COMPARATIVE EVALUATION OF THE PHYSICOCHEMICAL PROPERTIES AND PHENOLIC PROFILE OF GREEN TEA KOMBUCHA ENRICHED WITH GRAPE PEEL EXTRACT AND COMMERCIAL GRAPE KOMBUCHAS

Kombucha is a fermented beverage recognized for its bioactive properties. The addition of natural ingredients rich in phenolic compounds is a promising strategy to enhance its bioactive potential. This study evaluated the phenolic profile and physicochemical properties of a green tea kombucha enriched with aqueous grape peel extract and commercial grape-flavored kombuchas. Green tea kombucha was produced under controlled fermentation conditions, using an infusion time/temperature combination of 70 °C for 1 min. An aqueous grape peel extract (Vitis vinifera L.) was prepared at a 1:10 dilution and added at a proportion of 15% (v/v), resulting in the enriched kombucha (K0). Three commercial grape-flavored kombuchas (K1, K2 and K3) were purchased locally. The beverages were analyzed for total acidity, volatile acidity, pH, total phenolic content, and phenolic profile by LC-MS/HPLC. Differences in pH were observed among the samples (K0 = 3.59 ± 0.03, K1 = 3.48 ± 0.03, K2 = 3.43 ± 0.02, and K3 = 3.67 ± 0.01). Commercial kombuchas exhibited higher total acidity (0.431–0.482 g/100 mL acetic acid), whereas K0 exhibited higher volatile acidity (23.62 ± 1.78 mEq/L). These differences likely reflect variations in raw materials, the production and concentration of organic acids, and/or processing conditions. K0 exhibited the highest total phenolic content (0.651 ± 0.01 mg GAE/mL), indicating that grape peel extract increased the phenolic content compared with the commercial beverages. Higher concentrations of flavan-3-ols were observed in K0, particularly epigallocatechin (37.79 ± 4.49 mg/L), procyanidin B2 (18.61 ± 0.08 mg/L), epigallocatechin gallate (7.70 ± 2.30 mg/L), and catechin (2.22 ± 0.26 mg/L). In contrast, the commercial kombuchas exhibited higher concentrations of other phenolic compounds, including caftaric acid (K1 = 6.79 ± 0.33; K2 = 8.10 ± 0.39; and K3 = 6.55 ± 0.36 mg/L), gallic acid (K2 = 4.13 ± 0.23 mg/L), and procyanidin A2 (K3 = 26.34 ± 1.76 mg/L), demonstrating distinct phenolic profiles. These results highlight grape peel, an agro-industrial by-product, as a promising bioactive ingredient for kombucha production. It is therefore concluded that the addition of grape peel extract was a distinguishing factor in the phenolic profile compared with the commercial beverages, representing a promising strategy for the development of kombuchas with higher added value and enhanced bioactive potential.

The authors acknowledge the financial support provided by the Coordination for the Improvement of Higher Education Personnel (CAPES), the Research Support Foundation of the State of Minas Gerais (FAPEMIG), and the National Council for Scientific and Technological Development (CNPq).