By using different methods, we can hope to preserve dairy products such as cheese. These methods include non-thermal methods, such as the presence of lactic acid bacteria that produce bacteriocins, and thermal methods, the purpose of which is to use both to maintain hygiene, increase safety, and increase the quality of the product during the storage period. In this article, we will examine the autochthonous adjunct cultures and commercial cultures concerning cheese preservation.
Cheese production dates back thousands of years. From that time until today, cheese production has been done in different ways, so that we see a great variety of this product all over the world. Since the end of the 19th century, the use of relevant starter cultures and advanced cheese-making processes have undergone positive changes.
Today, starter cultures are considered essential ingredients in cheese production, which fall into two general categories:
1- Combined starters produced using different genera and species of lactic acid bacteria.
2- Defined starters that use the same and pure strains in their production.
The stability of the product in terms of sensory and texture characteristics is of particular importance, and the best way to reduce changes in the product and comply with standards is to use commercial starter cultures. Of course, this point should be kept in mind that by using commercial starter cultures for a long time, changes will be made in the microbial diversity of the product.
The microbial flora of milk contains lactic acid strains and non-lactic acid strains such as molds and yeasts. Lactic acid strains are naturally present in raw milk and are considered dominant microbial flora such as Leuconostoc, Lactococcus, Lactobacillus, Streptococcus, and Pediococcus. This group of bacteria, by adding adjunct cultures, is used to increase acidity, and curd formation, and create aroma and flavor during cheese ripening. In addition, they produce antimicrobial peptides such as bacteriocin, which naturally inhibit the growth of unwanted and harmful bacteria.
So, in summary, it can be said that the creation of microbial diversity in cheesemaking from the time of production to its ripening depends on factors such as the presence and transformation of natural raw milk bacteria, starter cultures, environment, and equipment.
Lactic acid bacteria are either starters or they exist naturally in milk and are mostly non-starter lactic acid bacteria or NSLAB.
Today, with genetic sequencing of natural or autonomous cultures and investigating the interactions of microbes and the enzyme system they have, their importance in the characteristics of the final product has become clearer.
How to reduce food production waste without using chemical preservatives?
Biological protection is the best way to deal with both pathogenic and spoilage bacteria. NSLABs are recommended as protective cultures for long storage and increased product safety. The activity of these bacteria against spoilage and pathogenic agents has been known for a long time, but from the genotypic and phenotypic point of view, the selected strains should be further investigated to obtain more reliable results. The main focus is on natamycin and other lactococcal bacteriocins produced by lactic acid bacteria. Researchers have conducted many studies with conditions such as functional characteristics of bacterial cultures in different dairies, practical methods to control the main pathogenic bacteria in industrial cheeses, and negative consequences in the production of certain cheeses, which have limited the use of bacteriocins.
Antimicrobial mechanisms:
Protective cultures can delay or even stop contamination, but this factor depends on technological factors (such as storage warehouse temperature and ripening time), and the type and extent of initial contamination. The mechanisms of protective cultures are:
1- Metabolites:
In the relationship of protective cultures with other microbes, a relationship called amnesalism is proposed. This means that these cultures can hurt other types of microbes, but they are not affected. Metabolites such as lactic, hydroxyphenyl lactic, acetic, propionic, and phenyllactic acids are produced as a result of dairy fermentation, which has an inhibitory effect on certain fungi and bacteria. The inhibitory effect is related to the following factors:
- Increasing acidity and diffusion in the cell membrane of bacteria and the creation of H+ ions, can make the cytoplasm of cells acidic.
- Blocking membrane transfers.
- Deviation interference of proton.
- Production of active oxygen species.
- Denaturation of membrane proteins.
- inhibition of bacterial enzymes.
Other antimicrobial substances of lactic acid bacteria include some fatty acids, acetoin, diacetyl, H2O2, and bacteriocins. Diacetyl probably shows its effect by sticking to DNA or interacting with arginine. Acetoin, like diacetyl, has an antimicrobial effect by interacting with arginine.
One of the effective antimicrobial compounds produced by Limousilactobacillus roteri is called rotrin, which is an effective factor in inhibiting the growth of gram-negative bacteria and fungi.
2- Bacteriocins:
Bacteriocins are proteins or peptides produced by gram-positive bacteria (mainly lactic acid bacteria) in the ribosome and have different antimicrobial properties.
Bacteriocins are divided into three categories in terms of peptide size:
- Modified small peptides.
- Unmodified bacteriocins.
- Large peptides that are sensitive to heat (greater than 10 kDa), which are divided into three categories:
The first category includes well-known lantibiotics such as nisin and lacticin.
The second category includes cyclic peptides such as enterosin and pediosin.
The third category is a new category including haloticin.
Generally, bacteriocins cause the destruction of bacterial cells by forming pores in the cell cover changes in the cytoplasm membrane, and damage to the proton motive force. Nisin performs its antimicrobial function by preventing the synthesis of the cell wall and creating a hole in it. Other bacteriocins work by inhibiting gene expression and protein production.
Factors such as purification costs, inactivation by proteolytic enzymes during cheese ripening, and low efficiency can limit their use. Pediocin, nisin, lacticin, rotrin, macdocin, thermophyllin, and enterocin are used in cheese production.
3- Ecological competition:
In competition with other organisms for oxygen nutrients and survival, protective cultures surpass spoilage factors and remove essential substances from their reach, such as the protection provided by lactobacilli in fermented milk products against fungal spoilage.
In some cases, protective cultures identify their environment and adjust their performance accordingly.
conclusion
Protective cultures include special strains of different species of lactic acid bacteria to control the growth of spoilage bacteria in different cheeses. During various research, before creating microbiological problems, single strains or a combination of strains have been proposed to evaluate the physicochemical, and organoleptic effects, the microbial environment of cheese, and the nutritional characteristics of the strains, but again, studies in this area should continue. The use of protective cultures in combination with natural preservatives shows useful results in this field.
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