Starter Cultures and Fermented Milk Products

Module 15. Probiotics, acidophilus and bifidus milk products

Lesson 26

PROBIOTICS: IMPORTANCE, DEFINITION, TYPES AND SELECTION CRITERIA FOR CULTURES

26.1 Introduction

GI tract is one of the most diverse and metabolically active organs in the human body. The human gut and its microbiota cannot be realistically considered as separate entities as they represent a dynamic biological system that has co-evolved from birth. The ability of the gut to sustain its beneficial microbiota, agains tharmful or opportunistic microbiota, in a desirable community structure, is critical for host health and reduction of disease risk. It is apparent that the intestinal microbiota directly influences gastrointestinal health and systemically affects host health. In healthy individuals, the gastrointestinal microbiota exists in a state of eubiosis. However, this dynamic equilibrium can be ‘disturbed’ by the stresses of modern-day living, or antimicrobial intake,with serious repercussions for the host. The failure of antibiotics to treat infection as a consequence of increased microbial resistance, and the fear that new, more successful, antibiotics will not be developed has necessitated a new perspective on an age-old problem. These circumstances, in combination with the consumer demand for dietary supplements to maintain gastrointestinal health,have fuel led scientific research into alternative approaches. Within this context, the potential for preventing dysbiosis or indeed fortifying the GI tract through modulation of the intestinal microbiota seems a tangible solution. Metchnikoff (1907) was perhaps the first to recognize the health-enhancing attributes of fermented products containing microbes. He hypothesized that the harmful effects of the undesirable bacteria could be overcome through ingesting LAB (probiotics) and that the longevity of Bulgarians was due to the consumption of large quantities of lactobacilli-fermented milk. In the ensuing 90 years, there has been a plethora of published studies to support Mechnikoff’s hypothesis. It is now well recognized that a healthy (balanced) microflora is pivotal to optimum health and that supplementation with probiotics could be used to shift the balance of the gut microflora away from potentially harmful/pathogenic bacteria towards abeneficial or health-promoting microorganisms, like lactobacilli,bifidobacteria. Fermented foods, including milk and dairy products, have played important roles in the diet of humans worldwide for thousands of years.Fermented milk with health-promoting “probiotic” properties is one of the oldest functional foods. Since the mid-1950s, there has been increasing knowledge of the benefits of probiotic gut flora and their impact on human biological processes and, at the same time, of the identity of certain dairy or non-dairy components of fermented milks and their role in human health and body function. Indeed, probiotics are food components fulfilling particularly the term “beyond nutrition” or “functional” since bacteria have no nutrient character.

26.2 Definition

Probiotic is derived from Greek and means pro-life. It is an opposite word of antibiotic and it means ‘for life’ or ‘in support of life’. Any microorganism and or substance which improve health can be called as probiotic. The term probiotic was coined by Lilly and Still well in 1965 who terms probiotics for growth promoting factors produced by microorganisms. Later on parker in 1974 used the term for‘organisms and substances’ and Fuller in 1989 defined probiotic as a live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance. During the journey of science from1965 to till date, probiotic’s definition has been revised several times. But at present, the definition given by WHO/FAO (2002) has been universally accepted and as per that probiotic is defined as “ Live microorganisms which when administered in adequate amount confer a health benefit on the host”.

26.3 Types of Probiotic Microflora

There are several microorganism which has been used as probiotics (see Table 1), but lactic acid bacteria enjoying the GRAS (generally regarded as safe) status have been most frequently used. This status is based on their historic association with fermented foods, which have been found to be safe and healthy. Several non-GRAS status microbes are also being used, but they need to prove their safety by appropriate safety trials. Recently one work group formed by International Dairy Federation is looking to gather information on microbes having long history of association with foods which can given GRAS status.

Table 26.1 Microorganisms reported as probiotics

26.3.1 Criteria for selection of probiotics

The probiotic microorganisms are required to function in vivo in the body and hence any orally administered microbe need to withstand the adverse conditions in gastro-intestinal (GI) tract and establish in human GI tract. Further, it need to remain viable in the food product and hence it need to resist production conditions and remain viable in sufficient numbers till the end of shelf life of the product. The most important condition is that the culture should be safe for human consumption. Following is the list of criteria used for selection of strain of probiotic microorganism.

1. The source from where the culture is isolated. There is host specificity.

2. Capability of passage in live condition to gastro-intestinal tract.

- tolerance to gastric acids

- tolerance to low pH

- tolerance to digestive enzymes

- tolerance to lysozyme

3. Capability of persistence in live condition in gastro-intestinal tract.

- tolerance to bile salts

- resistance to lower surface tension

- tolerance to phenolic compounds

- resistance to peristalsis

4. Ability of intestinal implantation

- production of exopolysaccharides

- hydrogen bonding

- surface structures

- non-specific ionic bridges

- surface hydrophobicity

5. Tolerance to production conditions

- resistance to temperature

- resistance to salt

- resistance to sugar

6. Resistance to antibiotics

7. Production of antibiotic like substances

8. Safety

As several probiotic cultures have come in market with several health claims, it has become important to protect the consumers from false claims and misleading information. Hence, FAO/WHO has given guidelines(see Figure 1) to explain that what can be called as probiotic? Only those cultures, which fulfills criteria for survival in GI-tract and which has clinically demonstrated some health benefit can be called as Probiotic.

Fig. 26.1 Guidelines for the evaluation of probiotics for food use

Health benefits of probiotics

1. Antimicrobial properties

2. Antimutagenic effect

3. Improved lactose digestion

4. Anticarcinogenic effect

5. Lower serum cholesterol level

6. Management of diarrhoea

7. Immune system stimulation

8. Lowering blood pressure

9. Management of inflammatory bowel disease

10. Control of urinary tract infection

11. Prevention of allergies.