Use of fresh cassava and sweet potato root pulps in cake making
Fresh pulps of three cassava cultivars (cv. Serexe, cv. Dnrika, cv. Namba munana) and two sweet potato cultivars (cv. MaaenQ-L4, cv. BiaalB) , were characterised for their physicochemical properties and related to those of commercial horne baking wheat flour in order to assess the possible use of the root pulps for cake production. The moisture content ranged between 63.70 and 64.87% for Cassava, 68.30 and 70.18% for sweet potato and 14.50% for wheat. The crude protein ranged between 0.89 and 1.20% for cassava, 1.29 to 1.53% for sweet potato and was 10.60% for wheat flour. The total sugar content ranged between 3.03 to 4.07% for cassava, 5.73 to 6.13% sweet potato and was 5.04% for wheat flour, while the starch content ranged 'between 24.01 and 25.33% for cassava, 16.56 and 20.20% for sweet potato and was 63.82% for wheat flour. Root pulps were generally low in crude fat, and ash content but higher in crude fibre than wheat flour. The 0.- amylase activity was 1.32 and 26.85 Sweet Potato Dextinising Units (SDU) for the two sweet potato cultivars, and 1.02 (SDU) for wheat flour. is-amylase ctivity was 3.2 and vi 1.95mg/maltose/ml/min for the sweet potato cultivars and 0.91mg/maltose/ml/min for wheat flour. No significant diastase activity was observed in the cassava cultivars used. The peak viscosity of cassava pulps ranged between 2400 and 2660 Brabender Units (BU), while that for sweet potato pulps was between 360 and 520 BU and was 740 BU for wheat flour. In developing a suitable processing technique, it was found necessary for the pulp to have fine particles of average size of 500~m in order for the texture of the pulpy cakes to be acceptable. 0.5% sodium metabisulphite and 0.5% citric acid were both effective in controlling enzymatic browning which was more prevalent in sweet potato than in cassava pulp. Citric acid was ., - more recommended as it had the additional effect of lowering pulp pH and hence improving cake keeping quality. For maximum reduction of cyanide content in cassava cakes, pulps had to be stored at room temperature for about 0.5, 2 and over 6hrs for the low, medium and high cyanide cultivars respectively before baking. To evaluate the pulps performance in cake making, cakes were made from pure pulps without wheat flour added, 80% pulp Vll l with 20% wheat flour added and 50% pulp with 50% wheat flour following recipes formulated during the study. A pure wheat flour cake was used as a control. Less sugar and shortening were required in order to produce acceptable cassava and sweet potato pulp cakes in comparison to the wheat flour cake. Sensoric quality evaluation of the cakes showed that significant differences existed in the colour, flavour, texture, and overall acceptance of the different type of cakes at both 95 and 99% levels of significance. Although pure pulp cakes generally had lower mean scores than the wheat flour cake, they were still acceptable to consumers and could be used as cheaper substitutes for the costly wheat flour cake.