Production of galacto-oligosaccharides from lactose by Aspergillus oryzae beta-galactosidase immobilized on cotton cloth

Knitted cotton terry cloth as a novel and inexpensive fibrous matrix was evaluated for the development of fibrous bed biocatalyst reactor. Aspergillus oryzae β-galactosidase was immobilized on cotton cloth with two different methods. The first method used p-toluenesulfonyl chloride (tosyl) to activate cotton cloth and the enzyme was then coupled to the tosylated sites. Approximately 50 mg enzyme per gram of cloth was coupled with an immobilization yield of 55%. The second method involving polyethylenimine (PEI) relied on PEI-enzyme aggregate formation and coating of the aggregates on the fibrils of cotton cloth. Immobilized enzyme activity under optimized condition reached to 90–95% of free enzyme at a loading of 250 mg/g. Thermal stability of the immobilized enzymes were greatly increased, with tosyl immobilized enzyme showing 25-fold increase as compared with the free enzyme.; The production of galacto-oligosaccharides (GOS) from lactose was studied by cotton cloth immobilized enzyme by both methods. The total amounts and types of GOS produced were mainly affected by the initial lactose concentration in the reaction media. A maximum GOS production of 27% (w/w) was achieved at 50% lactose conversion with 500 g/L of initial lactose concentration. Trisaccharides were the major types of GOS formed, accounting for more than 70% of the total GOS produced in the reaction. Monosaccharides produced during lactose hydrolysis severely delayed GOS formation and decreased 10–15% in GOS content.; A stable long-term continuous operation was demonstrated with the cotton cloth immobilized enzyme reactor. Overall, the high porosity (>95%) and low-pressure drop of cotton cloth allowed the reactor to be operated without any difficulties. Even with high enzyme loadings, cotton cloth immobilized enzymes showed no reduction in GOS formation and did not impose any significant diffusion limitation. GOS productivities in the reactor were 106 g/L/h with tosyl activated cotton cloth immobilized enzyme and 5200 g/L/h with PEI immobilized enzyme, which is 100-fold higher than those reported in the literature. The cotton-cloth enzyme reactor thus can be used for economical production of GOS from lactose. GOS product can be used as a prebiotic food ingredient because of its many health benefits.