Abstract
The endoenzyme beta-galactosidase (beta-d-galactoside galactohydrolase; EC 3.2.1.23) has been used at industrial scales for the preparation of lactose-free milk and for the conversion of lactose to galacto-oligosaccharides (GOS) prebiotics. In this study, using Plackett-Burman (PB) design and the response surface methodology (RSM), the batch growth conditions for the production of beta-galactosidase in DeMan-Rogosa-Sharpe (MRS) media have been studied and optimized for Lactobacillus leichmannii 313 (ATCC 7830 (TM)) for the first time. The incubation temperature (30 < T < 55 degrees C), starting pH (5.5 < pH < 7.5), and carbon source (glucose, lactose, galactose, fructose, and sucrose) were selected as the significant variables for optimization. The maximum crude beta-galactosidase production (measured by specific activity) was 4.5 U/mg proteins and was obtained after 12 h of fermentation. The results of the PB design and further optimization by RSM showed that the initial pH of 7.0 and 15.29 g/L of lactose were the levels that gave the optimum observed and predicted beta-galactosidase activities of 23.13 U/mg and 23.40 U/mg, respectively. Through RSM optimization, beta-galactosidase production increased significantly (over five-fold) in optimized medium (23.13 U/mg), compared with unoptimized medium (4.5 U/mg). Moreover, the crude enzyme obtained was able to hydrolyze lactose and also produce galacto-oligosaccharides. Because its ability to produce beta-galactosidase was significantly improved through optimization by RSM, L. leichmannii 313 can serve as a potential source of beta-galactosidase for food applications at an industrial scale.