Enhanced Conversion of Isoflavone Glucosides to Aglycones in Okara through Alkali Treatment and Fermentation with <i>Lacticaseibacillus casei</i>

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To increase conversion rate of isoflavone glucosides to aglycones in okara through solid-state fermentation with lactic acid bacteria (LAB), we investigated the effects of alkali treatment to okara on hydrolyzation of isoflavone malonylglucosides. After incubation of okara in a solid state at various pH adjusted with sodium hydroxide solution, malonyl groups of malonylglucosides were most effectively hydrolyzed at pH 11.0. As a result of the alkali treatment, the proportion of β-glucosides in the total isoflavones in okara increased from 32.1% to 86.4%. After fermentation of alkali-treated okara with Lacticaseibacillus casei, 93.3% of the total isoflavones were converted to aglycones, which were 1.8-fold higher than those of untreated okara. Moreover, similar hydrolysis of malonylglucosides was observed when potassium carbonate solution was used. Thus, the combination of alkali treatment and fermentation with LAB could be one of the useful practical methods to increase the isoflavone aglycones contents in okara as a food material at low energy costs.