Biotransformation of apple juice by water kefir grains: A synergistic enhancement of flavor complexity and health-promoting functions.

Abstract

This study evaluated the biotransformation of apple juice by water kefir grains (WKG) to develop a functional beverage with enhanced sensory and metabolic regulatory properties. Flavor characterization using HS-GC-IMS and HS-SPME-GC-MS revealed that apple-based water kefir (WK-A) possessed a more complex volatile profile than brown sugar-based water kefir (WK-B). WK-A was characterized by elevated levels of fruity esters, particularly ethyl hexanoate and isoamyl acetate, potentially linked to branched-chain amino acid and pyruvate metabolism. In vivo results demonstrated that WK-A intervention significantly attenuated hyperlipidemia and hepatic steatosis in high-fat diet-fed mice. These physiological effects were associated with increased colonic short-chain fatty acid levels (primarily acetate) and selective modulation of the gut microbiota, accompanied by enrichment of genera associated with metabolic regulation, including Acetatifactor and Dubosiella. Overall, under the present fermentation conditions, apple juice provided a favorable matrix for WKG fermentation, yielding a beverage with enhanced flavor complexity and metabolic regulatory potential.