malonylglucoside isoflavones to b-glucosides (Kudou et al., 1991), the conversion of b-glucoside isoflavones to aglycones (Góes- Favoni et al., 2010; Lima & Ida, 2014), and the degradation of these bioactive compounds (Wardhani et al., 2008). Niamnuy, Nachaisin, Poomsa-ad, and Devahastin (2012) evaluated the rate constants of degradation and conversion of all isoflavones and verified that isoflavones were more susceptible to inter-conversion than they were to thermal and oxidative degradation during the infrared drying of soybean (50, 70, 130, and 150 C). Interestingly, a higher degradation of isoflavones occurred at 55 C (with deionised water) than at the other temperatures used herein. However, an increase in the content of total isoflavones was observed after malonylglucoside isoflavones to b-glucosides (Kudou et al., 1991), the conversion of b-glucoside isoflavones to aglycones (Góes- Favoni et al., 2010; Lima & Ida, 2014), and the degradation of these bioactive compounds (Wardhani et al., 2008). Niamnuy, Nachaisin, Poomsa-ad, and Devahastin (2012) evaluated the rate constants of degradation and conversion of all isoflavones and verified that isoflavones were more susceptible to inter-conversion than they were to thermal and oxidative degradation during the infrared drying of soybean (50, 70, 130, and 150 C). Interestingly, a higher degradation of isoflavones occurred at 55 C (with deionised water) than at the other temperatures used herein. However, an increase in the content of total isoflavones was observed after soaking at 55 C (with buffer solution) for 1 h (Table 1) because of the formation of malonylglycosides (Fig. 2d). It is probable that isoflavones were not formed at 55 C, but their interactions with soybean proteins may have led to an underestimation of the isoflavone contents of the samples that underwent mild heating (<55 C) (Malaypally & Ismail, 2010; Nufer, Ismail, & Hayes, 2009). Nevertheless, the water imbibition by soybean seeds corresponds to the initial phase of the germination process, and metabolic pathways can be induced for the conversion of the precursors (naringenin and isoliquiritigenin) of isoflavonoids to isoflavones (Paucar-Menacho, Berhow, Mandarino, Chang, & Mejia, 2010). Thus, the increase that was observed in the content of malonylglucosides in the soaked grains at 25 C (Fig. 2d) would not be justified only by the improved extraction of isoflavones in the soybean samples that were subjected to the soaking process.
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