Biosynthesis of thermostable -amylase by immobilized Bacillus subtilis in batch and repeat batch cultures using fortified date syrup medium

Batch and repeat batch fermentation were performed to evaluate the potential of date syrup and immobilized cells technique for the economical production of α-amylase. The enzyme production by immobilized cells was greater than that of freely suspended cells. Khlas date syrup gave the highest enzyme yield (142.7 Uml-1) using the immobilized technique after 48 h of fermentation. The highest α-amylase production was obtained in a culture grown in a 2% tricalcium phosphate treated medium. The enzyme production was proportional to the amount of date syrup up to 1.0% sugar. Tween 80 was more effective in enhancing cell membrane permeability, and thus increasing enzyme secretion. A 1.4 fold increase in enzyme production was achieved using an optimized medium in a fermenter. The culture activity under repeated batch cultivation remained stable up to the third cycle, and retained about 85% of its initial efficiency during the first five batches when each cycle continued for 48 h. The stimulated activity and the thermo stability were observed in the presence of 10 mM Ca2+. The results show that date syrup is a promising economic carbohydrate source and cell immobilization is an excellent alternative method for enhanced α-amylase production.   Key words: α-Amylase, production, immobilization, Bacillus subtilis, date syrup