Valorization of wine industry by-products as a flavoring agent in water kefir: microbiological viability and functional properties

Introduction This study developed a functional water kefir beverage flavored with grape pomace ( Vitis labrusca .) and evaluated its physicochemical, microbiological, and sensory properties, alongside its functional effects in a Caenorhabditis elegans model. Methods Four treatments were tested: 0% (KC), 25% (K25), 37.5% (K37.5), and 50% (K50) pomace addition. Results Anthocyanin and phenolic contents were dose-dependent, peaking in K50 (33.56 mg L −1 and 4.31 mg g −1 , respectively). During 21 days of refrigerated storage, a decrease in reducing sugars, pH (4.3 to 3.5), and a concomitant increase in acidity (up to 6.60%) were observed, reflecting continuous microbial metabolic activity. Due to excessive acidity and residual taste, K37.5 and K50 were deemed unfeasible. Consequently, K25 was selected for biological and sensory validation. In K25, yeast and acetic acid bacteria (AAB) maintained high viability (10 7 CFU mL −1 ), whereas lactic acid bacteria (LAB) remained below 10 5 CFU mL −1 due to the selective pressure of the grape pomace. K25 achieved a sensory acceptance index of 76.11% and a 65% purchase intention. Discussion These results indicate that water kefir flavored with 25% grape pomace is a viable probiotic carrier rich in bioactive compounds with promising sensory appeal.