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ABSTRACTS
[Vol. XX, Part III
nearly two years. At frequent intervals, the content of sample cane were examined
organoleptically and by various physical and chemical methods. On the basis
of these tests, stored powders were further examined for changes in the biological
value of the proteins and for microbiological assay of ' essential ' amino acids.
Little change was observed in the powders of low and medium moisture content,
except in palatability and gas exchange at the higher temperatures. The powder
of the highest moisture content, particularly at the higher storage temperatures,
rapidly became unpalatable, discoloured and insoluble. In the case of nitrogen
packed sample ' heated ' or ' caramelized ' flavour was produced, while in case of
air packed powders more objectionable ' stale ' flavour developed.
The biological value of the proteins of dried skim milk of high moisture content
decreased progressively during storage in air at 37°C., whereas that of medium
moisture content proved more stable and of low moisture content seemed to be least
affected under any conditions of storage. The decrease in the biological value of
proteins was slightly more marked in air packed than in gas packed samples ;
the decrease being accounted for by the loss or inactivation of lysine and probably
some loss of histidine.
It is concluded that skim milk powders containing not more than five per cent
moisture can be stored in air or gas pack at temperatures upto 28.5°C. (83°F.) for
at least two years, without suffering detectable loss in the nutritive value of their
proteins, though with a serious loss of flavour in the former and a less marked loss
in the latter. Furthermore, it seems likely that under all conditions of storage
skim milk powder will become unpalatable before it suffers any appreciable loss in
the nutritive value of its proteins. (S.D.)
A Note on the Bacteriological Aspects of Distribution of Heat-treated Milk in Churn.
CROSSLEY, E. L. and PATTEN, E. M. (1949) Proc. Soc. app. Bact. (2), 58-61
P ERIODIC reports that the heat treated milk transported in churns from
long distances failed to satisfy the milk standards of authorities in retail
distribution areas, prompted this present investigation. Samples of milk were
collected from milk churns intended for transport and were stored in shade at atmos-
pheric temperature for the determination of total bacterial counts and presumptive
coliform tests at the end of 2, 24, and 48 hours of storage. Methylene blue reduction
time was also determined after 24 and 48 hours of storage under similar conditions.
Results showed that the increase in colony count was negligible even after 43 hours
of storage when the atmospheric temperature ranged between 30°F. and 49°F. ;
when, however, the temperature ranged between 60°F. and 70°F., the count exceeded
the legal standard of 100,000 bacteria per ml. even after 24 hours of storage. About
40 per cent of the samples reacted positive to the coliform test in 0.01 ml. amounts,
thus, failing to satisfy the legal standard. The methylene blue reduction time even
after ageing for 24 hours at 60°F. to 70°F. was 3 hours much longer than the legally
permissible standard of 30 minutes. When ageing was extended up to 48 hours
at 60°F. to 70°F. the reduction time was half hour. Thus, methylene blue reduction
test approved on an average 70 per cent of samples whereas colony count and coliform
test passed only 48 per cent of the samples maintained under similar conditions.