Novel process of hydration, followed by incubation and thermal processing, for high isoflavone bioconversion in soybeans

Abstract

The potentially bioavailable aglyconic isoflavone content of soybeans was increased by a process based on the controlled hydration of whole beans, followed by an incubation step and cooking. For developing the process, the effects of three operation variables: temperature, intermittent soaking and incubation time on the isoflavone profile of the processed soybeans were assessed. By hydrating the whole beans under controlled conditions (54 °C; 15 rpm for a rotating soaking basket) and holding the beans for an appropriate incubation time, it was possible to substantially increase the total aglycone content from (μmol·10−2·g−1) ~5 in the raw, to ~95 in the processed soybean. A conventional thermal treatment (1 kg⋅cm−2, 5 min), necessary to attain the nutritional and sensory characteristics, produced additional hydrolysis of glucosides, accounting for extra 14% of total aglycone yield. The entire process avoided the need to grind the bean and permitted an overall 21.8-fold increase (per-mole basis) conversion of all forms of isoflavone glucosides to aglycones, particularly to the (S)-equol precursor, daidzein, and with minimal back-diffusion or leaching to the outside medium.