Conversion of Isoflavone Glucosides to Aglycones by Partially Purified β-Glucosidases from Microbial and Vegetable Sources.

Abstract

Isoflavone aglycones have been shown to be more rapidly and efficiently absorbed into intestines than isoflavone glucosides. Helpfully, β-glucosidases can be used to convert isoflavone glucosides to aglycones. In this study, β-glucosidases from microbial (Aspergillus niger) and vegetable lima bean (Phaseolus lunatus) sources were characterized, purified, and then employed to convert isoflavone glycosides to aglycones. The microbial crude extract showed maximum activity at 60 °C and pH 5.0. It was highly stable between 40 and 60 °C and between pH 4.0 and 9.0. Optimum activity for the vegetable crude extract was achieved also at 60 °C and pH 5.5. Similarly, it presented great stability at high temperatures and a wide pH range. The microbial enzyme was purified by a factor of 14-fold to a yield of 2.2 % and a specific activity of 17 IU/mg. The vegetable enzyme was purified by a factor of fourfold to a yield of 77 % and a specific activity of 0.18 IU/mg protein. Both β-glucosidases produced satisfactory conversion rates of daidzin and genistin into daidzein and genistein; however, the microbial enzyme performed better than the vegetable enzyme. Our results suggest a potential use of these enzymes to enhance the bioavailability of isoflavones in food products.