Kombucha microbial starter with enhanced production of antioxidant compounds and invertase

The beneficial effects of antioxidant production activity during kombucha tea fermentation elevate the nutritional values of this product. The present study aimed to enhance antioxidant properties and invertase activity in kombucha tea and investigate the synergistic effects of both properties. Following preparation of kombucha solution, the Plackett-Burman design was used for determination of factors affecting the antioxidant and invertase activities in the product. Samples were collected from the fermenting solution on days 0, 7, 10 and 14. The total phenol content of samples was determined using the Folin-Ciocalteau method. In addition, antioxidant activity was measured using cupric ion reducing antioxidant capacity and DPPH (1,1-diphenyl 2-picrylhydrazyl) radical inhibition method. Invertase activity was determined in the samples using sigma protocol. After screening design, the dried starter containing the kombucha tea microbial consortium optimally produced using the vacuum freeze drying method. The results showed that pH of kombucha reduced as the fermentation time passed. Antioxidant activity increased in most samples over time, so that the average antioxidant activity was in the range of 0.99-224.86 nm of trolox equivalents/ml during fermentation. Invertase activity also increased in the most samples during fermentation and showed the range of 50.85-115.5 u/ml. By increasing the activity of invertase, the antioxidant activity of kombucha solution increased. The results of present study proposed that by induction of invertase activity in kombucha drink its effectiveness that resulted by antioxidant properties would be promoted and the drink will be more useful for diabetic patients.