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[Article]

Eating Quality Evaluationfor Cooked Rice (1)

-Application of Maltiple Regression on the SensoryEvaluation and Physical Measurements.-

Masako Konishi, Kuniyasu Ide, Keiko Hatae, Atsuko Shimada

The relationship between overall acceptability and physicochemical properties was carried out on31 types of rice employing sensory evaluation and objective analysis.

1. There was a high correlation between sweetness and overall acceptability in both analyticaland preference tests (r=0.88 and r=0.92), but differences between samples were small.

2. For taste, a high correlation (r=0.95) between desirability of taste and overall acceptabilitywas observed, but there was only a low correlation (r=0.23) between strength of taste and overallacceptability, and moreover, a low correlation (r=0.25) between preference and analytical tests.

3. A high multiple correlation coefficient (MR) of 0.97 for the overall acceptability using fourattributes desirability of stickiness, desirability of sweetness, whiteness, and transparency wasobtained by the multiple regression analysis.

4. Desirability of stickiness, transparency, and whiteness, which make a large contribution tooverall acceptability were substituted by objective measurements. Desirability of stickiness wasexpressed in terms of amylose ratio, thousand grain weight of rice, and whole rice grain rate (MR=0.87), transparency was expressed in terms of the L value and the luster as 60 and 75 angles ofincidence (MR=0.66), and whiteness was expressed in terms of whiteness level and the b value(MR=0.71).

5. Overall acceptability of cooked rice was expressed in terms of three attributes, amylose ratio,L value and luster (60), with a multiple correlation coefficient of 0.76.Keywords : multiple regression analysis, objective measurement, cooked rice, sensory evaluation

Introductionice is the staple food of Japanese people, and

since the middle of the Taisho period (1912 926)numerous studies') have been conducted with regardto evaluating the eating quality of cooked rice. Mostof these studies dealt with the physical properti-es215) of cooked rice by objective measurement, andsensory evaluations. Chikubu et al.16"7) reported that

the eating quality of Japonica type rice was expres-sed in five objective ways which relate to someattributes influencing the physical properties ofice ; Horino et al.' reported that the eating

quality of Japonica type rice was based on severalmineral components and their proportions. Theseresults were used in development of the rice tastenalyzer"'") utilizing a near-infrared photometer.

The rice taste analyzer have been commerciallyavailable, but at present, they could not be consid-ered to be sufficiently accurate23,24,42).

ensory evaluation values that are used as thebasis for the rice taste analyzer were judged less

* Tokyo Gas Co , Ltd. Fundamental Technology Research Labo-atory.** School of Human Life and Environmental Science , Ochanom-

zu University.

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than adequate since only limited attributes whichinclude appearance, aroma, taste, stickiness, hard-ness, and overall acceptability for judging rice qual-ity were evaluated. This sensory testing method wasdeveloped by the Food Agency and the NationalFood Research Institute 25,26,34-36).s reportedarlier27), Japanese people look for many different

elements in the eating quality of cooked rice, andparticularly cooked white rice. The appearancewhich includes gloss,- whiteness, plumpness, andtransparency are considered important in the eatingquality of cooked white rice. Furthermore, prefer-ence test using hodonic scale alone is insufficienttherefore, analytical test using intensity scale isessential.

This study aimed to understand the eating qualityof rice using sensory evaluations such as preferenceand analytical test'''. Furthermore, the relationbetween sensory values and objective method valuesof the eating quality of rice, including appearance,which have not been studied before except forwhiteness level,was carried out.

aterials and experimental methods. Materials

total of 31 kinds of rice were used (Table1) 8,29). rown rice, a domestically-produced brandrice was obtained immediately after harvest andwas milled while other samples were procured inalready milled form. The rice was stored for 0-6months at 4C.

) Milling and pulverizing methodsrown rice was milled using a household rice

miller (National KG-1 000) to 90%, and the branwas removed with a thin cotton cloth. Objectivemeasurement of the rice was done using either thegrains, or rice powder pulverized to a maximumparticle size of 300 um with a cyclone sample miller(UDY Corporation).) Cooking method

ater was added to washed 500g of rice to givefinal volume of 1.5 times w/w. The rice was leftimmersed for 1 hour at 20C, then cooked in agas-powered rice cooker (Tokyo Gas : PA-106) andsteamed. After 15 minutes steaming, it was lightlymixed and a cloth was placed over the cookingvesse. The vessel was left in a constant temperatureand a humid chamber at 20C and 60% respectivelyfor 1 hour before use for sensory evaluations andobjective measurements.

Table 1. Samples

Koshihikari Niigata (1)Akitakomachi Akita A

Kinuhikari Ibaraki AKirara 397 Hokkaido ASasanishiki Miyagi AHananomai Yamagata Aukuhikari Fukui Aulcinosei Niigata A

Ozora Mie A'Koganenishiki Kochi A'Koshihikari Chiba A'Koshihikari Nagasaki A'Tsugaruotome Aomori A'Nipponbare Shiga A'Notohikari Ishikawa A'Hatsuboshi Chiba A'Minamihikari Kagoshima A'Koganemasari Kagoshima

oyonishilci Akitaakateshinsenbon Okayama

Fuyo Naraukihilcari Hokkaido

Asukaminori Nara B'Rinkusu' 89

ishilci California U. S. A.Long grain rice California U. S. A.standard price rice Xstandard price rice Ystandard price rice ZKoshihikari (Stored rice) Niigata f StorageAsukaminori (Stored rice) Nara (37C1 month)

Table 2. Evaluation attributes

: conducted2. Sensory evaluationsn each session, two of the 31 rice samples were

evaluated using a 7 point scale anchored from +3to 3 ( + 3 = greater/like extremely, = lesser/

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dislike extremely) . Nipponbare was used as thereference sample anchored as 0 in all sessions. Twosessions were conducted in a day for 15 days. Thetransparency, gloss, whiteness and plumpness thatmade up the appearance were evaluated by analyti-cal test only. Other attributes, were also evaluatedby analytical test and preference test to determineits desirability. Tests were also conducted for over-all acceptability. The testing panel consisted of 15researchers from Ochanomizu University (Table 2)

. Objective measurement of rice) One thousand grain weight, whole rice grain

rate, whiteness levelvaluations were performed on rice grains. The

weight of 1,000 grains of brown rice or milled ricewas expressed as thousand grain weight. The wholerice grain rate (WRGR) for brown rice was consid-ered as the proportion of whole grains relative tothe total number of grains, calculated by gradinginto whole grains, immature grains, colored grains,opaque rice kernel, and cracked kernel rice. TheWRGR for milled rice was considered to be theproportion of whole grains relative to the totalnumber of grains, calculated by grading into wholegrains, powdery grains, broken kernels, and coloredgrains. The grade of grain was determined by pro-viding light on 1,000 grains of rice, discriminated bycolor and optical characteristics according to theamount of light passing through the rice using a ricegrain discriminator (Ketto Electric Laboratory RN-500) .

hiteness level was measured using a photodiodewhiteness lerel tester (Ketto Electric Laboratory c-300) according to the standard measuring method")published by the Food Agency.) Rice Composition

omposition was studied using rice powder.Water content was measured by heat drying atatmospheric pressure (105 1C, 5 hours)"). Nitro-gen was measured using micro-Kjeldahl method(Buchi 339), multiplied by 5.95 to obtain theamount of crude protein37). Ash content was mea-sured by the 550C direct ash conversion method'.Mineral composition was studied by shaking pow-dered rice for 24 hours in 1% aqueous hydrochloricacid (toxic metal measurement reagent) , then filter-ing and using the filtrate. Sodium and potassiumwere measured with ion chromatograhy equipment(Dionex) under the following test conditions. Sam-ple volume : 50 gil, column: Ion-pack cation column

(cs-3) , elution solvent : 20mM hydrochloric acid,regeneration solution : tetrabutyl ammoniumhydroxide, flow rate : 1 0 m//min. For magnesiumand calcium, 50ml of the fluid sample was placed ina beaker, 5m/ of hydrochloric acid (toxic metalmeasurement reagent) added, then poured into awatch glass, leaving a path for vapor to escape. Themixture was then heated using a burner and allowedto undergo acid decomposition until the residue wasapproximately 40m1. After cooling, purified waterwas added to make up to 50m/ again.Magnesiumand calcium are then measured using an inductivecoupled plasma emission spectrometry system(Seiko Denshi Kogyo JY 48 P) Amylose andamylopectin proportions were measured by iodinecoloration comparison') after adjusting the ricepowder off with purified starch using the alkaliethod31).

4. Objective measurements of cooked rice) Volumeater was added to the cooking vessel until it

was at the same height from the top of the vessel asthe surface of the cooked rice. The amount of waterwas then measured in a measuring cylinder.

) Coloration, luster120g sample was placed evenly in a laboratory

dish for color measurement. A chroma meterMinolta : CR-200, CM-500) was used to measureXxy, Lab, L*a*b*,WI (white chromaticity) and YI

(yellow chromaticity) . Luster was measured using avariable angle gloss meter (Nihon Denshoku VGS-300 A) obtaining the value of normal reflection/amount of scattered reflection when light is shone atangle of incidence of 60, 75 and 80 degrees.

) Water contentater content was measured by heat drying at

atmospheric pressure").) Textureardness, stickiness, adhesiveness, and cohesive-ness were measured by a texturometer (Zenken)

Eleven grams cooked rice was placed in a rice cup8mm wide and 13mm deep, then compressed using

an 18mm diameter lucite plunger, with a mastica-tion speed of 6 cycles/minute, clearance of 1.2 mm,chart speed of 750mm/minute and a measurementvoltage of 1 V.

esults and discussion1 Sensory evaluations

hree types of Japanese standard price rice,4 (256)

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Eating Quality Evaluation for Cooked Rice ( 1Table 3. Average values of sensory evaluation scores

Japonica and Indica type rice produced in Californiawere used in addition to 23 types of domestic brandrice produced in different areas in Japan and withdifferent Japan Grain Inspection Association grade,which included 5 ranks of eating quality of rice bysensory evaluation. The number of samples wasexpanded to a total of 31 by adding artificially agedrice produced by storing the highest and lowestranking rice packed in polyethylene bags at 37C for1 month after milling.

able 2 shows the result of preference and analyt-ical test on various attributes. Four attributes forappearance (transparency, gloss, whiteness, andplumpness) were found to have desirable character-istics27). In this study, aroma, taste, and texture

attributes were subjected to both preference andanalytical tests while the appearance was subjectedto analytical test only.

he average values for eating quality accordingto the sensory evaluations are shown in Table 3.Overall acceptability ranged from 0.93 to 2.53,showing that the samples had successfully includedrice with a variety of eating qualities. Statisticalanalysis was done using a data processing software"Multi -Tokei" of "Social survey Research Informa-tion Inc.". A one-way analysis of variance showedthat all 15 attributes, including overall acceptabilitywere significant at P 0.01. Koshihikari from Niigataprefecture was evaluated as the most desirable interms of overall acceptability and Indica type rice

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Table 4 Correlation between analyticalnd preference test

** a level of significance of 1%from California was considered least desirable.

able 4 shows the correlations between the ana-lytical and preference test for aroma, taste, sweet-ness, hardness and stickiness. A significant negativecorrelation (r= 0.66 and P

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2 Objective measurements of rice and cookedrice

Thirty one types of rice and cooked rice wereevaluated for their composition using objectivemethod. Table 6 shows the average values, atandarddeviations and coefficients of variation. Thecoefficients of variation were used to compare thedispersion for measurements of each attribute.

ince there was a high correlation between thethousand grain weight of brown rice and that ofmilled rice, only the results for thousand grainweight of milled rice with its large coefficient ofvariation was shown. Hokkaido's Kirara 397 andYukihikari had extremely low whiteness level buthigh protein values. Inatsul3) reported that averageprotein content of 214 rice samples produced in theSorachi area in Hokkaido were higher than forTohoku and Hokuriku regions, but were similar tothose in other regions. Consequently, the Hokkaidorice used in this study had high protein values.Indica type rice are said to have relatively highproportions of amylose, and our Long grain ricesamples (Indica type) has 26%, but Rinksu'89 (In-dica type) has only 18% which was similar to Japon-ica type rice (short grain). Potassium, magnesium,calcium, and sodium were most abundant in alltypes of rice. This concurred with the findings repor-ted by Horino et al.19). Texturometer measurementsshowed that Long grain rice (Indica type) had thehighest value for hardness, 17.9 T. U., and thelowest value for stickiness, 0 T. U..

he appearance of rice, which includes colorationand luster were measured.

ntil now, food colors have been used to as agauge to grade the quality of agricultural') foodand animal products"). Study on whiteness lever")and coloration in rice which describes quality con-trol of brown rice using image processing of trans-mitted light") were reported. Using WI (whitehronaticity : ASTM E 313) and YI (yellowhromaticity: ASTM E 313), values of Yxy, Lab,

and L*a*b* for color specifications in the measure-ment of cooked rice3739), we found high correlationsin L, L* and WI values, and b, b* and YI values, andbetween the values, L and b values had the largestcoefficients of variation. The L value was Hunter"slightness level of light and the b value representedyellow-blue. Futhemore there was a high correlationbetween a and a* values, but only a* values areshown in Table 6 because their coefficient of varia-

tion was larger than a. The x and y values re-presenting chromaticity were the same for all ricesamples, so we did not show the data.

n general, the value of luster (G value) is expres-sed in terms of the luster of glass with coefficient ofrefraction n=1.567 as a standard set to 100, regard-less of the angle of incidence. The G values of 31types of rice were 1.63-4.03 at 60, 1.39-3.45 at

5, 0.11-0.93 at 80. All G values were lower thana standard and with low coefficient correlationsbetween 60 and 75 (r 0.25), 75 and 80 (r 0.24) , and 60 and 80 (r= 0.77).

. Relation between sensory evaluations andobjective measurements

n attempt was made to use objective measure-ments to substitute sensory evaluation for desirabil-ity of stickiness, transparency and whiteness, wherethese attributes were considered to contribute to theoverall acceptability by stepwise regression analy-sis.

This study aimed to understand physical prop-erties using sensory values and objective methodvalues of desirability of stickiness, transparencyand whiteness. As a result, it was possible to repre-sent the attributes by the objective measurementsshow below.*Stickiness (Y)

0.18 amylose ratio +0.19 thousand grain-0.66**) (0.35**)

weight of rice0.05 whole rice grain rate+ 3.28-0.28*)= 0.87*Transparency (Y)=0.68 luster [60]-0.08 L value

0.55*) ( .31)0.36 luster [75]+2.820.23)= 0.66*Whiteness (Y)=0.09 whiteness level 0.37 b value 2.32

0.52*) (-0.43**)= 0.71: standardized partial regression coefficient*: P

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treatment of metals at a 60 angle of incidence couldbe objectively evaluated by luster. Metal and riceare very different materials, but there was a similar-ity in their transparency using objective measure-

ent.In the objective measurements, although L, L*,and WI are color indexes representing white-blackand they were expected to have strong relation towhiteness evaluated by sensory test, the combina-tion of whiteness level of rice and b value in multi-ple regression analysis was more suitable for ex-pressing the whiteness of coofed rice.ince overall acceptability could be successfullyexpressed in terms of the multivariate linear regres-sion model using sensory values (multiple correla-tion coefficient was 0.97) we substituted the sen-sory values with objective measurements. The crite-rion variable was overall acceptability , and theexplanatory variables were the eight objectivemeasurements selected by multiple regression anal-ysis : desirability of stickiness, whiteness, and trans-parency.Overall acceptability (Y)

= -0.18 amylose ratio +0.29 luster [60)-0.60") (0.25)0 .03 L value-F-3.87

-0.12): standardized partial regression coefficient*: P

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37) Nihon Shyokuhin Kogyo Gakkai Shyokuhin Bun-ekiho Henshyuiinkai hen: Shyokuhinbunsekiho

Korin) (1984)38) Huruya, T.: Jidoseigyorengo Koenkaimaezuri, 35,

53 (1992)39) Kurosawa, M., Nakanishi, S.: Nihon Fazy Gak-aishi, 6, 1, 42 (1994)

40) Hosokawa, A.: Nogyo Kikai gakkaisi, 40, 2171987)

41) Hirayama, Y., Kajiyama, T., Yoshida, K.: Kinzo-uhyomen Gijutukyokai Gakujutukoentaikai

oenyosisyu, 69, 136 (1984)42) Yanase, H: Japan Food Science, 8, 32 (1994)

Received Apr. 27, 1995)

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