Fermentation Improves the Antioxidant Activity, Flavor Components and Metabolic Characteristics of Coffee Pulp Beverage

This study aimed to evaluate the impact of four strains, Bifidobacterium longum BL11, Streptococcus thermophilus LB42, Lacticaseibacillus casei LC15, and Lactiplantibacillus plantarum XJ25, on the antioxidant activity, flavor components and metabolic characteristics of fermented coffee pulp beverage (CPB). Results indicated that the antioxidant activities were remarkably enhanced in the fermented CPB samples (p < 0.05). A total of 103 volatile compounds (VOCs) were detected by HS-SPME-GC-MS and GC-IMS, with 37 types of VOCs newly generated after fermentation, including esters, alcohols and ketones, thereby enhancing the flavor quality of CPB. In addition, a total of 334 differential non-volatile metabolites covering 20 subclasses were obtained in all CPB samples, such as D-tagatose, glyceraldehyde, isorhynchophylline and pyruvic acid, which showed remarkably increased levels after fermentation (p < 0.05). Organic acids, amino acids and derivatives were the two major classes of differential metabolites. The CPB samples had a different flavor profile after fermentation, while the group of Lactiplantibacillus plantarum showed the highest overall acceptability. These findings provide a systematic comparison of single-strain fermentation effects on VOCs and non-volatile metabolites in CPB samples, promoting its high-value utilization in innovative food applications.