Caracterização das frações proteicas de produtos lácteos por Kjeldahl e eletroforese em gel de poliacrilamida (SDS-PAGE)

Abstract

This dissertation, developed within the Graduate Program in Chemistry at the Federal University of Juiz de Fora (UFJF) and funded by the Coordination for the Improvement of Higher Education Personnel (CAPES), investigated the protein fractions of concentrated dairy products using different analytical methodologies, with whole condensed milk, traditional dulce de leche, and condensed dairy blend as the studied matrices. In the first stage of the study, the analytical conditions of the Kjeldahl method were established and optimized for protein determination in traditional dulce de leche and whole condensed milk samples. In the second stage, nitrogen fractions determined by Kjeldahl and protein profiles obtained by polyacrylamide gel electrophoresis with sodium dodecyl sulfate (SDS-PAGE) were evaluated in commercial samples of traditional dulce de leche, whole condensed milk, and raw milk. In the third stage, the number of commercial samples analyzed was expanded, including condensed dairy blends, in order to assess the variability in protein behavior among brands. Finally, in the fourth stage, laboratory-scale samples similar to the commercial products were produced to compare the obtained profiles and to better understand the behavior of protein fractions in concentrated dairy matrices under controlled processing conditions. Overall, the results provided a better understanding of the behavior of protein fractions in concentrated dairy products, demonstrating that protein fractionation methodologies originally described for raw milk are not fully adaptable to samples subjected to thermal treatments and concentration processes. In addition, the protein fractions obtained after thermal processing do not correspond to pure fractions but can be used as indicators of the degree of thermal processing to which the products were subjected. Furthermore, the behavior of protein fractions in laboratory-produced samples was similar to that observed in commercial samples. The Kjeldahl method and the SDS-PAGE technique proved to be complementary and fundamental for the protein characterization of the different matrices evaluated.