| Abstract [eng] |
In assessing the impact of the protective medium composition and storage temperature on the vitality of cells, the cultures of Lactococcus lactis subsp. lactis, Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, Salmonella typhimurium (ATCC 14028), Staphylococcus aureus (ATCC 25923), and Bacillus cereus (ATCC 10876) were studied. samples of protective medium were prepared, i.e. reconstituted dried skim milk with 20%, 30% and 40% glycerin and brain-heart infusion with 20%, 30% and 40% glycerin. The samples were tested at -18ºC and -72ºC. It is more appropriate to store cultures at -72ºC, however, the resistance of different microorganism species to storage conditions varies. At both temperatures major cells of S. typhimutrium survive in all the media samples, only at -18ºC more cells tend to die in the brain-heart infusion. The resistance of S. aureus to storage conditions is average. The resistance of B. cereus is the weakest: at the end of the experiment only percentiles of the culture remain in the samples. This culture is also characterized as requiring lower temperature conditions. Results show that the skim milk based medium is more advantageous while the concentration of glycerin is less effective. The resistence of lactic acid bacteria cultures (S. thermophilus, L. bulgaricus, and L. lactis) was found to be better; the vitality of the cultures was ensured by both temperatures (-18ºC and -72ºC) in the different samples of protective medium. A higher resistance of lactic acid bacteria under frozen storage has been proved by the results of a longer experiment. The strains of Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris frozen in reconstituted skim milk with 10% of glycerin were stored at -18ºC for three years. [...]. |
