| dc.description.abstract | Yoghurt is the best known of all cultured-milk
products and is very popular all over the world.
To manufacture yoghurt, bacterial cultures known
as starters are used. Bacteriophage attacks on milk
fermenting bacteria during yoghurt production
process causes loss of entire batches of yoghurt
resulting in economic losses to the company.
Culture bacteria (Streptococcus thermophilus and
Lactobacillus bulgaricus) in starter cultures (Direct
Vat Set-DVS) were isolated using Eliker medium.
Bacteriophage was isolated from affected yoghurt
using host bacteria grown on M-17 medium.
The bacteriophage attacked Lb.bulgaricus but
not St.thermophilus. After further confirmation of
phage attack using the setting delay of yoghurt,
starter cultures used in MILCO Company were
tested to find out resistant bacterial strains. Using
bacteriophage resistant strain of St.thermophilus
and Lb.bulgaricus, new starter culture was
prepared and yoghurt samples were reset with
different concentrations of culture bacteria at
1:1 ratio. Each yoghurt sample was tested for
its setting time, rate of acidity increase and pH
decrease to investigate the suitable concentration
of culture bacteria to be used in the process. The
optimum amount found was 1.5 ml from each of
culture bacteria at 107 CFU/ml per 80 ml of milk. | en_US |
