Limited enzymic degradation of proteins: A new approach in the industrial application of hydrolases

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Abstract
The industrial importance of hydrolases exceeds that of other classes of enzymes. A major application area for hydrolases is for the dissolution of biopolymers such as starch, pectin, cellulose and protein; in many cases it has been the desire to achieve as complete a solubilisation as possible. However, with food proteins, it has been demonstrated that a limited controlled hydrolysis may give rise to particularly interesting functional and organoleptic properties. The degree of hydrolysis (DH) is defined as the percentage of peptide bonds cleaved and is used as the controlling indice for the hydrolysis of food proteins. For a given enzyme‐substrate system, at least five independent indices can be defined: S (substrate concn), E/S (enzyme/substrate ratio), pH, T (temperature) and t (time). The advantage of the DH‐concept is that of these five variables, four (S, E/S, T, t) can be replaced by DH, i.e. within certain limits of S, E/S, T and t, the properties of a particular protein‐enzyme system are solely dependent on DH and pH of the hydrolysis. Empirically, this is demonstrated for soya‐protein isolate hydrolysed with Alcalase and theoretically the same result can be derived from the fact that there is substrate saturation throughout the reaction. These theoretical calculations are the basis for the so‐called θ(h)‐method, by which the significance of a particular hydrolysis indice can be studied. For each empirically derived hydrolysis curve, the hydrolysis time corresponding to any DH is found. Over a complete DH interval the proportion between the hydrolysis time for each DH is then calculated. If this term, denoted θ(h), is the same for all DH, the properties of the hydrolysates are independent of variations in the hydrolysis indice under study. A statistical procedure must be used to determine if θ(h) is constant or not. The θ(h)‐method is thus a valuable tool in the practical optimisation of industrial hydrolysis processes as the hydrolysis reaction curve under varying process conditions can be precalculated. The procedure may possibly be of interest in the hydrolysis of other biopolymers.