Monitoring the bioactive compounds in culinary transformation of soymilk : an in situ quantitative NMR study.
2015
Many products made from soybean are consumed in Asia. Soymilk, tofu and yuba are obtained by individuals at home. Changes of bioactive compounds during culinary process were rarely reported. In this study, the analytical method called “in situ quantitative nuclear magnetic resonance spectroscopy” (isq 1H NMR) was applied to the quantitative determination of the variation in taste and functional molecules that are sucrose, lysine, arginine and valine during various culinary transformations of soymilk, involving fresh, thermal process, vacuum evaporation, tofu and yuba. Results suggest that thermal process at 100 ̊C increased the amount of free sucrose but significantly decreased the amount of lysine. Sweetness of soymilk could be simply enhanced. Evaporation of soymilk caused a higher reduction of lysine than thermal processing at 100 °C, indicating that complexation and Maillard reactions of lysine could be enhanced. The arginine content also decreased, albeit in less quantities. The changes of molecular conformation could also be monitored. In particular, resonances associated with the side-chain of valine were observed when most proteins were unfolded at high temperature. In mild acidic condition using glucono-delta-lactone as a coagulant, the amount of lysine was maintained higher than thermal process and evaporation while sucrose content was reduced. Tofu containing of lysine and sucrose could have a sweetness taste. However, there was no free sucrose in yuba. Understanding the change of taste molecules in soymilk during culinary transformation could lead to a better formulate soymilk products, thus this would be benefit to culinary application at home and industrial.
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