Exploring heat treatment effects on trypsin inhibitors and protein digestibility in soybean meal

Justification: Soybeans are widely consumed as protein source for their nutrition and functional properties. However, soybean protein digestibility is negatively affected by the presence of trypsin inhibitors (TIs). This study aims to explore the effect of heat treatment on TIs concentration, protein digestibility and nutritional properties of soybean meals.

Methods: Two soybean varieties, categorized as high TI and low TI based on their initial TIs concentration, were used in this study. The soybean seeds were dehulled, milled, and defatted into soybean meals following industrial processing methods. The collected soybean meal samples were heat treated with steam at 60 °C, 80 °C, 100 °C, and 121°C for 10 min, respectively. The samples were then analyzed for in vitro protein digestibility, TI concentration, SDS-PAGE profiles, amino acid composition, solubility, and color.

Results: Heat treatment at 100°C significantly improved protein digestibility and reduced TI concentrations for both soybean varieties. A strong negative correlation (r = -0.738, P = 0.015) between protein digestibility and total TI concentration was observed. Notably, at 100°C the low TI variety displayed higher protein digestibility (81.40%) and lower TI concentration (0.68 mg/g) compared to the high TI variety. SDS-PAGE profiles revealed lower protein band intensity and fewer bands in samples treated at 100°C and 121°C. There is no obvious difference on amino acid composition after heat treatments, while higher temperature caused darker colors of samples.

Significance: This study identifies low TI soybean variety can be as a good alternative for industrial applications and recommends 100°C as an effective temperature for reducing TIs while maintaining protein quality. These findings provide valuable insights for improving soybean processing techniques and final product quality.