PARTIAL LEAST-SQUARES REGRESSION OF 4TH-DERIVATIVE ULTRAVIOLET ABSORBENCY SPECTRA PREDICTS COMPOSITION OF PROTEIN MIXTURES - APPLICATION TOBOVINE CASEINS

A method is described for the quantitative determination of the compos ition of protein mixtures using fourth-derivative ultraviolet spectros copy. The methodology was demonstrated by quantifying mixtures of the three main bovine caseins (alpha(s1)-, beta-, and kappa-casein). The 2 44-296-nm spectra region of protein mixtures of known composition, dis solved in 4 M guanidine hydrochloride, was used for the development of prediction models using the multivariate method of partial least-squa res regression analysis (PLSR), implemented in a commercial software. The standard errors of prediction for 16 test samples were 13.4, 5.5, and 11.9% for alpha(s1)-, beta-, and kappa-casein, respectively, and t he correlations between measured and predicted composition were 0.91, 0.99, and 0.94 for the three proteins, respectively. This method was f ound to be faster and simpler than alternate procedures (e.g., gel ele ctrophoresis), suggesting the possibility of using this methodology as a quality control tool in industrial protein fractionation environmen ts.