PROBIOTICS: “The Friendly Bacteria”
The word ‘probiotic’, derived from the Greek language, means ‘for life’ which is opposed to ‘antibiotics’ which means ‘against life’. The term “probiotics” was first introduced in 1953 by Werner Kollath. The definition of the term has evolved over the years. Perhaps the most appropriate definition, published by an Expert Consultation at a meeting convened by the FAO/WHO in October 2001, is ‘’probiotics are live micro-organisms which when administered in adequate amounts confer a health benefit on the host’’.
Viability and activity of the bacteria are essential concern, because the bacteria must survive in the food during shelf life and transit through the acidic conditions of the stomach, and resist degradation by hydrolytic enzymes and bile salts in the small intestine. Recommended lower limit of International Dairy Federation (IDF) for probiotic counts in dairy product is 106 cfu/ml. Several countries have established minimum values of probiotic bacteria for fermented milks during shelf life. In Japan, the Fermented Milks and Lactic Acid Beverages Association have introduced a standard of a minimum of >1×107 cfu/ml viable probiotic cells for fresh dairy products. It is necessary that products sold with any health claims meet this standard.
Since the renewed importance in probiotics, different types of products were proposed as carrier foods for probiotic microorganisms by which consumers can take in large amounts of probiotic cells for the therapeutic effect. Yogurt has long been recognized as a product with many desirable effects for consumers, and it is also important that most consumers consider yogurt to be ‘healthy’. Traditionally, yogurt is manufactured using Streptococcus thermophilus and Lactobacillus delbrueckii subsp. as starter cultures which exhibit a symbiotic relationship during the fermentation of yogurt. In recent years some yogurt products have been reformulated to include live strains of Lactobacillus strains such as L.acidophilus, and species of bifidobacterium in addition to the conventional yogurt organisms, S.thermophilus and L.bulgaricus.
There are number of potential benefits that might be derived from consuming dairy products containing probiotic bacteria. The probiotic species that show the most promise in treating diarrhea diseases in children include Lactobacillus spp., Lactobacillus reuteri, Lactobacillus casei, Saccharomyces boulardii, Bifidobacterium bifidum and Streptococcus. thermophilus. Beneficial effects such as decreased frequency of infections, shortening of the duration of episodes by 1–1.5 d, decreased shedding of rotaviruses or promotion of systemic or local immune response, and an increase in the production of rotavirus specific antibodies have been demonstrated for a number of food probiotics; Lactobacillus rhamnosus GG, L. casei Shirota, L. reuteri, L. acidophilus spec., Bifidobacterium animalis ssp. lactis BB-12, Streptococcus thermophilus and others.
As lactic acid bacteria actively converts lactose into lactic acid, ingestion of certain active strain may help lactose intolerant individuals to tolerate more lactose than they would have otherwise. The inability of adults to digest lactose is widespread, although those deficient in lactase generally tolerate lactose better from yogurt than from milk. Probiotic bacteria such as L. acidophilus, B. biﬁdum, Streptococcus thermophillus and Lactobacillus bulgaricus used in yogurt production produce β-d-galactosidase. This enzyme hydrolyses lactose, which results in increased tolerance for dairy products.
Probiotics have the capability of lowering cholesterol levels in serum, contributing to the prevention of cardiovascular disease. Some animal studies have demonstrated that probiotics are breaking down bile in the gut, thus inhibiting its reabsorbtion which enters the blood as cholesterol. Some human trials have revealed that fermented diary foods can produce modest reduction in total and LDL cholesterol levels in those with normal levels to begin with.
Several animal studies have shown that supplementation with particular strains of probiotics could prevent the establishment, growth, and metastasis of transplantable and chemically induced tumours. Studies in human subjects have also revealed that probiotic therapy may reduce the risk of colon cancer by inhibiting transformation of procarcinogen to active carcinogens, binding/inactivating mutagenic compounds, producing antimutagenic compounds, suppressing the growth of pro-carcinogenic bacteria, reducing the absorption of mutagens from the intestine, and enhancing immune function. The ability of lactobacilli and bifidobacteria to modify the gut microbiota and reduce the risk of cancer is in part due to their ability to decrease β-glucuronidase and carcinogen levels. Probiotics may suppress the growth of bacteria that convert procarcinogens into carcinogens, thereby reducing the amount of carcinogens in the intestine. Probiotics have demonstrated an ability to prevent the induction of allergic symptoms, particularly that of atopic dermatitis, in high risk infants. The ability of probiotics to regulate the induction of atopic dermatitis may be due to their ability to strengthen the mucosal barrier and prevent the circulation of undigested food proteins into the periphery of susceptible individuals, thus preventing stimulation of that particular antigen speciﬁc immune response.
We are still at an early stage in the development of effective probiotics for human use. Though the probiotic products in the market show a substantial increase in popularity recently, scientific approaches to establishing the functional benefits of probiotic foods are still a complicated case. Gene technology will certainly play a role in developing new strains, with gene sequencing allowing for an increased understanding of mechanisms and functionality of probiotics. As an example, the complete genome sequence of the probiotic Lactobacillus acidophilus has been determined and features contributing to survival in the gut and promoting interactions with the intestines have been identified. Moreover, Lactic acid bacteria (Lactobacillus spp.) have been genetically modified to increase proteolytic activity, to resist viruses, to metabolize complex carbohydrates or to enhance metabolism. Genetic modification of bacteria can be done by DNA transformation, transduction, a random ‘gene shuffling’ technique or by the use of plasmids. Genetic modifications are also continuously applied to improve fermentation efficiency and shelf life of probiotic bacteria. In addition to such basic research, industry centred research will focus on prolonging the shelf-life and likelihood of survival through the intestinal tract, optimizing adhesion capacity and developing proper production, handling and packaging procedures to ensure that the desired benefits are delivered to the consumer. Over time, new food products containing probiotics will emerge. However, the safety of these genetically modified bacteria should be considered as it has the potential of turning harmless, beneficial microbes into dangerous pathogens.