Identitication and determination of milk and soybean protein preparations using enzymatic hydrolysis followed by chromatography and chemometrical data analysis

This paper presents the problem of the qualitative and quantitative determination of bovine proteins in soybean protein isolate mixtures. Soybean protein isolate, bovine milk protein preparations and their mixtures with different content of milk protein preparations as described in our previous paper [J. Dziuba et al., 2004, Milchwissenschaft] were examined. The previously presented strategy of detecting and determining milk proteins in soybean protein preparation involved the statistical analysis of the chromatographic peaks with the greatest area variability which were present in the chromatograms of soybean and milk protein preparations and their mixtures. This enabled the determination of the milk protein preparation type added to soybean preparation and its content above 5%. In order to lower the detection limit for milk protein content, the present experiment was extended over five different levels of milk protein addition i.e. from 1 to 5%. However, the analysis was carried out in relation to the relative trypsin hydrolyzates obtained after specific hydrolysis. The trypsin hydrolyzates of the examined preparations of soybean and milk proteins and their mixtures had different compositions of freed peptides. At least two different peptide peaks-"markers" could be identified in each hydrolyzate. The chemometric analysis of chromatographically separated preparations of soybean and milk proteins and their trypsin hydrolyzates enabled the determination of the type of milk protein preparations added to a soybean protein preparation. Based on the results obtained, a special calculation sheet was created for the purpose of the quantitative detection of the milk protein preparation content in soybean protein isolate. (C) 2004 Elsevier B.V. All rights reserved.