Abstract:To investigate the flavor sensory characteristics of Fu brick tea, a quantitative descriptive analysis (QDA) was used to study it. The flavor wheel of Fu brick tea was constructed with 20 categories for aroma and taste, comprising a total of 37 descriptors. Different intensities of quantitative reference samples were established for 16 typical descriptors, and the vocabulary for quantitatively describing the sensory characteristics of Fu brick tea was established. The main sensory characteristic descriptors were selected by M value and variance analysis combined with multivariate statistical analysis including six aroma descriptors, i.e., stale, woody, floral, sweet, smoky and fermented, and five taste descriptors, i.e., mellow and normal, bitter, astringent, sweet and sour. The sensory quantitative description of Fu brick tea using the selected descriptors can be used to summarize the basic sensory characteristics of Fu brick tea and effectively differentiate the differences of flavor sensory characteristics among them.

Abstract:The present study employed homologous cloning to obtain the chitosanase gene from Bacillus subtilis, and prepared recombinant Bacillus subtilis chitosanase(CsnBh46) through heterologous expression. The recombinant CsnBh46 enzyme was characterized to determine its enzymatic properties. The full-length recombinant CsnBh46 consists of 278 amino acids, and its three-dimensional structure reveals it is divided into upper and lower domains, each containing nine α-helices and two β-strands. The maximum enzymatic activity of recombinant CsnBh46 expressed in Pichia pastoris X33 was 6 375 U/mL, with a total protein mass concentration of 4.3 g/L. The optimal reaction pH and temperature for purified recombinant CsnBh46 were 6.0 and 60 ℃, respectively. Meanwhile, CsnBh46 was activated by Mn²⁺, Ca2+ ^{and Mg2+. The favorite substrate for recombinant CsnBh46 was colloidal chitosan with 95% degree of deacetylation. Furthermore, recombinant CsnBh46 efficiently hydrolyzed colloidal chitosan and allowed for the targeted preparation of chitosan oligosaccharides with different degrees of polymerization based on reaction time. This study provides a foundation for the industrial application of CsnBh46.}

Abstract:In order to obtain lactic acid bacteria with high bacteriostatic property, Lactobacillus plantarum DY6 was selected as the starting strain in this study, which was mutagenized by a compound mutagenesis approach combining atmospheric room temperature plasma (ARTP) and nitrosoguanidine (NTG). The mutant strains AN-55, AN-58 and AN-68 with strong antibacterial activity were obtained, whose antibacterial activity increased by 19.83%, 21.91% and 18.40%, respectively. Subsequently, it was found that the bacteriostatic performance of strain AN-55 was more stable through the genetic stability test, and the antibacterial activity still increased by 20.51% even after 8 passages compared to the wild-type strain. At the same time, genome resequencing of strain AN-55 revealed that the changes of plnK, cps4G and pts9D gene sequences may have an important effect on improving the antibacterial activity of the strain, laying a theoretical foundation for the application of Lactobacillus plantarum as natural preservatives and antibiotic substitutes.

Abstract:Based on previous research, a genetically engineered strain of Escherichia coli BL21(DE3)-NF017 has been constructed which could synthesize of β-nicotinamide mononucleotide (NMN) using nicotinamide (NAM) and glucose as substrates with high yield. NMN synthesis was carried out in this study using a whole-cell catalytic approach. Initially, optimization was performed at the flask level for fermentation medium type, induction temperature, inducer isopropyl-β-D-thiogalactopyranoside (IPTG) concentration, and the factors of whole-cell catalysis process including the initial pH, reaction temperature, and ratio of substrate NAM to glucose. Under the optimal conditions, the NMN yield reached 1.84 g/L. Subsequently, to further improve NMN production, the control of different dissolved oxygen levels and various substrate NAM feeding strategies were optimized in a 5 L bioreactor. Finally, by a constant speed feeding rate of NAM, the NMN yield was increased to 12.24 g/L, with a molar conversion ratio of 85.65%. The research results could provide references for NMN production by whole-cell catalysis.

Abstract:To improve the salt tolerance of Zygosaccharomyces rouxii (Z. rouxii), the effect of pyridoxine on the tolerance to high salt stress of Z. rouxii was explored. A series of physiological characterization tests, including measurements of glycerol, trehalose levels and Na⁺/K^+-ATPase activity, were carried out to verify the changes of high-salt adaptability of Z. rouxii. The experimental results indicated that yeast cells during the lag phase under high salt stress accumulated intracellular glycerol 24 hours in advance and accelerate the catabolism rate of intracellular trehalose by addition of pyridoxine. In the mid-logarithmic growth phase, the ratio of intracellular Na⁺/+ decreased by 82.3%, while the activity of Na⁺/K⁺-ATPase on cell membrane increased by 16.9%. Additionally, the production of 2-phenylethanol (mass concentration) increased by 6.42-fold. In the stable phase, the biomass increased by 10.6%, the ethanol production (mass concentration) increased by 5%, and the 2-phenylethanol production (mass concentration) increased by 1.26-fold. In conclusion, the addition of pyridoxine could effectively improve the high salt stress tolerance of Z. rouxii, and further enhance the application prospect of Z. rouxii in high-salt fermented foods such as soy sauce.

Abstract:Acetohydroxy acid synthase (AHAS, encoded by the gene ilvBN) is the first rate-limiting enzyme in L--leucine synthesis pathway. Corynebacterium glutamicum XL-3 was used as the chassis cell to increase its preference for pyruvate and improve the yield of L--leucine by analyzing and modifying AHAS. Initially, the amino acid sequence of AHAS was used for homologous modeling. Then potential mutation sites were identified through alanine scanning of the protein structure. The optimal mutant was selected by measuring the catalytic activity of the mutant and theL--leucine yield of the recombinant strain. The results showed that substituting Gln157 with Arg effectively enhanced the ability of AHAS to catalyze pyruvate, resulting in a final L--leucine production of (23.5±1.8) g/L in the recombinant strain, which was a 51% increase compared to the parent strain Corynebacterium glutamicum XL-3. In addition, the yield of by-products L--isoleucine decreased. Therefore, the rational modification of AHAS could promote the synthesis of L--leucine. The research results have important implications for the subsequent use of protein engineering to strengthen the microbial synthesis of branched-chain amino acids such as L--leucine.

Abstract:In this study, 8 varieties of common Chrysanthemum in the market were selected to investigate the effects of harvesting period on sensory properties, as well as the content of volatile and non-volatile substances in Chrysanthemum infusion. The sensory and physicochemical properties were respectively analyzed through the quantitative descriptive analysis, gas chromatography-mass spectrometry, high-performance liquid chromatography, and ultraviolet spectrophotometry. The results showed that the harvesting period mainly affected the taste and mouthfeel of Chrysanthemum infusion. With partial least squares regression analysis, it was found that the contents of phenolic compounds and free amino acids were positively correlated with sensory taste. Furthermore, the volatile compounds in Chrysanthemum infusion were also affected by harvesting period, exhibiting a lesser extent compared to the differences in variety and conditions for growth of plants. Besides, it was further inferred that n-nonanal and eucalyptol were the main contributors of traditional Chrysanthemum aroma through the calculations of odor activity value of each volatile component. This study is beneficial for the marketing promotion of Chrysanthemum and directional manipulation of premium Chrysanthemum quality to meet consumer demands.

Abstract:In this research, fresh goat milk was frozen at cryogenic temperature(-16~-18 ℃) and ultra-cryogenic temperature(-76~-80 ℃) for 3 months, and thawed at room temperature(20~25 ℃). Then, the stored samples were subjected to spray drying to prepare fresh goat milk powder, goat milk powder that was cold-frozen and thawed at room temperature(CFHT), and goat milk powder that was ultra-low-temperature frozen and thawed at room temperature(UFHT). And the quality of resulting powders was compared and analyzed. The results showed that the moisture content of spray-dried goat milk powder met the national standard, with water activity(A_w) below 0.2 and total color difference(ΔE) below 0.3, indicating good storage characteristics. In addition, PDI values of all goat milk powders after rehydration were all below 0.3. Confocal laser scanning microscopy (CLSM) images revealed no significant differences in both fat globules and protein particles among the three groups of rehydrated goat milk powders. Compared with the fresh goat milk powder, CFHT and UFHT goat milk powders exhibited more severe fat loss(P<0.05), as well as protein and lactose losses of 10%~19%(P<0.05). Furthermore, UFHT goat milk powder had higher protein and lactose content than CFHT goat milk powder, while its moisture content andA_w were lower than those of CFHT goat milk powder. Therefore, frozen storage can be used in the preparation of spray-dried goat milk powder, and the quality of UFHT goat milk powder is better than CFHT goat milk powder.

Abstract:This study investigated the effects of Lycium barbarum polysaccharide(LBP) on the structure and metabolites of the human gut microbiota. The individual and mixed samples of fecal extracts from six healthy individuals was subjected to anaerobic fermentation in vitro. The structure and function of gut microbiota after LBP fermentation were analyzed by 16S rRNA gene high-throughput sequencing. The concentration of short-chain fatty acids(SCFAs) in the fermentation broth was detected by ultra-high-performance liquid chromatography(UPLC). The results demonstrated that LBP significantly changed the structure and function of human gut microbiota, increasing the abundance of probiotics Lactobacillus and Bifidobacterium in gut microbiota while promoting the production of SCFAs. Consequently, LBP can markedly modulate the structure and function of human gut microbiota.

Abstract:Efficient separation of eight common off-flavor metabolites in cyanobacteria was successfully achieved by optimizing extraction and enrichment conditions such as microwave distillation and solid-phase microextraction, and utilizing comprehensive two-dimensional gas chromatography separation. A detection method for odor metabolites from cyanobacteria in fish meat was established by the quantitative analysis using internal standards with precise mass-to-charge ratios of characteristic ions. The results demonstrated that the eight off-flavor metabolites exhibited good linearity within a concentration range of 0.01 to 100.00 μg/L. The method had detection limits ranging from 0.07 to 3.30 μg/kg and quantification limits ranging from 0.2 to 10.0 μg/kg. The recovery rates ranged from 72.5% to 103.7%, and the relative standard deviations(RSD) were between 2.26% and 14.30%(n=6). Analysis of freshwater fish products revealed the highest concentration of dimethyl trisulfide, geosmin, β-cyclocitral, β-ionone and indole could reach 7.21×10², 3.18, 1.85×10², 94.6, 4.69×10² μg/kg, respectively. This analytical method is accurate, highly sensitive, and exhibits good stability, greatly reducing false positive issues. It can be used as a screening and confirmation method for the presence of cyanobacteria odor metabolites in aquatic products.

Abstract:In order to achieve the sensitive detection of nitrite in meat products, this study used nickel foam as the carrier and prepared nickel foam supported Co₃O₄ composite material by hydrothermal method and high-temperature calcination method, which was used to construct a highly sensitive nitrite electrochemical sensor. The morphology and structure of the prepared nanocomposites were characterized by scanning electron microscope(SEM), high-resolution transmission electron microscopy(HRTEM) and X-ray diffraction(XRD). Meanwhile, cyclic voltammetry(CV) and chronoamperometric titration were used to further study the electrochemical behavior and electrocatalytic mechanism of the modified electrode for rapid detection of NO₂^- ions. The results showed that the peak current of the sensor exhibited a good linear relationship with NO₂^- concentration in the range of 5~2 100 μmol/L, with a detection limit of 3.14 μmol/L. Using soy sauce beef as the real sample, the content of nitrite was determined by standard addition method, with a recovery range of 97.9% to 101.2%. The sensor has the advantages of easy preparation, high sensitivity, easy operation, good stability and short detection time. It is suitable for the rapid detection of nitrite in meat products.

Abstract:A hypertensive rat model was established using a high-salt diet. Based on high-throughput sequencing technology, the potential injury mechanism of hypertensive target organs (ventricle and atrium, renal cortex and medulla, colon) and the effect of a high-salt diet on the intestinal microflora were explored. The results showed that rats exhibited a significant increase in blood pressure after 12 weeks of a high-salt diet. A series of dysregulated differential transcription factors were found in the transcriptome data analysis of target organs affected by hypertension. 16S rRNA sequencing results showed that the composition of intestinal microflora in rats was changed. The functional analysis revealed a close association between these changes and microbiome metabolic dysfunction. Co-expression analysis further explored the potential mechanisms of crosstalk between the genome and microbiome in the development of hypertension. In conclusion, this study provides candidate key genes and the intestinal microbiome associated with the treatment of high-salt diet-induced hypertension and heart-kidney-intestinal injury. Innovative multi-omics analysis may be a crucial approach to understanding gene expression patterns and disease development.