Bioactivity properties of fermented beverage made from various fruits after in vitro gastrointestinal digestion

Objective: This study aimed to develop a functional fermented beverage using whole forms of nine different fruits and to evaluate its bioactive properties under simulated gastrointestinal digestion. Material and Methods: A mixture of pomegranate, sour cherry, red and green apples, orange, lemon, pear, strawberry, nectarine, and raisins was fermented with kefir culture under controlled conditions. The beverage was evaluated for physicochemical properties, bioactive compound content, and biological activities, including antioxidant, antidiabetic, and antihypertensive effects. Results: After fermentation, the final product had a pH of 3.85, a soluble solids content of 5.4°Brix, and malic acid content of 0.73 g/100 mL. The beverage was analyzed for its content of total phenolics, total flavonoids, anthocyanins, and ascorbic acid, yielding results of 620 mg CE/L, 230 mg CE/L, 38 mg/L, and 14 mg/L, respectively. After undergoing in vitro digestion, the DPPH and ABTS radical scavenging activities were found to be 480 and 570 µmol TEAC/mL, respectively, indicating that the antioxidant potential was preserved. The ACE inhibition reached 32.1% following digestion, suggesting moderate antihypertensive activity. Moreover, the inhibitions of α-amylase and α-glucosidase indicated moderate antidiabetic activity. Conclusion: The data obtained indicate that fermentation of whole fruits with kefir culture can produce a bioactive-rich beverage that remains functionally active after digestion. This beverage, without heat treatment, added sugar, or juice extraction, has been evaluated as a functional alternative to traditional fruit-based beverages.