Evaluation of different protein sources for aquafeeds by an optimised pH‐stat system

This paper presents the results of some experiments oriented to optimise and standardise the measurement of protein hydrolysis by fish proteases using the pH‐stat technique. Various factors affecting the degree of hydrolysis (DH) were considered (autohydrolysis of the protein sources, type of enzymes utilised, substrate/enzyme ratio and effect of inhibitors). The crude extracts obtained from fish digestive tissues showed their suitability for the determination of protein hydrolysis, rendering better results than those obtained using mixtures of commercial enzymes. DH values for a given protein were greatly affected by the substrate/enzyme ratio, since small modifications in protein concentration resulted in significant variations in DH. Protease inhibitors present in various plant protein sources produced a reduction in DH values.