Influence of drying methods on isoflavones, soyasaponins, fatty acids, and aroma profiles in Thai fermented black soybean (thua nao)

Drying treatments significantly influenced non-volatile and volatile components in dried thua nao products. The effects of four drying methods, including natural sun drying (SUN), hot air oven drying (HOT), microwave vacuum drying (MIC), and vacuum oven drying (VAC), on isoflavone, soyasaponin, fatty acid, and aroma-active compound profiles were evaluated using mass spectrometry technique. The results showed that the profiles of isoflavones, soyasaponins, and aroma-active compounds were significantly affected by drying treatments, whereas fatty acid contents showed less pronounced differences. The SUN-treated samples contained higher levels of aroma-active compounds, while SUN treatment showed the greatest degradation of isoflavones and soyasaponins. In contrast, vacuum-based drying treatments (MIC and VAC) effectively preserved isoflavone, soyasaponin compounds but resulted in a loss of aroma-active compounds. The HOT treatment, as recommended drying method, provided both aroma-active compounds and retained isoflavones and soyasaponins. This research revealed the correlations among isoflavones, soyasaponins, and aroma components. • Microwave vacuum drying significantly preserved isoflavones and soyasaponins • Non-volatile breakdown correlated with aroma-active volatiles formation • Different drying methods did not significantly affect total fatty acid composition • First report in UHPLC-HRMS profiling of isoflavones in dried thua nao products