The purpose of diploma work was to present an overview of research involving the fermentation of non-dairy substrates with kefir grains, mainly fruit juices. Among consumers are increasingly popular products with positive health effects, high levels of functional components and good sensory properties. Many functional products also have probiotic properties, but most are dairy based, which can be problematic for some consumers due to lactose intolerance, milk protein allergy, high fat and cholesterol content and vegan diet. Fruit juices can serve as a good substrate for fermentation with kefir grains, which are composed of lactic acid bacteria, yeast and acetic acid bacteria, and carry out combined fermentation. After reviewing literature it was established that pomegranate juice, other fruit juices and mixed whey substrates are most commonly used as substrate. During fermentation the basic substrate is improved, which is the main purpose of fermentation of alternative substrates. The fermented beverage is improved in both functional and sensory terms, as it becomes more refreshing due to the formation of CO2 and changes of organic acids ratio. It also lowers the sugar content. The consistency, color, smell and taste also change. Typical changes can be observed in the lowering of the pH value, the increase of the mass of kefir grains, the increase of the lactic acid concentration, as well as the increase of antioxidant activity of the beverage. Kefir grains are characterized by their antimicrobial effect, and kefiran also has antibacterial, antifungal and antitumor effects. The composition of the fermented juice is altered, which can be attributed to both changes in the substrate and the microorganisms in kefir grains themselves.
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