The Effect of Milk Heat Treatment on the Growth Characteristics of Lactic Acid Bacteria

The ability to growth in milk is an important feature for lactic acid bacteria (LAB) used as starters for fermented milk products. Several decades ago the results of the studies varied widely: some of them showed that LAB grew better in raw milk and others demonstrated improved growth of the bacteria in heat-treated milk (Foster et al., 1952). The effectiveness of heat treatment of milk as a tool for modifying the functional properties of protein components has been extensively documented in the literature (Raikos, 2010), but the information on the influence of heat treatment of milk on the growth of LAB is not exhaustive. Peculiarities of growth of Streptococcus thermophilus ST12 and Lactobacillus paracasei S1R1 were studied using isothermal batch microcalorimeter TAMIII. Bacterial growth was monitored in pasteurized and ultra-high temperature (UHT) treated milk with different fat content, and also in reconstituted skim milk (RSM) prepared from low-heat skim milk powder (LHSMP). Heat produced during different growth stages (Qtot, Qexp), maximal specific growth rate (μmax) and lag–phase (λ) duration were determined by processing calorimetric curves, and detailed analysis of growth of the bacteria in differently pretreated milks were carried out on the basis of these data. The results of the experiments showed that primarily heat treatment and, to a minor extent, fat content of milk influenced the growth parameters of both bacterial strains, especially Lb. paracasei, growth of which was almost completely inhibited in UHT milk