Aroma evolution in lychee Juice: Distinct effects of water kefir grains and liquid cultures on volatile profiles

Water kefir, a traditional beverage made by fermenting sugary solutions or fruit juices with kefir grains, was consumed worldwide. This study employed gas chromatography-mass spectrometry (GC-MS), and gas chromatography-ion mobility spectrometry (GC-IMS) to analyze the volatile profiles of lychee kefir beverages. 134 volatile compounds were found in the lychee kefir juice, with alcohols, esters, and ketones increased and aldehydes decreased. Notably, 26 distinct volatiles were found to distinguish lychee kefir juices. The predominant aromas were characterized as floral, fruity, and alcoholic, with key volatiles including rose oxide, geraniol, linalool, and citronellol. Multiple volatiles were annotated in KEGG and involved in various metabolic pathways to form the unique aroma profiles. The microbiota community in lychee water kefir shifted to a lactobacillus system after fermentation. The integration of GC-MS and GC-IMS methodologies provides a robust framework for understanding the aroma characteristics of lychee kefir beverages. • Water kefir fermentation improved the aromatic characteristics of lychee juice. • OAV analysis identified 26 key VOCs, enhanced floral, citrus, and green notes • BK method increased rose oxide and citronellol but reduced alcohols compared to TK. • KEGG analysis revealed the metabolic pathways shaping lychee kefir's aroma.