Abstract:
Inability to utilize chemical additives and hydrocolloids successfully as improvers for high percentage cassava composite flour in baking, promotes reliance on importation of wheat despite its negative effects on the Nigerian economy. In the current study, enzymes from an indigenous yeast strain were explored as possible improvers for achieving high percentage cassava flour inclusion in bread. A total of sixty yeast strains were isolated from palm wine, decaying fruits and cassava effluent polluted soil. Best strains were selected based on the ability to produce cellulase, xylanase, lipase, pectinase and amylase and inability/poor ability to produce protease; also on the effect of their crude enzyme extract on high percentage cassava composite bread. Composite bread was evaluated in terms of their physical and sensory qualities, weight loss during storage, staling properties and shelf life. Molecular identification of the best strain (C18) was shown to be Candida Phangngensis, a non pathogenic yeast specie. To optimize the enzyme production for baking of cassava composite bread, effect of cell concentration and fermentation time was determined. The effect of the enzyme volume and percentage of cassava flour on product quality was also evaluated. Enzyme extract obtained from 4h fermentation with 2ml cell concentration (1.91x106cells/ml) gave the best loaf quality, while the least quality was from 8h fermentation with 5ml cell concentration (6.49x106cells/ml). Extract which gave the best quality product had in Uml-1: amylase (0.00), protease (0.00), xylanase (29.0), pectinase (0.499) and lipase (20.3), cellulose (0.466) as compared to amylase (15.75), protease (5.25), xylanase (36.0), pectinase (2.542), lipase (18.0), and no cellulose from extract which gave the least quality. Enzyme volume of 12.5ml gave the optimum loaf quality with specific volume (1.11) and loaf volume (198.9cm₃). Best quality product was achieved when wheat flour was substituted with 30-40% cassava. Remarkable improvements were observed in the loaf quality when the enzymes were partially purified. The results of the physical and sensory evaluation using partially purified enzyme showed that there was no significant difference (P ≥ 0.05) in the bread quality with up to 40% substitution compared to the 100% wheat bread. Our studies indicate that the proper use of these enzymes in baking will surmount some of the problems including physical, sensory and shelf life attributes associated with the use of cassava composite flour, and enable the achievement of 40% cassava substitution in bread
