FORMULATION AND VALIDATION OF SELECTIVE MEDIA FOR THE ENUMERATION OF LACTIC ACID BACTERIA IN FERMENTED MILK PRODUCTS
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Date
2021-07-01
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KARNATAKA VETERINARY, ANIMAL AND FISHERIES SCIENCES UNIVERSITY, BIDAR – 585 401
Abstract
Market samples of curd, yoghurt probiotic drink and domestic curd samples were
enumerated using formulated and readymade media like M17 for lactococci as well as
Streptococcus thermophilus and MRS media for lactobacilli incubated in candle jar at 30ºC
and 37ºC respectively for 48 h the readymade media gave better recovery of viable cells of
lactic acid bacteria. Reduction in lactic counts of fermented milk products was noticed in
both M17 and MRS agar after incorporation of calcium propionate and sodium benzoate
at 1.5 and 2 per cent each, respectively helped in control of both aerobic spore formers and
yeasts. Yeast glucose agar with Bromocresol Purple (BCP) with 0.05 per cent was used
which showed better viable counts of lactic acid bacteria than Elliker agar with BCP. In
order to reduce aerobic spore forming bacteria and yeasts, calcium propionate of 0.8 per
cent and sodium benzoate of 1.2 per cent incorporation to yeast glucose agar with 0.05 per
cent BCP led to formation of more than 8 log counts of both yellow and purple colonies.
Yellow and purple colonies when subjected for colony morphology demonstrated rods
(lactobacilli) and cocci (lactococci), respectively indicating the lactic acid bacteria present
in fermented milk products, when inoculated to sterile skim milk set the curd in 8 h with
0.65per cent lactic acid on an average. The correlation coefficient, r was 0.78 between
selective M17 of lactococci and selective yeast glucose agar for purple colony of lactic
cocci while r was 0.67 when MRS lactobacilli count was compared with yellow colonies
of lactobacilli on selective yeast glucose agar indicating good relationship between both
the types of selective agar media.