Estimating the degree of hydrolysis (DH) of commercial protein hydrolysates from their molecular weight (MW) median values generated by high performance size exclusion chromatography with UV detection (HPSEC/UV) was evaluated. DH is defined as the proportion (%) of cleaved peptide bonds in a protein hydrolysate. Several methods for DH determination are available, and protein hydrolysates are often tested both for DH by one of these methods and for MW profile by an HPSEC/UV method. We describe a means of estimating the DH of a protein hydrolysate from its MW profile, thereby eliminating the need for the performance of a second, separate test. In this study, a plot of average DH (%) vs. MW median (Da) was constructed from pancreatin digestion time data for seven protein substrates, determined by an HPSEC/UV system with a peptide gel filtration column. A general formula obtained from the plot enables DH estimation for a protein hydrolysate from its MW median value. By using this approach, the DH values for a total of thirteen commercial protein hydrolysates derived from whey, casein, and soy were estimated. Method accuracy was assessed by comparing the MW median-estimated DH to the DH determined by TNBS colorimetry, which generally agreed well, with R² > 0.95. This study demonstrated that a reliable estimate of protein hydrolysate DH may be obtained from its MW median so that the performance of a separate DH test may not be necessary.

Graphical abstract