BACKGROUND: A malto-oligosaccharide forming a-amylase from Bacillus subtilis KCC103 immobilized in calcium alginate beads was repeatedly used in batch processes of starch hydrolysis. The degree of starch degradation and operational stability of the immobilized system were optimized by varying the physical characteristics and composition of the beads. The products formed from hydrolysis of various starches by a-amylase immobilized in different supports were analyzed. RESULTS: Immobilized beads prepared from 3% (w/v) alginate and 4% (w/v) CaCl2 were suitable for up to 10 repeated uses, losing only 25% of their efficiency. On addition of 1% silica gel to alginate prior to gelation, the operational stability of the immobilized enzyme was enhanced to 20 cycles of operation, retaining >90%. of the initial efficiency. Distribution of malto-oligosaccharides in the starch hydrolyzate depended on the type of starch, reaction time and mode of immobilization. Soluble starch and potato starch formed a wide range of maltooligosaccharides (G1-G5). Starches from wheat, rice and corn formed a narrow range of smaller oligosaccharides (G1-G3) as the major products. CONCLUSION: The immobilized beads of a-amylase from KCC103 prepared from alginate plus silica gel showed high efficiency and operational stability for hydrolysis of starch. This immobilized system is useful for production of malto-oligosaccharides applied in the food and pharmaceutical industries. Since this KCC103 amylase can be produced at low cost utilizing agro-residues in a short time and immobilized enzyme can be recycled, the overall cost of malto-oligosaccharide production would be economical for industrial application. (C) 2008 Society of Chemical Industry