Recovery of functional materials with thermally stable antioxidative properties in squid muscle hydrolyzates by subcritical water.

Subcritical water hydrolysis was carried out to produce functional materials from squid muscle using a batch reactor. The reaction temperatures and pressures for hydrolysis of thermal dried squid muscle were maintained from 160 to 280 °C and 6 to 66 bar for 3 min. The ratio of material to water for hydrolysis was 1:25 (w/v) and it was stirred at 140 rpm. Hydrolysis yield was increased after increasing the temperature and pressure while the protein in hydrolyzate decreased with the rise of temperature. The reducing sugar yield was high at temperature 220 °C in subcritical water hydrolysis of squid muscle. Low molecular weight peptides were found in all hydrolyzates by SDS-PAGE. The highest yield of free and structural amino acid in hydrolyzate was 421.53 ± 1.24 and 380.58 ± 2.25 mg/100 g, respectively at 250 °C. All essential amino acids were identified in muscle hydrolyzates and it was high at 220 °C. Among the essential amino acids, leucine was the most abundant. Antioxidative properties were found in all hydrolyzates and it was high at 220 °C. More than 98 ± 0.26 % ABTS antioxidant activity was retained in hydrolyzates after long time heat treatment.