Important Sensory Attributes Affecting Consumer Acceptance of Sorghum Porridge in West Africa as Related to Quality Tests

Journal of Cereal Science 30 (1999) 217–225 Article No. jcrs.1999.0283, available online at http://www.idealibrary.com on

Important Sensory Attributes Affecting Consumer Acceptance of Sorghum Porridge in West Africa as Related to Quality Tests A. Aboubacar∗, A. W. Kirleis† and M. Oumarou‡ ∗ Department of Food Science and the Whistler Center for Carbohydrate Research, Purdue University, 1160 Food Science Bldg., West Lafayette, IN 47907-1160 U.S.A.; ‡INRAN, Labo-Sols, BP 429, Niamey, Niger Received 28 July 1998

ABSTRACT Studies were conducted in Niger, West Africa to determine the most important sorghum porridge quality parameters that affect consumer acceptance. Consumer sensory evaluation was carried out on 14 sorghum cultivars varying in pericarp colour and endosperm hardness. Laboratory analyses were then conducted to determine the physical and chemical properties of the grain responsible for porridge quality. Porridge texture was evaluated using three different techniques and porridge colour was measured using the Hunter Lab colorimeter. Results were compared with consumer ratings. The textural characteristics of stickiness in the mouth and cohesiveness were found to be the most important sensory attributes, followed by the taste and aroma of the product. Instron slope measurement was the most reliable objective method for predicting consumer response to texture followed by the penetrometer method. The gel consistency test showed some association with consumer rating for porridge texture but had no significant relationship with consumer ratings of porridge texture intensity. A wide range of porridge colour was acceptable to consumers with only brown or darkcoloured porridge being rejected. Consumer rating for porridge colour correlated significantly with Hunter L and DE values. Porridge quality was affected by grain hardness, but none of the proximate components (ash, fat, and protein) of the decorticated grains correlated with the texture of the product.  1999 Academic Press

Keywords: sorghum porridge, sensory analysis, quality tests, texture, physicochemical properties.

INTRODUCTION Cereal porridges are the major food staple in many African countries and India. Tuwo, a sorghum or  : AACC=American Association of Cereal Chemists; AHI=abrasive hardness index; L= lightness; LSD=least significant difference; TADD= tangential abrasive dehulling device; TKW=thousand kernel weight. This is Paper 15641 of the Purdue University Agricultural Research Programs. Corresponding author: A. Aboubacar. Phone: (765) 494-8278; Fax: (765) 494-7953; E-mail: [email protected]. † Deceased. 0733–5210/99/110217+09 $30.00/0

millet porridge consumed in Niger (West Africa), is usually eaten with the fingers and is accompanied by some type of vegetable or meat sauce. Porridge quality attributes of importance to consumers have been reported to be keeping quality, followed by texture, colour, and taste1. Porridge of good texture was described as firm, non-sticky, and possessing a good overnight keeping quality. Considerable effort has been expended on the development of a laboratory method for evaluating thick porridge texture/consistency. In a previous study2 using a back extrusion test on a Universal Testing Machine (Instron) the texture of cooked whole and decorticated sorghum grains was reported to be strongly influenced by grain hardness.  1999 Academic Press

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Table I Cultivars

Mota Maradi El Mota Fara Dawa INRAN-FI Sepon-82 UV1002 Hageen-Dura MDW Biyel guero N’gabari kime Dosso kuba BDF 1/2 MSB Aje-bitchi LSD

Physical characteristics of sorghum grain Pericarp Colour

White Orange red White Yellow Pale yellow Pale yellow Light brown Pale yellow Brown Red White Brown Pale yellow White —

TKWa (g)

Stenvert hardnessb (sec)

AHIc (sec)

Density (g/cm3)

27·0 19·5 19·9 22·6 20·4 25·1 23·7 35·1 38·3 32·2 25·7 31·4 15·0 24·1 1·2

10·1 10·7 18·6 23·4 25·9 23·8 11·5 18·9 10·8 11·5 14·4 14·4 29·5 15·1 1·4

5·8 6·8 6·6 7·2 7·2 6·9 5·0 8·3 6·6 5·9 6·5 5·8 7·9 7·1 0·2

1·332 1·363 1·343 1·382 1·350 1·368 1·348 1·367 1·329 1·320 1·346 1·309 1·370 1·353 0·01

a

TKW: Thousand Kernel Weight. Higher values indicate harder grain. c AHI: Abrasive Hardness Index. b

Sorghum porridge firmness measured by a compression test on the Instron was found3 to correlate significantly with starch properties but not with grain hardness. On the other hand, stickiness of sorghum porridge determined with the Instron was found to have a significant negative correlation with grain hardness4. Firmness measurements with the Precision Penetrometer have also shown that hard grains produced firmer porridge than soft grains5,6. The gel consistency test7 for eating quality of rice has also been used to determine the texture of sorghum gels8 indicating that hard grains produce less consistent gels than soft grains. All these laboratory methods were developed to provide sorghum breeders and processors with an estimate of the food quality of early generation material. Although these methods have shown the strong influence of grain hardness and starch properties on sorghum gel texture, none of them has been compared with consumer test panel results. Currently, improved sorghum cultivars developed by breeders in Niger are evaluated for food quality by testing the porridge acceptability with consumer sensory panels. Although food quality trials provide some very useful data for breeders, the trials involve substantial expenditure of time and money and limit the number of cultivars that can be evaluated. In addition, these trials require large quantities of grain which means the tests can only be done with advanced breeding material. The

objectives of this study were to determine the most important sorghum porridge sensory quality attributes that affect consumer acceptance and to determine the best instrumental methods that could be used to predict consumer response to porridge quality. MATERIALS AND METHODS Materials Fourteen food-grade sorghum cultivars grown in Niger during the 1990 crop season were used in this study. The grains were selected to cover a wide range of pericarp colour and endosperm hardness (Table I). All grain samples were decorticated in a tangential abrasive dehulling device (TADD, Venables Machine Works Ltd, Saskachewan, Canada) to yield 80% decorticated grain and ground into flour in a Tecator Cyclotec 1093 sample mill (Tecator AB, Hogana, Sweden) to pass through a 0·5 mm mesh screen. Physicochemical properties of grain and flour Moisture, fat, protein, and ash contents of the flours were determined by AACC approved methods9 44-10, 30-25, 46-12, and 08-01, respectively.

Consumer acceptance of sorghum porridge in West Africa

Grain hardness was evaluated by both the Stenvert hardness test10 and by the abrasive hardness index (AHI) method11 using the TADD. In the Stenvert hardness test, a 20-g grain sample was ground in a micro hammer-cutter mill (Glen Mills Inc., Maywood, NJ) and the time in seconds to collect 17 mL ground meal was reported as Stenvert hardness. AHI is defined as the time in seconds required to remove 1% of the kernel as fines. Grain density was measured by a gas displacement method12 in a stereopycnometer (Quantachrome Corp., Syosset, NY). Laboratory porridge preparation Porridge was prepared by cooking flour slurries (9·5 g flour dry weight basis and 40 mL water) for 5 min on an electric hot plate, poured into moulded, open-ended Nalgene polypropylene tubes, and left for 1 h at room temperature before being tested. Flour and porridge colour Flour and porridge colours were measured with a Hunter Lab colorimeter model D25-PC2 (Hunter laboratories, Reston, VA). Colour was expressed in terms of lightness (L) and colour difference from a standard tile (DE). DE was calculated as DE= (DL2+Da2+Db2)12 where L=lightness; a (+)= red, a (−)=green; b (+)=yellow, b (−)=blue colour value. Porridge and gel texture Porridge firmness was measured using a Precision Penetrometer (Precision Scientific Co., Chicago, IL) and an Instron model 1132 Universal Testing Machine (Instron Corporation, Canton, MA). For penetrometer firmness, porridge cylinders (11 mm height and 25 mm diameter) was removed from tubes and placed under a 9·5 g cone attached to the penetrometer5. The cone was then released and after 2 s, the depth of penetration was read on a dial calibrated in 0·1 mm. The higher the reading the softer the porridge. Another sample of porridge (cylinders 23 mm diameter and 29 mm thick) was placed on a hard surface under an Instron probe (8·5 cm diameter plate connected to a 2 kg compression cell) and compressed until the porridge sample completely fractured. The higher the force, the firmer the porridge.

219

Crosshead speed and chart speed were set at 5 and 10 cm/min, respectively. Force-deformation curves were recorded on a chart and the maximum force at fracture and the slopes of straight line portions of the graphs were measured. Gel consistency was evaluated using the gel consistency test method7.

Field porridge preparation Porridge was prepared by local women who were selected on the basis of their experience in porridge cooking. The women were asked to judge each woman’s preparation until they all agreed that the porridge was well cooked. Each day 4 to 5 cultivars were cooked into porridge by the same women and cooled to room temperature before being tested.

Sensory procedure The panel consisted of 57 judges who regularly consumed sorghum porridge in their respective households. Members of the panel were composed of employees of the National Institute of Agricultural Research of Niger and students at the Institute of Rural Development. Tests were made at ambient temperature in a large room and members of the panel were asked to avoid communications during the test. Each of the 57 panel members evaluated all 14 porridge samples using a questionnaire (Table II). The ordering of the attributes in the questionnaire mimicked the real situation for a porridge consumer. This has the advantage of guiding the panelist in evaluating the sample13. The questionnaire covered the relevant attributes of porridge, which included appearance, colour, aroma, taste, and texture. Each attribute was evaluated separately together with an overall preference for the porridge using an anchored 0 to 100 point scale. Besides making the panelist’s task easier, these types of scales generate almost the same type of data as magnitude estimation13. An orientation session, during which the panelists familiarized themselves with the terminology used and with the rating scales, was held a day before the first test. Samples were presented in a randomised order in coded aluminium bowls. Each panel member evaluated one cultivar at a time. Members of the panel were also presented with a cup of water and an extra bowl to rinse their mouth and wash

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Table II

Questionnaire for porridge sensory evaluation

Please answer each question below using the scale provided. You may go anywhere on the scale (from 0 to 100) to show your feelings. First look at the porridge sample (do not cut it). A. How much do you like the appearance of the porridge? (0=hate, 100=love) B. How much do you like the colour of the porridge? (0=hate, 100=love) Now, cut a piece but don’t eat it yet. C. How much do you like the aroma? (0=hate, 100=love) D. How firm is the porridge? (0=soft, 100=firm) Now, work up the piece in your hand as you would do before consuming it. E. How much do you like the way it holds together (cohesiveness)? (0=hate, 100=love) F. How sticky is the porridge to your fingers? (0=too sticky, 100=not sticky) Now, eat as much porridge as you want, and answer the following questions. G. How much do you like the overall taste? (0=hate, 100=love) H. How much do you like the chewiness? (0=hate, 100=love) I. How quickly does it dissolve in your mouth (mouthfeel)? (0=too slow, 100=too fast) J. How sticky is the porridge to the palate of your mouth? (0=too sticky, 100=not sticky) K. How much do you like the overall texture? (0=hate, 100=love) L. What is your overall liking (preference) of this porridge? (0=none, 100=high)

their hands after evaluating each sample. All 57 judges evaluated the 14 different cultivars in three days using this procedure. Statistical procedures Sensory data were statistically analysed using the analysis of variance procedure (ANOVA). The Fratio generated by ANOVA was used to measure panelists’ ability to discriminate among the porridge samples13. Higher F-ratio values indicate greater ability of panelists to discriminate among samples. The significance of differences between samples was determined using the least significant difference (LSD) method. Relationships between the sensory attributes were assessed using correlation and linear regression procedures taking preference as the dependent variable and each attribute as the independent variable. Relationships between sensory attributes and objective measurements of colour and texture were determined using simple correlation analysis. All statistical procedures were those given in SAS14. RESULTS AND DISCUSSION Grain and flour properties As shown in Table I, the sorghum cultivars used in this study varied widely in their physical properties. Pericarp colour varied from brown to white. A wide range in thousand kernel weight (TKW) was also obtained. TKW ranged from 15·0 g for 1/2

MSB to 38·3 g for Biyel guero. In general, cultivars with larger kernel size also had higher kernel weight. These findings agree with those of Kirleis and Crosby15 who reported that kernel size has a major influence on TKW. The ranking of the cultivars was different for the three methods of grain hardness evaluation. Sorghum cultivars 1/ 2 MSB, Sepon-82, UV1002 and INRAN-F1 were the hardest by the Stenvert hardness test whereas the hardest cultivars by AHI were MDW, 1/ 2 MSB, Sepon-82 and INRAN-F1. The softest cultivars where Mota Maradi, E1 Mota, Biyel guero, N’Gabari kime and Hageen-Dura by the Stenvert test and Hageen-Dura, Mota Maradi, BDF, and N’Gabari kime by AHI. Density and Stenvert hardness differentiated the cultivars into eight groups whereas the abrasive hardness classified the cultivars into 11 groups. Differences were expected since each method is based on a different principle. The abrasive hardness test mainly involves removal of outer layers of grain whereas in the Stenvert hardness method the grain is completely ground to flour. Density measurement does not involve any physical damage to the grain. Table III compares the mean ash, fat, and protein content of the whole and decorticated flours. Ash content of the whole and decorticated flours ranged from 1·58 to 2·01% and from 1·18 to 1·69%, respectively. Fat content ranged from 3·38 to 4·75% for whole flours and from 2·52 to 4·36% for decorticated flours. Protein content ranged from 9·8 to 14·3% for whole flours and from 9·5 to 13·7% for decorticated flours. Whole

Consumer acceptance of sorghum porridge in West Africa

Table III

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Chemical properties of sorghum flour Decorticateda

Whole Cultivars

Ashb (%)

Fatb (%)

Proteinb (%)

Ashc (%)

Fatc (%)

Proteinc (%)

Mota Maradi El Mota Fara Dawa INRAN-F1 Sepon-82 UV1002 Hageen-Dura MDW Biyel guero N’gabari kime Dosso kuba BDF 1/2 MSB Aje-bitchi LSD

1·81 1·70 2·01 1·65 1·58 1·85 1·67 1·59 1·77 1·85 1·87 1·80 1·77 1·86 0·1

3·96 3·46 3·54 3·43 3·38 4·19 3·44 3·98 4·75 3·77 3·74 4·41 3·74 3·75 0·1

11·6 12·2 14·3 10·7 11·0 13·9 9·8 13·6 13·8 13·0 11·8 12·4 14·2 11·7 0·06

1·65 1·39 1·63 1·19 1·19 1·38 1·47 1·18 1·55 1·69 1·55 1·66 1·36 1·54 0·1

3·78 2·94 3·25 2·66 2·66 3·31 3·09 2·52 4·36 3·79 3·32 4·27 2·57 3·35 0·1

11·8 12·4 13·7 9·7 10·2 12·9 9·5 12·8 13·4 12·2 11·9 12·7 13·5 11·8 1·09

Colour L DE 79 75 82 79 83 80 63 87 75 71 81 69 82 81 2·0

16 19 13 17 14 15 31 10 20 23 13 25 13 13 1·0

a

Decorticated to remove 20% of the kernel Dry weight basis of whole flour c Dry weight basis of decorticated flour b

flours contained more ash, fat, and protein than the decorticated flours. This was expected since decortication removed part of the outer layers (pericarp, aleurone layer, peripheral endosperm) of the kernel and the germ which contain high levels of ash, fat, and protein16. The decrease in the ash, fat, and protein content due to decortication ranged from 26 to 42%, from 20 to 49%, and from 18 to 28%, respectively. These values represent the amount of ash, fat, and protein removed during decortication. Percent decrease in ash and fat content significantly correlated with grain hardness measurements. The correlation coefficients between percent decrease in ash content and Stenvert hardness, abrasive hardness index, and density were 0·80, 0·81, and 0·89, respectively. Percent decrease in fat content correlated with Stenvert hardness (r=0·73), abrasive hardness index (r= 0·85), and density (r=0·82). These results reflect differences in the milling characteristics of the sorghum cultivars. The highest decrease in ash and fat was obtained with the harder cultivars. Because of their good milling properties, these cultivars did not break during decortication making it easier to remove the outer layers of the kernel and part of the germ.

Flour and porridge colour A wide variation in flour and porridge colour also existed among the cultivars as indicated by the range of Hunter L and DE values (Tables III & IV) obtained. Most flours appeared light before cooking. Flours from Hageen-Dura, BDF, N’Gabari kime, Biyel guero, and El Mota had the lowest lightness values. These cultivars were also among the softest, had poor milling characteristics and had a pigmented pericarp. Cooking flour into porridge decreased Hunter lightness (L) values and increased DE values in all the cultivars. Cultivars MDW, Sepon-82, 1/2 MSB and Fara Dawa were the whitest both before and after cooking. Porridge and gel texture Table IV compares the mean values for the textural characteristics of gels from the 14 sorghum cultivars. For the gel consistency test, the values ranged from 77 to 142 mm, with higher values for the harder grain types. Penetrometer readings ranged from 6·1 to 10·6 mm. Higher readings indicate deeper penetration of the cone into the porridge and hence softer gels. Instron force at

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Table IV

Colour and textural characteristics of porridge from 14 sorghum cultivars Instron measurementsa

Cultivar Mota Maradi El mota Fara dawa INRAN-F1 Sepon-82 UV1002 Hageen-Dura MDW Biyel guero N’gabari kime Dosso kuba BDF 1/2MSB Aje-bitchi LSD a

Colour L DE 50 43 63 51 62 63 29 70 38 37 55 37 64 57 1·0

Gel consistencya (mm)

Penetrometer readinga (mm)

Force (N)

Slope

106 88 123 129 115 113 77 142 121 104 103 93 134 102 6·0

8·2 9·0 6·7 8·0 6·1 6·6 9·2 6·5 8·5 8·8 6·9 10·6 8·5 7·5 0·2

11·5 7·0 11·4 13·1 12·8 11·4 9·2 13·0 12·2 13·8 11·0 11·2 8·4 11·5 2·0

0·338 0·463 0·300 0·319 0·331 0·275 0·413 0·225 0·325 0·319 0·300 0·363 0·358 0·313 0·03

42 49 30 42 32 31 63 24 54 55 38 55 29 35 2·0

Values reported are means of four determinations

fracture and slope value ranged from 7·0 to 13·8 N and from 0·225 to 0·463, respectively for the porridges. Higher force at fracture and lower slope values indicated firmer porridge texture. Penetrometer reading and gel consistency tests were more sensitive in differentiating between the cultivars than Instron measurements. The penetrometer reading and the gel consistency test separated the 14 cultivars into 11 and nine different groups, respectively, whereas both Instron measurements differentiated the cultivars into seven groups. The gel consistency test correlated significantly with Stenvert hardness (r=0·63, p<0·05) and abrasive hardness index (r=0·81, p<0·01). A slight but significant negative correlation coefficient (r= −0·55, p<0·05) was also obtained between penetrometer reading and abrasive hardness index. None of the two texture parameters measured with the Instron correlated with grain hardness. Results of correlation analysis between grain hardness and sorghum gel texture are in agreement with several previous studies3,5,6,8,17. A correlation analysis between the instrumental texture measurements revealed that only the slope value correlated significantly with gel consistency (r=−0·69), penetrometer reading (r=0·67) and force at fracture (r=−0·74). None of the chemical components (ash, protein and fat) of the decorticated grain measured in this study correlated significantly with the instrumental

measurements of sorghum gel texture. These results agree with those reported by Fliedel3. In studying 18 sorghum cultivars the author found that, of the chemical components of the grain, only starch and its properties were associated with sorghum porridge texture.

Sensory evaluation The average ratings of the different sensory variables and preference are presented in Table V. Panelists were able to discriminate between porridge samples for each variable using the 0–100 point scale. There was a wide range in rating for colour (8 to 87), appearance (9 to 83) and overall preference (15 to 88) but smaller differences in rating for chewiness (43 to 56) and mouthfeel (44 to 65). To measure discrimination among porridge samples, one way analysis of variance was used. The visual attributes of appearance and colour showed the highest F-ratio (Table V) which indicated that they exhibited the most discrimination. On the other hand, chewiness had the lowest F-ratio and panelists seemed to have more difficulty in discriminating between porridges for this particular attribute. Table VI presents the results of the correlation and linear regression analyses between preference and individual attributes. Except for chewiness, highly significant correlation coefficients were

Consumer acceptance of sorghum porridge in West Africa

Table V

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Comparison of the means of 14 sorghum cultivars for porridge sensory attributes rating Rating for sensory attributesa

Sensory intensity attributes Stickinessc

Cultivar

Overall AppearCohesMouth- Chew- Texture preference ance Colour Aroma iveness Taste feel iness overall

Mota Maradi El mota Fara dawa INRAN-F1 Sepon-82 UV 1002 Hageen-Dura MDW Biyel guero N’gabari kime Dosso kuba BDF 1/2 MSB Aje-bitchi F-ratio

48 26 68 51 78 68 15 88 36 34 62 34 53 63 12·4

38 20 60 39 82 65 9 83 23 19 56 23 63 57 17·4

34 16 61 36 83 68 8 87 34 17 60 20 64 56 21·4

49 35 59 51 68 61 25 70 41 42 60 42 62 55 8·9

48 34 53 48 60 55 33 68 37 46 53 42 47 54 6·6

55 34 58 54 70 65 29 71 45 50 63 51 50 61 5·7

55 44 59 53 65 60 48 63 44 57 63 51 47 60 5·4

52 51 48 45 51 48 56 54 50 50 43 43 44 46 4·0

42 30 62 55 76 63 29 73 40 44 61 44 55 58 8·1

Firmness Fingersb Fingers Tongue 52 51 56 52 56 57 41 73 44 46 50 51 39 53 5·5

29 30 45 42 45 49 32 58 27 44 37 40 37 47 7·3

25 43 60 54 62 55 40 68 27 51 53 57 52 57 5·7

a

How much do you like the ‘attribute’ (0=hate, 100=love) How firm is the porridge to your fingers? (0=soft, 100=firm) c How sticky is the porridge to your fingers, tongue? (0=too sticky, 100=not sticky) Data from 57 consumers (ages 23 to 48). b

found between the individual textural attributes and overall preference. The ratings for sensory attributes showed higher correlation with overall preference than did the sensory intensity attributes. Consumers tend to have more difficulty in rating sensory intensity attributes than in rating sensory attributes13. Cohesiveness rating and ‘overall’

Table VI Correlations and slopes of equations relating porridge preference to sensory attributes Attributes

Correlation

Slopea

Sensory liking Appearance Colour Cohesiveness Aroma Taste Mouthfeel Chewiness Texture ‘overall’

r 0·97∗∗∗ 0·96∗∗∗ 0·98∗∗∗ 0·97∗∗∗ 0·94∗∗∗ 0·81∗∗ −0·13 0·98∗∗∗

m 0·83 0·77 2·00 1·53 1·59 2·38 −0·65 1·38

0·74∗∗ 0·74∗∗ 0·90∗∗∗

1·87 1·79 2·55

Sensory intensity Firmness (fingers) Stickiness (fingers) Stickiness (tongue) a

Preference=m (attribute)+b. ∗∗,∗∗∗ significant at p=0·01 and p=0·001, respectively.

texture had the highest correlation coefficients followed by ratings for appearance, aroma and colour. Also listed in Table VI are the slopes of the straight-line equations relating overall preference as the dependent variable and each sensory attribute as the independent variable. The magnitudes of these slopes were used to prioritize the sensory attributes in importance18. Ratings for colour, appearance, and chewiness had the lowest slope values (m=0·77, m=0·83, and m=−0·65, respectively), whereas the textural attributes intensity of stickiness on the tongue, and cohesiveness rating (m=2·55, and m=2·00, respectively) were among the highest. This indicated that unit increase in the attributes with the highest slope values intensity stickiness on the tongue and cohesiveness rating generated the highest marginal increases in preference and thus were the most important in determining consumer acceptance. Mouthfeel rating also had a high slope (m=2·38) with overall preference, but the strength of the relationship between these two variables was relatively low (r= 0·81). Although appearance and colour ratings had very high correlation coefficients with overall preference, they generated the lowest slope values which indicated that they were less important in affecting consumer acceptance. This is in agree-

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Table VII

Correlation coefficients between sensory and objective texture measurements

Liking attributes Overall texture Cohesiveness Mouthfeel Chewiness Texture intensity Firmness Stickiness (fingers) Stickiness (tongue)

Gel Consistency

Penetrometer Reading

Instron Slope

Instron Force

0·67∗∗ 0·64∗ 0·27 −0·17

−0·84∗∗ −0·81∗∗ −0·77∗∗ −0·09

−0·78∗∗ −0·84∗∗ −0·73∗∗ 0·12

0·50 0·54∗ 0·59∗ 0·00

0·42 0·48 0·35

−0·60∗ −0·57∗ −0·45

−0·63∗ −0·72∗∗ −0·46

0·41 0·51 0·26

∗,∗∗ Significant at p=0·05 and p=0·01, respectively.

ment with previous sensory study1 conducted in Mali (West Africa) where consumers accepted a wide range of sorghum porridge colour with only very dark or brownish porridge being rejected. Relationships between grain hardness and sensory evaluation of porridge texture Grain hardness measured by the Stenvert test and abrasive hardness method correlated significantly with consumer overall texture rating (r=0·69 p<0·01 and r=0·69, p<0·01, respectively) and intensity stickiness on the tongue (r=0·59, p<0·05; and r=0·53, p<0·05, respectively). Abrasive hardness index also correlated with intensity stickiness on the fingers (r=0·54, p<0·05). Density did not show any significant relationship with consumer rating of porridge texture. Relationships between objective and sensory measures of porridge colour and texture Porridge colour measured with the Hunter Lab colorimeter showed highly significant correlation with consumer colour rating. Correlation coefficients of r=0·94, p<0·01 and r=−0·93, p<0·01 were obtained between consumer rating for sorghum porridge colour and Hunter L and DE values, respectively. This indicates that porridge colour measurements with the Hunter Lab colorimeter is an efficient method that can be used to predict consumer acceptance of sorghum porridge colour. The results of correlation analysis between sensory and objective measures of porridge texture are presented in Table VII. Both Instron parameters

significantly correlated with consumer ratings of texture. However, the slope values appeared to be more associated with consumer ratings. The slope is an indication of the stiffness of a material19 whereas the force at fracture measures the resistance of the food to complete breakdown. The slopes were measured in the straight line sections of the curves generated by the Instron machine. These sections corresponded to very small deformations, which are more compatible with consumer evaluation since firmness was judged by simply pressing the porridge sample with the fingers. The force at fracture gives an idea of gel cohesiveness and should logically correlate significantly with a failure type of test which the food experiences during biting or chewing. The force at fracture slightly but significantly correlated with consumer cohesiveness and mouthfeel ratings (Table VII). Except for ratings for chewiness and intensity stickiness on the tongue, all the sensory texture attributes correlated significantly with penetrometer readings. Da et al.5 measured porridge firmness with the penetrometer and reported that porridge of good texture had a firmness reading of less than 7·0 mm whereas soft-textured porridge had a firmness value of more than 8·0 mm. With the method of porridge cooking used it was found that porridge of acceptable firmness had a penetrometer reading of 8·0 mm, or less, whereas porridges that were rejected by consumers generally had a reading of more than 9·0 mm. The gel consistency test has been used7 as a good predictor of eating quality of rice varieties with amylose contents ranging from 24 to 30%. We found significant correlation coefficients be-

Consumer acceptance of sorghum porridge in West Africa

tween the gel consistency test and consumer rating for porridge texture, but no significant relationship was found between the test and consumer rating of texture intensity.

5.

CONCLUSION

6.

Results from these studies indicate that the most important sorghum porridge sensory attributes that determined consumer acceptance were texture, followed by taste and aroma. Since porridge is almost always eaten with a sauce, it is expected that the type of accompanying sauce will affect the taste and aroma of the product. Appearance and colour were the least important attributes; a wide range of porridge colour was acceptable to consumers. Of the three objective methods of porridge texture evaluation used, the penetrometer test and the Instron slope measurement were the most reliable methods for predicting consumer response. According to this study, although the gel consistency test can differentiate between sorghum cultivars, it cannot be used as a reliable predictor of consumer response to sorghum porridge texture. Finally, this study has shown that consumer acceptance of sorghum porridge colour can be predicted by Hunter lightness (L) and DE.

7. 8. 9. 10. 11. 12. 13.

14. 15.

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