Amaranth ( Amaranthus hypochondriacus ) seed protein hydrolysate with optimized hydrolysis degree in Nile tilapia ( Oreochromis niloticus ) diets: effects on antinutritional factors and in vivo digestibility

Abstract

This study evaluated the effect of optimized protein hydrolysate from amaranth ( A. hypochondriacus ) seeds on antinutritional factors and apparent digestibility in Nile tilapia diets. The hydrolysate was produced using Alcalase® 2.4 L (pH 8, 55 °C, 1:10 w/v), achieving an optimal degree of hydrolysis of 79.79% at 150 min (defined as the shortest time to reach the hydrolysis plateau). Three isonitrogenous diets were formulated: a reference diet (RD) and two experimental diets replacing 30% of fishmeal with raw amaranth meal (RAM) and hydrolyzed amaranth meal (HAM). Trials were conducted in triplicate (20±3 g) for 45 days. SDS-PAGE confirmed that HAM exhibited lower-molecular-weight bands (≤10 kDa) than RAM. Hydrolysis significantly reduced ( P < 0.05) saponin content by 36% (2304.25 to 1476.00 mg DE/g) and phytic acid content by 16.8% (37.47 to 31.18 mg/g). Although trypsin inhibitor activity was detected in HAM (1.67 TIU/g), attributable to greater bioaccessibility after hydrolysis, it did not impair apparent digestibility. The apparent protein digestibility of HAM ingredient (92.85%) was significantly higher ( P < 0.05) than that of RAM (78.13%). The results demonstrate that replacing 30% of fishmeal with HAM in O. niloticus diets is an alternative that effectively reduces antinutritional factors and enhances protein digestibility.