sensory texture profile, grain physico-chemical characteristics and instrumental measurements of...

SENSORY TEXTURE PROFILE, GRAIN PHYSICO-CHEMICAL CHARACTERISTICS AND INSTRUMENTAL MEASUREMENTS

OF COOKED RICE

SYLVIE ROUSSETI, BRIGITTE PONS2 and CARINE PILANDON'

Institut National de la Recherche Agronomique Station de Recherches sur la Viande

Theix, 63122 Saint Genh Charnpanelle, France

2Centre de Cooptration International en Recherche Agronomique pour le Dkveloppernent Dtparternent des Cultures Annuelles

Laboratoire de Technologie des Ctrtales Maison de la Technologie BP5035, 34032 Montpellier Cedex 1 , France

(Manuscript received April 21, 1994; in final form September 23, 1994)

ABSTRACT

Three samples of raw-milled rice, and 4 differently parboiled rices were used to study and to relate sensory perception to instrumental measurements. Variance analysis showed that some physico-chemical characteristics indicated great dv- ferences among rice samples: thickness of cooked grain, length/width ratio, water uptake, elastic recovery, white core rate and amylose and protein contents. The m s t discerning sensory attributes were: elasticity, stickiness, pastiness, mealiness, length of grain, prmness, crunchiness, time in mouth, brittle texture and juiciness. The correlation circle of the principal component analysis (PCA) showed high correlation between some sensory characteristics and instrumental measurements. Melting texture, surface moistness, juiciness, were positively correlated with water uptake (r = 0.70, 0.61, 0.71). Granular texture, crunchiness, brittleness and mealiness were significantly afected by white core presence (r = 0.81, 0.74, 0.86, 0.83). Elasticio was dependent upon elastic recovery and firmness measured by the Viscoelastograph, but not linearly. Length of cooked grain was correlated with the lengthlwidth ratio of raw grain (r = 0.83). Pastiness, compactness, stickiness were slightly influenced by the thickness of raw grain (r = 0.81, 0.67, 0.72). To a weaker extent, the sensory firmness was associated with the firmness measured by extrusion force using an Ottawa cell (r = 0.58). PCA showed great

'Corresponding author: Sylvie Rousset ,

Journal of Texture Studies 26 (1995) 119-135. All Rights Reserved. 0 Copyright 1995 by Food & Nutrition Press, h e . , Trumbull, Connecticut. 119

120 S. ROUSSET, B. PONS and C. PILANDON

differences in texture between rices. Two of the parboiled rices were very elastic, another was firm, granular, crunchy and mealy. The remaining two, cooked longer, were moister and more melting. Among the 3 samples of raw-milled rices, differences in grain length feeling and melting-granular-brittle characteristics. were distinguished.

INTRODUCTION

Many factors affect the texutre of cooked rice: agronomic conditions (Asaoka et al. 1984; Resurreccion et al. 1977), physico-chemical characteristics (Juliano 1979; Perez and Juliano 1979; Damardjati et al. 1986; Sowbhagya et al. 1987; Kaw and De La Cruz 1990), processing steps such as drying, storage (Chrastil 1990), polishing, parboiling conditions, and cooking conditions (Juliano et al. 1981; Okabe 1979). The classical approaches to the objective assessment of rice quality are based on physico-chemical analysis and instrumental measurements of cooking properties. There is a third method: sensory evaluation. However, information on sensory texture of rice is either limited or hedonic (Okabe 1979; Kumari and Padmavathi 1991; Perez et al. 1993). Many objectives of breeding programs are the selection of varieties with good cooking quality. Chataigner (1991) reports that the consumption of rice in France doubled over the last 20 years, particularly parboiled and quick-cooking parboiled rices, which now represents about 50% of the French market (Lechevallier 1990). The purpose of this study was to measure the differences in the texture of seven rices using instrumental and sensory methods and to relate these two sets of data.

MATERIALS AND METHODS

Rices and Physico-Chemical Characteristics

Seven milled rices of differeing physico-chemical properties were used (Table 1). Three (D, E, F) were raw-milled rices and the other four (A, B, C, G) were parboiled under different conditions: A and C were parboiled under type I conditions, and B, G under type II conditions. According to EEC commercial classification, all rices are “long B” type (length/width >, 3 and grain length 2 6 mm) except one (rice E), which is “long A” type (2 < length/width < 3 and grain length 2 6) . Length, width and thickness of 60 noncooked grains of milled rices were determined by using a grain measurement device with 0.01 mm gradua- tion. Chemical analysis were carried out on ground milled rices. Protein (% N x 5.95) was determined by a micro Kjeldahl method with a TECATOR KJELTEC apparatus (Sweden). Amylose content was determined on defatted rice meal by a colorimetric standard method (no. 6647, I S 0 1987).

MEASUREMENTS OF COOKED RICE 12 1

TABLE 1. LIST OF RICE SAMPLES

Samples Length Origin Cooking time Classification (min)

Raw-milled rice D Long B Basmati 12 E Long A EEC long grain 13 F Long B EEC Indica type 15

Parboiled rice Parboiling under type I condition A Long B EEC precooked 6

C Long B US precooked 10

Parboiling under type I1 condition B Long B EEC Indica type 10

H (G overcooked) Long B EEC Indica type 2s G Long B EEC Indica type 17

Cooking Procedure

A 125-g portion of milled rices were put into a perforated plastic bag and cooked for accurately timed periods in 1 L of boiling natural spring water (Volvic, France) containing 7 g of sodium chloride. The water was kept at moderate boil during cooking. Each rice sample was boiled during a specific cooking time recom- mended by the commercial supplier: A for 6 min, B and C for 10 min, D for 12 min, E for 13 min, F for 15 min. G was cooked for 2 different times: 17 and 25 min. Overcooked rice G for 25 min was named rice H.

Cooking Quality Instrumental Evaluation

Just after cooking, the perforated plastic bag containing the rice sample was taken out of the boiling water to let the water drain off for 30 sec. Then rice samples were transferred to a 1.25 mm sieve and strained for a further 30 s before weighing. The cooked rice texture was evaluated after a 4-min period.

Water uptake was defined by the quantity of water absorbed by 100 g of rice. After cooking, the percentage of grains with a white core (not completely gelatinised) for raw-milled rices or with an opaque core for parboiled rices was measured by crushing 10 rice grains between two glass plates.

Cooking losses were expressed as the total amount of soluble and insoluble matter in the cooking water after draining. The cooking water was stirred and 25 ml was taken and dried at 102C for 15 h in a fan-assisted oven. For this determination, rices were cooked in the boiling water without sodium chloride.

The texture of warm cooked rice was evaluated exactly 5 min after the end of cooking. Thickness, firmness and elastic recovery of cooked rices were determined with the Viscoelastography apparatus (no. 6648, I S 0 1985). Firmness was


also evaluated with an Instron Universal Food Testing Machine (Model 1140) using a modified method derived from Perez and Juliano (1979). Cooked rice samples (17-g portions) were put into an Ottawa Texture Measuring System Cell, modified with four side liners to reduce the cell cross-section to 15% of the original and used a 2.6 x 2.5 cm plunger. Firmness was defined as the average force (in kg/cm2) needed to extrude rice through the cell perforated base at a crosshead speed of 10 cm/min. Stickiness was not measured since the repeatability of the method was low when applied on warm cooked rice. For each sample, 3 cook- ings were carried out and each analysis was determined in duplicate on cooked rice.

Sensory Texture Profile

The assessors were first trained to taste products and to choose texture attributes that best described the products and the differences between them. The defini- tion and significance of texture attributes were previously determined by Mioche and Touraille (1990), Civille and Szczesniak (1973) and Skinner (1988).

At each session, all eight samples were evaluated under red light to mask col- our differences. A profile of 19 sensory descriptors selected by the panel was evaluated 3 times by 25 trained assessors on nonstructured scales (Table 2). Assessors were instructed to place a cursor across the scale at the point which best described the intensity of each rice descriptor.

Statistical Analysis

Instrumental data were analysed by one way variance analysis to assess the effect of rice sample. Sensory data were analysed by a two way variance analysis to assess the respective effects of rice sample, assessor and that of their interaction using the SAS package. Mean separation was performed using the Newman- Keuls test. Data were also analysed by Principal Component Analysis (PCA). In this study, PCA calculated the linear combination of .sensory variables (active variables) describing as much of the variance in the original data as possible. The first PCA scatter diagram showed the correlations between sensory variables and principal components. On this diagram, instrumental variables (supplemen- tary variables) were superimposed to show the relationships between sensory and instrumental data. In the second scatter diagram the sample scores were plotted to present the relationships between samples. Statistical and graphic programs by Schlich ([email protected]) were quoted. When the correlation coefficients were highly significant (p < O.Ol) , relationships between sensory and physico-chemical characteristics were shown.

MEASUREMENTS OF COOKED RICE 123

TABLE 2. LIST AND DEFINITIONS OF ATTRIBUTES

ATTRIBUTES Initial feeling

Smoolh Compact Perceived denseness Granular

Moist on surface

Length of grain Heterogeneous in size

Degree to which surface is devoid of roughness

Quantity of hard particules of small size Amount of water perceived on the surface

Perceived grain length Perceived difference in grain size

Fany Perceived fat

Beginning of chewing Firm

Crunchy Brittle Elastic

Juicy

End of chewing Pasty Stichy Mealy Flour-like sensation

Melting Salivation

Time in mouth

Force required to penetrate grains with teeth Heterogeneous in firmness Perceived difference in grain firmness

Perceived sound during the beginning of chewing Degree to which the bite provokes a clean fracture line and individualized fragments Degree to which a deformed product returns to its initial condition after the deforming force is removed Degree of liberation of juice resulting from the bite pressure

Perception of a paste when the product is mixed with the saliva Degree to which the grains adhere together

Degree to which grains pass through to the liquid state in the mouth Quantity of saliva necessary for swallowing the bolus Length of time between the initial feeling and swallowing

RESULTS AND DISCUSSION

Instrumental Measurements

Variance analysis determined that differences were significant in amylose content, protein content, morphological measurements, water uptake, white core rate, firmness measured by Instron or Viscoelastograph, elastic recovery and cooking losses (Table 3).

Means of instrumental measurements are shown in Table 3. All rice samples had intermediate amylose and protein contents. They ranged from 17.2 to 24.8% and from 7.3 to 8.7 % , respectively. D and F raw-milled samples had the highest amylose and protein contents. The E raw-milled sample had the lowest amylose content and B, G and H parboiled samples had the lowest protein contents.

Morphological determination of raw rice showed that the 8 rice samples were typical of long grain rice (length of noncooked grain greater than 6.4 mm and

TAB

LE 3

. IN

FLU

ENC

E O

F TY

PE O

F R

ICE

ON

TH

E PH

YSI

CO

-CH

EMIC

AL

CH

AR

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TER

ISTI

CS

(RES

ULT

S O

F V

AR

IAN

CE

AN

ALY

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D O

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EAN

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OM

PAR

ISO

N T

EST)

hlE

ASU

RE

ME

NT

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e F

(1)

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CT

S (2

)

Am

ylos

e (7

, 8)

100.

7 **

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2

2.0

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20.2

b

23.1

d

17.2

a

24.8

e

22.2

cd

22.2

cd

Prot

ein

(7, 8

) 13

8.2

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7

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7.6b

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7.

3a

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th o

f non

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width less than 2.6 mm). The differences in morphology were significant. The length of raw-milled rices was smaller than the parboiled samples. The increase in grain thickness due to cooking was smallest for A and C parboiled rices (27.5 and 35.6%) as compared to the others (35-63%).

Type of rice and cooking time seemed to influence water uptake. The treat- ment of A and C samples favoured a high water uptake over a short time. In- creasing cooking time induced a higher water uptake by sample H than by G. This effect was not reproducible on different rice types: E rice sample was cooked for longer than sample D, it absorbed significantly less water than D.

White core rate (in terms of percentage of grains) after cooking varied from 0 to 96.7%. Parboiling and cooking time affected these results. Among the parboiled samples, A and C had very low rates of white core: 0% and 50%, respectively. G and H samples also obtained a low core rate (55% and 25%). For the same rice (G), the increased cooking time (over 8 min) reduced its white core rate. The B sample had a high white core rate (96.7%). Therefore, the type of parboiling induced great differences in perception of texture.

As regards firmness, 3 and 4 groups of samples were discriminated by the extrusion force using an Ottawa cell and Viscoelastograph method, respectively. The groups determined by the Newman-Keuls test were different according to the method (extrusion force or Viscoelastograph). For example, sample B had the highest score in firmness measured by Instron, whilst the highest score in firmness measured by the Viscoelastogrpah was obtained by sample C. This means that each method measured different characteristics.

The A and C parboiled rices showed the highest elastic recovery (3 times as much elastic recovery) as compared to B, G , H parboiled rices. Raw-milled rices showed a lower elastic recovery than parboiled rices. Finally, irrespective of the rice sample, cooking losses increased with increased cooking time.

Sensory Evaluation

Influence of Type of Rice, Assessor and Their Interaction on Sensory At- tributes. Two way variance analysis showed that the effect of rice sample was significant on all sensory attributes except for heterogeneity of grain size (Table 4). Assessor effect was always important and due to the difference in use of scor- ing scale among assessors. This is common in the sensory evaluation of a profile (Schlich and Issanchou 1990; Schlich 1993). The interaction product* assessor indicated that assessors partially disagreed on the classification of the rice samples. However, the product effect was significant, as it was always much greater than that of the interaction.

Among the different attributes, elasticity was the most discriminating with F = 104.6 and p < 0.001. This means that the greatest difference in rice texture was due to the property of returning, more or less, to its original size after chew-

TAB

LE 4

. IN

FLU

ENC

E O

F PR

OD

UC

T, A

SSES

SOR

AN

D T

HEI

R I

NTE

RA

CTI

ON

ON

SEN

SOR

Y A

TTR

IBU

TES

(RES

ULT

S O

F A

NA

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S O

F V

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IAN

CE)

FAC

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S (2

) P

rodu

ct

Asse

ssor

In

tera

ctio

n D

egre

e of

free

dom

(7

,382

) (2

4,38

2)

(168

,382

)

AT

TR

IBU

TE

S Fi

rst f

eelin

g sm

ooth

co

mpa

ct

gran

ular

m

oist

in s

urfa

ce

fatty

le

ngth

of g

rain

he

tero

gene

ous

in si

ze

F

24.2

0 **

* 20

.50

***

21.8

0 **

* 25

.90

***

14.8

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.30

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1.20

N

S

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7.10

9.

50

12.7

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60

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B

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1.

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12.9

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95

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a 9

5

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bc

c

99

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11

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cd

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b

107

b 10

8 b

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a

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bc

96

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Begi

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41

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S 11

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s in

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ness

24

.90

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8.90

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80

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8.5

b 11

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40.9

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4 b

12.7

e

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c

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bc

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a br

ittle

32

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90

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1 b

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104.

60

***

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1 a

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2 b

juic

y 32

.30

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17.9

0 *

lit

1.90

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c

5.5

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8 c

10

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End

ofc

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past

y 75

.60

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9.30

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00

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7.3

a 10

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b 7.

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10.5

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88.4

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6.8

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67

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12.7

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ting

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livat

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3640

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test

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ifica

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spec

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S: n

ot s

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fican

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)- N

~~vi

nan-

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o 11

01 d

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(~40

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.

c

N

o\


ing. This result was not usually found in the bibliography. The main attributes used to describe differences in rice texture were sticky and firm (Okabe 1979; Juliano et al. 1981, 1984). In our work, sticky, pasty, mealy, crunchy and length of grain were also conclusive discriminators, but less so than elastic (F values equal to 88.4, 75.6, 60.4, 40.9 and 54.3, respectively).

The comparison of means for elasticity showed that the rices parboiled under type I condition (A and C) were significantly more elastic than all the others (Table 4).

The evaluation of grain length was significantly higher for sample D. One parboiled rice (B) and two raw milled samples (E, F) were perceived as

the most brittle, firm and crunchy. Total salivation and time in mouth were also higher for these samples than for the others. Scores of smoothness were higher for parboiled A and C samples and raw milled sample D.

Increased cooking time of rice H decreased the firmness, elasticity, total salivation and time in mouth but it increased the perception of juiciness, surface moistness, fatty and melting texture. Scores for smoothness, compactness, granular texture, grain length, stickiness and mealiness (measured on G and H samples) were not affected by cooking time.

Sensory characteristics seemed to underscore strong differences between both types of parboiled rices.

Principal Component Analysis - Correlation Matrix. Compact texture had a high positive correlation with pasty and sticky texture (0.81,0.86,respectively, Table 5). Granular texture was positively correlated with crunchy and brittle texture, heterogeneity in firmness, total salivation, and negatively with smoothness. Juiciness, melting texture, fattiness and surface moistness were positively correlated among themselves but opposite to firmness and mealy criteria.

Elasticity had no positive correlation with other variables except with smoothness, but the correlation between them was low (0.59), indicating that this term showed a sensory dimension weakly associated with the other attributes. Moreover this term was opposed to brittle, granular and pasty.

Grain length feeling was also evaluated in opposition to other criteria: compact texture, firmness, heterogeneity, and mealy texture. Therefore the longer it was perceived, the less compact, mealy, heterogeneous it was assessed.

Correlation Circle. The first three components accounted for 86% of the variation. The fourth and following ones were not described because they had too low a percentage of variance (5% for the fourth one).

The 19 sensory attributes were inscribed into a unit circle using their correlation with the first two components. The 14 physico-chemical and cooking properties characteristics were superimposed on this plot by calculating their correlation coefficients with the principal components (Fig. 1).

TAB

LE 5

. C

OR

REL

ATI

ON

MA

TRIX

BET

WEE

N S

ENSO

RY

ATT

RIB

UTE

S A

ND

IN

STR

UM

ENTA

L M

EASU

REM

ENTS

Sm

oot.

Com

p.

Gan

ul.

Moi

st

Fat

ty

Leng

th S

ire

hete

r. Fi

rm

Firm

het

. C

runc

hy B

rittle

Ela

stic

Ju

icy

Pas

ty

Stic

ky M

ealy

Mel

ting

Sal

ivat

. Tim

e

- w

m

Srn

oulli

C

ompa

ct

Gan

ular

M

oist

F

atty

Le

ngth

S

ize

hete

r. F

irm

F

irm

het

er.

Cru

nchy

B

rittle

E

last

ic

Past

y S

ticky

M

ealy

M

eltin

g S

aliv

atio

n T

ime

Am

ylos

e P

rote

in

Leng

th

Wid

th

Leng

lhiw

idth

Th

ick.

(not

coo

kr

lhic

k.(c

ooke

d)

Wat

er u

ptak

e W

hite

cur

e F

irm.(

Inst

run)

F

irm.(

Vis

co)

Ela

s.re

cov.

C

ook.

loss

Juic

y

I .oo

-0.5

9 1.

00

-0.7

1 0.

27

0.75

-0.3

3 0.

02

0.50

0.6

0 -0

.82

-0.4

1 0.

05

-0.2

8 0.

26

-0.6

9 0.

46

-0.5

2 0.

34

-0.5

6 0.

13

0.59

-0

.16

0.72

-0

.36

-0.7

6 0.

81

-0.8

0 0.

86

-0.8

5 0.

53

0.35

-0

.17

-0.5

2 0.

54

-0.2

7 0.

51

-0.0

5 -0

.60

0.24

-0

.39

0.63

-0

.34

-0.1

6 0.

76

0.47

-0

.83

:d -0

.71

0.67

-0

.49

0.36

0.

38

-0.3

4 -0

.58

0.26

0.

00

0.00

0.

44

-0 1

8 0.

68

-0.3

3 -0

.30

0.29

I .oo

-0.6

5 1.

00

-0.2

5 0.

52

1.00

-0

.22

0.41

-0

.37

1.00

0.

43

-0.4

2 -0

.23

0.07

0.

47

-0.5

5 -0

.43

-0.3

6 0.

79

-0.6

6 -0

.22

-0.5

2 0.

79

-0.6

7 -0

.41

-0.3

1 0.

89

-0.6

6 -0

.44

-0.0

1 -0

.64

0.40

0.

07

0.03

-0

.73

0.87

0.

48

0.44

0.4

7 -0

.42

0.43

-0.7

4 0.

56

-0.4

6 0.

38

-0.7

9 0.8

3 -0

.64

0.00

-0

.44

-0.3

7 0.

58

0.49

0

34

0.61

-0

.62

-0.1

8 -0

.58

0.32

-0

.37

-0.0

7 -0

.58

0.09

-0

.01

-029

0.

43

0.11

0.

41

-0.0

7 0.

42

-0.7

7 0.4

4 0.

11

0.27

-0

.05

-0.1

0 0.

35

-0.7

4 -0

.31

0.35

-0

.22

0.83

0.33

-0

.55

0.29

-0

.65

0.05

-0

.18

0.40

-0

.40

-0.5

9 0.

61

0.34

0.

39

0.81

-0

.54

-0.2

3 -0

.18

0.16

-0

.56

-0.5

7 -0

.09

-0.3

1 -0

.1 I

-0.3

7 0.

05

-0.6

2 0.

25

-0.1

9 0.

17

-0.1

4 -0

.07

0.39

-0

40

1 .oo

0.22

1.

00

0.39

0.

74

1.00

0.

40

0.80

0.

89

0.59

0.

49

0.73

-0

.31

0.21

-0

.31

-0.2

7 -0

.68

-0.8

1 0.

11

0.01

0.

50

0.17

0.

19

0.65

0.

44

0.24

0.7

4 -0

.24

-0.8

9 -0

.69

0.31

0.

84

0.82

0.

13

0.88

0.

69

0.24

-0

.37

-0.1

3 0.

03

-0.0

7 0.

08

-0.3

0 -0

.20

-0.6

8 -0

.23

0.45

0.

31

0.05

-0

.54

-0.6

3 0.

15

-0.0

4 0.

28

0.04

-0

.50

-0.0

8 -0

.28

-0.8

1 -0

.81

0.37

0.

26

0.69

0.15

0.5

8 0.

27

-0.0

8 0.

45

-0.0

9 -0

.24

0.21

-0

.38

-0.0

6 -0

.49

-0.1

9

1 .oo

0.84

-0

.32

-0.8

3 0.

29

0.44

0.

65

-0.6

9 0.

79

0.65

-0.1

7 0.

10

-0.6

7 0.

23

-0.5

3 0.

14

-0.2

4 -0

.83

0.74

0.4

7 0.

08

-0.2

6 -0

.32

1 .oo

-0.6

7 -0

.73

0.28

0.

37

0.76

-0

.38

0.52

0.

25

0.16

0.

13

-0.7

6 -0

.20

-0. I

8 0.

22

-0.0

4 -0

.60

0.86

0.32

-0

.19

-0.5

4 -0

.22

1 .oo

0.43

-0

.56

-0.4

9 -0

.80

-0.2

3 0.

00

0.36

-0.4

3 -0

.07

0.78

0.42

-0

.02

-0.5

1 -0

.58

0.03

-0

.79

0.15

0.

67

0.88

-0

.38

1.00

-0

.41

1.00

-0

.50

0.96

1.

00

-0.7

1 0.

76

0.80

0.

69

0.07

-0

.12

-0.6

6 0.

39

0.54

-0

.48

0.20

0.

39

0.04

-0

.20

-0.2

7 0.

18

-0.3

0 -0

.19

0.61

-0

.56

-0.6

4 -0

.16

0.38

0.

48

0.48

-0

.60

-0.7

3 -0

.42

0.81

0.

72

-0.0

6 0.6

5 0.

51

0.71

-0

.20

-0.3

5 -0

.68

0.48

0.5

5 -0

.49

-0.1

7 -0

.14

-0.0

2 -0

.50

-0.4

7 0.

33

-0.6

6 -0

.65

0.05

0.

51

0.38

I .oo

-0.2

3 1.

00

0.51

-0

.72

1.00

0.

20

-0.7

6 0.

88

0.11

0.

19

-0.4

3 -0

.04

0.07

-0

.19

-0.8

4 0.

17

-0.3

8 00

3 -0

.36

0.55

-0

.43

0.47

-0

.70

0.61

0.

05

0.28

0.4

6 0.

38

-0.2

2 -0

.41

0.69

-0.8

3 0.

83

-0.1

9 0.

42

0.01

-0

.55

0.49

-0

.51

-0.4

2 0.

25

-0.7

9 -0

.24

-0.0

5 0.

28

0.34

-0

27

E I .o

o 0

a z G

-0.6

3

z -0

.14

-0. I

2 U

0

Z 0.7

3 -0

.73

0.05

-0

.43

-0.7

4 0.

12

0.42

0.

40

0.2

I -0

.41

Coo

k.tii

ne

-0.2

6 0.

21

-0.1

5 0.

05

0.45

-0

.20

-0.0

8 -0

.68

-0.3

5 -0

.46

-0.2

2 -0

.48

0.19

0.

48

0.31

0.

25

0.56

-0

.45

-0.5

Y R

is c

igni

fican

tly d

iffer

ent

from

0 w

hen

r>O

40, p

i0 05 a

nd r>

O SO

, p<O

01

-1

0 1

-1

0 1

pel=

52%

pe

l= 52

%

FIG

. 1. C

OR

REL

ATI

ON

CIR

CLE

S (L

EFT:

FIRST A

ND

SEC

ON

D C

OM

PON

ENTS

; RIG

HT:

FIR

ST A

ND

TH

IRD

CO

MPO

NEN

TS)

AM

YLO

SE: A

rnyl

ose,

PR

OTE

IN: P

rote

in, L

RG

: Len

gth

of n

onco

oked

gra

in, W

RG

: Wid

th o

f non

cook

ed g

rain

, LN

: Rat

io

Leng

Ww

idth

, TR

G: T

hick

ness

of

nonc

ooke

d gr

ain,

TH

ICK

G: T

hick

ness

of c

ooke

d gr

ain,

WA

TE

R W

ater

upt

ake,

CO

RE:

W

hite

core

rate

, FIR

MIN

ST: F

irm

ness

(Ins

tron

), FI

RM

VG

: Fir

mne

ss (V

isco

), ER

V: E

last

ic R

ecov

ery

(Visc

o),

CO

OK

LOSS

: C

ooki

ng l

osse

s, C

OO

KTI

ME:

Coo

king

tim

e.

130 S . ROUSSET, B. PONS and C. PILANDON

The first principal component showed an opposition between the granular-brittle- crunchy-texture, mealiness, salivation, firmness, heterogeneity and juiciness, surface moistness, melting texture, smoothness, grain length. The second component had a high positive correlation with pasty, fatty, compactness and stickmess and a negative correlation with firmness. The third axis separated elasticity from grain length and crunchiness (Fig. 1).

Six main groups of sensory attributes were distinguished qualitatively by their coordinates on the three components (Fig. 1). The first group was composed of mealy, sticky and pasty; the second one: juicy, moist and melting; the third one: brittle, granular and crunchy; the fourth: elastic; the fifth: grain length; the last: firm, salivation and time in mouth.

The results of plotting the instrumental measures in Fig. 1 indicated that white core rate was associated with granular, brittle and mealy perceptions. Therefore the presence of white cores indicated that a part of starch was not gelatinised and remained solid, During chewing these solid particles were cracked and transformed into meal by the assessors.

Water uptake was well related to melting characteristics, juiciness and surface moistness. Therefore, the feeling of melting texture was probably due to the amount of water absorbed by the rice samples.

The firmness measured by the extrusion force using an Ottawa cell approached the firmness evaluated by assessors, whilst the firmness measured by the Visco- elastograph was closer to elasticity. This confirmed that each instrumental method of firmness measured different characteristics. Elastic recovery also approached elasticity.

Noncooked grain lengthlwidth ratio seemed closely correlated with cooked grain length. This may mean that noncooked grain lengthlwidth ratio could predict its characteristics after cooking. This conclusion should be specific for age of crop, variety, processor of our samples.

The noncooked grain thickness was associated with pasty, compact, sticky and mealy textures. This morphological characteristic measured on noncooked grain also seemed to significantly determine the texture of grain cooked under the conditions of our study.

Figure 2 and Table 5 show the most interesting relationships between an instrumental measure and a sensory attribute of each group listed above. The relationships between core rate and brittle texture, noncooked grain thickness and pasty texture, length/width ratio and cooked grain length feeling, water uptake and juiciness were linear, and the associated correlation coefficients were high: 0.86, 0.81, 0.83 and 0.71, respectively, while firmness and elasticity were less well associated with the instrumental measurements. The correlation coefficient between the sensory firmness and the firmness measured by Instron was low (0.58,


Table 5). This result did not agree with the findings of Perez et al. (1993) who found an excellent correlation (0.95). In their study the rice samples were raw milled and very different in their amylose content (from 1.4% to 28.6%), whilst in our study 5 out of 8 rice samples were parboiled and amylose content ranged only from 17.2 to 24.8%. Other authors (Ohtsubo et al. 1990) found that hardness measured by Instron and amylose content showed very high positive correlation. There was no positive correlation of amylose with any of the sensory attributes except a weakly significant relationship with grain length (0.43, Table 5). However, amylose content was negatively associated with compactness (-0.60), length of time (-0.63), total salivation (-0.43) and elasticity (-0.43). The parboiling process had an effect more important than the amylose content on the firmness of rice. Moreover, the proteins seemed to have no influence on any of the sensory attributes except on the perception of grain length (0.42).

Cooking time, cooking losses and thickness of cooked grain were associated with pastiness. It is therefore clear that an increase in cooking time leads to an increase in losses and swelling.

The relationship between elasticity and elastic recovery was not perfectly linear. Between 7 and 42% of the elastic recovery values, the difference in elasticity was not perceived by assessors. Possibly, the assessors and the Viscoelastograph may have been measuring different characteristics or the Viscoelastograph may have been more sensitive than the assessors to differences in elasticity less than 42%. When sensory characteristics were not well associated with any of the in- dividual physico-chemical parameters, MacFie and Hedderley (1 993) suggested seeking multiple variable relations or new instrumental measures. Because of our limited number of samples, multiple regression was difficult to perform.

Plot Description. The eight rice samples replicated three times (24 points) were represented on a plane with the percentage of variation associated with the first and second components or with the first and third axes (Fig. 3). B, E and F samples were opposed to A, C, D and H on the first axis. On the other hand, A and C parboiled samples, located on the negative part of axes 1 and 2, were characterised mainly by their elastic texture. B, E and F were perceived as having a granular texture. Furthermore, E was compact and mealy, while B was rather firm, brittle and crunchy. The G sample was located near the middle of the plot and its characteristics were intermediate among those of the other samples. Increasing cooking time modified the texture of sample G . Therefore H (cooked 8 min longer than G ) was much more melting than both G and all the others. Finally sample D was discriminated from the other samples on the third axis. Its grain length was the highest.


' Relationship between the core rate and the brittle texture.

I= 0.86 1 3 5 -

B .

0 50 100

Core rate 1%)

Relationship batween the raw grain thickness and pasty texture.

F 0.81

16 i

P I a 12

14 1 m :I 8

m m

' 611

4 L - ; I

1.55 1 6 1 6 5 1.7 1.75

Thickness (mm)

_ ~ _ _ -

Relatianship between the elastic recovery and the alasticity.

I= 0.88 16

1 4 - : I

8 s 10

' I

A- 4 --

1 5 21 5 41 5 61 5

Elastic recovery (Yo1

Relatmnsh!p between the water uptake and juiciness

I= 0.71 12

J 10

I 8 U

C

v 6 I 4 _ _ ~ _ _ 110 130 150 170 190

Water uptake i%l

-

L e n

9 t h

~

I Relationship between the lengthtwidth ratio

and sensory length r-083

I 1

6~

4 1- __i

2.4 2 9 3 4 3 9

Length/width ratio

Relationship between the firmness measured by lnstron and assessors

I= 0.58 16 -

I ,

I 6 L m m 8 : s ' .

- 1 4 1 5- 0 6 0 8 1 1 2 1 4

Ftmness iKgicm21

FIG. 2. RELATIONSHIPS BETWEEN INSTRUMENTAL MEASURES AND SENSORY ATTRIBUTES (P < 0.01)

MEASUREMENTS OF COOKED RICE

I t

133

134 S. ROUSSET, 8. PONS and C. PILANDON

CONCLUSION

Rice texture was described by numerous sensory attributes. However, six main sensory dimensions (elasticity, juiciness, grain length, firmness, brittle and pasty texutre) emerged from the profile to discriminate the rice samples. Among these sensory attributes, some correlated with instrumental measures. The next step could be to test other rice samples and to confirm the relevance of relationships between white core rate and brittle texture, water uptake and juiciness, raw grain thickness and compact texture, length/width ratio and cooked grain length feeling. For the other attributes less well correlated with instrumental measures, it would be interesting to find other measurements or to carry out multiple regression with a greater amount of data.

REFERENCES

ASAOKA, M., OKUNO, K., SUGIMOTO, Y. , KAWAKAMI, J. andFUWA, H. 1984. Effect of environmental temperature during development of rice plants on some properties of endosperm starch. Starch 36, 189-193.

CHATAIGNER, J . 1991. Les tendances de la consommation du riz en Europe: Comparaison avec les Etats-Unis. In La consommation du riz en Europe, ( J . Chataigner, ed.) pp. 21-45, (Serie et Documents, no. 97: INRA-ENSA. Montpellier) .

CHRASTIL, J. 1990. Chemical and physicochemical changes of rice during storage at different temperatures. J. Cereal Sci. 11, 71-85.

CIVILLE, V.C. and SZCZESNIAK, A.S. 1973. Guidelines to training a texture profile panel. J. Texture Studies 4, 204-223.

DAMARDJATI, D.S. , BARlZI, SOEKARTO, S.T., SIWI, B.H. and JULIANO, B.O. 1986. Major factors of physicochemical properties affecting the eating quality of some Indonesian rice varieties. Indones. J . Crop Sci. 2, 1-6.

ISO. 1985. IS0 no. 6648: Rice. Evaluation of cooking behaviour using a viscoelastograph. 3p.

ISO. 1987. IS0 no. 6647: Rice. Determination of amylose content. 4p. JULIANO, B.O. 1979. The chemical basis of rice grain quality. In Proceedings

of the Workshop on Chemical Aspects of Rice Grain Quality, pp. 69-90, In- ternational Rice Research Institute, Los Banos, Laguna, Philippines.

JULIANO, B.O. et al. 1981. International cooperative comparison of instrument methods for cooked rice texture. J. Texture Studies 12, 17-38.

JULIANO, B.O. et al. 1984. International cooperative test on texture of cooked rice texture. J. Texture Studies 15, 357-376.

KAW, R.N. and DE LA CRUZ, N.M. 1990. Interrelations among physico- chemical grain quality characters in rice. J. Genet. Breeding 44, 1139-1 142.


KUMARI, S. and PADMAVATHI. 1991. An objective and sensory assessment of cooking quality of some rice varieties grown in Andhra Pradesh. J. Food Sci. Technol. 28(1), 31-34.

LECHEVALLIER, C. 1990. La commercialisation du riz de Camargue; Bilan 88/89: Perspectives. MCmoire ingCnieur Purpan, Toulouse. 107 p.

MacFIE, H.J.H. and HEDDERLEY, D. 1993. Current practice in relating sensory perception to instrumental measurements. Food Qual. Pref. 4 , 4149 .

MIOCHE, L. and TOURAILLE, C. 1990. Mise au point d’un profil de texture pour l’analyse en bouche de produits alimentaires. Sci. Aliments 10, 697-7 11.

OHTSUBO, K., SISCAR, J.J.H., JULIANO, B.O., IWASKI, T. and YOKOO, M. 1990. Texturometer and Instron texture measurements on cooked Japanese milled rices. Rep. Nat Food Res. Inst. 54, 1-9.

OKABE, M. 1979. Texture measurement of cooked rice and its relationship to the eating quality. J. Texture Studies 10, 131-152.

PEREZ, C.M. and JULIANO, B.O. 1979. Indicators of eating quality for non- waxy rices. Food Chem. 4 , 185-195.

PEREZ, C.M. JULIANO, B.O., BOURNE, M.C. and ANZALDUA- MORALES, A. 1993. Hardness of cooked milled rice by instrumental and sensory methods. J . Sensory Studies 24, 81-94.

RESURRECCION, A.P., HAM, T., JULIANO, B.O. and YOSHIDA, S. 1977. Effect of temperature during ripening on grain quality of rice. Soil Sci. Plant Nutr. 23, 109-112.

SCHLICH, P. 1993. Contributions la sensomktrie. Thbe de Docteur en Sciences de 1’UniversitC Paris XI Orsay.

SCHLICH, P. and ISSANCHOU, S. 1990. Les mCthodes de profils et leurs alter- natives. Premikres JournCes Agro-Industrie et Mithodes Statistiques. Angers,

SKINNER, E.Z. 1988. The texture profile method. In Applied Sensory Analysis of Foods (H. Moskowitz, ed.) pp. 89-107, CRC Press, Boca Raton.

SOWBHAGYA, C.M., RAMESH, B.S. and BATTHACHARYA, K.R. 1987. The relationship between cooked-rice texture and the physico-chemical characteristics of rice. J. Cereal Science 5, 287-297.

254-272.