Effects of the β-glycosidase reaction on bio-conversion of isoflavones and quality during tofu processing

Background: Isoflavones are the most common group of phytoestrogens which are present in significantly large amounts in soybean and soy products such as tofu. Isoflavones occur naturally in glycoside forms having lower bioavailability than their aglycone forms. β-Glycosidase acts as a bio-catalyst for the conversion of isoflavone glycosides to isoflavone aglycones, raising the bioavailability of isoflavones; therefore, it can be used to improve the quality of tofu. We need to establish process conditions for the optimal outcome of the enzyme reaction in tofu. Results: By using the β-glycosidase (0.02% w/v) reaction at 55°C for 30 min, a maximum 84.5% conversion of isoflavone glycoside to isoflavone aglycone was obtained. The enzyme reaction caused no significant effects on the sensory acceptability of soft tofu. The hardness of enzyme-treated hard tofu increased with the coagulant amount whereas prolonged heating resulted in decrease of hardness. Incorporation of enzyme reaction before the coagulation process during soft tofu processing provided a sufficient bio-conversion of isoflavones at optimal conditions. Conclusion: β-Glycosidase can be effectively used for the bioconversion of isoflavones in soft tofu manufacturing process at optimal reaction conditions before the onset of coagulation process.