Effects of pasteurization, microfiltration, and ultraviolet-c treatments on microorganisms and bioactive proteins in bovine skim milk

Abstract

Effects of high-temperature short-time (HTST) pasteurization, microfiltration (MF) with 1.4/0.8 μm pore diameters, and ultraviolet-c (UV-C) irradiation with a coiled tube reactor on reducing microorganisms and somatic cells, and retaining bioactive proteins/enzymes along with protein oxidation in skim milk were studied. Bacteria were reduced by 2.3 log using HTST and UV-C, and 3.0 log using MF. Coliforms were not detected after all treatments. Spores were unaffected by HTST, reduced by 0.3 log using UV-C, and not detected after MF. Somatic cells remained unaffected by HTST and UV-C, and were undetectable after MF. Bioactive xanthine oxidase (XO), immunoglobulin G (IgG), lactoperoxidase (LPO), lactoferrin (LF), IgM, and IgA were retained at 87, 78, 69, 57, 48, and 41% using HTST, and 100% using UV-C and MF-1.4, while MF-0.8 retained fully the IgG and LPO, and 93, 92, 91, and 86% of IgA, XO, LF, and IgM. Native serum proteins were retained at 89% using HTST, 95% using UV-C, and 100% using MF. Carbonyls were increased by 26% using UV-C, and sulfhydryls were reduced by 14% using HTST, while both were unaffected using MF. Flux for MF-1.4 was higher and remained steady after an initial decrease of 12%, while flux for MF-0.8 decreased progressively by 45% until end of processing, resulting in complete and 89% passages of casein micelles using MF-1.4 and MF-0.8. MF-1.4 and UV-C could be proposed as nonthermal technologies alternatives or as hurdle-technologies to HTST for reducing microorganisms while retaining bioactive proteins/enzymes in skim milk, without inducing significant oxidative effects.