509. Bacteriological studies on pasteurized milk

Abstract

1. The numbers and species of micro-organisms surviving in commercial high-temperature short-time pasteurized milks sampled direct from the cooling section of the pasteurizer have been determined and compared with those in the corresponding raw milk and in the raw milk after low-temperature pasteurization in the laboratory. 2. The geometric mean counts at 37° C. for twenty-five samples of raw, L.T. and H.T.S.T. pasteurized milks were 74,130, 1,740 and 3,200 per ml. respectively. The corresponding figures at 30° C. were 123,030, 7,080 and 8,510 per ml. 3. The percentage destruction of the bacteria was slightly smaller at all four plants for the H.T.S.T. pasteurized milks than for the corresponding L.T. pasteurized milks. The mean percentage destruction for the L.T. pasteurized milks was 97·7% for bacteria growing at 37° C. and 94·3% for bacteria growing at 30° C. The corresponding figures for the H.T.S.T. pasteurized milks were 95·9 and 93·1%.