% to about 80%.

Studies on effects of different heat treatments (cooking, microwave

cooking, pressure cooking) on the rate of hydrolysis, hydrolysis

index, and glycaemic index values of kudzu starch and

cornstarch showed increase in digestible starch and decrease in

RS following heat treatment. The rate of hydrolysis of kudzu starch

and cornstarch increased following heat treatment, especially after

microwaving .

Miscellaneous treatments.

Milling. Leguminous seeds, in which cell structures are preserved

after cooking (that is, bread with whole seeds); bean flour

with intact cells ,foods containing

large particles such as bread with whole seeds have lower physical

accessibility of starch to amylase action, and thereby contribute

to higher RS contents. In some foods, physically inaccessible

starch is likely to be an important fraction of the total starch that is

resistant to digestion in vivo. found

evidence of 20% starch malabsorption from a diet containing

bean flour with intact cells. About half of the malabsorbed starch

was retrograded amylose. The precooked flours (PCF) prepared

from dried lentils and beans, rich in intact cells filled with starch

granules, indicated that they contained important quantities of RS,

such as retrograded amylose (3% to 9%, DM).

Germination. Germination is shown to decrease the RS content

in bengal gram, field beans, cow pea, and green gram .

Fermentation. Fermentation reduces RS content. Flour from sorghum

cv. Tabat was mixed with water and previously fermented

dough starter, and fermented at 37 C for a maximum of 36 h


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showed an increase in the in vitro starch digestibility and a decrease

in the content of RS and total starch .RS formation has also been shown to decrease in the

fermented products, idlis and dhoklas .

Storage conditions

Generally, RS increases on storage, especially low-temperature

storage. Cold storage seems to support an increase in RS content.Whole corn bread and corn bread crumb, when stored at different

temperatures (20 C, 4 C, or 20 C) for 7 d showed RS contents

to reach a maximum between 2 and 4 d at all storage temperatures,

after which they decreased . Lowest RS levels

in whole corn bread were found after storage at 20 C (2.18

g/100 g) for 7 d.

Preparation of RSRS can be prepared by using heat treatment, enzyme treatment,

combined heat treatment and enzyme treatment, and chemical

treatment.

Heat treatment

Heat treatment of starch to various extents leads to formation of

RS. RS can be obtained by cooking the starch above the gelatinization

temperature and simultaneously drying on heated rolls like

drum driers or even extruders. The gelatinization of starch granules

by heat processing strongly influences their susceptibility to

enzymatic hydrolysis. In a high-moisture environment, amylose

leaches from the granules, increasing the solubility of starch and

thereby its susceptibility .

Good yields of RS can be obtained by gelatinizing starch at

120 C for 20 min, followed by cooling to room temperature

. The starch gels are then frozen overnightat 20 C and dried at 60 C before milling.

Many combinations of time and temperature treatments have

been used to make type III RS from various sources of native

starch. Even for starches with normal amylose levels, it is recognized

that cooking at >100 C can increase the yield of type III RS.

The temperature treatments have included autoclaving the starch


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at 110 C , at 121 C for periods ranging from 30min. to 1 hr.

An enzyme-RS type III, which has a melting point or endothermic

peak of at least about 140 C, as determined by differential scanning

calorimetry (DSC) can be produced in yields of at least 25%

by weight, based on the weight of the original starch ingredient

. A gelatinization stage, nucleation/propagationstage, and preferably a heat-treatment stage are required to

produce reduced calorie starch-based compositions that contain

the enzyme-resistant starch. It is produced using crystal nucleation

and propagation temperatures, which avoid substantial production

of lower melting amylopectin crystals, lower melting amylose crystals,

and lower melting amylose-lipid complexes. The nucleating

temperature used is above the melting point of the amylopectin

crystals. The propagating temperature used is above the melting

point of any amylose-lipid complexes but below the melting point

of the enzyme RS. The high melting point of the enzyme RS permits

its use in baked good formulations.

Partial acid hydrolysis (PAH) of a high-amylose corn starch (ae-

VII) enhances the effects of hydrothermal treatments used to produce

granular RS, which is stable to further heat treatment at atmospheric

pressure . PAH ofae-VII starch involved heating 35% (w/v) starch suspensions with

1% (w/w) HCl at 25 C for up to 78 h. PAH followed by heat moisture

treatment tended to increase yield of boiling-stable granular

RS to the maximum of 63.2%.

Selective heat treatment of high amylose starch in the presence

of agents inhibiting the swelling of starch like alkali and alkaline

earth metal salts of halides, sulfates, and phosphates yield granular

RS with high dietary fiber.

Recently, pyrodextrinization has been recognized as a way of

producing a RS that is water-soluble and has non-starch linkages

. Pyroconversion refers strictly to the

modification of dry starch through heat treatments, with or without

addition of acids. Acids used include hydrochloric acid at 0.15%

(based on starch dry weight) and orthophosphoric or sulfuric acids


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at 0.17% . Commercial pyrodextrins are generally

produced by heating dry, acidified starch in a reactor with agitation.

Acid may be sprayed on the starch to facilitate hydrolysis and transglycosidation.

Depending on reaction conditions, pyroconversion

produces a range of products that vary in digestibility, available

starch, viscosity, cold-water solubility, swelling power, color, andstability. The production of indigestible

dextrins or pyrodextrins by heat-treating potato starch in

the presence of an acid and then refining the product has been described

.

Enzymic treatment

The possibility of preparing a RS concentrate from isolated pea

starch was investigated, and sorption of hydrophobic substances

(indicative of health-benefiting properties) by such a concentrate

. By use of a thermally

stable _-amylase, a preparation of up to 70% RS containing a

mixture of mineral and organic N compounds was obtained. The

pea RS concentrate had an affinity to bile acid, deoxycholic, and

cholesterol; however, its affinity to cholesterol was not as efficient as

that of native pea starch. The results concluded that the pea RS concentrate

may be potentially used as a food component in special

diets, or for preventive, prophylactic, and therapeutic purposes.

Readily fermentable heat-stable RS of optimal chain length from

poly-1,4-_-D-glucan useful in various functional foods can be

obtained by in vitro synthesis by adding an enzyme extract containing

the amylosucrase of Neisseria polysaccharea to sucrose

solutions, followed by incubation at 37 C over several hours

.

A method has been discovered to produce an RS product that

retains the same cooking quality as found in untreated rice starch

or flour, but has a higher percentage of starch resistant to _-amylase

digestion . This method uses a debranching

enzyme, that is, pullulanase, to digest the starch, but does not

require pretreating the starch source before enzymatic treatment.

This method produced RS from low amylose starches, rice starch


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(24%), and rice flour (20%). Surprisingly the RS product formed

by this method retained the pasting characteristics of the untreated

flour or starch and was heat stable. This method may also be

used to produce RS from other botanical sources, that is, corn,

wheat, potato, oat, barley, tapioca, sago, and arrowroot.

Heat and enzyme treatmentPreparation of RS to be used as a food-grade bulking agent, by

retrogradation of starch followed by enzymatic or chemical hydrolysisto reduce or remove the amorphous regions of retrograded

starch . RS can be prepared from high amylose

starch by gelatinization followed by treating the slurry with debranchingenzymes like pullulanase and isolating the starch product

by drying/extrusion. Controlled heat treatment of starch so asto achieve swelling and at the same time retain its granular structure

followed by enzymatic debranching and annealing at suitable temperature followed by dr

produces RS. These RS find applications in a variety of foods and

beverage products.

Purified RS products having at least 50% RS content can be

produced by forming a water-starch suspension wherein the ratio

of starch to water is approximately 1:2 to 1:20, heating the waterstarch

suspension in an autoclave at temperatures above 100 C.

to ensure full starch gelatinization and then cooling to allow amylose

retrogradation to take place. It is reported that best resultswere obtained at a temperature of 134 C, with 4 heating and

cooling cycles and a starch:water ratio of 1:3.5. The RS was purified

by comminuting the starch gel and mixing it with an amylase

to digest non-RS fractions, leaving RS. The amylase is inactivated

by heat treatment above 100 C .

For the preparation of a fragmented starch precipitate for use in

reduced-fat foods, a debranched amylopectin starch is precipitated

and then fragmented. The debranched amylopectin starch may be

derived from a starch that contains amylopectin, for example, common

corn starch and waxy maize starch, by gelatinizing the starch,

followed by treatment with a debranching enzyme, such as

isoamylase or pullulanase, and precipitation of the debranched

starch. To form the precipitate, the solution is cooled to ambient

temperature, to reduce the solubility of the debranched starch. The


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precipitate may then be heated to about 70 C, while in contact

with a liquid medium, to dissolve at least a portion of the precipitate.

Reprecipitation by cooling of the suspension/solution may

then be employed. Repetition of the dissolving and the reprecipitation

tends to improve the temperature stability of the resulting aqueous

dispersion as was observed on repeating the cycle of heatingand cooling, a total of 8 times .

A process for increasing the amount of amylase-RS (to a minimum

of 15%) in high amylose starch, such as Hylon V or Hylon

VII consisted essentially of gelatinization of a starch slurry, enzymic

debranching of the starch, and isolation of the starch product

by extrusion or drying. A further increase in amylase-resistant

starch was obtained by addition of an inorganic salt to debranched

starch before isolation .

Chemical treatment

In type IV RS, the enzyme resistance is introduced by modifying

the starch by crosslinking with chemical agents

. Crosslinked starches are obtained by the reaction of starch

with bi- or polyfunctional reagents like sodium trimetaphosphate,

phosphorus oxychloride, or mixed anhydrides of acetic acid and

dicarboxylic acids like adipic acid. Cross-linking carried out by sulphonate

and phosphate groups between various starch molecules

involves their hydroxyl group thus bringing resistance to amylolytic

attack on the starch molecule. Figure 9 shows the preparation of

distarch phosphate ester.

Distarch phosphates with 0.4% to 0.5% phosphorus have been

prepared and they contain both slowly digested starch (SDS) and

RS4. The modified starches were obtained

in quantitative yield, and provided 13% to 69% of SDS and 18%

to 87% RS4. RS4 starches with low swelling power have also been

prepared similarly from wheat, corn, waxy corn, high amylose

corn, oat, rice tapioca, mung bean, banana, and potato starches.

Phosphated di-starch phosphate, a modified RS made from high

amylose maize starch, is currently used as food additive (E1413)

in the EU.


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Determination of RS

In vitro methods

The main step of any method to measure the content of RS in

foods must first remove all of the digestible starch from the product

using thermostable _-amylases . At

present, the method is consideredthe most reproducible and repeatable measurement of RS in

starch and plant materials, but it has not been shown to analyze all

RS as defined (Champ and others 2003). It is based on the principle

of enzymic digestion and measures the portions of starch resistant

to digestion at 37 C that are typically not quantitated due to the gelatization

at 100 C followed by digestion at 60 C.

Two general methods specifically proposed to determine RS

remove digestible starch

using different amylases, and the residual fraction is quantified after

solubilization in 2M KOH.

The Siljestrom and Asp procedure includes

preparation and quantification of dietary fiber residue before

RS determination. This is usually done by drying the samples

at 105 C. As heating influences the RS content in foods, results

may be modified by this step.

A modified method for measuring RS in dietary fiber residues

from various sources involves mixing fiber residues with KOH, acetate buffer,

and HCl. After incubation with amyloglucosidase samples are

centrifuged and diluted with distilled water. RS is calculated as

glucose (mg) 0.9. Advantages of the method are the use of small

amount of sample, less reagents and elimination of drying.

In vivo methodsDifferent methods are used to analyze RS in vivo.

One of the ways to assay RS physiologically is to determine

starch in the undigested ileal content. Terminal ileal samples can

be recovered by intubation or from ileostomy bags. This implies

measuring the area under the curve (AUC) of the serum glucose

concentration over the first 2 h after administering a starch and dividing


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this by the serum glucose response after consumption of

an equal amount of glucose.

Determination of breath hydrogen (breath tests) can also be

used as a semiquantitative measurement for RS. In a study on effect

of RS on human colon, increased fermentation was verified

by elevated breath hydrogen excretion .From the different animal models, the antibiotic-treated rat model

is the one commonly used.

References:

Champ, M.,Langkilde A.M, Brouns, F. and Kettlitz, B. (2003a).Advances in the dietary characterization .1. Definition of dietary fibre, physiological relevance ,health ben

and analytical aspects Nutr. Res. Rev. 16: 71-82,http://journals .cambrorg/action/display Abstract from pg=online&aid=607688.

Champ, M.,Langkilde A.M, Brouns, F. and Kettlitz, B.(2003b). Advances in dietary

characterization. 2. Consumption, chemistry, physiology and measurement of resisstarch; implication for health and food labeling. Nutr. Res. Rev. 75:733-

http://journals. Cambridge.org/action/display abstract from page

aid=online=607768.Champ,M. (2004). Resistant Starch,Starches in food, Elisson, Ann-Chalotte, ed.,

Raton: CRC-Press: 560-574.

Englyst, H.N. and Cummings, J.H. (1987). Digestion of the polysaccharides of potato insmall intestine.Amer. J. Clin. Nutr, 45: 423-431.

Englyst, H.N., Kingsman S.M. and Cummins, J.H. (1992). Classification and measureme

nutritionally important starch fractions. Eur. J. Clin. Nutr.46(2): 33-50.

Hylla, S. Gostre. A. Duesl, G., Anger, H., Bartram, H.P., Christl, S.U., Kasper, H., ScheppW. (1998). Effects of resistant starch on the colon in the healthy volunteers: pos

implications for cancer prevention.Amer. J. Clin. Nutr. 67: 136-142.

Premavalli, K.S., Roopa, S. and Bawa, A. (2006). Resistant starch:A functional dietary fIndian food Industry. 25(2): 40-45.
http://journals/http://journals/http://journals/http://journals/


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Resistant starch: An alternative source of dietary fibre.

peaker: Monika Mathur Addm. 2006FST145M


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