Lactic acid bacteria - fermentation

The term fermentation comes from the Latin word ferveo - boil, ethereal. Just think of the natural, sparkling fermentation of pickeld cucumbers or even wine.

Fermented food is prepared by bacteria and yeast strains. Cheese, yoghurt, sourdough bread, sauerkraut, fermented cucumbers, beer, wine, ripened ham, salami,  kimchi, olives, etc. are unable to be without fermentation.  

Lactic fermentation play an essential role in the preparation of most dairy products and many other fermented-acidified food and drinks. Foods fermented with the help of lactic acid bacteria and selected yeast strains are fundamentally transformed. Billions of small chefs are working on the new dish. Fermentation changes everything: the texture is transformed, the structure of the fibers is transformed, new flavors, new scents, new colors are formed. The food thus created will last for a long time and can be stored safely. Easily digestible, immune-boosting, intestinal flora enriching. It's live flora, rich in enzymes and vitamins. All its components are transformed in a favorable direction for us, so sugars, fats, proteins also decompose and transform. Bacteria create new vitamins and enzymes.

During controlled fermentation, bacteria prepare new healthy foods.

Last but not least: these new dishes are very tasty.

Bacteria that produce lactic acid are present in our lives. They can be found everywhere: on vegetables, fruits, on our skin, in our digestive system. They are incorporated into the milk during milking, and then mixed in large numbers in raw milk during storage, transport and processing. The energy needed to survive and reproduce is obtained from carbohydrates found in milk, lactose, glucose, galactose. Carbohydrates are digested while producing lactic acid. As a result of lactic acid production, the PH of the product decreases rapidly, the product quickly acidies. This sour medium (PH<4,5) no longer favors the bacteria that cause the most deterioration and unwanted processes, therefore their reproduction stops and enters a dormant phase. (stationary state)

That is in a professionally acidified dairy product undesirable bacteria stagnate a significant part of lactose is decomposed and enzymes that help the digestion of lactose are formed. This is good news for lactose sensitive people, because in a nicely fermented clotted milk, yoghurt, kefir, cheese, etc., the amount of lactose is significantly reduced, and during fermentation enzymes are produced that help to break down lactose. If the bacteria are surrounded by optimal conditions, then they begin to multiply suddenly. On average, in 20-40 minutes, the number of cells doubles, their mass doubles. This rapid reproduction persists as long as the environment is favorable and nutrients are available.

Conditions for high-quality lactic fermentation:

- The starting raw material (milk, vegetables, fruit, etc.) is of fresh, reliable quality

- Clean processing conditions, clean vessels and utensils. (no condition required for sterility)

- Inhibitor free equipments (free from chemicals)

- Optimal growth temperature for the bacterial varieties used (incubation temperature is adapted to bacteria)

- Large quantities of lactic acid-producing bacteria

- Anaerobic (oxygen-poor) environment

- The bacterial culture is not shocked when mixed (shock can be avoided by acclimatisation at room temperature and culture dissolving in lukewarm medium at intermediate temperatures)

The metabolism of lactic acid bacteria can basically be of two types:

homofermentative, where the product of carbohydrate processing is more likely to be lactic acid (85-95%)

heterofermentative, where in addition to lactic acid, carbon dioxide, acetic acid, ethanol, formic acid, glycerin are also produced.

The formation of sour tastes and aromas, the powerful shrinkage-drying of curds or sour clotting (clotted milk) are mainly carried out by homofermentative bacteria.

In terms of the formation of additional flavors, aromas, gasholes, the role of heterofermentative cultures is stronger.

Enzymes produced by lactic acid bacteria

Bacteria create enzymes during their metabolic processes, which are actually proteins that promote some process. Countless enzymes also play a very important role in the metabolic processes of our organism. Enzymes are all specific, so they can only perform a certain task and can be divided into two groups according to the place of production. Enzymes produced outside the cell (extracellularly) and within the cell (endocellularly). Lactic acid bacteria produce enzymes belonging to the second group, which play an important role in cheese making, the proteins and fats in milk are broken down by specialized enzymes and form aromas, thus playing a key role in the development of the taste of cheese.

So, these enzymes can only enter milk/cheese after the cell wall has been broken down. Fortunately for us, these microbes also contain a cell-wall-breaking enzyme (peptido-glycol hydrolase), which often begins to self-digest (autolysis). This is often caused by some kind of stress. This can include temperature, pH, nutrient deficiency, or changes in salt concentrations. Controlling and increasing autolysis at the right time is an essential parameter when maturing cheese. So, after the disintegration of the cell wall, enzymes useful to us, such as peptidase, lipase, or enzymes used for the breakdown (catabolism) of amino acids, enter the cheese.

Rennet added to milk that contains protease enzymes breaks down casein into peptides. The released enzyme peptidase then breaks down the peptides into free amino acids. Later catabolism of amino acids, aromas are formed from them through various enzymatic pathways. In addition, the enzymes esterase and lipase play an important role in the breakdown (hydrolysis) of triglycerides in milk fats, which are also later converted into aromaic components.

Bacteriocin effect, nisin production, preservative bacteria

Certain bacteria are able to produce bacteriomycin, an inhibitory substance consisting of a protein or protein complex. This substance inhibits the metabolic processes and reproduction of all organisms like the producerexcept the producer organism strain. Some lactic acid bacteria are also able to produce these bacteriocins, so foods fermented with such cultures will last a long time and can be produced more safely.

Since lactic acid bacteria also belong to the group of Gram-positive bacteria, antimicrobial protein natured substances produced by them, so these substances primarily inhibit the growth and reproduction of Gram-positive microorganisms.

The most important bacteriocin producing bacterium is Lactococcus lactis subsp. lactis produces nisin, which is considered an antibiotic and is authorised as a natural food preservative E234. Nisin contains lantionins, therefore it is also called an antibiotic.

This natural protective agent-producing bacterium is found in mesophilic starters and in most culture mixtures. The most favorable conditions for the production of nisin are formed in kefir and camembert cheese, because these two types of fungi and mesophilic bacterium stimulate each other's growth.

The reproductive temperature range of lactic acid bacteria basically divides these microbes into two groups.

Mesophilic lactic acid bacteria:

The optimum reproductive temperature is in the range of 20-40°C.

Their most important reproductive environment is the skin surface, intestinal tract, body cavities of warm-blooded organisms, as well as the leaves and flowers of plants.

Optimally, these bacteria dominate the milk. If they are present in sufficient quantities and the cheesemaker "treats them well", then they will soon become dominant. They take away space from the growth of harmful bacteria present in milk.

Mesophilic bacteria are important allies of the cheesemaker!

Thermophilic lactic acid bacteria:

They multiply strongly in the range of 40-50°C.

Thermophilic bacteria appeared on the ground much earlier than mesophiles. The prefer of higher temperatures refers to the origin of the ancient sea. In general, thermophilic microbes are capable of multiplying faster than mesophiles due to higher temperatures. These bacteria prevail during postheating. They produce new powerful aromas in the curds, as well as help to release more whey. They shrink and dry the curd. They play an indispensable role in the preparation of semi-hard - hard cheeses, fermentation of yogurt. Their enzymes also determine the longer-term ripening of cheese. They are able to multiply at a slow pace, but also during colder ripening.