Thermostable α-amylase production by Bacillus subtilis entrapped in calcium alginate gel capsules

Bacillus subtilis cells were immobilized by entrapment in calcium alginate gel capsules and the immobilized biocatalyst was used for the semi-continuous production of α-amylase. The α-amylase yield and operational stability of the immobilized system were increased by tailoring the capsules' characteristics. Capsules prepared from 2% (w/v) sodium alginate and 3.5% (w/v) CaCl₂ were the best support for cell immobilization, providing 2.5-fold higher α-amylase production in comparison to the freely suspended cells. Immobilized biocatalysts sustained 90% of their initial productivity over five sequential batches in a 10-day period, while amylase production by free cells declined sharply after the second use. Even higher operational stability was achieved when the capsules were treated with 2% (w/v) CaCl₂ for 30 min before each batch. In this case the appearance of free cells in the medium was minimized and the immobilized system retained more than 85% of its initial efficiency after 15 fermentation batches, producing more than 1,450,000 units of extracellular α-amylase during this period.