Combined ultrasound and heat pretreatment improve the enzymatic hydrolysis of clam (Aloididae aloidi) and the flavor of hydrolysates

The effects of pretreatments with ultrasound (UP), heat (HP), and combinations of heat-ultrasound (HP-UP) and ultrasound-heat (UP-HP) on the flesh enzymolysis of clam (Aloididae aloidi) and the flavor characteristics of hydrolysates were investigated. The optimum UP pretreatment conditions for the hydrolysis were obtained at ultrasound power of 500 W, ultrasound time of 20 min, and liquid/solid (L/S) ratio of 2:1 (v/w), yielded 41.33% of hydrolysis degree (DH). Among the different pretreatments, the UP pretreatment had the highest DH value, while the HP-UP pretreatment obtained the highest soluble peptide content. The UP pretreatment efficiently enhanced the contents of taste-active components, including free amino acids, 5′-nucleotides, and succinic acid. The HP pretreatment promoted the formation of pleasant volatile compounds and reduced the content of unpleasant volatile compounds, such as 1-octen-3-ol and 2-ethyl-1-hexanol. The combined HP-UP pretreatment was an effective method for improving the enzymatic hydrolysis of clam and the flavor of hydrolysate.