Effects of NaCl and soaking temperature on the phenolic compounds, α-tocopherol, γ-oryzanol and fatty acids of glutinous rice

Soaking is one of the important steps of the parboiling process. In this study, we investigated the effect of changes in different sodium chloride (NaCl) content (0%, 1.5% and 3.0% NaCl, w/v) of soaking media and soaking temperatures (30 °C, 45 °C and 60 °C) on the phenolic compounds (α-tocopherol, γ-oryzanol) and on the fatty acids of glutinous rice, compared with unsoaked samples. Overall, the total phenolic content, total phenolic acids, γ-oryzanol, saturated fatty acid and mono-unsaturated fatty acid of the glutinous rice showed an increasing trend as NaCl content and soaking temperature increased, while α-tocopherol and polyunsaturated fatty acids decreased. Soaking at 3.0% NaCl provided the highest total phenolic content, total phenolic acids and γ-oryzanol (0.2 mg GAE/g, 63.61 μg/g and 139.76 mg/100 g, respectively) for the soaking treatments tested. Nevertheless, the amount of α-tocopherol and polyunsaturated fatty acid were found to be the highest (18.30/100 g and 39.74%, respectively) in unsoaked rice.