Diastatic enzymes malting process optimisation of African finger millet for biotechnological uses

Abstract

This study sought to understand the importance of variation of steeping and germination conditions (temperature, pH and salts) on the quality of African finger millet malt in terms of diastic power (a-amylase and β-amylase), endo- (1,3) (1,4)-β-D-glucanase, b-glycan content and protein profile. The results show that the physiological responses of African finger millet malted seeds are correlated to pH (acidity and alkalinity) but inversely correlated to temperature stress. The effect of the stresses on the activity of a-amylase, b-amylase and endo-(1,3)(1,4)-b-D-glucanase as well as b-glycan content was significantly different in magnitude except for the β-amylase activities obtained after acidic and alkaline treatment at 40°C which are not statistically different. Alkaline pH and heat stress at 30°C were the dominant factors for malting optimization from the result of diastic power indices. a-Amylase activity is a better predictor of diastic power. The grains subjected to the steeping and germination process carried out in Tris-HCl buffer solution (25 mM, pH 9) containing 100 mM NaCl at 30oC during 96 h showed higher α-amylase and β-amylase activity. This shows that for a salt–alkali-heat mix stress, a reciprocal enhancement among salt stress, alkali and heat stress was a characteristic feature with no significant change in the hordein protein expression. The influential effect of the stress conditions indicate that alkaline pH steeping and 30°C malting is the most effective condition for producing malted African millet flour with a promising potential of distinct malting quality metrics.   Key words: African finger millet, diastatic enzymes, malting, stresses.