H.
LAXMINARAYANA
et
al
21
of Microbacterium) which formed yellow rings on the surface of dahi. Characteristic
colonies of moulds belonging to Oidium, Cladosporium, Aspergillus, and Penicillium
species as well as a few species of Actinomyces were also found in old samples. These
organisms were probably dormant in the freshly made dahi. The greatest number
of samples showing the above types of contaminants were found in Gujarat and
a smaller number in south India.
The variations in fat, protein, ash, and lactose contents as well as total bacterial
counts and titratable acidities of the dahi samples collected from different areas
are shown in Table III. The figures for lactose are available for a few samples
only, as. its determination was discontinued for reasons explained earlier. In
view of the extremely wide variations in the values, averages have not been drawn
but only the ranges of variation have been given in all cases.
It is seen (Table III) that the total bacterial counts as well as the results of
chemical analyses are highly variable and cannot be correlated with either seasonal
or geographical conditions. This may be due to the highly variable initial quality
of milk used, the type of starter added, temperature of storage, age of the samples,
etc.
The total bacterial counts of the samples ranged from 13 to 22 millions per
gram of dahi in the case of samples collected from Delhi and adjacent centres during
winter while samples of a similar quality from Lahore showed counts varying from
319 to 590 millions. In the case of samples collected from Bombay, the counts
ranged between 18 and 730 millions per gram of dahi. Since lactic acid bacteria
derived from the starter constitute the predominant flora in dahi, the bacterial counts
are influenced mainly by the types of starter organisms, temperature of storage and
age of dahi. Due to uncertainty in regard to these factors very little reliance can
be placed on the present data as an index of the quality of dahi or of the sanitary
conditions during its production. On the other hand an estimate of the relative
numbers of streptococci and lactobacilli might be of some value in determining the
quality of the starter. Since the conditions in dahi are not favourable for the growth
of coliform organisms or spore-forming bacteria, their presence in dahi samples
may be expected to serve as an indication of unsatisfactory processing of milk,
use of contaminated starter or insanitary conditions of manufacture and handling.
Excessive numbers of yeasts or fungi may also be considered to be indications of
poor quality of dahi.
The values for titratable acidity and lactose are affected to the greatest extent
by microbial activity. The initial acidity of the milk is also important in assessing
the significance of titratable acidity of dahi. A very large percentage of the samples
in south India have shown acidities exceeding 1.5 per cent (expressed as lactic
acid), which accounts for their highly acidic taste. This is obviously due to the
preponderance of lactobacilli in the starter used, age of the sample and the high
temperatures to which the product was exposed during handling. The north Indian
samples on the other hand, which were generally not more than 24 hours old at
the time of sampling and also contained a preponderance of streptococci, had acidity
values usually below 1.5 per cent. Most of the samples associated with pleasant
aroma and sweet taste showed acidities ranging from 1.0 to 1.3 per cent. The
figures for lactose content are available only for a limited number of samples collected
5