THE CORRELATION BETWEEN THE NUMBERS OF LIVING BACTERIA AND THE MONTHS ELAPSED SINCE MANUFACTURE IN POWDERED MILK II. : STUDIES ON SPRAY-DRIED MODIFIED MILK POWDER

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In order to know how the number of living bacteria in spray-dried modified milk powder changes with the lapse of time after manufacture, a series of observations of the bacterial count in milk powder preserved till 1 year after manufacture was designed. The results were subjected to statistical analysis. The bacterial counts were calculated in 18 samples originated from 3 cans with the same lot number. In advance all the milk powder of 3 cans was aseptically well mixed and redivided into many small bags; then these bags were kept at room temperature. The number of living bacteria in each of bags selected at random was counted at two week intervals from 14th to 52nd week after manufacture. The result of this observation shows that there is a negative correlation between the logarithmic survival rates of living bacteria and the weeks elapsed after storage. When the test period was divided into 3 groups, A (0∿10th week after storage), B (8∿30th) and C (28∿38th), the coefficients and regression equations for each group were obtained as follows : A group γ=-0.837,Y=2.021-0.042X B group γ=-0.151,Y=1.612-0.002X C group γ=-0.995,Y=3.355-0.059X From these equations, it was shown that the survival rate of living bacteria in modified milk powder tends to decrease remarkably in the first group A, slightly only in B group and rapidly again in C group (Fig. 1).
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