β-Glucosidase from Lacticaseibacillus casei TISTR 1463: Biochemical characterization and application on biotransformation of pigmented leaf extract from Oryza sativa L. (Luem Pua glutinous rice)

Abstract

This study aimed to biochemically characterize a purified β-glucosidase from a probiotic Lacticaseibacillus casei TISTR 1463 and to apply the enzyme for improving antioxidant activities of Luem Pua (Oryza sativa L.) pigmented rice leaf extract (PRLE-LP). The effect of PRLE-LP supplementation in de Man, Rogosa, and Sharpe (MRS) medium, inoculum size, initial pH, and temperature were investigated using one-factor-at-a-time (OFAT) approach. Under optimal conditions, the maximal β-glucosidase activity of 38.43 ± 0.01 U/g _DCW was achieved by cultivation strain TISTR 1463 in MRS-PRLE-LP medium (20:80% (v/v)), 10% (v/v) inoculum size, initial pH 3.5 at 30 °C for 36 h. Afterward, β-glucosidase was purified to 7.5-fold with 37% recovery yield and a molecular weight (MW) of 75 kDa. This purified enzyme had an optimal pH and temperature of pH 4.5 and 35 °C. It was stable under pH of 3.0–5.0 and temperature of 30–35 °C and showed the highest specific activity toward 4-nitrophenyl β-D-glucopyranoside (p-NPG) with the K_m and V_max of 1.31 mg/mL and of 0.06 μmol/min/mg. The enhancement of antioxidant activities of PRLE-LP by purified β-glucosidase from strain TISTR 1463 and commercial enzyme was also studied. An in-house β-glucosidase displayed superior antioxidant activities over the commercial enzyme from Aspergillus niger. In addition, LC-QTOF-MS analysis confirmed that β-glucosidase efficiently converted glycone into aglycone, resulting in enhanced antioxidant activities. The potential for producing antioxidant-rich substances from anthocyanin-containing alternative crops with applications in food and pharmaceutical industries that are both health and eco-friendly is thus addressed.