According to the definition of WHO, the beneficial microbial strains in order to be called probiotics should be ‘live’. Therefore, the viability of the probiotics is an important issue which needs to be addressed so that they can render their beneficial effects. However, a number of factors compromise the viability of probiotic lives within the food and other supplementation products besides those faced during the gastrointestinal passage. The potentially beneficial but relatively susceptible weaker strains are prone to severe damage during the harsh conditions faced while processing and curing as well as in food products. Efforts are being carried out to improve the viability of the probiotic strains. But in order to make the process really effective, one should be fully aware of the various agents that are capable of challenging the survival of the probiotics in packaged food products. The major thrust would not only be on reducing these adverse affects but also to make the strains more resistant to them.
Viability Compromise in Probiotic Food Products:
Probiotic viability is a matter of biological as well as of technological and economic significance. The storage of probiotic strains in food products encounters conditions which are not suitable for their survival and hampers their longevity. Like the presence of acidic conditions in fermented food products. Good and healthy resistance to the presented stresses is therefore a prerequisite to make probiotics remain active and viable and with increased shelf-life. Gueimonde et al. has suggested that in many commercial products including multiple probiotic strains, it has often been observed that the probiotics does not meet the effective regulatory criterion towards the end of the storage time. Hence, the testing of viability and stability among potential probiotic strains has to be routinely carried out to screen for the possibility of newer beneficial resistant strains. The model test mechanisms can include both normal as well as accelerated methods, e.g., elevation in storage temperatures. Traditionally the viability of the bacterial cultures through these tests is measured using plate counting methods. The works of several researchers have shown in recent times that the viability testing of the probiotics in food through such methods is not always the right choice. The study of Lahtinen et al. has shown that probiotics during the period of storage might enter a period of inactivity (latent period) although they may show viability on plates and grow quite normally. Culture independent processes have to be developed to get the real picture of the number of viable cells. Infact, very recently such techniques have been devised.
Oxygen Toxicity and Probiotics:
Various strains of L. acidophilus and Bifidobacterium are routinely incorporated in dairy food products like yoghurt. But the bacteria face stiff challenge for survival in yoghurt thereby limiting its beneficial potency. The major reason behind the cell deaths under these conditions is oxygen toxicity. These probiotic strains are mostly microaerophiles or anaerobes with an intestinal origin making them highly susceptible candidates when exposed to oxygen in the food products. Though the oxygen toxicity of these probiotic strains is well known yet the biochemical knowledge for such toxic effects is very paltry. Besides, another point to consider is the level of differences in oxygen toxicity shown by the strains of Lactobacillus acidophilus and Bifidobacterium although both being susceptible to oxygen presence. Looking into the biochemistry that can protect some bacterial strains against oxygen suggests the action of a series of complex reactions that occurs simultaneously. The enzymes, NADH (peroxidase and oxidase) are crucial in providing resistance against the toxic effects of oxygen.
However, the knowledge about the different pathways involved in their regulation is not well elucidated. Schell and his co-workers have found the presence of proteins that can reverse the effects of oxidative damage Bifidobacterium longum while Kleerebezem et al. has discovered similar proteins in Lactobacillus plantarum. Therefore, research oriented towards the identification of the biochemical differences between the probiotic strains with respect to their response to oxygen can improve upon the menace of toxicity caused by it. It is also possible to gradually increase the concentration of oxygen through subsequent passaging of the cells and enhance their adaptability to it. It should also be kept in mind that most of the probiotic strains are tested for their oxygen tolerance at 37°C since it is suitable for the growth of the culture. On the other hand, the yoghurts are usually kept stored at around (4-8) °C. The oxygen may influence the strains quite differently at this temperature as compared to the normal physiological temperature. The biological activities of the enzymes oxidase and peroxidase can also be inhibited at such low storage temperature. It is therefore quite obvious to carry out the oxidative study under conditions which would mimic those during storage of the probiotic cells in the food products. The use of different packaging systems for food products with oxygen impermeability or the inclusion of oxygen scavenging agents can be useful.
Natural and Technological Remedies to The Problem:
So what can be the answer to the question of probiotic viability? The isolation of different acid resistant probiotic strains and their subsequent development to be used in food products is one of the ways to get robust probiotic products. The proper characterization of such strains would enable the biotechnologists and genetic engineers to incorporate such genes of interest in other beneficial probiotic cells. This would allow the cells to be able to survive in the acidic conditions which prevail during fermentation. In addition, the cells must also be protected from oxygen toxicity. This can be achieved either through the adaptation of the cells at sub-lethal concentration of oxygen at temperatures that is encountered during the storage period or the genetic manipulation of the oxygen resistant and scavenging genes into probiotic strains. Some other methods may involve artificial scavengers, modification in packaging materials and or application of microencapsulation techniques.
The probiotics need to be viable particularly if it’s required to colonize the site of action within the recipient in order to render its effects. Therefore, the issue of probiotic viability in food products gains significance. With research in this field being on a high, better viable probiotic strains in packaged food is a good possibility.