288
ABSTRACTS
[Vol. XX, Part IV,
samples to reach the end of their oxidation-induction periods, as found from graphi-
cal data. The oxidation tests were made under two conditions: (a) a practical
test at 38ºC. ('Indian Summer Temperature') for 4-8 months and (b) an accelerated
test at 100ºC. (Swift oxidation tester).
The keeping property of ghee was only slightly influenced by the type of culture
(dahi, L. bulgaricus and L. acidophilus) used for souring though the flavour was
markedly influenced. It was not affected by differences in initial acidity from
0.17 to 0.90, initial moisture content and souring of milk to give 2.5 to 3.0 per cent
lactic acid.
The heat treatment was found to be the most important factor affecting the
keeping property of ghee as it improved with the higher final temperature of
clarification of butter (110º-150ºC.) provided the heating was conducted rapidly, in
contact with the curd and with a minimum amount of stirring. The authors con-
sider the improvement to the due to the antioxidants (apparently phospholipids)
extracted from the curd during heating at higher temperatures as heating of
butterfat with 1 per cent egg-yolk to 110º and 130ºC. promoted increase in oxida-
tion-induction periods. They also suggest that high temperatures in addition to
favouring the incorporation of phospholipids might also convert other substances
into antioxidants.
The rate of oxidation at 100ºC. by the 'Swift oxidation tester' is shown to
predict with fair accuracy the storage life of ghee at 38ºC. (P.D.)
The Types of Bacteria Commonly Found in Farm and Creamery Water Supplies and
their Action on Milk and Milk products. S. B. THOMAS (1949). J. Soc. Dairy
Tech. 2, (4) 224-232
A BOUT 170 species of bacteria have their natural habitat in fresh water but
only half of this number is encountered in the routine bacteriological examina-
tion. The natural microflora of water is composed of the species of Pseudomonas,
Flavobacterium and Microccocous. These organisms are quite distinct from the
bacilli and actiomysetes washed in with soil, and also from the intestinal and sewage
organisms found in polluted water.
Bacterium aerogenes, B. cloacae, B. coli, and Alcaligenes Viscosus have often
been found responsible for the outbreaks of ropiness in farm milk and the causative
organisms have been isolated from water used for washing dairy utensils or from
streams or ponds to which cattle have access. Large numbers of coliform
bacteria may also be introduced when polluted surface-water is used for washing
butter. B. aerogenes and Intermediate types of coliform bacteria grow rapidly in
unsalted butter held at 15ºC. and above, and produce objectionable odours and
flavours.
At refrigeration temperatures fairly rapid proteoloytic and lipolytic spoilage of
milk, cream, butter and cheese are brought about by the faculatative psychrophilie
bacteria which are often found in appreciable numbers in polluted surface-waters.
The majority of the lipolytic bacteria that hydrolyse milk fat and produce
rancidity in cream, butter and cheese are gram-negative rods of the genera Pseu-
domonas, Achromobacter, Flavobacterium and Alcaligenes, generally found asso-
ciated with surface-water.