Lactose hydrolysis in milk as affected by neutralizers used for the preparation of crude β-galactosidase extracts from Lactobacillus bulgaricus 11842

Abstract

Three different neutralizers (NaOH, KOH, NH 4OH) were employed for pH maintenance during the growth of Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842, used as a source of β-galactosidase extracts. The crude enzymatic extract (CEE) was obtained by bead milling of the cell paste, collected from the cultivation of the source microorganism in skim milk at 43 °C and constant pH. Lactose hydrolysis kinetics in skim milk and proteolytic activity during the hydrolysis were evaluated. The use of NH 4OH as a neutralizer resulted in significantly ( P<0.05) higher enzyme activity of the CEE than that obtained using NaOH or KOH. The kinetic parameters, k cat and K m, of the Michaelis–Menten model were determined for lactose hydrolysis in skim milk using 1% (v/v) addition of a CEE. There was no significant ( P>0.05) difference in k cat among the different extracts, with a clear temperature dependence following Arrhenius kinetics. The rate of lactose hydrolysis was dependent on the initial enzyme activity and temperature. The highest initial rate was observed at 65 °C; however, the enzyme deactivation occurred within 1–1.5 h. The proteolytic activity determined by HPLC peptide mapping was significantly ( P<0.05) higher in the moderate temperature range (20 and 37 °C) than at 7 or 55 °C. Industrial relevance: Since lactose intolerance affects a large proportion of the world's population, an economically feasible and effective process with a cheap source of β-galactosidase may have a substantial potential. The use of crude β-galactosidase extracts from Lactobacillus bulgaricus 11842 appears to be a promising approach for development of a technologically feasible process of lactose hydrolysis for food or non-food uses.