Flavor modulation of fermented degummed coffee beans by ultrasound and ultra-high pressure: metabolomic and volatile profiles

This study established an process in which physical pretreatments were applied after microbial fermentation and degumming, and evaluated how these treatments affected green coffee bean metabolite profiles and roasted-bean flavor. Relative to fermented green coffee beans without physical pretreatment (GF), ultrasound-pretreated fermented green coffee beans (GUS) and ultra-high-pressure-pretreated fermented green coffee beans (GUHP) showed significantly increased extractable contents of total sugars, reducing sugars, polyphenols, and flavonoids ( P < 0.05). Metabolomic analysis identified 144 and 656 differential metabolites in GUS and GUHP, respectively, with amino acid metabolism and α-linolenic acid metabolism among the commonly enriched pathways. Compared with green beans, roasting increased the number of compounds of pyrazines and ketones by 13% and 16%, respectively. The two physical pretreatments were associated with different patterns of volatile composition in the roasted beans. GUS showed higher relative abundances of several furans and phenols, whereas GUHP showed greater changes in aldehydes, ketones, acids, and specific pyrazines. The three roasted groups had similar overall cupping scores but differed in the relative distribution of individual sensory attributes. These two physical pretreatments therefore produced different flavor-related compositional and sensory tendencies. Correlation analysis identified associations between volatile compounds and metabolites related to shikimate/phenylpropanoid metabolism, lipid metabolism, and amino acid derivatives. This study provides a theoretical basis for the precise modulation of roasted coffee flavor through the application of microbial fermentation and physical field pretreatment technologies.