Fermentation of sugared tea with a symbiotic culture of acetic acid bacteria and yeast (tea fungus) yields kombucha tea which is consumed worldwide for its refreshing and beneficial properties on human health. Important progress has been made in the past decade concerning research findings on kombucha tea and reports claiming that drinking kombucha can prevent various types of cancer and cardiovascular diseases, promote liver functions, and stimulate the immune system. Considering the widespread reports on kombucha, we recognized the need to review and update the research conducted in relation to kombucha tea, its products and tea fungus. Existing reports have suggested that the protective effects of kombucha tea are as good as those of black tea, however, more studies on kombucha tea and its composition are needed before final conclusions can be made.

The antioxidant activity of organic extracts of eight fungal species, Ganoderma lucidum, Ganoderma applanatum, Meripilus giganteus, Laetiporus sulphureus, Flammulina velutipes, Coriolus versicolor, Pleurotus ostreatus and Panus tigrinus, was evaluated for free radical (DPPH· and OH·) scavenging capacity and an effect on lipid peroxidation, and the antibacterial activity was tested by the agar well diffusion method. The highest DPPH· scavenging activity was found in the methanol extract of G. applanatum (12.5 μg/mL, 82.80%) and the chloroform extract of G. lucidum (510.2 μg/mL, 69.12%). The same extracts also showed the highest LP inhibition (91.83%, 85.09%) at 500 μg/mL, while the methanol extracts of G. applanatum and L. sulphureus showed the highest scavenging effect on OH· radicals (68.47%, 57.06%, respectively) at 400 μg/mL. A strong antibacterial activity against Gram-positive bacteria was also manifested. The antioxidative potencies correlated generally with the total phenol content (0.19-9.98 mg/g). The HPLC determination showed that the majority of analysed species contained gallic and protocatechic acids. Consequently, these fungi are shown to be potential sources of antioxidative and antibacterial agents.

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This paper investigates the antioxidant activity of fermented milk products obtained by kombucha fermentation. Two starter cultures were used as follows: starter obtained after kombucha fermentation on sweetened stinging nettle extract; as well as starter obtained after kombucha fermentation on sweetened winter savory extract. The starters were added to milk with 0.8, 1.6 and 2.8% milk fat. Fermentation was carried out at 37, 40 and 43oC and stopped when the pH reached 4.5. Antioxidant activity to hydroxyl and DPPH radicals was monitored using response surface methodology. Kombucha fermented milk products with stinging nettle (KSN) and with winter savory (KWS) showed the same antioxidant response to hydroxyl and different response to DPPH radicals. Synergetic effect of milk fat and fermentation temperature to antioxidant activity to hydroxyl radicals for both types of kombucha fermented milk products (KSN and KWS) was established. Optimum processing conditions in term of antioxidant activity are: milk fat around 2.8% and process temperature around 41 and 43°C for KSN and KWS respectively