Functional plastein from fish waste

Enzymatic hydrolysis of fish waste has been examined using proteolytic enzymes under different conditions of pH, enzyme to substrate ratio, and substrate concentration. Proteolytic enzymes have then been used to synthesise a protein-like product (plastein). The particular enzymes used in both parts of this study were bromelein, a-chymotrypsin, pepsin and papain. Reasonable yield was obtained. The yield of plastein was found as a function of substrate concentration. enzyme to substrate ratio, degree of hydrolysis and enzyme used. Generally, the plastein appeared to be odourless, yellowish to creamy in colour. tasteless and rich nutritionally. The insoluble plastein formed was washed, dried and then tested for its functional properties, particularly with respect to water absorption capacity, swelling capacity, oil absorption capacity. foam and foam stability, emulsion stability, gelatination, viscosity, and heat-setting properties. The functional properties of the plastein precursor (fw*hydrolysate) and of commercial proteins have also been examined. The dried plastein which was tested under different conditions was found not only to possess functional properties such as fat/water absorption, swelling and emulsion stability. but also excellent foaming properties were observed. Although plastein appeared to be gel-like before drying, it was, however. not able to retain its gelatinity after drying. Therefore, it would be possible to use it in a food system as an alternative to the material substituted without changing the texture (e.g. in cereal products). The viscosity of the plastein was varied under the conditions used. It was found to be mainly a function of the temperature and the concentration. Finally. it was noted that plastein shows heatsetting properties when prepared under certain conditions.