Triton X-114-aided Extraction and Partial Characterization of β-Galactosidase from Grape Berry Pulp (Vitis vinifera L.)

Abstract

β-Galactosidase from grape berry pulp was extracted after a 2 hr digestion with the non-ionic detergent Triton X-114. Subsequent phase partitioning eliminated ~75% of the phenolic compounds, enabling the enzyme to be recovered in the aqueous upper phase with an 8-fold increase in its specific activity. The enzyme was kinetically characterized using o-nitrophenyl β-galactopyranoside as substrate and was active at acidic pH with an optimum at pH 4.2, a value at which V_max and K_m were 0.009 μmol/min/mg protein and 1.2 mM, respectively. β-Galactosidase was competitively inhibited by free galactose with K_i of 0.8 mM. The enzyme had an optimum temperature of 65°C, although its thermostability is very low at this temperature.