Recovery and valorization of food industry by-products through the application of Olea europaea L. leaves in kombucha tea manufacturing.

The present study investigated the application of a sustainable production model to the manufacturing technology of kombucha. In order to comply with the principles of circular economy, a newly-formulated beverage, obtained through the use of olive mill by-products as a fermentation substrate, was examined. The total polyphenol content, antioxidant activity and sensory profile of the final product was analyzed with the intention of evaluating the bioactive and sensory contribution made by olive leaves, when used in substitution of tea for kombucha fermentation. The initial level of oleuropein (394.7 mg/L) obtained in the olive leaves extract did not inhibit the natural fermentation process of Symbiotic Culture of Bacteria and Yeast (SCOBY). The addition of increasing percentages of the by-product during the fermentation produced several kombucha samples rich in secoiridoid bioactive compounds with a concentration of oleuropein and hydroxytyrosol ranged from 306.4 mg/L to 91.2 mg/L and from 29.0 mg/L to 9.3 mg/L, respectively. Since tea stands out as one of the main cost items in kombucha tea manufacturing, this study demonstrated that the use of olive leaves, as a polyphenol-rich substrate, may represent a viable strategy to valorize the agro-industrial waste, reduce production costs, preserve the antioxidant properties of kombucha and enrich its sensory profile.