This study employed headspace solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME-GC-MS) and liquid chromatography–mass spectrometry (LC-MS) for non-targeted metabolomics analyses to examine the impact of mixed fermentation with various lactic acid bacteria (LAB) on the flavor compounds and metabolites of peach and apricot mixed juice (PAMJ), specifically focusing on the alterations of volatile compounds and non-volatile metabolites, as well as their metabolic pathways during the fermentation process. A total of 185 volatiles were identified using HS-SPME-GC-MS analysis, revealing significant differential metabolites, including eugenol, benzaldehyde, and γ-decalactone etc. The results indicated that lactic fermentation significantly enhanced the overall flavor of the juice toward the end of the fermentation process. In the interim, untargeted metabolomics utilizing LC-MS identified 1846 divergent metabolites, with 564 exhibiting up-regulation and 1282 demonstrating down-regulation. The metabolic pathway study performed by the Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed significant changes in the metabolic levels of amino acids and saccharides after the lactic fermentation of PAMJ. Primarily associated with amino acid metabolism and starch and sucrose metabolism pathways. This work establishes a theoretical foundation for advancing fermented fruit juices with superior quality.

Fruit vinegar is typically produced through a two-stage deep liquid fermentation involving alcohol fermentation (Saccharomyces cerevisiae) and acetic acid fermentation (Acetobacter pasteurianus). In order to enhance the flavor and texture of sea buckthorn fruit vinegar, Lactobacillus fermentum was introduced into the alcoholic fermentation stage. At the end of fermentation, the total acid and acetic acid of sea buckthorn (Hippophae rhamnoides L.) fruit vinegar were both enhanced compared with sea buckthorn vinegar brewed through the traditional liquid fermentation method, and in terms of the main active ingredients, the total flavonoid content was slightly enhanced. Non-targeted metabolomics (LC-MS) was used to characterize the characteristic metabolite profiles during the fermentation process. A total of 55 differential metabolites, including organic acids, flavonoids, and amino acids, were identified, and the contents of citric acid, malic acid, and manganic acid, which are the sources of the irritating taste of sea buckthorn berry vinegar, were significantly reduced. In addition, the co-fermentation of Lactobacillus fermentum promoted both glycolysis and the TCA cycle and also led to a significant up-regulation of aromatic metabolites, such as ethyl acetate, ethyl lactate, and ethyl caproate. These results will provide new information on the dynamics of the characterized metabolites during the fermentation of sea buckthorn fruit vinegar.

The substantial quantity of discarded tomato pomace (TP) results in the waste of valuable resources. This study utilizes these tomato by-products by mixing them with water in a specific proportion and fermenting the mixture in two stages: first with yeast, and then with lactic acid bacteria. The most suitable microbial strains for TP fermentation were identified by evaluating parameters such as peptide content, degree of hydrolysis, and gel electrophoresis analysis. Subsequently, tomato pomace peptides (TPPs) were separated into peptides of different molecular weights using ultrafiltration. The IC₅₀ values, ACE inhibitory activities, and in vitro stability of these peptides were compared, and their secondary structures and microstructures were characterized. The results indicated that the soluble protein concentration increased from 26.25 mg/g to 39.03 mg/g after 32 h of fermentation with strain RV171. After an additional 32 h of fermentation with Bifidobacterium thermophilum, the peptide content reached 49.18 ± 0.43%. SDS-PAGE gel electrophoresis showed that the TPP molecular weights were predominantly below 10 kDa. The IC₅₀ results demonstrated that fractions with smaller molecular weights exhibited greater ACE inhibitory activities. Structural analysis confirmed that the TP hydrolysate was indeed a peptide.