LAB Starter Cultures

LAB used for industrial application can be divided in two categories: thermophilic and mesophilic bacteria, on the bases of their optimal growth temperature.

Table 1.2.2.1 Physiological Characteristics of Lactic Acid Bacteria Rods (adapted from Axelsson, 1998).

Carnobacterium

Lactobacillus

Lactic acid produced from glucose b

L

D, L, DL

Homofermentative

-

+/-

Heterofermentative

-/+ c

+/-

Low temperature tolerance: 10°C

+

+/-

High temperature tolerance: 45°C

-

+/-

Acid tolerance: pH 4,4

ND

+/-

Alkaline tolerance: pH 9,6

-

-

Salt tolerance:

ND

+/-

6,5% NaCl

-

-

18% NaCl

Table 1.2.2.2 Physiological Characteristics of Lactic Acid Bacteria-cocci (adapted from Axelsson, 1998).

Aeroc.

Enteroc.

Lactococ. & Vagococ.

Leuc. & Oenoc. Pedioc.

Streptoc.

Tetragenoc.

Weissella3

Tetrad formation

+

-

-

-

+

-

+

-

Lactic acid produced from glucoseb

L

L

L

D

L, DL

L

L

D, DL

Homofermentative

-

-

-

-

-

-

Heterofermentative

+

+

Low temperature tolerance: 10°C

+

+

+

+

+/-

-

+

+

High temperature tolerance: 45°C

-

+

-

-

+/-

+/-

-

-

Acid tolerance: pH 4,4

-

+

+/-

+/-

+

-

-

+/-

Alkaline tolerance: pH 9,6

+

+

-

-

-

-

+

-

Salt tolerance:

+

+

-

+/-

+/-

-

+

+/-

6,5% NaCl

-

-

-

-

-

-

+

-

18% NaCl

+ positive; - negative; +/- response varies between species; ND: not determinated.

  • a) Weissella strains may also be rod-shaped.
  • b) production of D-; L-; DL configuration is different among species.
  • c) small amounts of CO2 can be produced, depending of media.

Dairy starter cultures can be categorized as defined- or mixed-strain cultures and may be:

  • • Single-strain starter: one strain of a specific species
  • • Multiple strains starter: several defined strains belonging to only one species
  • • Multiple-mixed strains starter: mixed defined strains belonging to different defined species
  • • Raw mixed-strain starter: strains and species known and unknown (undefined cultures)

It is important to note that mesophilic starter cultures very often contain mixtures of 2-6 phage unrelated strains whereas defined strains of thermophilic cultures are used in rotation.

Thermophilic cultures are usually used for the production of yogurt, fermented milks, soft cheese (e.g., mozzarella, some blue cheese) and hard cheese with high cooking temperatures (e.g., Emmental, Gruyere, Grana Padano, Parmigiano Reggiano, etc.).

These cultures can be either raw mixed starters or defined strains starters. Raw mixed cultures are widely used in traditional cheesemaking in Greece, Italy, France, and Switzerland. They are prepared from cooked or uncooked whey or from milk, either raw or thermized, and their composition is naturally complex and variable.

Thermophilic cultures are represented by two genus: Lactobacillus and Streptococcus, with optimum growth temperature between 40° and 50°C.

Lactobacillus is used in different industrial applications: some species of this genus are involved in milk fermentation: Lactobacillus delbrueckii ssp. bulgaricus together with Streptococcus thermophilus constitute the specific starter for yogurt production, while Lactobacillus delbrueckii ssp. lactis and Lactobacillus helveticus are used for the production of hard cheeses with high cooking temperature.

Other thermophilic species (e.g., Lactobacillus acidophilus) are part of human microbiota and/or vagina, but they can also be used for fermented or unfermented milks (acidophilus milk or sweet acidophilus milk, respectively).

Some lactobacilli are used in combination with Streptococcus thermophilus, because of its fast acidity development and redox potential reduction at the high temperatures generally used in industrial fermentations.

There is a protosymbiotic relationship between Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus (e.g., yogurt): Streptococcus thermophilus produces formic acid-like compounds, promoting the growth of Lactobacillus delbrueckii ssp. bulgaricus, which, in turn, stimulates Streptococcus thermophilus by releasing ami- noacids (mainly valine, glycine, histidine, leucine and isoleucine). These two species have a long history of use, in particular, in fermented milks, where they were always present as autochthonous microorganisms capable to lower the milk pH, thus increasing its durability. For hundreds of years, fermented milks, and notably yogurt, have been consumed as traditional foods—in particular, in specific geographic areas such as Caucasic countries, Greece, Turkey, but also in Northern and Eastern Europe. At the beginning of the twentieth century, thanks to the development of microbiology, the microbiological composition of yogurt and other fermented milks has been defined and the related properties and health benefits studied.

Mesophilic cultures are able to grow from +10°C to + 35°-37°C with optimum temperature at 24°-25°C, although some species grow well at 30°C. Mesophilic cultures include acid-forming, often flavor producers, lactococci: They are used in many categories of cheese, fermented milk/cream/buttermilk, as well as in ripened cream butter. Mesophilic cultures are mainly composed of one or more bacteria belonging to the species Lactococcus lactis ssp lactis; Lactococcus lactis ssp cremoris, Lactococcus lactis ssp lactis var diacetylactis, Leuconostoc lactis, Leuconostoc cremoris. Mesophilic cultures may also include some species of lactobacilli such as: Lactobacillus paracasei, Lactobacillus plantarum, Lactobacillus rahmnosus, and others. Mesophilic lactobacilli can growth as natural contaminants in cheese, but can also be used as ancillary cultures, thanks to their proteolytic activity and their capacity to develop at high salt concentrations, at high or/and low temperature. Ancillary cultures are normally used in cheese making as commercially manufactured auxiliary cultures to manage the technological process and to get a good flavor, the correct balance of all compounds of the final product.

Lactococci are of great importance in cheese manufacturing and contribute to their final organoleptic qualities by:

  • • Fermentation of sugars, leading to a rapid pH decrease: Important for the reduction and prevention of the growth of pathogenic bacteria
  • • Protein hydrolysis: Important for the texture and taste of the cheese
  • • Synthesis of flavor compounds
  • • Synthesis of texturing agents for the consistency of the product
  • • Production of inhibitory compounds
 
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