Enzymatic hydrolysis of soy protein for nutritional fortification of low pH food

Enzymatic hydrolysis of proteins is an attractive means of obtaining the changes in the functional properties often necessary for incorporating the protein in low pH food, e.g. soft drinks. The main problem associated with protein hydrolysis is the welldel-known formation of bitter-tasting peptides. The bitterness seems to be related to a too high degree of hydrolysis (DH). DH is defined as the percentage of cleaved peptide bonds and serves as the controlling parameter for the hydrolysis process. The choice of hydrolysis parameters is briefly discussed in relation to studies on the hydrolysis kinetics which in many respects can be described by classical enzyme kinetics. Several pilot plant productions of isoelectric soluble soy protein hydrolyzates have been carried out using soy isolate or soy concentrate as the raw material. The preferred enzyme for this type of hydrolysis is Alcalase 0.6 L, a food-grade liquid preparation of subtilism Carlsberg. The chosen hydrolysis parameters are : Substrate conc. : 8 per cent protein (N x 6.25). Enzyme-substrate ratio : 2 per cent. pH : 8.0. Temperature : 50 degrees C. The optimal DH value with regard to taste seems to be 10 per cent, corresponding to about 2 hours' hydrolysis time. The hydrolysis is terminated by the addition of citric or malic acids until pH reaches a value of 4.2. Separation of the supernatant from the unconverted protein is carried out in a continuous, solids-ejecting centrifuge. Preliminary rat trials show a satisfactory nutritional quality of the hydrolyzates. Possible end-uses for soy protein hydrolyzates are briefly discussed.