Electrophoretic Distinction of the Origin in Different Dairy Products and Milk Samples

Caseins, lacto-albumin, and lacto-globulin are major milk proteins. These globular proteins could be significant indicators of the milk and dairy products origin. Knowing that caseins, lacto-albumins and lacto-globulins vary in molecular weight and concentration in different types of milk, this fluctuation can be used for determination of milk origin. The aim of this study was to develop an appropriate method for distinction of milk proteins from different origin. Twelve samples of milk, white cheese, yellow cheese and whey cheese from cow, sheep and goat were obtained and studied. The protein separation was made using SDS-PAGE. SDS is an anionic detergent that breaks all inter and intramolecular bonds and leaves the polypeptide subunits of proteins in forms that can be separated on the basis of their molecular weight. Polyacrylamide gels, used as support medium, restrain larger molecules from migrating as fast as smaller molecules. In order to optimize the conditions of the experiment, some of the parameters were modified (polyacrilamide concentration from 10-15% according to the molecules size, duration of electrophoresis, quantity of applied material, sonification treatment of the different samples). Bovine milk proteins standards were used for the determination of the proteins. The results have shown differences, as well as other fractions that can be used for identification of the origin. In yellow and white cheese the differences among the samples from different origins appear in lacto-albumin fractions and some digested fractions below the caseins. The main differences in whey cheese samples were identified in casein fractions. The milk samples showed differences in upper fractions, probably serum albumins that remained in the milk samples

DIFFERENT APPROACHES IN ANALYZING CHYMOSIN PURITY

Chymosin is a specific proteolytic enzyme found in rennet, and is the key enzyme in cheese production classified in the aspartic endopeptidases (EC 3.4.23.4). The aim of this study was to determine the purity of different commercially available chymosins and its equivalents using electrophoretic and chromatographic techniques. Chymosins produced by the company Chr. Hansen, CHY-MAX 200 and CHY-MAX Plus, CHY-MAX PowderExtra NB, as well as Maxiren 1800 Granulate from the company DSM, Sirnik from SZR – Travnik, Kraljevo and Planika from Mikroprocessing, Bileca were used as materials for this study. The purity level of the commercially available enzymes was analyzed using electrophoretic (sodium dodecyl sulfate polyacrylamide gel electrophoresis or SDS-PAGE) and chromatographic (Rapid Resolution Liquid Chromatography or RRLC) techniques. Results showed no presence of undeclared protein fractions due to inappropriate purification process in the samples except for CHY-MAX М 200 which had two protein fractions, most likely as a result of a polymorphism. All the CHY-MAX and Maxiren samples have chymosin as the active component (36 kDa), except for Planika and Sirnik which have a natural protease from R. miehei. Chromatographic analysis showed that beside the active component (chymosin), the preservative sodium benzoate was present in varying concentrations in all but CHY-MAX PowderExtra NB