IN VITRO PROTEIN DIGESTIBILITY OF BROWN RICE AFTER HIGH-PRESSURE FREEZE-THAW CYCLES AND GERMINATION-PARBOILING TREATMENTS

The objective of this study was to evaluate the in vitro protein digestibility of brown rice (BR) after high-pressure (HP), freeze-thaw cycle (FTC), and germination-parboiling (GP) treatments. Four-cycle freeze-thaw (FTC-4) treatment enhanced digestibility, and all treated BR released more essential and total amino acids after digestion. To evaluate the nutritive value of free amino acids released after digestion (on the premise of the same intake of BR products), a BR amino acid score (BR-AAS) was used, based on the patterns of protein digestibility-corrected amino acid scores with modifications. Results suggested that BR treated with 24 h of germination followed by 10 min of parboiling (G24P) was a better choice for supplementing amino acid intake in a daily diet. All treatments resulted in decreased protein solubility, which was negatively correlated with surface hydrophobicity and disulfide bond contents. The HP, FTC, and GP treatments affected certain protein properties, which was helpful in explaining the differences in protein digestibility of BR. Changes in other constituents were considered important with respect to the treatment influence on protein digestibility.