Characterization of functional water kefir beverages enriched with different fruit juices and lyophilized apricot kernel extract and determination of gamma-aminobutyric acid content

This study investigated the changes in chemical, microbiological, sensory, and bioactive properties of water kefir beverages produced using different fruit juices (mulberry, apricot, cherry, and grape) and fermented lyophilized apricot kernel milk (L-AKM) during storage.Water kefir beverages were produced using the conventional fermentation method, thermosonication was applied to the fruit juices, and samples were analyzed on days 1, 7, 14, and 21 of storage. Bioaccessibility assessments were performed on the samples in terms of pH, total dry matter, water-soluble dry matter, color, viscosity, organic acid and sugar profile, ethyl alcohol content, microbial counts (total viable count, lactic acid bacteria, and mold-yeast), volatile compounds, free amino acid and GABA profile after in vitro digestion, total phenolic content, and antioxidant capacity (DPPH and CUPRAC). In addition, the color, appearance, consistency, taste-aroma, odor, and overall acceptability parameters of the products were determined by sensory analysis. The results showed that the addition of fruit and the use of L-AKM significantly affected the fermentation dynamics and the functional component profiles of the products. The increase in antioxidant capacity values after in vitro digestion revealed that the bioaccessibility of the products increased with the digestion process. Sensory analysis results showed that water kefir beverages exhibited high acceptability on days 1 and 7 of storage, but a decrease in sensory scores occurred after day 14 due to increased fermentation and disruption in sugar-acid balance. While control samples received higher sensory scores, samples with added L-AKM stood out in terms of functional properties. In conclusion, the research findings showed that the apricot sample had the highest GABA content (225.79±14.53 mg/100 mL), maintained its functional quality by preserving probiotic viability during storage, and remained within acceptable limits in terms of sensory perception.