The Potential of -Galactosidase Enzyme from Indigenous Lactobacillus plantarum B123 Strain for Lactose Hydrolysis of UHT Milk.

Abstract

Lactose concentration in milk is 4.6% (w/w) in average (Walstra 2006). The content of lactose with less than 1% (w/w) of final product is acceptable for people with lactose intolerance problem (Tuure and Corpela 2004). Enzymatic hydrolysis of lactose is one of the important biotechnological processes in the milk industry because of some beneficial effects including the elimination of lactose in milk for people with lactose intolerance, prevention of lactose crystallization and contribution to the product sweetness (Jurado et al, 2002). -Galactosidase enzyme can be produced by lactic acid bacteria. In this study, indigenous Lactobacillus plantarum strain B123 was isolated from Indonesian traditional fermented vegetable product. The use of this local potential strain was to increase its role to the added value products such as low lactose UHT milk. Even though low lactose UHT milk product has not been commercially marketed yet in Indonesia, however the need of low lactose milk for people with lactose intolerance was already present. This research was aimed to: (1) determine the growth condition of indigenous Lb. plantarum strain B123 to produce β-galactosidase (2) determine the production condition of -galactosidase from Lb. plantarum B123 strain with partial purification and (3) determine the potential of β-galactosidase from indigenous Lb. plantarum B123 strain to hydrolyze lactose of full cream and low fat-UHT milks, containing total fat 3.5 and 1.0% (w/v) respectively, in batch process. The result showed that the growth condition of indigenous Lb. plantarum B123 in MRSB to produce β-galactosidase were 2% inoculum, 1% of lactose, medium pH 8, and 24 h incubation time at 37°C. The enzyme showed an optimum activity to hydrolyzed oNPG substrate at pH 6.5 and temperature 50°C . Specific activity of -galactosidase has increased during the partial purification given 15.05 U/mg in crude enzyme to 109.58 U/mg in dialysed enzyme (at first production) and 87.09 U/mg in crude enzyme to 109.58 U/mg in dialysed enzyme (at second production). Lactose in full cream-UHT milk was hydrolyzed at a maximum rate of 60.0% (lactose concentration from 3.82% w/v to 1.52% w/v) and in low fat-UHT milk 81.1% (lactose concentration from 4.44% w/v to 0.84% w/v) by 7.2 U β-galactosidase/mL milk for 9 h at 50°C. Enzyme concentration, hydrolysis time and total fat concentration had a significant influence on the hydrolysis of lactose in UHT milk (p<0.05). According to the different analytical methods to monitor the lactose hydrolysis, a correlation between the results of glucose concentrations in full cream-UHT milk analyzed by GOD-POD kit and HPLC was observed. There was a positive correlation between analysis of glucose concentrations in full cream-UHT milk with GOD-POD kit and HPLC (r = 0.923).