What are probiotics?
‘Probiotic’ is a Greek term, which means - “for life.” It was first used by Lilly and Stillwell in 1965 to describe “substances secreted by one microorganism which stimulates the growth of another” and thus was contrasted with the term antibiotic.
However, as per FAO/WHO, probiotics are live microorganisms which, when consumed in adequate amounts, confer a health benefit on the host. Among livestock foods, fermented milk and milk products are rich sources of probiotics.
Probiotic organisms are classified as lactic acid bacteria (LAB) and are important bacteria for food fermentations. They play crucial roles in the fermentation of milk, soy and meat products, and vegetables such as cabbage. Incorporation of probiotic organisms such as Lactobacillus acidophilus, Bifidobacterium sp., and L. casei in fermented products provides a potential to improve the quality of the product and the health status of consumers.
Dairy and soy foods may serve as the ideal system for delivery of probiotic bacteria to the human gastrointestinal tract due to provision of a favourable environment that promotes the growth and enhances the viability of these microorganisms. Probiotic foods are defined as ‘foods that contain live microorganisms, which upon digestion, actively enhance the health of consumers by improving the balance of microflora in the gut.’ A growing public awareness of diet-related health issues and mounting evidence regarding health benefits of probiotics have increased consumers’ demand for probiotic foods.
How much of these are required?
To observe a positive health effect of their consumption, a minimum level of live microorganisms is required; this level, depending on the strains used and the required health effect, is usually between 108 and 1011 cfu/d. Therefore, assuming a daily consumption of fermented dairy products of 100 g, they should contain between 106 cfu/g to 109 cfu/g of these live bacteria at the time of consumption.
How do these work?
The exact mechanism of action by which probiotics confer health benefits, is not clear. However, according to a view, some strains produce certain health promoting metabolites such as proteins and fatty acids, which are important from nutritional and physiological point of view.
What should be the characteristic features of an effective probiotic?
It should have a beneficial effect on host; It should be non-toxic as well as non-pathogenic; It should contain large number of viable microbial cells; It should be capable of surviving and metabolising in the intestine; It should remain viable during storage and use; It should have favourable sensory attributes; It should be isolated from the same species as its intended host.
What are the health benefits of probiotics?
There are a number of health benefits of probiotics. These benefits are strain-specific; therefore, there is no universal strain that would provide all proposed benefits, not even strains of the same species. Moreover, not all the strains of the same species are effective against a defined health conditions. The important health benefits of probiotics are as follows: Alleviation of symptoms of lactose intolerance; Increase in natural resistance to infectious diseases of the intestinal tract; Antihypertensive and anti-carcinogenic; Reduction in blood cholesterol level; Improved digestion; Stimulation of gastrointestinal immunity; Improve the weight gain especially in infants; Various strains such as L. casei are useful for treatment of acute diarrhoea in children; Oral administration of L. acidophilus has also been shown to be effective against bacterially induced gastroenteritis; Oral administration of Bifidobacterium may be effective against campylobacter-induced enteritis in children; Improve hormonal balance in postmenopausal women; Some Bifidobacterial probiotics reduce the growth of Candida albicans and the incidence of enterocolitis in infants; and Probiotics produce bioactive peptides by enzymatic breakdown of milk proteins, which further confer a number of health benefits.
What is the viability of probiotics?
In order to obtain the desired health effects, probiotic bacteria must be able to grow in milk/soymilk and survive in sufficient numbers. But surveys have shown poor viability in some yoghurts. Therefore, in order to provide the therapeutic benefits, attempts to increase viability in dairy and soy products have drawn the attention of researchers in recent years. Meanwhile, there is much evidence to show that Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus survive at high concentration (>107 cfu/g) in yoghurts after manufacture until the time of consumption in comparison to probiotic microorganisms. Therefore it is important to understand some of the factors which affect viability of probiotic cultures in fermented milk/soy products.
What are the factors affecting viability of probiotics?
Type of strains of LAB; Interactions between species present; Acidity of medium; pH of medium; Presence of hydrogen peroxide due to bacterial metabolism; Storage temperature; Oxygen content; Concentrations of acetic and lactic acids; Nutrients limitations in milk/soymilk to sustain growth; Growth promoters and inhibitors; Inoculation level; and Fermentation time and post-acidification.
What are the strategies for improving viability of probiotic microorganisms?
Selection of type of culture; Supplementation of milk and soymilk with nutrients; Microencapsulation; and Use of growth enhancers such as prebiotics.
What are the delivery systems of probiotic microorganisms?
For a potential therapeutic effect, probiotic organisms need to be delivered in the active form. Dairy and soy foods may serve as ideal systems for the delivery of probiotic bacteria to the human GIT (gastrointestinal tract), since they may provide a favourable environment, which promotes growth and enhances viability of these microorganisms. While various health claims have been associated with the consumption of probiotic organisms, they may in some instances be influenced by composition of a delivery matrix. In dairy and soy applications, probiotic organisms are delivered with different fermented dairy and soy products, most notable yoghurt and soy yoghurt. The nutritional value of the final product is also affected by processing factors, including temperature, duration of heat exposure, exposure to light, and storage conditions (Fox, 2003). Furthermore, some of these milk or soy constituents may be modified by microbial action during fermentation, which may affect the nutritional and physiologic value of the final product. In addition, bacterial strains used in the fermentation in conjunction with different added ingredients and fermentation conditions will also play an important role in the final nutritional composition of probiotic products. During the bacterial fermentation, major constituents including lactose and milk proteins, soy proteins, raffinose, stachyose and other soy carbohydrates are utilised for the bacterial growth, which results in the conversion of fermentable materials into a range of products such as lactic acid, acetic acid, peptides, amino acids and vitamins. In addition to exceptional nutritional attributes, milk and soy derived products such as fermented milk or soy contain components that possess a range of different bioactive compounds. Some of these bioactive compounds are considered functional, thus making dairy and soy products important part of functional foods and nutraceuticals. From the above discussion, it is clear that probiotics are very important for our life and can prove the following slogan to be true, “Healthy Food, Healthy Nation”
