Cultures of Streptococcus lactis subsp. diacetylactis and Leuconostoc cremoris were added together in the amount of 0.5% to raw milk in a farm bulk tank. This treatment did not significantly reduce the psychrotrophic or coliform population as hypothesized; however, the shelf-life was extended on products made from this raw milk by an average of 1 day. Also, the legal question of adding viable bacteria to the raw milk needs to be considered by state health departments and appropriate federal agencies. Since hydrogen peroxide is reported to be the toxic agent (to the psychrotrophs) released by the citrate fermenters, the obvious fact is noted that this agent can already be added to milk designed for cheese manufacture.
1Present address: Dean Foods Company, 1126 Kilburn Ave., Rockford, Illinois.