Yulian Chen

Debaryomyces and Bacillus are dominant microbial groups in dark teas such as Fu brick tea and play a key role in the formation of their characteristic flavors. In this study, dark tea infusion was co-fermented using Debaryomyces hansenii and Bacillus subtilis isolated from Fu brick tea. A comprehensive analytical approach was employed, including headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME-GC-MS), high-performance liquid chromatography (HPLC), relative odor activity value (rOAV) analysis, molecular docking, and sensory evaluation, to systematically investigate changes in tea polyphenols, catechins profile, and volatile organic compounds (VOCs) during fermentation and to identify key aroma-active substances. The results demonstrated that co-fermentation significantly reduced the contents of total tea polyphenols (by 45.12%) and ester catechins (by 92.63%), while promoting the accumulation of gallic acid. Volatile component analysis revealed that the co-fermentation integrated the aromatic profiles of both monocultures, retaining key aroma compounds such as linalool and nonanal, and introducing unique constituents such as α-cadinol, collectively forming a complex aroma profile dominated by floral, fruity, and woody notes. Molecular docking analysis confirmed strong binding affinity between key floral aroma compounds (e.g., linalool) and the olfactory receptor OR1A1. Sensory evaluation indicated that the co-fermented tea infusion achieved the highest overall scores in aroma and taste, exhibiting a mellow and sweet aftertaste along with a pure, bright, and refreshing aroma, highlighting the synergistic effect of co-culture fermentation. This study reveals that co-fermentation with D. hansenii and B. subtilis can effectively improve the flavor quality of dark tea infusion through synergistic regulation of polyphenol transformation and volatile compounds formation, providing a controllable bioprocess for the development of flavor-oriented, quality-stable fermented tea beverages with potential for industrial scale-up and commercial application.

Introduction: This study aimed to investigate the regulatory effects of mulberry leaf flavonoids and carnosic acid complex (MCC) on the growth performance, intestinal morphology, antioxidant, and p38 MAPK/Nrf2 pathway in broilers.Methods: A total of 256 healthy 8-day-old female yellow-feathered broilers were randomly divided into 4 equal groups: a control group (CON) fed a basal diet, an antibiotic group (CTC) supplemented with 50 mg/kg chlortetracycline, and two experimental groups (MCC75, MCC150) fed basal diets with 75 mg/kg and 150 mg/kg of MCC, respectively. The experiment lasted for 56 days, with days 1–28 designated as the initial phase and days 29–56 as the growth phase.Results: The results on the growth performance showed that diets supplemented with MCC and CTC decreased the feed-to-gain ratio (F/G), diarrhea rate, and death rate, while significantly increasing the average daily weight gain (ADG) (p < 0.05). Specifically, the MCC150 group enhanced intestinal health, indicated by reduced crypt depth and increased villus height-to-crypt depth ratio (V/C) as well as amylase activity in the jejunum. Both the MCC and CTC groups exhibited increased villus height and V/C ratio in the ileal (p < 0.05). Additionally, all treated groups showed elevated serum total antioxidant capacity (T-AOC), and significant increases in catalase (CAT) and glutathione peroxidase (GSH-Px) activities were observed in both the MCC150 and CTC groups. Molecular analysis revealed an upregulation of the jejunal mRNA expression levels of PGC-1α, Nrf2, and Keap1 in the MCC and CTC groups, as well as an upregulation of ileum mRNA expression levels of P38, PGC-1α, Nrf2, and Keap1 in the MCC150 group, suggesting activation of the p38-MAPK/Nrf2 pathway.Discussion: These findings indicate that dietary supplementation with MCC, particularly at a dosage of 150 mg/kg, may serve as a viable antibiotic alternative, enhancing growth performance, intestinal health, and antioxidant capacity in broilers by regulating the p38-MAPK/Nrf2 pathway.