Effect of added purple-fleshed sweet potato and cassava flour on the quality of wheat-based biscuits
The need to find alternatives to wheat flour for bakery applications has become pressing, especially in countries where wheat is not grown. This study was undertaken to assess the quality of biscuits produced from a composite flour of purple-fleshed sweet potato (PFSP), high quality cassava flour (HQCF) and wheat flour (WF). Using a simplex centroid mixture design method, biscuits were formulated from composite flour developed according to a 10-point design matrix. The effect of flour variation on physical properties (weight, spread and colour) and sensory attributes (colour, aroma, texture and taste) of the formulations were evaluated. The weight and spread ratio of biscuits varied from 7.3 to 9.8 g and 7.8 to 9.3 g correspondingly for the two indices. Whereas changes in proportion of purple flesh sweet potato flour (PFSPF) did not directly affect weight of the biscuits, increasing amounts of HQCF resulted in heavy biscuits with low spread ratio. The biscuit has a dark brown chocolate appearance, with L* value between 44.5 and 50.4. This dark colour was imparted by PFSPF. Sensory evaluation showed that texture received a mean score of 5.7 (Like very much) and both colour and taste obtained 5.3 (like slightly). PFSPF influenced the scores for colour positively but lowered the scores for taste and flavour. Biscuit formulations containing less than 50% PFSPF were widely acceptable. The study indicates the possibility of successfully replacing up to 86% of wheat flour with one or more flours from root crops for biscuit production.
Keywords: PFSP, HQCF, mixture design, sensory evaluation, biscuits.