Preparation of the Starter
Strains were activated first via sterilization of the
skim milk at 105°C, of which the solids concentration is
11% (wt/wt). The lyophilized powder of S. thermophilus,
L. delbrueckii ssp. bulgaricus, and L. rhamnosus GG
was activated in the skim milk and then stored at 4°C.
Mother culture was prepared with sterilized skim
milk that had 5% inoculation amount of the activated
strains. The mother cultures of S. thermophilus and L.
delbrueckii ssp. bulgaricus were incubated at 42°C and
the mother culture of L. rhamnosus GG was incubated
at 37°C. They were then stored at 4°C until the curd
was firm.
Fermentation of Goat Milk Yogurt
The raw goat milk was purified using a filter cloth.
After adding sugar, goat milk was heated to 95°C for
5 min using pasteurization and cooled to 45°C. Then
the goat milk was inoculated with S. thermophilus, L.
delbrueckii ssp. bulgaricus, and L. rhamnosus GG in different
ratios, which were determined by the preliminary
experiments; finally, goat milk was fermented at 4°C.