Yoghurt is the common fermented dairy product consumed worldwide and it is considered a potential source of probiotic bacteria (Lactobacilli and Lactococci). To assess the in-vitro probiotic properties of lactic acid bacteria, Lactococcus lactis subsp. lactis, Lactobacillus delbrueckii and Lactobacillus plantarum species isolated from yoghurt sold in different local markets of Chittagong region in Bangladesh were examined by morphological characteristics and biochemical tests. In the preliminary test, all isolates were grown well at acidic pH (pH 3-5) while the optimum growth temperature was 37°C and better growth was observed in the presence of 1-8% NaCl concentrations. In addition, the selected isolates were able to survive up to 3% bile salt concentrations while the best tolerance was at 1% bile salt. The strains successfully inhibited the growth of common pathogenic bacteria likely Escherichia coli, Pseudomonas aeruginosa, Salmonella Paratyphi, Staphylococcus aureus and Bacillus subtilis examined by in vitro growth inhibition test. Most of the isolated strains exhibited resistance pattern against ten commonly used antibiotics in foodborne illness in the country. However, the strains in yoghurt sold at Chittagong city have ideal probiotic characteristics and this fermented dairy product could be a potential source of human probiotic bacteria.

Fermentation is known as a method that improves the nutritional value of foods in addition to preserving them. Various traditionally produced fermented foods such as yogurt, kefir, kombucha, some cheeses, sausages and pickles have probiotic potential. Hence, consumption of fermented foods plays an important role in modulating of gut microbiota and supplying positive effects on health. With the help of beneficial microorganisms, the intestinal barrier can be improved which induces the activity of the immune cells associated to the gut. In recent years, probiotics have been used in foods in order to produce functional foods that have the potential to improve gastrointestinal health. It is known that intestinal microbiota and probiotics can interact in immune system and these interactions provide positive health effects like reducing risk of hypertension, improving gut microbiota, regulating immune system, preventing diabetes, allergies and diarrhea. In this paper, fermented foods having probiotic potential and the effects of consuming these foods on the immune system are revised.

There is an increasing trend for development of alternatives to deliver probiotics with non-dairy products. Fruit juices have become one of main food products for delivery of probiotics. The availability of different fruit juice types, their fresh and healthy perception from the consumer's side and demand for plant-based products increase attention to fortification of fruit juices with probiotics. Yet, development of probiotic fruit juices is still an emerging area for the functional food concept. Probiotic juices can be developed by using both probiotic Lactobacillus and Bifidobacterium and their viability can be strain specific as well dependent on the utilized fruits. The transformation of the fruit components can play roles for the improvement of the potential health promoting functions of fruit juices which should be well-characterized. The insufficient viability of probiotic strains during shelf-life of fruit juices is one of the main challenges and efficient and relatively cheap encapsulation techniques should be developed to ensure their viability. In this study, recent achievements and developments to produce probiotic fruit juices have been summarized. Also, potential role of probiotic fortification for the health promoting functions of fruit juices related to probiotic metabolism has been discussed. Finally, strategies to increase the viability of distinct probiotics have been discussed.