Lactic acid bacteria in meat and yogurt

Lactic acid bacteria are a group of helpful bacteria, which have similar properties and produce lactic acid as an end product in the process of fermentation (Farnworth 2003). Hofman and Thonart (2001), state that these bacteria, though widespread in nature, are also found in the digestive system of both human beings and animals. Lactic acid bacteria find their use mostly in the production of fermented food products. Hofman and Thonart (2001) argue that in the past, people used lactic acid bacteria to produce a variety of fermented foods with characteristic tastes. Foods produced this way used to stay for a very long time without getting bad. These people however, did not have any information concerning lactic acid bacteria though it was the main factor behind fermentation. Presently, a wide variety of fermented foods products such as meat products, yoghurt and cheese are produced with the help of lactic acid bacteria. Fermentation, according to Ramon and Rodriguez (2008), is the process through which sugars, for example lactose, are converted to lactic acid and other compounds. The acid then accumulates thereby changing the structure in addition to the texture of the food in question. Flavor and aroma of the food may also change due to the effect of various end products of the process of fermentation. Temperature, bacteria composition of food and the types of food are some of the factors that determine the rate of fermentation (Dugas n.d).

Lactic acid bacteria are made up of various genera that comprise of more than a hundred species (Hofman and Thonart 2001). These species differ from each other in that they have different structural make up, different optimal growth temperatures, and diverse major fermentation pathways. Lactobacillus, according to Dugas (n.d), is one of the largest groups that make up the lactic acid bacteria. Lactobacilli are heterogeneous they are composed of species with a large variety of physical, chemical and physiological characteristics. Fermentation patterns of carbohydrates, in addition to the configuration of the lactic acid produced, hydrolysis of arginine, nutritional and temperature requirements have for long been used as the distinguishing factors between different species of lactobacilli (Herich and Leevkit 2002). Numerous species of lactobacilli have been extensively used in the food industry. These species are mainly the acid tolerant species of the lactic acid bacteria. The role they play in the production of various fermented food products such as yoghurt and cheese is of great significance to human beings (Dugas n.d).

Lactic acid bacteria are associated with the normal flora in the gastrointestinal tract, oral and vaginal cavities of both human beings and animals (Dugas n.d). Lactic acid bacteria are naturally found on numerous materials and food substances such as milk, meat and flour that are utilized in making various food products (Peng, Lin and Lin 2007). Lactic acid bacteria are usually contained in fermented food products. They are employed as natural starters during food fermentation (Chandan 2006). Milk, meat, and wine are some of the food products that are fermented using lactic acid bacteria (Hui 2006). Strains of lactic acid bacteria for starter cultures are selected according to their fermentation capacities in addition to their flavor characteristics (Dugas n.d). The robustness of lactic acid bacteria cells in addition to the sustenance of various strains in a mixed starter is also considered during selection of a lactic acid bacteria for starter cultures.

Lactic acid bacteria are gram positive organisms. They are facultative anaerobes and do not form spores. They are non motile coccus or rod shaped and do not have cytochromes. They have acid tolerant and fastidious rods or cocci.  They utilize sugars on the surface of meat and milk for reproduction. On meat surfaces lactic acid bacteria utilize glucose, whereas in dairy products they utilize lactose as their source of energy (Food Science 2007). These bacteria produce acidic components such as lactic acid and acetic acid which increase the concentration of hydrogen ions in the food products being fermented. As a result they increase acidity and thus keep foods safe from putrefying and pathogenic microorganisms. Food Science (2007) states that lactic acid bacteria in yoghurt and meat produce antifungal compounds such as fatty acids that greatly inhibit the growth of pathogenic fungal micro-organisms. Hofman and Thonart (2001), point out that lactic acid bacteria also produce other compounds that are active against other harmful bacteria.

In addition to food preservation lactic acid bacteria are beneficial to human beings because they act as probiotics. Probiotics, according to Adams (2007) are believed to offer numerous health benefits to human beings. They are utilized in treating adverse health conditions such as gastrointestinal disorders and circulatory problems. Various probiotics are found in the digestive tract and they assist in strengthening the immune system. They also assist in the proper functioning of the digestive system (Types of Bacteria 2010). Probiotics also minimize the chances of proliferation of harmful microorganisms in the gut. They assist the body to generate more of its normal defenses against illness (Adams 2007).

Lactic acid bacteria in meat and yogurt
Total bacterial account of yogurt and meat
Total bacterial account of yoghurt and meat refers to the sum-total of colony forming units of lactic acid bacteria.  Standard plate count is the mostly used technique for identifying the overall bacteria count as well as the quality of yoghurt and meat (Duffy and Sheridan 1998). Duffy and Sheridan (1998) states that direct count rapid method is the other commonly used method of determining the total viable counts of bacteria on both yoghurt and processed meat. A membrane filtration epifluorescent is one of the direct count rapid techniques employed for determining the total bacterial count of yoghurt. Membrane filtration epifluorescent method involves pre-treating the yoghurt or the meat sample through centrifugation, with a proteolytic enzyme alcalase and surfactants (Duffy and Sheridan 1998). The treated samples are then sieved through a polycarbonate membrane, which have been stained with a fluorescent dye and observed under ultra violet light. Acridine orange and baclight are the two fluorescent dyes mainly used in this method (Duffy and Sheridan 1998). A recovery step is also included in this procedure to make it easy for injured and stressed cells to recover. Polycarbonate film from the sieved meat samples are placed for approximately an hour at 25C on the surface of the count agar in the recovery process (Duffy and Sheridan 1998). Acridine orange direct count may also be carried out without involving the recovery process, but this yields a poor association with the standard plate count for processed meats and yoghurt. Including the recovery step in direct rapid count technique enhances the association with the standard plate count. Baclight stain direct rapid count can be carried out either including the recovery step or not. There is a good correlation between baclight direct count with standard plate count regardless of whether the recovery step was include or not (Duffy and Sheridan 1998).

Counting chambers, according to Mozzi, Raya and Vignolo (2010) may also be used to determine the total count of lactic acid bacteria on meat and yoghurt. These chambers are set in such a way that they are filled with predetermined volumes of bacteria. These cambers are filled with bacterial liquid culture in accordance with the manufacturers instructions. A slide is then placed under the microscope for viewing. The bacteria are then counted in accordance with the instruction sheet. The numbers of bacteria per milliliter of the original sample are then calculated using the standard volume on the instruction sheet (Mozzi, Raya and Vignolo 2010). This method, however, has a disadvantage in that it does not help a researcher tell apart the types of bacteria which are alive from the ones which are dead. Membrane filter method may also be used to count the number of viable bacteria in yoghurt (Soni 2007). Yoghurt is diluted with water and then filtered through a membrane containing tiny holes than the bacteria. The filter is then put on a dish containing growth media to facilitate growth of bacteria. The number of bacteria that grow is then counted. Laboratory pasteurized count is used to determine the total bacterial count that is not affected by heat during pasteurization. Preliminary incubation count is also one of the techniques that may be used to determine the total count of bacteria that may grow at low temperatures. This procedure is, however, carried out after the standard plate count has been conducted (Mozzi, Raya and Vignolo 2010).

Isolation of lactic acid bacteria and type of strain in meat and yogurt
Isolation of microorganisms from natural sources have for long been one of the most important ways for obtaining bacterial strains that are pure and genetically stable. The interaction between lactic acid bacteria and various types of foods for a long time have attracted the attention of researchers (Mozzi, Raya and Vignolo 2010). Lactic acid bacteria can be isolated for use as starter cultures from naturally fermented foods, mostly dairy products. Isolated species are further developed for commercial fermentation of foods. Lactic acid bacteria can also be isolated from the gut, but a major hindrance is that most of them cannot be cultured outside the body. Moreover, only a small proportion of the total culturable and only a few species that can be cultured are known (Soni 2007). Contemporary molecular typing techniques, which utilize DNA technology, have come in hardy and made it easy to identify various species of bacteria without cultivation (Soni 2007). This facilitates the isolation of various bacteria species

There are three procedures which can be used to isolate lactic acid bacteria enrichment of the source in broth culture and then plating this culture onto an agar medium inoculating the sample directly onto an agar medium and filtering the sample through a membrane and then incubating the membrane onto an agar medium (Soni 2007). Soni (2007) states that direct incubation of the sample onto an agar medium is the best procedure because of the fact that the colonies that develop can easily be counted, differentiated according to their appearance, and isolated for identification. Various mediums that are used during the isolation and enumeration of lactic acid bacteria from different food samples include tomato juice wine agar, Irrmann agar, extract agar and Man Ragosa Sharpe agar (Soni 2007). Inoculated plates are incubated under carbon dioxide rich atmosphere in order to enhance the growth of lactic acid bacteria colonies. The method for classification of lactic acid bacteria, that is currently being used, is based on the 16S ribosomal ribonucleic acid analysis and sequencing (Soni 2007). The predominant species of lactic acid bacteria that are mostly isolated from meat are Lactobacillus curvatis, Lactobacillus plantarum, pediococcus species, Carnobacterium pisciola, Leuconostoc carnosum, Leuconostoc gelidum Carnobacterium divergens, and Lactobacillus sakei. Several strains of lactic acid bacteria that are commonly isolated from yoghurt include Lactobacillus fermentum, Lactobacillus casei, Lactobacillus brevis, Lactobacillus cellobiosus, Lactobacillus coryniformis, Lactobacillus coprophilus, and Lactobacillus lechmanii among others (Herich, and Leevkit 2002).

Lactic acid bacteria that are isolated for industrial purposes must be culturable and stable on an industrial base and through the manufacturing processes as well as storage conditions of yoghurt, meat and other food products over the numerous years of industrial application. This is particularly significant for probiotics strains that are required to retain their metabolic activity so as to exert the much sought-after beneficial health effects (Types of Bacteria 2010). After consuming yoghurt or meat products that have been injected with yoghurt, various strains of lactic acid bacteria are deposited in the alimentary canal where they stay for a considerable period of time.

Effect of lactic acid bacteria on spoilage and pathogenic bacteria from various strains and how the contents of meat and yogurt effect on these strains

A starter culture of two types of lactic acid bacillus, namely Lactobacillus bulgaricus and Streptococcus thermophilus are commonly used in the production of yoghurt (Chandan 2006). In the process of growth these bacteria use sugar, mainly lactose, in milk as their source of energy to produce carbon dioxide, lactic acid, acetic acid, acetaldehyde, and diacetyl in addition to other components that change the physical and chemical characteristics of milk (Farnworth 2003). In the initial stages of fermentation, Streptococcus thermophilus ferments the lactose, a disaccharide composed of monosaccharide galactose and glucose, producing lactic acid in large quantities (Ramon and Rodriguez 2008). Increase in the level of lactic acid, as clarified by Dugas (n.d), leads to its accumulation which results in suppression of further reproduction as well as activity of lactic acid bacteria. The more acid tolerant bacteria, Lactobacillus bulgaricus, carry on the work of fermenting the remaining lactose. During fermentation process, the potential hydrogen concentration (pH) of milk drops to around 4.5 from 6.5 (Konings, Kuipers and Huis 1999).

This drop in pH is a significantly advantageous aspect in food preservation. This is because of the fact that it slows down the growth of various microorganisms that spoil foods such as staphylococcus and Pseudomonas species (Lengey and Andriani 2009). Lactic acid produced by Lactobacillus acidophilus, as stated by Ramon and Rodriguez (2008), inhibits the development of various types of putrefying bacteria and in the process preserves milk even though it becomes sour. The growth of Lactobacillus acidophilus in milk is very slow and this is an important aspect in the protection of milk against contamination (Ramon and Rodriguez 2008). Lactic acid bacteria have got an inhibitory activity on microorganisms that spoil foods. This is the main reason why yoghurt can stay for a very long time without getting contaminated.  Fermentation is one of the oldest food preservation techniques used by human beings, in which lactic acid bacteria are utilized either knowingly or unknowingly. Various strains of lactic acid bacteria are currently being incorporated in various food products for purposes of preservation (Farnworth 2003).

Fermentation of meat can, in simple terms, be referred to as spoilage of meat by bacteria. If this process is left uncontrolled, the meat in question gets contaminated completely to a point where it cannot be consumed by human beings (Konings, Kuipers and Huis 1999). However, if this process is controlled the resultant product is fermented meat. Lactic acid bacteria are the organisms attributed to meat fermentation. These bacteria may either be naturally present in animal protein or added as starter cultures. Hui (2006) states that lactic acid bacteria feed on the glucose present on the surface of meat and produce lactic acid. Fermentation in meat, if controlled is beneficial because it leads to prevention of growth of microorganisms that spoil food, for example Pseudomonas aeruginosa, and also suppress the growth of pathogenic bacteria such as Staphylococcus aureus (Lengey and Andriani 2009). Meat naturally contains some bacteria which grow over time, spoiling the meat and adversely affecting anyone who may consume that meat. Manufacturers may add commercially prepared acidic components to prevent their products from getting contaminated at a rapid rate, but this introduces a sourly taste to these products (Konings, Kuipers and Huis 1999).  They therefore opt to use yoghurt as a source of lactic acid bacteria. Though there is a fierce competition for energy by various groups of bacteria in packaged meat and milk products, Lengey and Andriani (2009) states that strains that are beneficial to human beings slowly gain an upper hand in this competition and eventually eliminate the food spoiling bacteria in addition to pathogenic microorganisms.

Accumulation of lactic acid in milk results in a change of milk structure and texture. It also gives yoghurt and meat their characteristic taste and smell (Adams 2007). Lactic acid bacteria on both yoghurt and meat also play a significant role in the prevention as well as control of various pathogenic bacteria that would otherwise lead to diarrhea, constipation, bowel cancer, and vaginal infection in human beings (Ramon and Rodriguez 2008). It also brings down the effects of lactose intolerance in people suffering from lactose malabsorption. Lactic acid bacteria are therefore beneficial organisms because in addition to preventing gastrointestinal disorders they also boost the activity of the immune system (Herich and Leevkit 2002). Herich and Leevkit (2002) assert that lactic acid bacteria are indigestible, and they selectively enhance the growth of helpful intestinal bacteria while inhibiting the growth of disease causing microorganisms. This greatly improves the health status of the host organism (Lengey and Andriani 2009). These bacteria are also believed to block the action of carcinogens in the intestines. They do so by inhibiting the bacteria that actively convert pro-carcinogens to carcinogens through catalytic activity (Herich and Leevkit 2002).

Lactic acid bacteria further increase the potential hydrogen concentration in the intestines, thereby producing an acidic environment that is not favorable to most pathogenic microorganisms (Konings, Kuipers and Huis 1999). Various end products in fermentation are bactericidal they destroy various bacteria that may otherwise result in infections in an individual. Bacteriocins, which are antimicrobial proteinaceous components that inhibit the growth of sensitive strains, are produced during the process of fermentation (Savadogo, Ouattara, Basole and Traore 2006). Bacteriocins, as asserted by Savadogo, Ouattara, Basole and Traore 2006), are usually referred to as safe lactic acid bacteria and are mainly used in preservation of food to avoid growth of pathogenic bacteria. They are made up of heterologous subsets of antimicrobial peptides that have been synthesized in the ribosome (Savadogo, Ouattara, Basole and Traore 2006). They display hydrophobic characteristics and mainly target the bacterial membrane in their activity. A variety of bacteriocins have been isolated and also characterized from lactic acid bacteria. Some of them have been shown to possess antimicrobial activity as a result of their potential in food preservation in addition to their antagonistic characteristics against a wide range of pathogens (Herich and Leevkit 2002). Some of the bacteriocins that have been isolated from lactic acid bacteria include nisin, helviticins, plantaricins, diplococcin, bulgarican, lactacins and acidophilin (Savadogo, Ouattara, Basole and Traore 2006).  Hofman and Thonart (2001), state that Lactobacillus bulgaricus have a proteolytic activity against other pathogenic microorganisms. Streptococcus thermophilus produces formic acid that stimulates the growth of lactobacillus bulgaricus. Lactic acid bacteria have got beneficial properties on people who have been infected with Helicobacter pylori, an organism responsible for peptic ulcers and gastritis. Lactobacillus acidophilus inhibits the growth as well as the binding ability of Helicobacter pylori, thereby minimizing its effect on an individual (Peng, Lin and Lin 2007). Peng, Lin and Lin (2007), state that various strains of lactic acid bacteria also block the action of putrefactive bacteria present in the gut. The effect of lactic acid strains on different spoilage and pathogenic bacteria have been extensively utilized for both home and commercial production of various food products. However, although food products containing lactic acid bacteria are regarded as safe, various strains of lactic acid bacteria have the ability of transferring antibiotic resistance genes to other bacteria in the human alimentary canal (Orrhagea, Sjstedtb, and Norda 2000). This may expose an individual to great health risk especially when antibiotic resistance gene is transferred to pathogenic microorganisms in the intestines. Lactic acid bacteria develop antibiotic resistance because they exist in large numbers in environments that are often challenged with a wide range of antibiotics thereby disposing them to selective pressure (Orrhagea, Sjstedtb, and Norda 2000).

Possibility to cross using strains of lactic acid bacteria
In order to introduce lactic bacteria to meat products, a piece of meat is injected with yoghurt and then mechanically processed with an aim of uniformly distributing the yoghurt all over the piece. Yoghurt injected into the piece of meat may range from 5-50 by weight (Marianski and Marianski 2008). The preferable pH of the yoghurt may range from 3.5 to 5.2. This pH is preferred due to the fact that it improves the shelf-life of an uncooked meat product. The meat product may alternatively be made from cooked meat. In that case the pH of the yoghurt used should range from 4.8 to 5.1 to make sure that the total pH of the meat product is not close to the isoelectric point of the piece of meat (Marianski and Marianski 2008). This helps to preserve the juiciness as well as the natural moisture of the meat in the process of cooking and also after cooking. Yoghurt has been used traditionally in recipes aimed at marinading in addition to pickling meat.  In the United States today numerous meat products, particularly pet foods, are conserved with substantial amounts of fermented dairy products (Hofman and Thonart 2001). Meat products comprise approximately 25 of the total mixture (Marianski and Marianski 2008). Fermented dairy products are made up of hydrolyzed milk that has been fermented with one or more strains of lactic acid bacteria. Vitamins and minerals are also added in the mixture to improve quality. Meat products produced this way have got a lot of benefits they provide a highly nutritious diet to animals and also have a longer shelf-life.

Marianski and Marianski (2008) makes it clear that meat products for human consumption such as hamburgers and sausages are made up of sliced meat and fermented dairy products. Dairy products that have been fermented are distributed in a homogeneous manner all over the meat products. Anaerobic bifidus bacteria is the strain of lactic acid bacteria used for fermenting dairy products for use in making meat products for human consumption (Marianski and Marianski 2008). Presence of anaerobic bifidus bacteria greatly hinders the growth of other bacteria during storage, which may bring about food spoilage. This increases the shelf-life of the meat product. There are sausages made up of a combination of meat blend and fermented milk products, which have been homogeneously distributed throughout the meat blend (Marianski and Marianski 2008).  Sugars, mainly lactose, may also be added in commercial production of sausages. Marianski and Marianski (2008) state that corn syrup and different starches may also be incorporated these act as substrates for lactic acid bacteria for production of lactic acid and other end products. This consequently results in a reduction in pH. The final mixture has a pH of approximately 5.5 or slightly more. This helps retain the moisture holding capacity of the meat product thereby improving the quality of sausages (Marianski and Marianski 2008). The structure of the meat product in addition to its consistency is maintained.  Dairy products for use in this technique may be prepared from inoculated milk mixtures. Meat products developed this way, as Marianski and Marianski (2008) illustrates have got fewer calories per unit as compared to the traditional meat products. Aroma and taste of these products is greatly improved. These products are also easier to digest. This technique establishes an industrial base for processing such meat products in large quantities.

The other way in which lactic acid bacteria in yoghurt may be introduced into meat products is through mechanically tenderizing or tumbling to distribute injected yogurt throughout the piece of meat (Tamime and Robinson 1999). Yoghurt injected into meat products fills all the cavities and pores on the meat. Higher proportions of yoghurt saturate the meat product. This improves the organoleptic qualities of the meat products (Tamime and Robinson 1999). Yoghurt helps reduce the calorie-content per unit weight of meat. This technique, mechanical processing of meat after injecting with fermented dairy products, greatly disrupts the meat structure, particularly proteins, thereby opening them.  As a result free water is incorporated considerably in the meat structure (Marianski and Marianski 2008). This leads to production of tender and juicy meat products even after cooking. Meat products that are supplied raw are mixed with yoghurt of pH less than 5.2 (Marianski and Marianski 2008). The use of fermented dairy products with a very low pH increases the acidity of the meat product, an aspect that inhibits the growth of harmful microorganisms before the product is cooked. This tends to increase the storage life of raw meat products.

It is important that yoghurt be treated before injecting it into meat products in order to destroy all unwanted yoghurt cultures in addition to other microorganism that may be present in the yoghurt. However, yoghurt containing live culture may be injected into meat pieces. Live yoghurt cultures injected into meat products provide a protective mechanism, which inhibits the growth of unwanted bacteria in the meat (Tamime and Robinson 1999)

Future trend and chance for this cross using strains of lactic acid bacteria
Mutagenic heterocyclic amines are produced when meat is cooked. Studies have revealed that milk cultured with strains of lactic acid bacteria posses anti-mutagenic properties. Lactic acid bacteria are believed to possess anti-mutagenic properties due to their ability to bind the heterocyclic components produced by cooked meat (Hui 2006). This reduces the effectiveness of the mutagenic components. It has also been suggested that lactic acid bacteria may be used for protecting human beings against colon cancer (Hofman and Thonart 2001). Available epidemiological evidence is, however, insufficient to support the idea that yoghurt can be used as a strategy for preventing colon cancer. Preliminary findings however, offer a base on which future studies shall be conducted. Yoghurt containing high levels of lactic acid bacteria is believed to reduce the level of cholesterol in the body (Ramon and Rodriguez 2008). Lactobacillus acidophilus in conjunction with other bacteria found in the gastrointestinal tract is capable of breaking down bile acids in the intestines (Hofman, M and Thonart 2001). After being broken down these bile salts cannot be reabsorbed and taken back to the liver. The recycling process is therefore obstructed (Chandan 2006). This automatically leads to a reduction in the level of cholesterol in the liver, due to the fact that stored cholesterol is utilized in making new bile salts as a result of lack of recycling (Lengey and Andriani 2009). It has, for that reason, been proposed that this effect could be enhanced if the gastrointestinal tract is inhabited by a large population of lactic acid bacteria strains such as Lactobacillus acidophilus. Based on the fact that cholesterol found in blood serum is generated from the liver, various adverse effects associated with high cholesterol levels such as hypertension would be drastically reduced (Hofman, M and Thonart 2001).

There are numerous benefits of live culture yoghurt milk. Research, according to Tamime and Robinson (1999) has found out that almost everybody would greatly benefit from eating yoghurt regularly or during the times of infection. It has been recommended from various studies that people take considerable quantities of yoghurt every time they take antibiotics so as to prevent yeast infections and diarrhea that may occur as a result of treatment with antibiotics (Ramon and Rodriguez 2008). Scientists believed that lactic acid bacteria lower the risk of developing diarrhea in both children and adults (Chandan 2006). Yoghurt containing lactic acid bacteria, according to Adams (2007), also lower the adverse effects associated with antibiotic remedy such as flatulence, abdominal distress and abdominal pain. Diarrhea in healthy people can also be prevented by consumption of yoghurt.  Lactic acid bacteria produce lactic acid at a very slow rate in cultures used for the production of yoghurt. Scientists, as indicated by Lengey and Andriani (2009), recommend yoghurt as a dietary product due to the fact that Lactobacillus acidophilus in beneficial in human beings. Chandan (2006), states that yoghurt has a plain acid flavor, but may be combined with other strains of bacteria to improve its taste.
 In real sense products of lactic acid bacteria have been popular globally since time immemorial. Yoghurt was first recommended for medical purposes in a research carried out in 1907. It was realized that yoghurt has the ability to bring the rate of various infection down even though consumers were not aware of this themselves. Recent researches are documenting more and more benefits associated with consumption of yoghurt (Lengey and Andriani 2009).

Almost 90 of yoghurt is digested within an hour thereby reducing the chances of getting intestinal discomfort as compared to fresh milk which takes a longer time to be digested (Tamime and Robinson 1999). People who do not absorb lactose efficiently usually complain of gastric distress any time they consume fresh milk. Lactose malabsorption is a disorder in which lacrosse, the main carbohydrate of milk, is not completely hydrolyzed into its constituent monosaccharides. Yoghurt is well tolerated by lactose malabsorbers. These people also suffer fewer symptoms after consuming fermented foods. Malabsorbers are therefore advised to take more of fermented dairy and other food products (Chandan 2006).

The milk of breastfeeding mothers contains very high proportions of lactic acid bacteria. This milk provides babies with defensive and healthy bacteria from the very beginning of life. It has been suggested that various strains of lactic acid, especially Lactobacillus acidophilus, enhances the production of antibodies such as Immunoglobulin-A (IgA). This subsequently improves the immune system of an individual. Lactobacillus acidophilus, are also believed to enhance the production of secretory immunoglobulin-A (sIgA), which prevents harmful microorganisms from attaching and penetrating the gastrointestinal tract wall. Lactic acid bacteria also enhance the process of phagocytosis. Lactobacillus acidophilus, as illustrated by Herich and Leevkit (2002), boosts the bodys production of macrophages in case an infection occurs. Scientists are therefore urging people to consume more quantities of yoghurt as compared to milk and other fluids.

Research has made it clear that yoghurt minimizes the danger of vaginal yeast infection. It has also been revealed that eating yoghurt, which contains a very high percentage of lactic acid bacteria, is an effective strategy in treating vaginal bacterial and yeast infections (Tamime and Robinson 1999). Eating yoghurt severally is also believed to reduce the chances of re-infection. It has been suggested from available studies that yoghurt is an effective strategy of treating vaginosis, a bacterial vaginal infection (Herich and Leevkit 2002).  It is also believed that yoghurt with its high concentration of lactic acid bacteria decreases tubal infections that result in infertility (Ramon and Rodriguez 2008). It is also believed to increase the success rate of in-vitro fertilization. It has been suggested that yoghurt can be used to decrease the dangers of contracting various sexually transmitted diseases in women such as Chlamydia and gonorrhea (Ramon and Rodriguez 2008). Lactic acid bacteria are more and more being administered to pregnant women and children in order to improve their health (Allen, et al 2010). It is, however, important to carry out research to identify the effects of these bacteria to the vulnerable populations. It has been suggested that lactic acid bacteria has beneficial properties that may be useful on mediating immune regulation. These bacteria are believed to regulate the activity of pro-inflammatory and anti-inflammatory cytokines.

Scientists are advocating for increased consumption of yoghurt containing high quantities of Lactic acid bacteria which acts as probiotics to reduce chances of intestinal inflammation in addition to down-regulating various hypersensitivity reactions like allergies. It has been proposed that the high level of occurrence of childhood allergies is as a result of an increase in hygiene. Consequently any contact with a microbe leads to serious reactions. It has therefore been suggested that in future children be exposed to friendly bacteria such as lactic acid bacteria found in yoghurt in order to alleviate the subsequent danger of allergic reactions.

Lactic acid bacteria are a group of helpful bacteria which utilize lactose from various food products to produce lactic acid as an end product in the process of fermentation. They are made up of various genera that comprise of more than a hundred species. Lactobacillus is one of the largest groups that make up the lactic acid bacteria. They are composed of species with different physical, chemical and physiological characteristics. Various species of lactic acid bacteria are acid tolerant. Lactic acid bacteria are gram positive organisms. They are non motile, non sporulating facultative anaerobes and do not have cytochromes. They are naturally found on various materials and food substances such as milk, meat and flour and are employed as natural starters during food fermentation.

These bacteria produce acidic components, which reduce the pH of food products being fermented. As a result they keep foods safe from putrefying and pathogenic microorganisms. Reduction in pH greatly inhibits the growth of pathogenic microorganisms. Lactic acid bacteria also produce antifungal compounds such as fatty acids, and bacteriocins which are antimicrobial proteinaceous components that inhibit the growth of sensitive strains of pathogenic micro-organisms. It can therefore be concluded that lactic acid bacteria are beneficial to human beings.  Lactic acid bacteria are beneficial in dairy and food sectors due to the fact that they produce lactic acid, a component that acts a natural food preservative as well as taste and aroma enhancer.

Various species of lactic acid bacteria are isolated for use as starter cultures from naturally fermented foods and further developed for commercial fermentation of foods. The predominant species of lactic acid bacteria that are isolated from meat include Lactobacillus curvatis, Lactobacillus plantarum, Leuconostoc carnosum, Leuconostoc gelidum, and Lactobacillus sakei among others. Lactic acid species isolated from yoghurt include Lactobacillus fermentum, Lactobacillus casei, Lactobacillus cellobiosus, and Lactobacillus coprophilus among others. Enrichment of food products in broth culture and then plating this culture onto an agar medium inoculating food samples directly onto an agar medium and filtering the sample through a membrane and then incubating the membrane onto an agar medium are the three techniques mainly used in cultivation and isolation of lactic acid bacteria. Lactic acid bacteria may be introduced in meat products by injecting yoghurt and distributing it allover the piece of meat. However, unwanted yoghurt cultures must first be destroyed by treating yoghurt. The use of fermented food products such as yoghurt is steadily gaining roots in the modern world.

Researchers recommend the use of yoghurt as dietary component because it contains a large proportion of lactic acid bacteria believed to be beneficial to human beings. Lactic acid bacteria effectively compete with harmful microbes in the gut for establishment of dominance. Lactobacillus species are the predominant species of lactic acid bacteria in the upper alimentary canal. The action of various strains of lactic acid bacteria in the alimentary canal results in a reduction in lactose intolerance, serum cholesterol level, and some diarrheas. They also boost the immune system and prevent the development of various types of cancer. Lactic acid bacteria also alleviate gastrointestinal disorders.


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