The optimization of enzymatic protein hydrolysis often represents a tedious task due to complicated analytical methods. The simplest system of continuous analysis consists of monitoring the base consumption during a pH-controlled reactor operation. However, there are other criteria commonly used for characterizing the extent of protein hydrolysis, comprising the degree of hydrolysis (DH) and the SN-TCA index, that is the fraction of nitrogen soluble in trichloroacetic acid under well-defined conditions. Taking the SN-TCA index, expressed in terms of the so-called fraction of non-protein nitrogen NPN, as an example, it is shown that these criteria may be correlated with base consumption. The advantages and limitations of this method are discussed.