Development and Quality Characteristics of Yam Bean (Pachyrhizus Erosus) Flour and its Performance in Bread

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This study was undertaken to develop a standard method for the production of high quality flour from Pachyrhizus erosus (P. erosus) tubers and to evaluate the quality characteristics of the flour as well as its use in baked products. The experimental design used was a 2 x 3 factorial design with three replicates involving the two factors of peeling (peeling and no-peeling) and three pre-treatments (blanching at 100oC for 3 min; soaking in 0.1% sodium metabisulphite solution for 3 min; and a no-treatment control). Quality determinants used to establish standard process include ease of drying, colour, pH and ease of milling as indicated by the particle size. Blend formulations with P. erosus flour at 0, 10, 20 and 30 % replacement levels for wheat flour were used to assess the effect of the P. erosus flour in bread making. Peeling with sodium metabisulphite pretreatment produced the whitest P. erosus flour as indicated by the highest L*-value of 90.89. Flour samples from unpeeled roots had lower pH (5.96) than those from peeled samples (6.65). The combined effects of peeling and metabisulphite or blanching treatment produced flours with desirable pH values. The standardized flour produced recorded a moisture content of 5.8%, which is within the acceptable range for commercial flours. The crude fat content was 0.54% and crude protein was 5.68%. Total carbohydrates content was 85.85% with a crude fiber content of 6.26%. Total sugars and sucrose contents of the flour were 30.46% and 19.12% respectively, with a starch content of 21.0%. The P. erosus flour produced and pasting temperature of 70.6°C which is lower than that of sweet potato or taro flour. Peak viscosity was 14.5 BU. The swelling power obtained for the P. erosus flour was 752.9g/100g at 85°C with a solubility index of 54%. With regards to the performance of the P. erosus flour in bread production with wheat flour, loaf weight of composite bread samples ranged from 521 to 530 g, while loaf volumes ranged from 1,221 to 1,269 cm3 with significant differences (p < 0.05) among the different bread samples. As the level of P. erosus flour substitution increased, the loaf volume decreased. Overall acceptability scores of all the bread samples prepared with the flour blends were only slightly lower than that for the traditional bread. It is concluded that the standard procedure established is able to produce flour of high quality grade that could be used in composite flours for bread making to reduce the over dependence on imported wheat flour.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirement for the award of Master of Science degree in Food Science and Technology, May-2013