The lactic acid bacteria are a group of homofermentative organisms that play an important role in the production of fermented dairy products. In recent years, the industry has produced probiotic dairy products that contain lactic acid bacteria. However, the use of lactic acid bacteria in starter culture to produce high-quality fermented dairy products is the main application. Their metabolic activities allow proper product acidification, which inhibits the development of pathogens and other microorganisms, improves product flavor and texture and prevents spoilage of the product. Due to many requests from consumers, immunity benefits have attracted the attention of scientists to the use of lactic acid bacteria, such as those that are classified as probiotics [1,2].

The dairy industry relies heavily on microorganisms, both beneficial and harmful. Among the lactic acid bacteria, the most exploited applications are their use as dairy starters used in the manufacture of fermented dairy products to provide functional and biotechnological properties. The dairy starters have to compete in situ with different milk properties, the commensal microbiota in the point of manufacturing and pathogenic agents. It seems like a good strategy to provide new tools to lactic acid bacteria, controlling them and using the molecular methods of DNA array and different methods of proteomics. Controlling pathogenic bacteria, lactic acid bacteria may be used as parietal microorganisms, providing a new approach. Stimulating the gut immune response without causing inflammation has become a major emphasis, including the innate response from specific microenvironments such as intestinal epithelia or the presence of beneficial microorganisms such as ingested probiotics [3,4].

Fermentation Processes in Dairy Production

Dairy products are a rich and varied type of food. In addition to being snack food or a meal ingredient, they are also an excellent energy source. Due to their slightly acidic flavor and pleasant closeness, dairy products are universally appreciated by people. The unique flavors and different types of dairy products are the result of a diverse gap in the lipospecific substance in the primary and secondary metabolic activities of the microorganisms with which they engage. Although most dairy products are produced via fermentation, two biological types, such as lactose-fermenting enzyme yeast, exist that use fast fermentation systems to produce acidic dairy products. The fermentation metabolism of dairy production refers to the microorganisms' transformation of raw food materials through fermentation and biochemical reactions to produce saturated organic acids, high alcohols, higher boiling point esters, fatty acids, volatile fatty acids, sulfur compounds, nitrogen compounds and small organic molecules. These chemical molecules determine the texture, color, aroma and flavor of fermented dairy products, such as solidification, coagulation and gelling of the milk colloid system. Milk coagulation accelerates the rebeckonthin membrane method, ensures the curd is solidified and hinders curd precipitation. When these milk fermentation pathways become unstable, adverse chemical substances or toxic gases, off-flavor and poor mouthfeel will be produced and the appearance, taste and nutritional quality of the fermented dairy product deteriorate. Improper fermentation leads to the formation of excessive substitution, fermentation and poor sensory quality in cheese. The increasing number of larger cheese packaging companies and consumers' growing attention to cheese quality have greatly stimulated experts to conduct in-depth research on modulation and glypolysaccharide stability. Fermentation on the fermentation system in cheese [5-7].

Fermentation is the production of organic acids, alcohols, gases (CO₂ and H₂) and other compounds by microorganisms grown in a production medium containing nutrients. Using fermentative lactic acid bacteria such as Lactobacillus, Streptococcus and Lactococcus to convert lactose from protein, lactic acid increases acidity and solidifies milk. Sugar is broken down to form non-alcoholic substances and CO₂. Fermentative bacteria have also been developed to produce lactic acid from their native microflora and organically pure milk whey, thereby promoting mammary gland growth. Lactic acid vigorously increases milk acidity, dissolves calcium of casein, which is then hydrolyzed by native proteases, resulting in whey and curd separation. Fermentation under anaerobic conditions at low temperatures is required to prevent and reduce the production of odor compounds such as diacetyl and acetone in sour milk. Fermented milk products mainly include full solidified yogurt containing lactic acid adhering to protein filaments and sour milk containing abundant whey. Lactoperoxidase can extend the storage period of sour milk. Fermentation requires sufficient storage time to undergo extensive digestion and enzymatic ripening in sweet cheese production from lactic acid milk and artificial lactic acid hydrolysis of fat and protein, thereby improving the flavor of the fat protein. Fermentative bacteria can acidulate milk to pH 6 to promote enzymatic detachment of Alpha-caseinomorphin. Fermentation increases the gelling ability of non-casein proteins such as kappa-cassie, resulting in the formation of protein coagulum. Sourcing products leaking from full lactic acid cheese include protein coagulum, fatty acids and souring medium. Fermentation strengthens the sensory quality, taste and shelf-life of cheese. Fermentative yeast utilizes lactose to produce carbonic acid and ethanol at the bottom of the fermentation process, creating a sweet fizzy cordial drink, which is later displaced by whey beverage production. Fermented yeast vegetatively produces a small amount of lactic acid [8,9].

Lactic Acid Bacteria in Fermentation

We customarily measure acidification by LAB by determining their capacity to reduce pH and synthesize organic acids. This is one of the most important characteristics because it determines most of the subsequent transformation processes undergone by the lactic acid bacteria, as well as that affecting other microorganisms present. When microorganisms accumulate organic acids to titrable values close to, equal to or greater than 0.6 M of lactic acid, they inhibit the growth of other microorganisms present in the ecosystem. They consolidate their ecological position and control the transformation processes and optimize the final product characteristics. The fact that LAB can grow at low pH values is very important in the manufacture of acidic foods because it allows them to acidify the environment, perform other metabolic activities and multiply cell numbers without having to compete with microorganisms not very well adapted to acidic pH such that LAB can resist [10,11].

In the manufacture of fermented dairy products, part of the microflora responsible for the transformation processes, conversion of substrates and obtaining the final products comes from microorganisms indigenous to the technological process. However, starter cultures provide a more predictable fermentation and contribute to the obtaining of consistent and standardized products. Lactic Acid Bacteria (LAB) are the most important group of microorganisms that form the starter culture (or part of it) for the manufacture of fermented dairy products, with their production being the most developed area of the use of fermentations associated with dairy products. To be used as starters, commercial cultures of LAB must comply with certain technological requirements concerning their metabolic activities. Growth, acidification, aeration, protease and peptidase activities are some of the most important activities [2].

Role of Microorganisms in Cheese Making

Some believe that cheese making was discovered by chance, during the transport of milk from one place to another. The point is that after a period, depending on the geographical and environmental characteristics of places, the milk started to smell bad and then took on a solid consistency. The process was discovered because the cheese was preserved for a long period without alteration. After the revelation of this unique process, people started to perform particular phases to preserve the milk, including a particular milk processing step known as the cuanture. It must be underlined that those activities allowed the development of cheese making in a specific mode with respect to the surrounding environment with some biochemical and microbiological specific reactions. After the Roman period, cheese was produced in Europe, North Africa, America and India. In the Middle Ages, the use of cheese in the diet significantly grew; in this period started the bordering/fence in the flavor of cheese. In fact, during this period, some sectors of the production of cheese were dominated by monks. These people were only responsible for the cheese production in monasteries; they selected the few animals, managed the breeding system, took care of the feeding of the animals, processing and maturation of the products. In this manner, the first generic regions of the origin (D.O.P.) of the cheese were born. The monasteries spread their tradition for the cheese production by giving to the areas on which they had particularly any information and teaching the people working around them. This point concerns the oldest cheeses in the world (Gorgonzola, Parmigiano Reggiano and Grana Padano) [12-15].

Microorganisms play a most important role in cheese making, being responsible for flavor, texture and aroma. The major types of microorganisms involved are bacteria, molds and yeast, which accomplish a series of functions. Many factors influence the microbial ecology of cheese: milk supply, bacterial culture, manipulation of B/A/Y and chemical composition of milk. The processes which affect the conditioning of curd in the tanks and break the curd mass and weight production needle of retentate, inoculation and type of mold and ripening conditions rind development. Cheese making occurred all over the world: buttercase (India), fig tubs (Greece), pop in swamps (Romania) and smear-ripened cheese (France). Medieval monks played a most important role in the proliferation and fame of cheese making in the medieval period [16,17].

Starter Cultures and Ripening Bacteria

The LAB are fast acidifying, fermentative and nonpathogenic microbiota in which the genus Lactobacillus and Streptococcus can transform lactose into lactic acid, which is the main metabolite. This microorganism can be used independently or in association to perform controlled fermentations to obtain fermented milk, cheese, buttermilk, pudding and others. These began to be used before the knowledge of the existence of these microorganisms. During the ripening process, called lactic fermentation, metabolites are generated that give the final product a determined aspect, texture, taste, flavor and aroma. There is another large group of LAB, used since a long time ago to improve the organoleptic and physical properties of different foods. Some of these strains are readily able to express, under specific induction stimuli, additional recombinant molecules of interest. They are called probiotic strains [18,19].

Starters are strains of microorganisms used in food production to carry out fermentation in a controlled way so that the final fermented product could have the characteristics that the consumer wishes. There are two main groups of starters in the dairy industry: The LAB-used in the production of fermented milks and cheeses-and yeasts that produce alcoholic fermentation [20].

Probiotics in Dairy Products

Probiotics can be used in a wide range of dairy products, although they are mainly introduced into fermented type products since they exemplify the typical types of products in which lactic acid bacteria occur naturally. A large number of fermented milks have appeared on the market containing these types of bacteria and their consumption is increasing progressively. The beneficial effects of probiotics are well known and supported by scientific information: The consumption of some probiotics may entail benefits such as stabilization of the intestinal flora, reduced risks of colon cancer or those results from the consumption of lactose for lactose intolerants, reinforcement of the immune system and reduction of plasma cholesterol levels [18,21,22].

Over the last few years, there has been an increasing interest in the use of microorganisms for product development in order to enhance human health. Several studies have demonstrated the beneficial effect of some lactic acid bacteria on human health when they are consumed, in particular the genera Lactobacillus and Bifidobacterium. This kind of microbe is known as probiotics and they are used for legal reasons to describe food containing these types of microbes [4].

Microbial Contamination in the Dairy Industry

The expression "spoiled milk" is well known, due to the fact that conventional spoilage bacteria can contaminate milk very easily. The main target of spoilage microorganisms is the level of antimicrobial proteins present in milk, particularly caseins. Many species of proteolytic, lipolytic and ureasic bacteria have the ability to colonize milk and survive in different environments, promoting serious problems during most technological steps in the transformation of milk into dairy products. Milk preserves some natural antibacterial and antipathogenic systems that are the basis of a very sensitive and sensitive sensor of human health and nutrition. Furthermore, nutritional milk represents an enormous waste of resources. Therefore, the control of the survival and activity of the different groups of microorganisms that come to colonize milk is a crucial goal in the dairy industry [20,21].

The dairy industry involves the use of many different microorganisms for the production of diverse products, including milk fermentations by lactic acid bacteria to produce yoghurts, cheeses and fermented milks, industrial enzyme production and the development of products that have different technological or healthy properties. However, the presence of some microorganisms not only could provoke physicochemical and organoleptic spoilage of the products but could also affect the health of consumers. The use of nonpathogenic microorganisms with antipathogenic effects represents a potential novel approach to reduce the potential spread of pathogenic microorganisms through the food chain. Furthermore, with the costs associated with the rotation and substitution of current anti-pathogenic treatments through the food production chain, one of the principal advantages of biopreservation as a tool for innovative, natural and sustainable solutions for food safety is the addition of value to consumable foods. This chapter focuses on different matrices of interest in the dairy industry [20,23].

Sources and Prevention

To prevent contamination of manufacturing processes and materials, it is important to prevent the sources of undesirable microorganisms present in the dairy farm environment, as well as providing a clean working circle with factories. To prevent spoilage, contamination of raw materials by microorganisms in the dairy environment should be minimized. The antigen challenge test has been shown to adjust the environment to alter the regulation of immune responses, the microbiota and the crosstalk that occurs between mammals and their resident bacteria, leading to reduced animal disease susceptibility. Since microbial regulation might be a common consequence of resistance to certain diseases, factors within the animal, the environment or the external foodstuff usage requirement could contribute to that regulation. Thus, in the animal-human relationship, minor environmental adjustment was demonstrated to have major physiological influences [24,25].

The dairy industry uses a wide variety of microorganisms to produce a variety of dairy products such as butter, cheese, fermented milk and evaporated milk. The dairy industry is irrevocably dependent on the fermentation of microorganisms such as lactic acid bacteria for many manufacturing processes. However, if the indigenous microorganisms of the raw materials contaminated in the manufacturing process are undesirable microorganisms that are present in large numbers, the quality of the manufactured product may deteriorate. In addition, it becomes a factor that increases the number of microorganisms to be germs in the factory environments which affects workers' health [26].

Biotechnological Applications of Microorganisms in Dairy Processing

In order to reduce the cost of obtaining cheese and shorten the period of ripening cheeses, over the centuries, there have been attempts to make species of cheeses by changing the existing milk proteins or by using yeasts that produce certain proteins in the manufacturing of such cheese. Diverse yeasts, especially the species with debittering activity, are used in the dairy industry in the production of kefir, yucca, kumis, viili and Caspian Sea yogurt. With the aim of forming the adopted taste and flavor and improving the nutritional properties of milk and dairy products, it is possible to use yeasts in the milk of the female animal of the industry for the dairy industry. Such preparations consist of nutrients that allow rapid yeast training and to counter the influence of unfavorable factors, it is also suitable to use compositions that invariant active yeast [27-29].

As already presented, in the dairy industry, various microorganisms are used in the production of fermented or non-fermented dairy products. These include dairy lactic acid bacteria, lactic acid bacteria that are non-dairy origin, dairy propionic acid bacteria, dairy yeasts and some fillers. However, in order to increase the production of these products, standardize their composition, speed up the dairy production technology or use cheaper raw materials, the use of strains with adaptive qualities in the dairy environment and good technological properties has been pursued [30-32].

Quality Control and Assurance in Dairy Products

The absence of visible signs of spoilage does not guarantee that the product is satisfactory for its intended use. Hence, it is vital to establish quality criteria for each type of dairy product, in order to be able to ensure its conformity. At the production level, in the past, emphasis was put on the detection of pathogenic germs and legislation was focused on this. However, with the development of the food processing industry and with the appearance of production issues in a global environment, new concerns and new challenges have arisen in the field of hygienic quality. The establishment of vitamins, amino acids, fatty acids or indigenous cells and the control of the production process through the use of starter cultures, plus the control of spoilage microorganisms, are aspects that have become essential in the international regulation of cheeses. However, the assessment of these quality parameters is a complicated task and may only be possible if an appropriate control system is established for the products destined for the marketplace [5,[34,35]. 

The dairy industry is subject to numerous constraints at each stage of production, processing and distribution of milk and its derived products. These constraints generally fall into three areas: technological, microbiological and marketing. This chapter will provide an overview of these constraints at the various stages, as well as the quality systems and the means currently used to control and ensure the quality of dairy products, focusing on the various types of microorganisms. These include pathogenic bacteria, which are naturally present in milk and the use of microorganisms, for example, starter cultures and their role in the reduction of spoilage microorganisms and the structure and characteristics of the various quality labels in the boosting of the dairy industry through the promotion of higher added value products from the milk supply chain concept [5,35,36].

Future Trends and Innovations in Microbial Applications in the Dairy Sector

The innovation in the fermentation of dairying for the production of flavor and texture has been of enormous benefit to society. The possibility of adding a step to dairying by incorporating ingredients that contribute definitively and in a targeted way to health and well-being will surely align well with the natural perception of the healthiness of the products. It also opens the possibility of increasing value within the same production volume, thus decreasing the environmental impact per unit of product [37-39].

There are a number of components in milk that have implications for human health and well-being. Some of these have been the focus of scientific study for many years and we have an excellent understanding of their metabolism and nutritional value. However, we now know that recent advances in our understanding of the minimal genome required for bacterial growth and the metabolic pathways that are shared between bacteria, mammals and humans have implications for the exploitation of microorganisms for synthesis of high-value compounds to increase the health benefits of milk [40,41].

However, there are still technical limitations to the industrial utilization of phages. Integration and regulation are key challenges that need to be addressed. Efforts from scientists and industrial researchers are essential to promote the mass utilization of bacteriophages. Research gaps can be addressed by establishing optimized legal criteria for the development of new products. By strategically using technologies such as sensory, physical-chemical and safety assessments, a better approach to controlled phage applications can be achieved, ensuring that environmentally valid alternatives are in line with regulatory specifications.

The use of microorganisms against microbial pathogens can offer several advantages to the food industry. While there may be potential negative effects, careful isolation and selection of microorganisms, as well as their industrial-scale use, can lead to a better understanding of responsible industrial applications. These studies suggest that non-thermal treatments can be a promising alternative to conventional methods, reducing the need for harmful chemical additives in consumer foods. Additionally, the use of microorganisms can help overcome some of the limitations of bacteriophages, such as temperature and pH sensitivity.

There is a growing interest among consumers in minimally processed foods that are free of chemical additives and maintain the organoleptic characteristics of the original product. As a result, there has been an increase in studies on the use of microorganisms to produce safer minimally processed foods without compromising their characteristics. These emerging technologies offer a promising alternative to non-thermal techniques for managing pathogenic microorganisms and spoilage bacteria in milk, whey and dairy products.

For decades, traditional non-thermal treatments have been used to deactivate microorganisms and preserve milk and milk products. These treatments include
chemical treatments (e.g., organic acids, esters, enzymes, bacteriophages) and bacteriocin. However, these traditional methods have negative effects on the milk constituents, the consumer and the environment.

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