Production of β-glucosidase from okara fermentation using Kluyveromyces marxianus

The effective utilization of okara (soybean residue) has become a considerable challenge in recent years. In this paper, the potential advantages of β-glucosidase production from okara fermented by Kluyveromyces marxianus were evaluated and the properties of the β-glucosidase were also characterized. The results showed that okara can significantly induce the production of β-glucosidase from K. marxianus. The β-glucosidase activity was up to 4.5 U/mg under optimized fermentation conditions. The optimal parameters were as follows: fermentation temperature 35 °C, cultivation time 98 h, inoculum concentration 10%, and 30 g/L of okara. After two steps of purification using ammonium sulfate precipitation and Sephadex G-75 column chromatography, the activity of β-glucosidase was 71.4 U/mg. The native enzyme was an approximately 66 kDa dimer consisting of two different subunits (22 and 44 kDa). The kinetic parameters of the K. marxianus β-glucosidase, using pNPG as substrate, were V 8.34 μmol min^-1 mg^-1 and K 7.42 mM. The β-glucosidase showed high thermostability and acid-alkali tolerance as well as low inhibition by DMSO (10-50%). In conclusion, this study supports the notion that okara fermentation by K. marxianus could be a useful process to produce β-glucosidase.