250. The influence of various factors on the fermentation end-products of the heterofermentative streptococci

1. The influence of temperature,pH, oxygen tension and yeast autolysate on the production of by-products and the ratios of by-products formed to sugar utilized and lactic acid produced in milk by the heterofermentative lactic acid streptococci has been investigated. 2. The total production of lactic acid is increased by anaerobic conditions and low temperature. The ratio of lactic acid formed to sugar utilized is increased by anaerobic conditions and the presence of chalk. 3. The total amount of acetic acid is higher in the presence of chalk, at the lower temperatures and in yeast milk, but is decreased by anaerobic conditions. The ratio of acetic acid both to sugar utilized and to lactic acid formed is smaller at lower temperatures, in the presence of “growth factors” and chalk and under anaerobic conditions. 4. The total alcohol production is higher when yeast or chalk is added to milk, under anaerobic conditions and at lower temperatures, and similarly the ratio of alcohol formed to sugar utilized and lactic acid produced is increased. 5. Hydrolysis of residual lactose occurred in all cultures ofStr. citrovorusand with some of the other streptococci in cultures to which chalk had been added. 6. Although the heterofermentative lactic acid streptococci possess respiratory enzymes, these fail to suppress aerobic fermentation (i.e. the Pasteur effect is slight).