Physical and functional characteristics of sorghum protein hydrolysate and in-vitro digestibility

Sorghum (sorghum bicolor (L) Moench) is the fifth most important cereal in the world. The extraction of starch from sorghum yields by-products such as protein which can be hydrolyzed to form a potential new food ingredient. Therefore, this study aimed to investigate the effect of enzymatic hydrolysis using bromelain enzyme on the functional characteristics and digestibility of sorghum protein hydrolysate. An experimental method was used with a group randomized trial design in each modification stage. The first modification stage was the concentration of bromelain enzyme at 133,663.5 U/mg protein, 267,325 U/mg protein, 400,987.5 U/mg protein, and 534,650 U/mg protein with a hydrolysis time of 2 h. The second stage was the concentration at 534,650 U/mg protein with a hydrolysis time of 2.5 h, 3 h, 3.5 h, and 4 h, while the third stage was the concentration at 1,069,300 U/mg protein, 1,603,950 U/mg protein, and 2,138,600 U/mg protein with a hydrolysis time of 4 h. The results showed that enzymatic protein modification using bromelain at a concentration of 534,650 U/mg protein for 4 h led to a degree of hydrolysis at 56.40%, protein fractions with molecular weights at 12.52 KDa (δ-kafirin fraction) 20.64 KDa (β-kafirin fraction), 30.47 KDa (α-kafirin fraction) and 47.53 KDa (γ-kafirin). Furthermore, the particles of sorghum protein hydrolysate were heterogeneous with a polydispersity index of 0.795 and an average particle size of 0.909 µm. The modified hydrolysis process with bromelain enzyme improved protein quality under alkaline conditions, suggesting great potential as an emulsifier. Sorghum protein hydrolysate had digestibility of 47.14 ± 0.06% tested in vitro, 16.34% better than the concentrate.