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Many studies have been published lately verifying the probiotic character of kefir grains. Most of them focused on the benefits to human health through the consumption of fermented food with kefir grains. However, the challenge is to characterize and isolate specific probiotic microorganisms involved in the kefir microbiota. The main reason for this is that the food industry prefers to apply isolated probiotic microorganisms from kefir grains rather than kefir grains in order to produce respective fermented products with added value. Thus, modern molecular techniques such as polymerase chain reaction (PCR)-based amplification, new generation sequencing (NGS) or denaturing gradient gel electrophoresis (DGGE) analyses have been applied. Furthermore, this review emphasizes the latest outcomes regarding the health benefits of the consumption of foods fermented with kefir grains and particularly the isolation of microorganisms from kefir grains worldwide, some of them exhibiting probiotic properties.

Fermentation of pomegranate juice as single or mixed substrate with orange juice, without addition of extra nutrients, using kefir grains is proposed. Sugar consumption and ethanol production were monitored during fermentation, while the formation of lactic acid and the survival of lactic acid bacteria were determined during storage at 4 oC for 4 weeks. The results showed that addition of orange juice improved the ability of kefir grains to ferment pomegranate juice, and increased the survival rates of lactic acid bacteria (LAB) contained in kefir grains during storage. Specifically, 75% cells survived (6.48 log cfu/ml) after 4 weeks of storage in the fermented mixed substrate (24% in plain pomegranate juice). Lactic acid formation was observed in all products, especially in the mixed substrate (1.3-1.9 g/l), indicating metabolic activity during storage. In all cases a low decrease of pH was observed. The results show the possibility to produce low-alcoholic nutritious fruit beverages with potential antioxidant (due to pomegranate constituents) and probiotic properties (due to the probiotic species present in kefir grains). In addition sensorial tests that were conducted showed the consumers acceptance for all the fermented juices.

Over the last decades there is an increasing demand for consumption of functional foods which claim to provide health benefits. These days the majority of probiotic products are well established by the form of dairy products. However lactose intolerance, cholesterol substances and the increase of vegetarianism lead the research for commercial production, to find new, non-dairy, suitable media for probiotic products. Therefore, a preliminary research has been conducted regarding fermentation of Cornus mas L. juice with one potential probiotic microorganism (Lactobacillus paracasei K5) and one probiotic Lactobacillus plantarum ATCC14917 for functional beverage production. The viability of the aforementioned microorganisms was monitored during fermentation in different pH values, at 0 min, 24 h and during storage (5 oC) for 1,2,3 and 4 weeks. The results showed that Lactobacillus.plantarum ATCC 14917 and Lactobacillus paracasei K5 retained their viability at high levels (at least 6 log cfu/ml) under storage at 5 oC for 4 weeks, which is considered as an important prerequisite for the characterization of the product as probiotic. Likewise the outcome showed that it is likely to produce a potential functional Cornus mas L. beverage with antioxidant activity (due to Cornus mas L. ingredients) and potential probiotic activities (due to the potential probiotic strains).

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