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.

Recently the demand for functional food components such as prebiotics, probiotics, and phenolic compounds are increased. Nowadays, β-glucan, dietary fiber, and biologically active natural polysaccharide, exhibit properties like a prebiotic effect and immune system support. Furthermore, clinical studies have shown that daily intake of 250-500 mg β-glucan has several benefits on the immune system, showing low glycemic index, antimicrobial and anti-inflammatory properties. It is a polysaccharide composed of D-glucose monomers connected with β-glycoside bonds, found in natural sources like yeast (Saccharomyces cerevisiae), some edible mushrooms, algae, and cereal grains. β-Glucan is more resistant and preserves its stability during food processing technologies (drying, freezing, etc.). Especially, β-glucan originated from baker's yeast (S. cerevisiae) has many immunostimulatory properties, such as hypoglycemic, anti-inflammatory, immune-modulatory, antioxidant, and anticancer activities. Also, the utilization of β-glucan in the food industry has increased regarding to their techno-functional properties like gelation, viscosity, solubility, and encapsulating agent. Therefore, this review highlights recently published research results on the functional properties, health benefits and clinical studies, the effects on the interaction with the other food compounds, and the potential food applications of β-glucans.