AIM
To
isolate and identify the Lactobacillus
spp. and Streptococcus lactis from the given curd sample.
PRINCIPLE
Milk
contains high nutritive food value for the new borne mammal and human beings.
It is also an ideal growth medium for the microbial proliferation. Fermented
milk and milk based products at different formulation in different name are
popular throughout the world for their taste as well as health benefits. Lactic
acid bacteria (LAB) are widely distributed in nature; occur as natural
adventitious contaminants in raw milk, yoghurt, etc. and sometimes with the
coexistence of yeasts, moulds and some other pathogenic microorganisms. LAB as
indigenous flora in raw milk acidifies the milk very slowly due to their low
numbers. Hence most of the dairy industries now a day’s use LAB as starter
culture for the manufacture of fermented products including milk products such
as yoghurt, cheese; meat products, bakery products, wine, and vegetables
MATERIALS
REQUIRED
·
Curd
sample
·
Man,
Rogosa and Sharpe (MRS) agar media
·
Yeast
Glucose Lemco Agar (YGLA).
·
Test
tubes
·
Conical
flask
·
Pipettes
·
Petri
plates
·
Inoculation
loop
PROCEDURE
·
10 ml of curd
sample was homogenized with 90 ml of 0.85% (w/v) sterile sodium chloride
solution to make an initial dilution (10−1).
·
Serial
dilutions upto 10−6 were made for each sample.
·
1 ml
sample from each of the corresponding dilutions (10−5 and 10−6)
were inoculated into various selective media such as MRS agar, and Yeast
Glucose Lemco Agar (YGLA).
·
MRS agar
(pH 6.2-6.6) used for the lactobacilli isolation, while YGLA (pH 7.0) for the
isolation of streptococci of LAB origin.
·
Inoculated
plates were then incubated at 37°C for 48-72 hours both at aerobic and
anaerobic conditions.
·
|
After incubation,
plates with 30–300 colonies were enumerated and the calculated results were
expressed as colony forming unit (cfu) per gm or ml by multiplying the average
number of colonies with the reciprocal of dilution factor
·
Observe
the colony morphologies such as form, elevation, margin, surface, color and
consistency and isolated.
·
The
isolated colonies were subjected to staining method to observe the morphology
characteristics of Lactobacillus spp
and Streptococcus lactis.
RESULTS
After incubation
creamy to white color colonies were observed on the surface of MRS and YGLA agar
plate. The morphological characteristics were further identified on the basis
of microscopic observation. Microscopic examination shows the Gram 
