PURIFICATION AND CHARACTERIZATION OF SOY COTYLEDON β-GLUCOSIDASE

Treatment of sugarcane bagasse for the immobilization of soybean β-glucosidase and application in soymilk isoflavones

Abstract Sugarcane bagasse from agro-industrial residues was autoclaved at 121 °C for 15 min, treated with 2% NaOH and activated with 2.5% glutaraldehyde for the immobilization of soybean β-glucosidase. Scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy characterized and confirmed the immobilization of the β-glucosidase on the sugarcane bagasse. The immobilization efficiency was influenced by the type of bagasse modification and was 99% at maximum. The optimum immobilization conditions were 1 mg mL-1 protein, pH 7.0, 2.5% glutaraldehyde, 110 rpm and 8 h of incubation at 4 °C. The immobilized system could be reused for 15 cycles without the complete loss of activity. The thermal stability indicated a residual activity of 15% after 180 min incubation at 70 °C. The conversion efficiency of glucosides to aglycones in commercial soymilk by β-glucosidase immobilized on sugarcane bagasse was evaluated and the total aglycone content increased by 23.8% after incubation at 50 °C for 120 min.

A novel soybean (Glycine max) gene encoding a family 3 β-glucosidase has high isoflavone 7-O-glucoside-hydrolyzing activity in transgenic rice

A previous study demonstrated that purified Glycine max β-glucosidase (GmBGL) could hydrolyze glucosyl isoflavone to the aglyconic form. This study reports the cloning and functional characterization of a soybean cDNA encoding the β-glucosidase. GmBGL was isolated by use of a purified soybean N-terminal amino acid sequence and conserved sequences of β-glucosidase genes from other plants. Sequence analysis of GmBGL revealed an open reading frame of 1884 bp encoding a polypeptide of 627 amino acids with a calculated molecular mass of 69 kDa. Phylogenetic analysis classified the GmBGL into the glycosyl hydrolase 3 family. In soybean, the GmBGL transcript was predominantly accumulated in roots and leaves. To examine the enzymatic activity and substrate specificity, GmBGL was ectopically expressed in transgenic rice. Purified GmBGL protein from transgenic rice could catalyze the hydrolysis of genistin and daidzin to produce genistein and daidzein, respectively, which confirmed GmBGL as a functional β-glucosidase with isoflavone glucoside-hydrolyzing activity. This paper reveals that GmBGL is a key enzyme in transforming glucosyl isoflavones to aglycones in soybean, which may help in genetic manipulation of aglycone-rich soybean seeds.