Yogurt starter, lactic starter is the most important technology in production of products of daily consumption.
Milk is an amazing food,
prepared by nature.
I. P. Pavlov
Starters – pure cultures or symbiosis of pure cultures of lactic-acid bacteria added into milk for the purpose of receiving high-quality fermented milk products, the soft and hard cheeses. Production of many dairy products (dairy drinks, cottage cheese, cheese) is based on biochemical processes of fermentation of lactose (lactose) and coagulation of a casein of milk. Lactose fermentation, i.e. turning into compound with a smaller molecular mass, happens under the influence of lactic-acid, propionate, acetic bacteria and yeast.
Lactic streptococcus and lactobacillus belong to the lactic bacteria causing lactic fermentation. The group of lactic streptococcus includes mesophilic (lactic, creamy and aroma-producing) and a thermophilic streptococcus, and the group of lactobacillus includes Bulgarian and acidophilic, and also the bacteria used in cheese making.
Propionate bacteria ferment glucose, lactic acid into propionic acid and other products which enrich taste and a smell of a product. In the course of reproduction these bacteria can synthesize B12 vitamin. Acetic bacteria are activators of acetic fermentation as a result of which the acetic acid is formed.
Pure cultures of lactic-acid bacteria and other microorganisms (yeast) are produced in express laboratories of pure cultures from milk, high-quality dairy products and plants. For bacteriemic starters such cultures of microorganisms should be picked up as a result of whose activity high-quality dairy products are produced.
Selection of the bifidus bacteria used for preparation of dairy products of treatment-and-prophylactic purposes is made taking into account features of their properties. Bifidus bacteria are sluggishly reproduced in milk, separate strains of these bacteria ripen milk at an optimum temperature of development in 2–4 days that is unacceptable in technology of dairy products. Therefore they make selection of strains of the bifidus bacteria with increased acid-forming ability.
The preventive and medical value of dairy products is defined not only by quantity of the received starter population, but also by ability to survive in intestines of the person. An indirect indicator of ability of microorganisms to survive in intestines is their phenol resistance which always is in intestines contents. Strains of bifidobacteria strongly differ on this property. Therefore there is a need of selection of bifidobacteria for this property. Besides, it is necessary to select bifidobacteria for their ability to form antibiotic substances. Now the following criteria of selection of bifidobacteria in composition of ferments are defined: