Preparation and evaluation of liquorice (Glycyrrhiza uralensis) and ginger (Zingiber officinale) kombucha beverage based on antioxidant capacities, phenolic compounds and sensory qualities

Kombucha is a well-known tea-based fermented drink that contains various bioactive compounds with potential bioactivities. In addition to traditional Camellia sinensis tea, preparation of kombucha using alternative raw material has attracted increasing attention to obtain significant health benefits and good sensory properties. In this study, liquorice and ginger were selected as alternative raw materials for the preparation of kombucha beverages due to their extensive health benefits. Moreover, the effects of fermentation with or without residues on antioxidant activities and phenolic contents of liquorice and ginger kombucha beverages at different fermentation times were examined and compared using the ferric-reducing antioxidant power assay, Trolox equivalent antioxidant capacity assay, Folin-Ciocalteu method, and high-performance liquid chromatography. The results found that kombucha beverages based on liquorice and ginger showed strong antioxidant capacities and high phenolic contents. Fermentation with liquorice residues significantly improved the antioxidant capacities (maximum 2.41 times) and phenolic contents (maximum 3.88 times) of liquorice kombucha without influencing the sensory qualities when compared with fermentation without residues. However, fermentation with ginger residues did not effectively enhance the antioxidant capacities and phenolic contents. Moreover, it could reduce the sensory properties of ginger kombucha. In general, liquorice is well-suited for producing kombucha with residues, while ginger is more suitable for making kombucha without residues. These kombucha beverages might be used for the prevention and management of several oxidative stress-related diseases. This study expands the options of raw materials for producing novel and functional kombucha beverages.