Subjective and objective assessment of `agbelima' (cassava dough) quality

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1 Food Control 10 (1999) 63±67 Subjective and objective assessment of `agbelima' (cassava dough) quality N.T. Dziedzoave a, W.O. Ellis b, *, J.H. Oldham b, A. Osei-Yaw a a Food Research Institute (C.S.I.R.), Box M. 20, Accra, Ghana b Department of Biochemistry, University of Science and Technology, Kumasi, Ghana Abstract Investigation into developing quality speci cations for agbelima ± a fermented cassava product ± led to the identi cation of aroma, colour, smoothness, cohesiveness and sourness as ve attributes consumers and producers associate with good quality agbelima. A study was conducted to identify objective indicators of human evaluation of each attribute. The results showed signi cant di erences in total titratable acidity, ph, starch content, hot paste stability and colour attributes of the agbelima. It also showed more detectable di erences between agbelima when uncooked than when cooked. Objective indicators were identi ed for three of the attributes ± namely colour, smoothness and sourness. The identi ed indicators were b and C for colour, average particle size for smoothness and ph and total titratable acidity for sourness. These results are expected to aid in evaluating cassava varieties for processing into agbelima, and enhancing routine quality control activities. Ó 1999 Published by Elsevier Science Ltd. All rights reserved. Keywords: Agbelima; Cassava fermentation; Kudeme 1. Introduction * Corresponding author. The sensory quality of any food product is an important factor in determining consumer acceptability. The identi cation of the most important sensory attributes associated with a particular product is a necessary pre-requisite to the development of quality standards (Kramer & Twigg, 1962). Considering the high cost of carrying out routine sensory evaluation as a means of monitoring product quality, it is imperative that objective indicators of human evaluation of speci c sensory attributes be identi ed to facilitate quality control. Agbelima is a fermented cassava food product of major dietary importance in Ghana. Its preparation involves the use of a traditional inoculum called kudeme which aids in breaking down the texture of the product through the activity of a number of tissue degrading enzymes (Amoa-Awua & Jakobsen, 1995). In agbelima production fresh cassava is peeled, washed and grated. The inoculum is added before, during or after grating. The grated mash is loaded into polypropylene sacks to ferment for two to three days whilst undergoing dewatering simultaneously. After this the product (agbelima) is ready for use. Like most traditional cassava based foods, the product has not been standardized and the quality is variable. Studies have shown that the quality of various cassava products is very much in uenced by varietal di erences (Safo-Kantanka & Owusu-Nipah, 1992; Cabrera, 1986). Thus, the use of di erent cassava varieties in agbelima production is therefore likely to contribute to the variability in product quality. Considering that on the international markets, legislation for quality control in a wide range of products including cassava products for export has become widespread (Ingram, 1975), the need for standardization of agbelima is even more important. In an attempt to develop quality speci cations for agbelima ve attributes, colour, smoothness, cohesiveness, aroma and sourness were identi ed as playing a role in determining consumer acceptability of the product (Dziedzoave, 1996). The identi cation of objective indicators of human evaluation of these attributes would very much facilitate routine quality control of the product. This study was therefore carried out to identify objective indicators of human evaluation of the colour, smoothness, cohesiveness, aroma and sourness of agbelima /99/$ ± see front matter Ó 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S ( 9 8 )

2 64 N.T. Dziedzoave et al. / Food Control 10 (1999) 63±67 2. Materials and method 2.1. Sample selection for assessment Twenty (20) market selected by a probability sampling procedure (Cochran, 1963; Gomez & Gomez, 1984) were screened for variations in colour, particle size and total titratable acidity. For each of the three attributes, were divided into four modal ranges. One sample from the rst modal range for colour which falls within another modal range for either particle size or total titratable acidity (TTA) was selected. A second sample from the second modal range of colour falling into yet another modal range of either particle size or TTA was selected. The process was continued until four were obtained. The four with values distributed as much as possible over the full range of values for these three parameters were selected for sensory and objective analysis Objective assessment ph Five grams of agbelima was weighed and made into a slurry using 50 ml distilled water. The ph of the slurry was determined using the Corning ph meter (model 240) Total titratable acidity Total titratable acidity was determined by means of the Ghana Standards Board Method for gari and cassava chips. Eighteen grams of agbelima was made into a slurry in 200 ml of distilled water in a ask. The ask which was loosely stoppered was placed in a water bath at 40 C and shaken for 1 h. The slurry was ltered through a dry lter paper (Whatman no. 1). One hundred milliliters (100 ml) of the ltrate was titrated against 0.2 M NaOH using phenolphthalein as indicator. Total titratable acidity was calculated as percent lactic acid Colour Colour of agbelima were determined with the Minolta Chroma Meter (Model CR 200, Minolta Camera Co. Ltd, Japan) using the CIELAB Colour systems as follows. Agbelima sample was packed into a petri dish and levelled to obtain a smooth at surface. The sensor of the Chroma meter was then placed on the surface of the sample and the value read on the meter. The chroma meter was calibrated using a standard white tile (L ˆ 97.63, a ˆ 0.48, b ˆ +2.12) Starch content Starch content was determined based on the anthrone colorimetric method as described by Hassid and Neufeld (1964) Pasting characteristics The AACC o cial method as described by Shuey and Tipples (1980) was used with a slight modi cation to suit the sample under investigation using the Brabender amylograph (ICC Standard no. 126); 14 g of agbelima and a total of 450 ml of water was used. Operating conditions were as follows: starting temperature ± 25 C; rate of heating ± 1.5 C/min; 30 min holding at 95 C; natural cooling to 50 C. The following measurements were taken from the amylograph curves; pasting temperature, peak (maximum) viscosity, viscosity at 95 C, viscosity after holding at 95 C for 30 min and viscosity after cooling to 50 C. From these measurements, the setback viscosity, retrogradation tendency and the hot paste viscosity were computed Average particle size and uniformity index A modi cation of the method of Henderson and Perry (1979) for dry our was used. The modi cation was made to suit the sample under investigation which was a wet sample; 100 g of agbelima was washed down a set of graded Tyler sieves with 10 l of water. The aperture sizes of the sieves used were 1.00, 0.5, 0.25 and mm. Fractions retained on each sieve were oven-dried at 120 C for 2 h, cooled and weighed. The dry matter content of the agbelima was determined and used to estimate the amount of the sample that would otherwise have collected in the pan. The results were used to calculate the neness modulus from which the average particle size, in millimetres was calculated according to the method of Henderson and Perry (1979). The uniformity index was calculated as the ratio of the weight fractions retained above the 0.5 mm sieve, to the sum of weight fractions passing through it Subjective assessment ± sensory evaluation The ranking test was used for evaluating the sensory qualities of the agbelima (Poste, Mackie, Butler & Larmond 1991). Samples of the agbelima were prepared into a sti dough by cooking 400 g of each sample in 400 ml of water at 100 C for 20±30 min. The cooked and uncooked were coded and presented at room temperature to a 36-member laboratory sensory panel to assess and rank separately the intensity of the ve attributes of colour, sourness, smoothness, cohesiveness and aroma, on a 4-point scale ranging from least intense to most intense Statistical analysis The Friedman Rank Test was used to assess di erences between. Linear, semi-log and log±log correlations between the sensory scores of each attribute and the corresponding possible objective parameters were also calculated to identify the most adequate ob-

3 N.T. Dziedzoave et al. / Food Control 10 (1999) 63±67 65 jective indicator of human evaluation of each of the attributes. 3. Results and discussion The results of the study showed that signi cant differences (P < 0.01) existed between the four agbelima especially with respect to total titratable acidity (TTA), ph, percent starch content, hot paste stability and the colour attributes (Table 1). The results also showed that there is a more detectable di erence between the agbelima when uncooked than when cooked, especially for the attributes of colour, aroma and smoothness (Table 2). However, since the nal product is consumed in the cooked form, evaluation of the sensory results were based on the cooked product rather than the uncooked product. Table 3 shows the correlation between the objective data and the subjective data. In the correlation of objective and sensory data, a correlation coe cient of 0.90 and above is considered an excellent indicator of human evaluation whilst a value of less than 0.80 is unsatisfactory (Kramer & Twigg, 1962). The very high correlation between total titratable acidity and ph with sourness is not surprising since the taste modality of sourness is elicited by acid condition or H ions (Guyton, 1991; Jenkins, 1978). The b parameter of the CIELAB colour system which is an indicator of the degree of yellowness in the product (Pen eld & Campbell, 1990) also showed a very high correlation with human evaluation of colour. In relation to other objective parameters for colour it shows that the colour of the product is judged principally by the degree of yellowness rather than by its degree of whiteness (L ) or the degree of greenness ( a ). Table 1 Results of objective measurements of agbelima Parameters Objective values a Sample A Sample B Sample C Sample D Total titratable acidity (% ) 0.69 (0.02) 1.35 (0.00) 0.98 (0.01) 1.19 (0.01) ph 4.26 (0.02) 3.89 (0.01) 4.06 (0.02) 3.89 (0.02) Starch content (% ) (1.06) (0.35) (0.26) (0.10) Pasting temperature ( C) Peak viscosity (BU) Retrogradation tendency (BU) Hot paste stability (BU) Average particle size (mm) (0.01) (0.01) (0.01) (0.00) Uniformity index (0.02) (0.03) (0.04) (0.01) Colour parameters: L (0.42) (0.67) (0.43) (0.05) a 1.51 (0.52) 0.54 (0.19) 0.43 (0.30) 1.25 (0.28) b (0.69) (0.76) (0.42) (0.49) c (0.55) (0.76) (0.42) (0.51) H (0.42) (0.78) (1.34) (0.92) a Values are averages of duplicate determinations except for the colour parameters which are averages of triplicate determinations. BU ± Brabender units. Figures in parenthesis are standard deviations. Table 2 Rank totals for individual sensory attributes of cooked and uncooked of agbelima Sample Colour Aroma Smoothness Cohesiveness Sourness A 64a 85b 86a 86a 109b 97bc 110b 107b 53a 59a B 137b 137c 84a 69a 113b 110c 89ab 78a 111b 103b C 86a 89b 98a 90ab 73a 71ab 81a 81ab 88b 87ab D 73a 49a 93a 115b 65a 52a 62a 74a 106b 111b Rank totals followed by the same letter are not signi cantly di erent.

4 66 N.T. Dziedzoave et al. / Food Control 10 (1999) 63±67 Table 3 Correlations between objective measurement and subjective assessment on agbelima Subjective (sensory) parameter Objective parameter Correlation coe cients Linear relationship Semi-log relationship Log±log relationship Colour L* a* b* C* h* Aroma ph Total acidity Smoothness Av. particle Uniformity index Cohesiveness Starch content Pasting temp Peak viscosity Retrogradation tendency Hot paste viscosity Sourness ph Total acidity The C parameter of the L C h colour system which is the metric chroma (McLaren, 1980), representing the purity of the colour hue resulting from the combined e ect of the two colour shades of yellow and green in the product also showed a very high correlation. This re- ects the predominance of the yellow shade over the green in in uencing human evaluation. It may also suggest that the product is judged more by the brightness of the colour rather than the colour itself. The correlation of average particle size with human evaluation of smoothness, though not excellent is very satisfactory (Table 3). This con rms the fact that particle size is an adequate measure of kinaesthetic property (Stewart & Amerine, 1982) and could therefore be conveniently applied in the assessment of agbelima texture. With the exception of starch content which showed an almost satisfactory negative correlation (r ˆ 0:79) with cohesiveness of the uncooked sample in a semi-log relationship, none of the possible objective indicators for cohesiveness correlated satisfactorily with human evaluation of cohesiveness. Since cohesiveness is thought to be an important attribute in determining acceptability of cassava dough (agbelima), further investigation would need to be carried out to establish a suitable objective indicator for assessing human evaluation of the cohesiveness of agbelima. In this study no objective indicator was identi ed for the aroma of agbelima. 4. Conclusions It may be concluded from this study that average particle size was the most objective indicator for human evaluation of smoothness. The b and C colour parameters are the most adequate objective indicators for human evaluation of colour. Total titratable acidity and ph are the most excellent indicators for human evaluation of sourness. No adequate objective indicators were established for aroma and cohesiveness, however, starch content may be used as a measure of human evaluation of cohesiveness for uncooked of agbelima but only in a semi-log relationship. References Amoa-Awua, W. K. A., & Jakobsen, M. (1995). The role of Bacillus species in the fermentation of cassava. Journal of Applied Bacteriology, 79, 250±256. Cabrera, L. J. (1986). Cassava our utilisation ± technical functional evaluation of cassava ours in bread making. Final Report, Bogota, Columbia, Instituto de Investigacioues Technologicas, Es Sum Es. 16 Ret. Cochran, W. G. (1963). Sampling Techniques, 2nd edn. John Wiley and Sons, New York. Dziedzoave, N. T. (1996). Quality control studies on agbelima ± development of quality speci cation and evaluation of cassava

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