Effect of ultrasound-assisted pretreatment in combination with heating on characteristics and antioxidant activities of protein hydrolysate from edible bird’s nest co-product

Protein hydrolysates (P-HS) from edible bird’s nest co-product prepared without and with ultrasound (US) pretreatment in combination with heating before hydrolysis using alcalase at different concentrations were characterized. US treatment of co-product in water at 60% amplitude for 20 min, followed by heating at 95 °C for 3 h was done before enzymatic hydrolysis. The degree of hydrolysis (DH), yield and sialic acid (SL) content of P-HS samples were not different (p > 0.05) when 1 or 2% alcalase was used for hydrolysis. The highest protein content and lightness (L^*) were observed in P-HS prepared from co-product subjected to US treatment (60% amplitude for 20 min) using 1% alcalase for hydrolysis. When antioxidant activities of dried P-HS were determined, P-HS from co-product subjected to US treatment had higher DPPH and ABTS radical scavenging activities, ferrous reducing antioxidant power and oxygen radical absorbance capacity, compared to those prepared from non-US treated co-product. P-HS with higher DH contained greater amount of small peptides having MW lower than 1,883 Da. The P-HS produced under optimum condition had major essential amino acids (EA-A) including leucine, threonine, lysine and valine of 4.28, 3.53, 3.30 and 3.08%, respectively. Therefore, P-HS from co-product could serve as both nutrients and functional ingredients.