Mingzheng Huang

Constructing physical entanglement networks is an effective strategy to enhance the mechanical properties of protein-based gels. However, it remains challenging to induce the formation of stable and controllable physical entanglement structures in food-grade natural polymer systems. In this study, fish gelatin (FG) and carboxylated cellulose nanofibers (CNFc) were used as raw materials. The effects of ultrasound pretreatment duration (0-16 min, 360 W, 25 kHz) on the properties of FG-CNFc composite gels were systematically investigated, with the aim of revealing the regulatory mechanism by which ultrasound promotes the formation of gelatin-fiber physical entanglement networks. The results showed that the 12 min ultrasound-pretreated group (GC-U12) exhibited the best overall gel performance. Compared with the non-ultrasonicated group, the GC-U12 group exhibited significantly reduced particle size and markedly enhanced storage modulus. Meanwhile, its melting temperature increased to 36.19 °C, indicating improved thermal stability. In terms of mechanical properties, the tensile strength, toughness, and compressive strength of the GC-U12 group increased by 0.6-fold, 1.2-fold, and 0.3-fold, respectively, relative to the control group. Structural characterization revealed that ultrasound pretreatment induced an increase in β-sheet content of fish gelatin from 36.8% to 47.51%, accompanied by a transformation of the gel network from a loose and porous structure to a dense and uniform one. Stress damage resistance tests demonstrated that after 10 cycles of stress damage, the GC-U12 group exhibited superior thermal stability and crack propagation resistance compared with the GC-U0 group. In summary, moderate ultrasound pretreatment promotes the formation of physical entanglement networks between FG and CNFc, thereby significantly enhancing the mechanical properties and structural stability of the composite gels. This study provides a green and feasible technical pathway for constructing high-performance protein-polysaccharide composite gels.

Understanding how leaf maturity affects the flavor attributes of green tea is crucial for optimizing harvest timing and processing strategies. This study comprehensively characterized the flavor profiles of Fudingdabai green teas at three distinct leaf maturity stages—single bud (FDQSG), one bud + one leaf (FDMJ1G), and one bud + two leaves (FDTC2G)—using a multimodal approach integrating electronic nose, electronic tongue, HS-GC-IMS, relative odor activity value (rOAV) evaluation, and machine learning algorithms. A total of 85 volatile compounds (VOCs) were identified, of which 41 had rOAV > 1. Notably, 2-methylbutanal, 2-ethyl-3,5-dimethylpyrazine, and linalool exhibited extremely high rOAVs (>1000). FDQSG was enriched with LOX (lipoxygenase)-derived fresh, grassy volatiles such as (Z)-3-hexen-1-ol and nonanal. FDMJ1G showed a pronounced accumulation of floral and fruity compounds, especially linalool (rOAV: 7400), while FDTC2G featured Maillard- and phenylalanine-derived volatiles like benzene acetaldehyde and 2,5-dimethylfuran, contributing to roasted and cocoa-like aromas. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis revealed significant enrichment in butanoate metabolism and monoterpenoid biosynthesis. Random forest–SHAP analysis identified 20 key flavor markers, mostly VOCs, that effectively discriminated samples by tenderness grade. ROC–AUC validation further confirmed their diagnostic performance (accuracy ≥ 0.8). These findings provide a scientific basis for flavor-driven harvest management and the quality-oriented grading of Fudingdaibai green tea.

Understanding how leaf tenderness influences flavor attributes in green tea is crucial for optimizing harvest timing and processing strategies. This study comprehensively characterized the flavor profiles of Fudingdabai green teas at three tenderness levels—single bud (FDQSG), one bud + one leaf (FDMJ1G), and one bud + two leaves (FDTC2G)—using a multimodal approach integrating electronic nose, electronic tongue, HS-GC-IMS, relative odor activity value (rOAV) evaluation, and machine learning algorithms. FDQSG was dominated by fresh, grassy, and herbal volatiles such as (Z)-3-hexen-1-ol and nonanal, suggesting active LOX pathways. FDMJ1G showed a metabolic surge in floral compounds, especially linalool (rOAV > 7400), along with minty and fruity notes. FDTC2G featured roasted and cocoa-like aromas due to enhanced Maillard reactions and phenylalanine metabolism. KEGG analysis revealed significant enrichment in butanoate metabolism and monoterpenoid biosynthesis. Random forest–SHAP analysis identified 20 key flavor markers, mostly VOCs, that effectively discriminated samples by tenderness grade. ROC–AUC validation further confirmed their diagnostic performance (accuracy > 0.8). These findings provide a scientific basis for flavor-driven harvest management and the quality-oriented grading of Fudingdaibai green tea.

This study elucidates the adaptive mechanisms of Saccharomyces cerevisiae CZ under octanoic acid stress, revealing concentration-dependent growth inhibition (76% lethality at 800 mg/L) and notable tolerance at 600 mg/L. Initial exposure (≤6 h) showed no growth impairment, but prolonged treatment induced dose-dependent lethality, accompanied by reduced H⁺/K⁺-ATPase activity and elevated malondialdehyde (MDA) levels, indicative of oxidative damage. Transcriptomic profiling of 5665 genes highlighted the predominant downregulation of ribosomal functions (translation, ribosome biogenesis) and amino acid metabolism pathways (e.g., ARO10, ARO9). Strain-specific regulatory dynamics were observed: (1) TPO1-mediated efflux was active at 400 mg/L but absent at 600 mg/L, suggesting compensatory mechanisms under high stress; (2) HTX1-related genes exhibited bidirectional regulation (downregulated at 400 mg/L vs. upregulated at 600 mg/L), reflecting metabolic flexibility; (3) ACC1 downregulation (600 mg/L) and unaltered SFK1 expression contrasted with lipid-remodeling strategies in engineered strains; and (4) PMA2 suppression diverged from literature-reported PMA1 activation, underscoring strain-specific energy reallocation. Suppression of ergosterol biosynthesis and ribosomal genes revealed a trade-off between stress adaptation and biosynthetic processes. These findings reconcile prior contradictions by attributing discrepancies to genetic backgrounds (CZ vs. laboratory/engineered strains) and methodological variations. Unlike strains relying on phospholipid asymmetry or oleic acid overproduction, CZ’s unique tolerance stems from integrated membrane homeostasis (via lipid balance) and metabolic conservation. This work emphasizes the critical role of strain-specific regulatory networks in octanoic acid resistance and provides insights for optimizing yeast robustness through targeted engineering of membrane stability and metabolic adaptability. Future studies should employ multi-omics integration to unravel the dynamic gene regulatory logic underlying these adaptive traits.

The purified yeast strain H4, identified as W. anomalus through morphological, genetic, and phylogenetic analyses, was characterized and compared to a commercial Saccharomyces cerevisiae strain X16. W. anomalus H4 exhibited distinct morphological features. It demonstrated notable tolerance to 11% ethanol, 220 g/L glucose, and 200 mg/L octanoic acid, similar to X16, except for having a lower tolerance to SO₂. Survival analysis under various stress conditions revealed that ethanol and octanoic acid had the most detrimental effects, with 56% cell mortality at 13% ethanol and 400 mg/L octanoic acid. Transcriptomic analysis under octanoic acid stress showed that at 200 mg/L, 3369 differentially expressed genes (DEGs) were induced, with 1609 being upregulated and 1760 downregulated, indicating broad transcriptional reprogramming. At 400 mg/L, only 130 DEGs were detected, suggesting a more limited response. KEGG pathway analysis indicated that most DEGs at 200 mg/L were associated with the “ribosome” and “proteasome” pathways, reflecting disruptions in protein synthesis and turnover. At 400 mg/L, the DEGs were primarily related to “DNA replication” and “pyruvate metabolism”. These findings highlight the adaptive mechanisms of W. anomalus H4 to environmental stresses, particularly octanoic acid, and its potential for use in brewing and fermentation processes.

Aroma plays a pivotal role in defining tea quality and distinctiveness, and tea producers have often observed that specific drought conditions are closely associated with the formation and accumulation of characteristic aroma compounds in tea leaves. However, there is still limited understanding of the differential strategies employed by various tea cultivars in response to drought stress for the accumulation of key volatile aroma compounds in fresh tea leaves, as well as the associated metabolic pathways involved in aroma formation. In this study, two widely cultivated tea cultivars in China, Fuding Dabai (FD) and Wuniuzao (WNZ), were examined to assess the impact of mild field drought stress on the composition and accumulation of key volatile aroma compounds in fresh leaves using headspace gas chromatography–ion mobility spectrometry (HS-GC-IMS) and headspace solid phase micro-extraction gas chromatography–mass spectrometry (HS-SPME-GC-MS) technologies. Results revealed that drought stress led to a substantial increase in the diversity of volatile compounds (VOCs) in FD, while WNZ exhibited a notable rise in low-threshold VOC concentrations, amplifying sweet, floral, fruity, and earthy aroma profiles in post-drought fresh leaves. Through partial least squares discriminant analysis (PLS-DA) of HS-GC-IMS and HS-SPME-GC-MS data, integrating variable importance projection (VIP) scores and odor activity values (OAVs) above 1, 9, and 13, key odor-active compounds were identified as potential markers distinguishing the drought responses in the two cultivars. These compounds serve as crucial indicators of the aromatic profile shifts induced by drought, providing insights into the differential metabolic strategies of the cultivars. Additionally, KEGG enrichment analysis revealed 12 metabolic pathways, such as terpenoid biosynthesis, fatty acid synthesis, cutin, suberine, and wax biosynthesis, and phenylalanine metabolism, which may play crucial roles in the formation and accumulation of VOCs in tea leaves under drought stress. These findings provide a comprehensive framework for understanding the cultivar-specific mechanisms of aroma formation and accumulation in tea leaves under mild drought conditions.