Starter cultures are more important for the cheesemaking.
They Produce lactic acid and flavor compounds, particulary acetic acid, acetaldehyde and diacetyl.
Acid production has three functions:
- it promotes rennet activity
- aids the expulsion of whey from the curd, thus reducing the moisture content of the cheese
- helps to prevent the growth of undesiderable bacteria in the cheese.
MESOPHILIC CULTURES (18 < T < 32°C)
One possible subdivision can be made according to the type of the citrate fermentation.
O Cultures (homofermentative)
Lactococcus lactis subsp. lactis e Lactococcus lactis subsp. cremoris, convert lactose into lactic acid and are used when you want to have, at low temperatures, a fast acidification: they don’t ferment citrates and therefore they don’t produce gas.
Generally, they are single strain well defined.
LD Cultures (heterofermentative)
Lactococcus lactis subsp. Lactis biovar diacetylactis (D) and Leuconostoc mesenteroides subsp. cremoris (L), are multi-species lactic cultures undefined that contains bacteria which ferment citrates, that help the developement of gas and the aroma production.
Both Diacetylactis and Leuconostoc can turn citrates into diacetyl and CO2. The function of the Leuconostoc is to metabolize the citrates in CO2, diacetyl and acetate and also it is capable of producing gas metabolizing the lactose. The formation of diacetyl and acetate is however very important for the development of aroma.
Lactococcus lactis subsp. lactis biovar diacetylactis ferments the citrate in a very quick way, starting from a pH of 6.20 while Leuconostoc mesenteroides subsp. cremoris begins to fermentate the citrates starting from a pH of 5.60-5.50.
A correct and regular fermentation of the citrates causes the formation of a very homogeneous structure in cheese. However, a faster fermentation of them can cause irregolar holes issues.
THERMOPHILIC CULTURES (35 < T < 45°C)
Streptococcus thermophilus (cocci)
Lactobacillus delbrueckii subsp. lactis (bacillo)
Lactobacillus delbrueckii subsp. bulgaricus (bacillo)
Lactobacillus helveticus (bacillo)
Cocci and bacilli produce acidity when they are made to develop together: the development of acidity is an excellent indicator of the growth of lactic cultures.
Streptococcus thermophilus produces a very small amount of CO2 which it is not sufficient to alterate the characteristic of the cheese; it produces also formic acid from lactose, necessary for the growth of the lactobacilli; some strains of streptococci are not able to ferment galactose, like Lactobacillus helveticus, which converts the galactose into lactic acid and contributes to the development of the flavor profile.
The accumulation of galactose, on the production of mozzarella cheese and pasta filata, determines the browning caused by the Maillard reaction during the cooking of the pasta at high temperatures: in order to reduce this problem, usually it should be good introduce a small amount of Lactobacillus helveticus .
Below is a table which lists the main features of the most used lactic acid bacteria: