Study Viability and Survival Microflora of Cheeses Under the Influence of Freezing and Low-Temperature Storage

This study has shown the degree viability and survival microflora of cheeses under the influence of freezing and low-temperature storage. To establish optimal storage conditions and periods, the sensitivity of microorganisms to low temperatures was studied. The different sensitivity of microorganisms to low temperatures will make it possible to correctly approach the establishment of optimal modes and shelf life. The activity of psychrotrophic microorganisms, especially resistant to low temperatures, capable of developing at low positive temperatures of refrigerated storage, was studied. The hygienic safety of defrosted cheeses was considered. The regularities of the withering away of useful and technically harmful microflora of cheeses under the influence of low temperatures of freezing and storage were investigated for the purpose of hygienic justification of shelf life. To substantiate the storage duration of a whole group of hard cheeses, the modes of intensive withering away of the total number of bacteria with the preservation of useful lactic acid microflora were taken into account. On the basis of the research carried out, the regulations for the technology of low-temperature storage of cheese have been developed. Study Viability and Survival Microflora of Cheeses Under the Influence of Freezing and Low-Temperature


Introduction
Currently, Russia is actively developing and producing fermented milk products enriched with useful microflora, the range is expanding due to the creation of new types of fermented milk products. It is a generally accepted fact that fermented milk products improve the health of the human body. The production of fermented milk products is based on the use of starter cultures of microorganisms in the form bacterial concentrates, which are specially selected and prepared combinations of lactic acid bacteria [1][2][3]. The most important characteristics that determine the quality of food products are their safety and microbiological resistance. Safety is understood as the absence of harmful impurities of a chemical and biological nature, including pathogenic microorganisms and toxic products of their vital activity.
Microbiological resistance implies the potential for preserving food without spoilage [2,4,5]. Low temperatures have peculiarities in their effect on various types of microorganisms. Some of them, being transferred to favorable conditions after prolonged exposure to low temperatures, lose their ability to develop or develop extremely weakly; others, on the contrary, are developing well.
In this regard, it is advisable to study the survival of microflora, including sanitary indicative, pathogenic and opportunistic groups of microorganisms after low-temperature long-term storage. The vital activity of microorganisms is one of the main causes of changes in food products during storage. By changing environmental conditions and exerting one or another effect on the product, it is possible to regulate the composition and activity of microflora, limiting or preventing the reproduction of pathogenic and technically harmful microflora [3,[6][7][8][9]. All this indicates the urgency of the problem under discussion. Previous studies have shown that, nevertheless, in conditions of deep freezing, leading to a state of suspended animation, microorganisms only partially die.
However, after thawing the product, microorganisms remaining during freezing can reactivate and multiply, negatively affecting the quality. During refrigerated storage, psychrophilic microorganisms most actively manifest their vital activity, causing biochemical processes leading to a deterioration in the quality of products. In this regard, we should especially talk about the physiological and biological properties of microscopic molds and yeasts, which have high lipolytic and proteolytic activity.
The consequence of their multiplication in cheeses during refrigerated storage is the appearance of defects of the following nature: rancidity, salting, unpleasant odor, deterioration of the presentation of the product. In addition, mesophilic microorganisms, including conditionally pathogenic and sanitaryindicative microorganisms, the excess of which can lead to human intoxication, can persist in frozen products. Ensuring hygienic conditions for production and storage is important because the synthesized enzymes and toxins can act even after the death of the microorganisms themselves. Therefore, in order to preserve the quality of the product during freezing and low-temperature storage, it is necessary to create such temperature regimes of refrigeration processing that would be below the temperature limits for the growth of the most stable psychrophilic microorganisms. To establish the expected shelf life, one or another temperature regime was selected taking into account the dynamics of changes in the state of microflora. Yeast and mold fungi have the lowest minimum development temperatures (minus 2 ... minus 10°C), and at a rather low water activity. If at low temperatures yeast and mold are resistant and able to grow, then at the same temperatures mesophilic bacteria already die off or their vital activity slows down significantly [2,10,11].
In our opinion, it is advisable to consider the microbiological aspects of low-temperature cheese storage technology, starting from the freezing stage. Consideration of the impact of freezing onmicroorganisms were considered from the point of view of a possible change in the quality of perishable products. In frozen form, cheeses can be stored for a long time without changing the quality, while maintaining organoleptic properties and satisfactory appearance... It is cost effective to use low temperature refrigeration.
Storage at production bases and refrigerators with their subsequent transportation to distribution refrigerators and into the distribution network requires the creation of low temperatures and strict adherence to them [12][13][14][15]. The list of microbiological indicators under study has been expanded in comparison with the standardized indicators to obtain a detailed description of the sanitary and hygienic state of frozen cheeses. This series of studies examined the effect of freezing on the condition of opportunistic microflora that determines food safety.

Objects and Methods
The objects of low-temperature storage were selected hard rennet cheeses of various species groups. Among them were distinguished cheeses of the Soviet type (with a high temperature of the second heating), such as Holland (with a low temperature of the second heating) and Russian (with a high level of lactic acid fermentation). These cheeses are in the greatest demand and popularity in the domestic cheese market, therefore the task is to preserve the quality of these types of cheeses for a long period of time. An experimental stand has been developed and created to conduct research on freezing finely packaged cheeses by air. The prototypes were subjected to freezing in an air flow at a cooling medium temperature of minus 50°C and minus 30°C. The design of the installation made it possible to change and maintain the temperature in the freezer to minus 100°C and create an air

Results and Discussion
Microbiological control of experimental cheeses was carried out before freezing, the results of which are shown in Table 1   Soviet cheese, before freezing, the total number of bacteria was 9.1 · 10 7 CFU / g, and after freezing, it decreased to 2.0 · 10 6 CFU / g.
In Dutch cheese, before freezing, the total number of bacteria was

Conclusion
The research results showed that frozen cheeses after