β-galactosidase: Biotechnological applications in food processing

beta-Galactosidases produced by microorganisms are being used in food technology for hydrolysis of lactose in milk and milk by-products. The enzyme has attracted much attention in view of lactose intolerance in human population and due to importance of milk in human diet. -Galactosidase hydrolyze -galactopyranosides, that is, lactose, and form a range of trans-galactosylation products or galactooligosaccharides (GOS) capable of providing several health benefits as prebiotics. In addition, the enzyme also finds applications in production of lactose based sweeteners from high lactose containing effluents of cheese manufacturing industries. Currently, the enzyme is mainly obtained from Aspergillus niger and Kluyveromyces lactis, however, they are thermolabile with optimum pH between 4.0 and 6.0 accompanied by low chemical resistance and high product inhibition properties. Thermostable enzymes are suitable to perform the hydrolytic process at relatively high temperatures, minimizing pathogen contamination, psychrophilic -galactosidases are preferred for treatment of milk under refrigerated conditions (<15 degrees C), without heating and maintenance of temperature. Lactic acid bacteria (LAB) are a potential source of food grade enzymes and other metabolites. Although reports on the use of -galactosidase of LAB in pure form is reported for hydrolysis of lactose in milk and production of fermented milk products for reduced lactose content, methods of immobilization for use in continuous bioreactors are less explored. Recombinant DNA technology has attained much significance to reveal molecular aspects of enzyme catalysis, protein structure, gene organization for expression, and enhancement of thermophilic, psychrophilic, and mesophilic -galactosidases. Heterologous expression of extremozymes with -galactosidase would help in overcoming the limitations faced within the bioprocess technology. Lactic acid bacteria (LAB) producing extracellular cell bound -galactosidase have been isolated and enzyme production was carried out using modified MRS medium incorporating lactose as enzyme inducer. Process for growing probiotic lactic acid bacteria for -galactosidase from fermented milk products has been patented (Indian Patent No. 247904). Thermostable -galactosidases were also extracted from Kluyveromyces lactis a yeast, isolated from curd samples and Bacillus sp. MTCC 864. An Indian patent has been granted for a simple, cost effective perforated two compartment immobilized enzyme bioreactor was designed and fabricated for lactose hydrolysis (Indian Patent No. 264609). The bioreactor can be operated continuously at temperature between 5.0 and 75.0 degrees C, employing different immobilized enzyme preparations for different operational temperatures. -galactosidase of cell confined LAB and yeast have been immobilized in agarose and galactooligosaccharides (GOS) production was observed at 40% lactose concentration in 0.05M phosphate buffer at pH 6.5. Immobilized bioreactor preparation could be used for lactose hydrolysis of milk between 45 and 70 degrees C with 75% efficiency.