There has been a great rise in interest about probiotics and related products with the wide range of benefits that it can render. However, research suggests that a minimum colony forming unit (CFU) of the probiotic strains is needed in order to provide the desired beneficial traits. The poor survival of the bacteria as indicated by several reports is a major question to that effect. Several environmental factors like the oxygen toxicity (as most of the probiotic strains are microaerophilic in nature) challenges its existence during processing and storage. Also, the passage through the gastro-intestinal tract offers a variety of extreme conditions like low pH that reduces a significant proportion of the probiotic population. So, efforts are being carried out to develop and design effective modes of administration of the probiotics to the recipients in forms that are resistant to the different survival challenges and increase its overall viability. Microencapsulation is one of the latest technologies that can increase the survival rate of the probiotic bacteria.
What is Microencapsulation?
The technology involved in the small sized packaging of solids, liquids and gases within microcapsules so that the inner components may be released at regulated rates under certain specific set of conditions. The microcapsules are generally semi-permeable membranes, strong enough to withstand the rigors during passage, thin and spherical in shape. The capsules vary between the ranges of µm to 1mm. Anal and his team has devised encapsulation technique in which hydrocolloid beads are used to immobilize and entrap the bacterial cells providing protection from harsh environment. Several techniques of microencapsulation of the microbial cells are being used so as to turn them into powdered concentrated state. Some of the most common types include freeze dry, spray dry and fluid bed but they need modifications since the encapsulated cells through these methods are released completely.
So, the cultures may not get proper protection from the environment of the product or during their move through the GI tract. Polymers which are food grade have been a hit in recent times that include carboxy-methyl celluloses or sepharoses, chitosans, alginates, pectin, gelatin and carrageenan to be employed in various microencapsulation methods. However, the most common polymerizing material used in encapsulation among them is alginate which is formed of L-glucuronic acid and D-mannuronic acid. Various species of algae are a rich source of this hetero-polysaccharide. Such easy source of availability favors its use due to cost effectiveness as also biocompatibility and simplicity.
Krasaekoopt has shown that alginate beads are developed by emulsion as well as extrusion processes. Some other formations used are locust bean and k-carrageenan mixtures, chitosans and gelatin. Rao and group have improved upon the cellulose beads to a derivative of acetate phthalate. All these polymers when used in emulsion technique have been found to prevent the release of the cells into the food product and avoid the exposure of the bacteria to food environment.
Considerations Before Microencapsulation of Probiotics:
Multi-factorial reasons are to be considered before the efficient microencapsulation of the probiotics and their proper utilization in terms of viability maintenance and controlled release on the site of action.
The size of the microcapsule, material (generally polysaccharide beads) used, whether the capsules are coated or uncoated, the microencapsulation process employed are the factors to be assessed before the application of useful encapsulation strategies. The response of the probiotics to processing, heat stable or heat labile, their adaptation to the low pH of the gut and the potential synergistic effects of the prebiotic-probiotic combinations have been found to significantly influence the survival and viability of the probiotics.
As such focus of the probiotic microencapsulation should be on the development of designs to ease out these problems of probiotic viability. Scientists have been now able to devise microencapsulated formulations that can lead to active and gradual release of probiotics. According to a report published in Medical Plastics and Biomaterials, once inside the body the microcapsules might be opened by either of diffusion, pressure, heat fracture or solvation. The actual mode of opening will depend on the material of choice for encapsulation and the condition it encounters in the target.
Some designs have employed a specific coating so as to open them at specific sites in the recipient body. e.g., acid-labile materials contained in microspheres should not open in the stomach so that they can pass undamaged and reach their target in the intestines. In such circumstances, the coating must be so designed as to actively tolerate the acidic pH of the stomach and pass through it. There are a variety of utilities of cell entrapped culture techniques as compared to fermentations under free-cell conditions. Some of the added advantages include higher cell concentrations, recycling of biocatalysts, improved stability of plasmids, inhibition to wash-out in continuous fermentation methods, enhanced tolerance to contamination and attack of bacteria killing phages as also the chemical and physiological properties of the bacterial cells.
Microencapsulated Probiotics and Their Application:
There are several reports to suggest improved survival rate and efficient activity of the microencapsulated probiotic bacteria. The study by Shue et al. have shown a 40% survival increment of Lactobacillus strains in freezed milk when they were encapsulated within calcium alginate as compared to the free cells. B. bifidum and B. infantis strains also showed similar improvement in viability rates when incorporated within beads of k-carrageenan and alginate during the entire storage period of nearly 10 weeks. Supplements of probiotic strains are now routinely available as lyophilized powders or capsules. Several microencapsulated formulations of L. acidophilus strains are being tried out with increased efficacy during and after delivery.
The viability of the probiotic lives is a key issue to the effective mode of therapeutic interventions. Therefore, the need of the hour is to develop technologies that would improve upon the existing methods and provide higher cellular yields and better survival in the food product as also within the body. Microencapsulation techniques and its various adaptations has definitely been able provide the useful and effective protection to the probiotics with active delivery at the site of action.