Sorption isotherms and glass transition temperatures of fish protein hydrolysates with different degrees of hydrolysis

Abstract

The objective of this research was the determination of the sorption isotherms and glass transition temperatures of five protein hydrolysates with different degrees of hydrolysis (DH). The hydrolysates were obtained by proteolysis of concentrated myofibrillar proteins obtained from Nile tilapia (Oreochromus niloticus) using the enzyme Flavourzyme™. There was no significant difference between the different isotherms. Agglomeration and/or compactation was observed in all samples stored in atmospheres with relative humidities (RH) of 57%. The glass transition temperature (Tg) of the hydrolysates, determined by differential scanning calorimetry (DSC), diminished with increasing moisture content, showing values between 1° and 55°C for moisture values between 17 and 6 g water/100g solids. Contrary to what has been reported in the literature, the increase in degree of hydrolysis of the hydrolysates was not reflected in a decrease in Tg. It was observed that Tg increased with increasing DH, when the hydrolysates were stored at low RH (22% to 32%). When stored at 57% RH, the Tg decreased with increase in DH.