Influence of Combinations of Lactobacillus lactis and Potassium Sorbate on Growth of Psychrotrophs in Raw Milk

Abstract

Cells of Lactobacillus lactis from frozen concentrated cultures were added (1×108/ml) to refrigerated raw milk to determine their effect on growth of psychrotrophs during storage of the milk at 5 or 7°C. Some strains of Lactobacillus lactis were significantly inhibitory toward the psychrotrophs in refrigerated raw milk at both temperatures. Two selected strains of Lactobacillus lactis were added along with potassium sorbate (.1 and .2%) to refrigerated raw milk stored at 5°C to determine their combined effect on growth of the psychrotrophs. The combinations of cells of lactobacilli and sorbate were more inhibitory than either lactobacilli or sorbate alone. The measurement of hydrogen peroxide produced by strains of Lactobacillus lactis indicated that the strains most antagonistic toward psychrotrophs also were the more active producers of hydrogen peroxide. Addition of sorbate had no apparent effect on hydrogen peroxide production by the cultures during refrigerated storage.