Effect of raw milk storage and bacterial development on subsequent lactic culture activity.

In investigations on slow acid development by lactic acid starter cultures,2 only limited consideration has been given to the effect of other bacteria present in the raw milk. Attention has been directed to inhibitory effects of such substances as nisin produced by certain streptococci and to possible inhibition by other bacteria (Cox and Whitehead, 1931; Babel, 1955). However, little specific information on the latter aspect of starter slowness is available. Olson et al. (1955) found no reduction in acid production when milk had high bacterial counts due to incubation at 80 F before heat treatment. Different seasons and different sources of milk were not investigated. Conditions of milk production and handling have changed markedly in the last 10 years. Under farm bulk tank systems, some milk may be several days old before being pasteurized for cheesemaking. Cases of slow acid development in starters and cheesemaking often are not traceable to bacteriophage, antibiotics, or germicides (Czulak and Meanwell, 1951; Keogh, 1958). As indicated by the report of Mosely and Winslow (1959), the problem appears to be more complex than previously considered. Accordingly, investigations were conducted to determine if, during different seasons, the storage or raw milk with accompanying bacterial development would increase the incidence or degree of lactic starter inhibition.