ارزیابی زیست پذیری باکتری های لاکتیک اسید آزاد و انکپسوله با استفاده از مدل معدی روده ای in vitro و مطالعات قابلیت بقا میکروکپسول های سین بیوتیک در ماتریکس غذایی خشک در طی ذخیره سازی Evaluation of the viability of free and encapsulated lactic acid bacteria using in vitro gastro intestinal model and post storage survivability studies of synbiotic microcapsules in dry food matrix

۱٫ Introduction There has been an explosion of health-based probiotic products since over a decade. The biological activity of probiotic bacteria owes to their ability of attachment to enterocytes thereby inhibiting the enteric pathogens from binding as a result of competitive exclusion. Probiotic bacteria are used in the food industry due to various beneficial properties including reduction of irritable bowel syndrome symptoms, immunomodulatory effects, and cholesterol reduction (FAO/WHO, 2006). Inclusion of probiotic bacteria in fermented products enhances their value as better therapeutic functional foods. It is necessary for all products having probiotic health claims to have minimum 106 CFU/mL probiotic bacteria till expiry date, since minimum therapeutic level per day is considered to be 108 –۱۰۹ cells (Kailasapathy and Chin, 2000). Karimi et al. (2011) stated that probiotic products when consumed 100 g per day deliver about 109 viable cells into the intestine. Reports indicate poor survival of probiotics in food products as well as in the human gastro-intestinal system. Viability of probiotics in a product during consumption is important for their efficacy, as their survival is essential during processing and storage of food products (Mortazavian et al., 2012). Selecting better probiotic strains and providing them physical layering to enhance their survival, including the use of appropriate prebiotics and the optimal combination of probiotics and prebiotics (synbiotics), can increase the delivery of sufficient viable probiotics in functional food products to the consumers. Viability of probiotics in food matrix is affected by factors like pH, acidification during storage of fermented products, production of hydrogen peroxide, oxygen toxicity, processing and storage temperatures, rate and proportion of inoculation, micro-encapsulation, and stability during storage (Mortazavian et al., 2012). In order to act as probiotic in the gastrointestinal tract (GIT) and to exert their beneficial effect on the host it is essential for the bacteria to have protective mechanisms to withstand the low pH in the stomach, digestive enzymes, and bile in the small intestine (Argyri et al., 2012). In-vitro gastro intestinal model (one pot system) is preferably used to mimic this GIT micro-environment. Microencapsulation is defined as a process in which the cells are retained within a membrane to reduce cell injury and death, producing particles in the nanometer (nanoencapsulation), micrometer (microencapsulation) or millimeter scale (Burgain et al., 2011). Encapsulation stabilises the probiotic cells, significantly enhancing their viability and stability in the production and handling of functional food as well as during their rehydration and lyophilisation. It also preserves the metabolic activity of probiotics in the gastrointestinal tract (Picot and Lacroix, 2004), and ensures viability during long-term storage (Zuidam and Nedovic, 2010). In addition, encapsulation improves and stabilises the sensory properties of the food as well as aids in the homogeneous distribution of probiotics throughout the product (Krasaekoopt et al., 2003). Mushrooms seem to be a potential candidate for prebiotics as it contains carbohydrates like chitin, hemicellulose, β and α-glucans, mannans, xylans, and galactans. Previous studies suggested that the polysaccharides from mushroom have immunomodulating properties like enhancement of lymphocyte proliferation and antibody production (Bao et al., 2001) as well as antitumor properties (Wasser, 2002) and help in cholesterol removal and prevention of obesity. Latest finding by Hearst et al. (2009) and Tsai et al. (2009) revealed antimicrobial and antioxidant properties of mushrooms, respectively. Other than its medicinal properties, edible mushrooms also show significant health improvement as they have low content of calories, sodium, fat, and cholesterol, while they are rich in protein, carbohydrate, fibre, vitamins, and minerals. These nutritional properties give mushrooms the potential to become a food supplement as well as a pharmaceutical agent. They are able to manipulate the composition of colonic microbiota in human gut by inhibition of exogenous pathogens (Rycroft et al., 2001), thus improving the host health (Roberfroid, 2002). Synytsya et al. (2009) showed that mushroom extracts were able to stimulate the growth of probiotics. The probiotic drinks generally contain live bacteria. They must also contain a source of nutrition for the bacteria to feed upon (Savini et al., 2010). Consequently, there is storage and shelf-life issue shortened for some live products. Furthermore, competition for nutrition between bacterial strains within a drink is another important complication. In addition, liquid probiotics all require refrigeration. On the other hand probiotic powders consist of probiotics that have been freeze-dried under low temperature and pressure without damaging the cells. This provides a suitable growth suspended state for the long-term storage of probiotic bacteria. Once moisture becomes available again after ingestion they rehydrate and subsequently, a proportion of cell start to divide again as before being freeze-dried. Researchers have found that the rehydrated probiotics are capable of effectively providing their respective benefits (Bohbot and Cardot, 2012). Whether or not refrigeration is required for probiotics is dependent upon the actual strains, some of which are heat and shelf stable and some of which are not. Hence, the present work was planned to study the efficiency of microencapsulation in protecting the LAB from acid, bile, and digestive enzymes. This work also aimed to evaluate the efficiency of encapsulation along with prebiotic molecules to increase their survivability during storage in dry food matrix.