Evolution of microbial and protein qualities of fractions of milk protein processed by microfiltration

Abstract

In dairy industry there has always been great concern about the microbial and protein quality of liquid milk protein fractions obtained by microfiltration (MF). The objectives of research were to study the impact of MF on the evolution of protein and microbial quality of microfiltered milk (MFM), liquid micellar casein concentrates (LMCC) and serum permeates (SP) during storage at 4 °C. This study was carried out with three different batches of milk using diafiltration. Samples were characterized by physicochemical properties; evolution of microbial load and protein (RP-HPLC). Ceramic MF (pore size 1.4 μm) did not change the protein profile, but reduced microbial load by up to 2 log CFU/mL. Polymeric MF (pore size 0.1 μm) was not a sterilizing process since all samples from the permeate presented bacterial growth after 6 days. Protein degradation was observed after 13 days at 4 °C in all studied products. Caseins (CN) were much more affected than whey proteins. β-CN A2 content was reduced by 25–50%, αs1-CN by 30% and β-CN A1 by 10–30%.; κ-CN was the most stable casein. The contents of the whey proteins remained unaltered for 21 days. Protein degradation was likely due to the action of endogenous and bacterial enzymes.