Introduction

Lactic acid bacteria (LAB) constitute a diverse group of lactococci, streptococci and lactobacilli. Enzymes obtained from these bacteria (LAB) are extensively studied for their use in food based industries. Lactic acid bacteria are found widely in nature and predominates the habitat that is rich in carbohydrates, protein breakdown products and vitamins. Нe utilization of the milk sugar lactose is a primary function of lactobacilli and other LAB [1]. Moreover, they are commonly associated with food fermentation and play a sLJnLficant role in enhance nutritional quality and digestibility of food. β-Galactosidase derived from lactic acid bacteria are studied extensively because of safety aspects and application in food industries. It catalyzes the hydrolysis of β-1,4-D-galactosidic linkages and has been used in dairy industry as an important biocatalyst [2]. Нe sources of this enzyme are plants, bacteria, animal organs, yeasts and moulds. Bacteria are preferred sources of β-galactosidase due to ease in their handling, stability and high enzyme activity [3]. НLs enzyme is used for the conversion of cheese whey, a waste from dairy industry into dLوٴerent valuable products [4]. It catalyzes hydrolysis of milk sugar lactose and structurally related galactosides and transgalactosylation reactions in which lactose serve as galactosyl acceptors, yielding a series of di, tri-, and tetrasaccharides called galacto-oligosaccharides (GOS) [5]. Galacto-oligosaccharides along with the fructo-oligosaccharides are best studied prebiotics oligosaccharides that beneficLall\ aوٴect the host by selectively stimulating the growth and/or activity of probiotic bacteria in the colon. Нe stability of GOS at high temperature and acidic conditions make them important in food and drink industries especially in confectionaries, acidic beverages and fermented milk products. Using β -galactosidases from isolates originated from fermented foods for the synthesis of prebiotic GOS is an interesting approach for the production of new carbohydrate-based functional food ingredients. Нe objective of present work was to purify β-galactosidase from L. brevis PLA28 and to study its transgalactosylation activity for the synthesis of GOS.

Materials and methods

Chemicals

All chemicals used in present study were purchased from Alfa Aesar, Johnson Matthey Company and Sigma (India). Man de, Rogosa and Sharpe (MRS) medium, Elliker HiVeg broth, and other media components were purchased from Himedia, Mumbai (India). Microorganism and culture conditions Нe LAB isolate L. brevis PLA28 was obtained from Research Lab II of Himachal Pradesh University (Shimla, India). It was isolated from chhang, a barley based traditional alcoholic beverage of Ladakh, India