Improving stress tolerance by functional genes is very important for efficient utilization of cellulose hydrolysate to produce ethanol. Candida glycerinogenes is an industrial strain with multiple stress tolerance. The rRNA methyltransferase gene CgBmt5 was obtained by screening of the genomic library. Overexpression of CgBmt5 in Saccharomyces cerevisiae improved acetic acid tolerance, and the ethanol yield of the recombinant bacteria reached 60.5 g/L with an increase of 17.7% under acetic acid stress. In C. glycerinogenes, overexpression of CgBmt5 also enhanced ethanol yield by 17.6% under acetic acid stress. Besides, the ethanol yield per cell, glucose conversion, and production intensity of both recombinant strains were improved. The ethanol yield, glucose conversion rate, and production intensity were improved by 71.7%, 65.0%, and 155.7%, respectively, using cellulose hydrolysate as substrate. Under acetic acid stress, the lipid peroxidation level of overexpressed strain was decreased, and the activities of superoxide dismutase (SOD) and catalase (CAT) were increased. Transcriptional analysis showed that Pfk1 and Arg3 genes were up-regulated, and Gpd1 and Cox3 genes were down-regulated in the C. glycerinogenes CgBmt5, suggesting that CgBmt5 may promote acetic acid tolerance and fermentation performance by reducing lipid peroxidation levels, increasing SOD and CAT activities, and affecting glucose metabolism and arginine synthesis. This study provides new information for the stress tolerance of yeast and the development of cellulosic ethanol technology.

Seasonings have an important effect on the quality of Fengdu spicy chicken. To evaluate the flavor characteristics of Fengdu spicy chicken seasonings, the numbing and spicy intensity, aroma components, and sensory characteristics were analyzed by HPLC, electronic nose, GC-MS, and sensory evaluation. Results showed that the contents of sanshool and capsaicinoids in Fengdu spicy chicken seasonings from different manufacturers were 0.023-4.053 mg/g and 0.123-0.471 g/kg, respectively. Their intensity of numbing and spicy difference was significant. An electronic nose combined with principal component analysis could be used to quickly distinguish Fengdu spicy chicken seasonings from different manufacturers. A total of 81 volatile components were detected in Fengdu spicy chicken seasoning. The difference in composition and proportion resulted in different flavor of Fengdu spicy chicken products from different manufacturers. 13 main aroma components were screened out by odor activity value (OAV) analysis, including myrcene, linalool, (Z)-2-decenal, D-limonene, and linalyl acetate. The sensory scores of S4, S8, and S9 were significantly higher than those of other samples, and their spicy taste was more coordinated and palatable. On the whole, the numbing and spicy intensity and aroma of Fengdu spicy chicken seasonings from different manufacturers were different. Combined with the results of the numbing and spicy intensity analysis and sensory evaluation, the intensity of numbing (1.512-4.053 mg/g) and spicy (0.184-0.200 g/kg) may be the more suitable range for Fengdu spicy chicken seasoning. The overall flavor of Fengdu spicy chicken seasoning was mainly fatty, floral, and spicy.

Taro is the staple food of residents in Africa and parts of Asia, and also an important source of carbohydrates. It has a long history of cultivation and consumption in China. Modern pharmacological research shows that non-starch polysaccharide is an important active ingredient in taro, which has the effects of immune regulation, anti-oxidation, hypoglycemia, and hyperlipidemia, which could stimulate the application potential of taro polysaccharides in food, medicine, and other fields. This paper reviewed the extraction, purification, structure characterization, functional activity, and application of taro polysaccharides in China and abroad in recent years, providing a reference for further research, development, and application of taro polysaccharides.

The changes of microbial community structure and biomass of different layers of Daqu for the production of special-flavor Baijiu (Te-Daqu) and its correction with flavor compounds are not well understood. In this study, the absolute quantitative and relative quantitative amplification sequencing techniques were used to determine the microbial compositions as well as their changes of different layers of Te-Daqu. Moreover, microbial source tracking was used to analyze the origins of dominant bacteria and fungi. Headspace solid phase micro-extraction combined with gas chromatography-mass spectrometry was used to analyze the content of flavor compounds in different layers of Te-Daqu. The results showed that the total bacterial biomass in core of Te-Daqu was significantly lower than that of surface-layer and middle-layer, i.e, was 55% of that of surface-layer and 53% of that of middle-layer. Weissella, Lactobacillus, and Enterobacter were the dominant bacteria within the surface-layer. Thermoactinomyces was the specific bacteria of the core-layer, whereas Saccharopolyspora only dominated in the middle- and core-layer rather the surface-layer. Isatchenkia and Pichia were the main yeasts within the surface-layer, while Aspergillus was the dominant mold within the core-layer. The total contents of alcohols, aldehydes and ketones, pyrazines, ethers, and phenols in the core-layer were higher than that in the surface- and the middle-layers, while the total contents of esters in the surface-layer were higher than that in the core-layer. These results provided an essential reference to optimize the Te-Daqu making process and to improve the quality of Te-Daqu by using ecological fermentation technology.

Ribosome binding site (RBS) is an important biological control element for fine-regulation of genes expression, which has been widely applied in microbial metabolic engineering and synthetic biology. Corynebacterium glutamicum is an important industrial microorganism for industrial fermentation of several amino acids and organic acids. However, there were few researches on the RBS element for C. glutamicum. In this study, a random RBS library was designed and constructed based on the common RBS characteristics in C. glutamicum. Then, a high-throughput screening technology was developed by coupling flow cytometry and 96-well plate screening technology for screening of the artificial RBS library. After two-step screening, an artificial RBS element library with wide range of regulation and uniform coverage was constructed, and the regulation strength range of the library was 29.04-fold. Next, the artificial RBS library was further characterized by α-amylase expression system, and the results showed that the RBS library had high stability and versatility. Subsequently, the artificial library was applied for the regulation and optimization of the L-homoserine biosynthetic pathway. The expressions of LysC^r and Hom^r, the key enzymes in L-homoserine synthesis pathway, were fine-regulated using RBS elements with different intensities. Finally, the best combination of LysC^r and Hom^r for L-homoserine synthesis was obtained, and the resulted strain accumulated 12.7 g/L of L-homoserine, which was 3.6 times higher than that of the wild-type strain. Therefore, an artificial RBS library was constructed and exhibited wide regulation range and high stability in this study, which provided the effective control elements for metabolic engineering and gene expression regulation in C. glutamicum.

L-serine is widely used in medicine, food and cosmetic industry, however, the industrial production of L-serine by microbial fermentation has not yet been realized. In previous studies, we found that there had a significant difference in L-serine titer by Corynebacterium glutamicum A using sucrose and glucose. In this paper, comparative metabolomics analysis method was used to study the differences of intracellular metabolites of C. glutamicum A in different carbon sources, revealed the key metabolites of L-serine synthesis, and then investigated the influence of the addition of key metabolites on L-serine production. Through GC-MS, principal component analysis, and partial least squares discriminant analysis, 15 kinds of intracellular metabolites were found to be closely related to L-serine synthesis, including glucose, glucose 6-phosphate, 3-phosphoglycerate, pyruvate, fructose 6-phosphate, alanine, succinic acid, fumaric acid, citric acid, malic acid, phenylalanine, tryptophan, proline, glycine and methionine, among which fumaric acid, succinic acid, α-ketoglutaric acid, malic acid, and citric acid in the tricarboxylic acid cycle had great influence on the synthesis of L-serine. The fermentation results showed that the addition of 2.5 g/L fumaric acid had the significant inhibition on the cell growth, and the biomass (OD₅₆₂) decreased by 33.9%. Although fumaric acid was added to inhibit the cell growth, it was significantly beneficial to L-serine production. When 2 g/L fumaric acid was added, L-serine titer increased by 29.8%. These results showed that the optimal medium based on comparative metabolomics analysis could improve the L-serine production.

β-nicotinamide mononucleotide (NMN) as the direct precursor of the important coenzyme NAD⁺ in the human body has received widespread attention, and the current industry mainly uses chemical method or chemical-enzyme catalytic method for synthesis, and the fermentation method has not yet made a breakthrough. In order to obtain an engineered strain with high NMN yield, the metabolic pathway of Escherichia coli was modified. Firstly, nicotinamide phosphoribosyl transferase from Chitinophaga pinensis was expressed heterologous in E. coli, and a remedial synthesis pathway for NMN was constructed. In order to enhance the supply of the precursor 5-phosphate ribose-1-pyrophosphate (PRPP), multiple pathway enzymes originating from glucose were expressed, which promoted the flow of glucose to the pentose phosphate pathway; Further, in order to facilitate the accumulation of NMN, by knocking out the NMN downstream metabolic catalysis pathway genes pncC and ushA and regulating the NAD⁺ derivative gene nadR, the yield of recombinant strain obtained reached 60 mg/L, notably, which was 4.95 times over the initial level, and the fermentation was further performed on a 5 L fermenter, and the yield reached 390.1 mg/L. The strain exhibits significant potential for fermentation production of NMN.

In order to explore the alleviating effects of two strains of Lactobacillus plantarum on muscle injury and decreased muscle energy metabolism ability in mice after high-intensity exercise and its relationship with the changes in intestinal environment, a high-intensity exercise mouse model was established through 6-week weight-bearing swimming, during which L. plantarum strains were used to treat these model mice. After 30 min of non-weight-bearing swimming, the changes of relevant biochemical indexes and gut microbiota in mice with the intervention of L. plantarum (6-week, 2×10⁸ CFU/d) were checked. The results showed that the content of lactate in muscle and the activities of lactate dehydrogenase and creatine kinase in serum of mice were significantly increased by high-intensity exercise. L. plantarum 73L1 significantly reversed this change, suggesting that this strain can relieve lactic acid accumulation and injury of gastrocnemius muscle under high-intensity exercise. In addition, the intervention of this strain significantly increased the relative abundance of Oscillibacter, and decreased the relative abundance of Candidatus Saccharimonas and Ruminococcaceae UCG-005. Correlation analysis results showed that the relative abundance of Candidatus Saccharimona was significantly positively correlated with lactate dehydrogenase activity (P<0.001). In conclusion, L. plantarum 73L1 has a good ability to relieve muscle injury caused by high-intensity exercise in mice. This ability is significantly related to its specific regulation on gut microbiota. These results suggest that reducing the relative abundance of intestinal Candidatus Saccharimonas may be a potential mechanism by which L. plantarum 73L1 alleviates muscle injury caused by high-intensity exercise in mice.

Thin film solid-phase microextraction and gas chromatography-mass spectrometry were used to analyze and compare the volatile flavor components of four beef tallow hotpot seasoning brands with high market share for business (B end) and consumers (C end) and established a mathematical model to evaluate their difference. Results showed that 154 kinds of flavor substances were detected in B-end products and 158 kinds of flavor substances were detected in C-end products, while the same 25 flavor compounds were detected in all eight samples. By comparing products of the same brand, it was found that the proportion of hydrocarbons in the C-end product had dropped significantly. Principal component analysis was used to analyze the flavor composition of hotpot seasoning products, and the results showed that the cumulative variance contribution rate of the first seven principal component factors reached 100%, which could effectively characterize the flavor information of hotpot seasoning materials. Finally, a principal component analysis model was constructed. The comprehensive evaluation index was calculated and the flavor was evaluated and ranked. The Pearson correlation analysis found that the correlation between the comprehensive score of the principal component and the sensory evaluation results was extremely significant (P<0.01), and the correlation coefficient was 0.908, indicating that the constructed model could effectively evaluate the flavor of hotpot seasoning.

The objective of this study was to investigate the influence of tamarind seed polysaccharide (TSP) on ice crystal growth. Ice recrystallization, ice growth habit, and calorimetric behavior of TSP solutions were studied by the “sucrose sandwich” assay with Lifshitz-Slyozov-Wagner (LSW) theory, dynamic ice shaping assay, and differential scanning calorimetry (DSC) analysis. TSP showed a concentration-dependent conformational change in the aqueous solution. Adding 0.25% TSP could effectively reduce the ice recrystallization rate, with a 10-fold reduction of growth rate in 30 min compared to a blank (49% sucrose). The dynamic ice shaping study showed weak ice-shaping activity of TSP, implying a weak binding with ice. DSC analysis showed that TSP significantly depressed ice nucleation temperature but had little impact on the melting point. Notably, as TSP concentration increased above threshold concentration (0.5% in IRI experiments and 1.5% in DSC experiments), the ice recrystallization inhibition (IRI) activity and the nucleation depression effect dropped. An ice-growth inhibition mechanism of TSP based on an interface-related effect was proposed. These results suggested the potential of naturally sourced TSP as a novel ice growth inhibitor in frozen food and also shed new light on understanding the antifreeze mechanism of natural polysaccharides.

To investigate the suitable forced air pre-cooling conditions for broccoli and the effect of forced air pre-cooling on the storage quality of broccoli, this study used alpine broccoli as the research material and chose to precool the broccoli with different air speeds and different wind temperatures. Results showed that the use of a high air speed of 7.4 m/s and a low air temperature of 0 ℃ precooling could reduce the precooling time and save electricity. It also reduced cell membrane damage, increased the activity of superoxide dismutase, ascorbate peroxidase, and peroxidase, improved the ability of broccoli to decompose reactive oxygen species, and maintained the quality of broccoli during storage. This study provides a feasible precooling treatment for the preservation of alpine broccoli, which can provide a theoretical basis for the logistical preservation of alpine vegetables in the industry and a research basis for exploring the biological mechanism of the effect of forced air pre-cooling on the storage quality of broccoli.

To investigate the hypolipidemic effect of flaxseed oil krill oil with different proportions, 80 male rats were randomly divided into 8 groups, including the blank group, model control group, and flaxseed oil and krill oil (46:50, 62:34, and 78:18) with different ratios in high and low dose groups. The rats were fed a high-fat diet for 7 days and orally treated with different doses of flaxseed oil and krill oil with different ratios for 30 days. The serum triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) in each group were detected to evaluate the efficacy of flaxseed oil krill oil in alleviating hyperlipidemia and optimal ratio of different functional components. Results indicated that compared with the blank control group, the serum TC, TG, and LDL-C contents in the model group were significantly increased (P<0.01), indicating that the model was established. Compared with the model control group, the contents of TC, TG, and LDL-C in different dosage groups were significantly decreased (P<0.05 and P<0.01), and there were no significant differences in body weight and HDL-C in different dosage groups, which showed that flaxseed oil krill oil with different ratios had assistant hypolipidemic effect. When the ratio of flaxseed oil to krill oil was 62:34, the decrease of TG and LDL-C in hyperlipidemia rats was the most significant.

Isomaltulose is an isomer of sucrose and has many excellent physiological functions, so it is widely used in the food industry. Sucrose isomerase can isomerize sucrose into isomaltulose. Compared with sucrose isomerase derived from other microorganisms, the sucrose isomerase derived from Pantoea dispersa UQ68J can obtain higher yield of isomaltulose and fewer by-products when converting sucrose. In order to better apply isomaltulose to the food field, P. dispersa sucrose isomerase was recombinantly expressed in food safety microorganism Bacillus subtilis, the enzymatic properties of recombinant sucrose isomerase were studied and the reaction conditions for preparing isomaltulose were optimized in this study. The results showed that the optimal pH and temperature of recombinant sucrose isomerase were 6.0 and 30 ℃, respectively. The recombinant sucrose isomerase had good stability in the range of pH 5.0-8.0, and its half-life at 45 ℃ was 68 min. Using this recombinant sucrose isomerase to prepare isomaltulose, the yield was 90.61% with 400 g/L sucrose as the substrate, when the amount of enzyme was 20 U/g, at 30 ℃ and pH 8.0 for 10 h. When the sucrose concentration increased to 700 g/L, the yield of isomaltulose still reached 89.20%. This research improves the safety characteristics of sucrose isomerase, realizes the high yield of isomaltulose, and lays the foundation for the industrial production of isomaltulose.

Streptomyces albulus is an industrial strain for ε-poly-L-lysine (ε-PL) production. ε-PL is a homopoly (amino acids) produced by S. albulus,which is currently used as an excellent natural food preservative in many countries due to its eminent antibacterial activity. It often suffers low-pH stress during fermentation, which easily cause a decrease in the capacity of ε-PL biosynthesis. As a result, the adaptive evolution strategy with increasing the selection pressure step by step was introduced to improve the low-pH tolerance of S. albulus GS114 in this study. We first determine the initial transfer pH (pH 4.0) and transfer time (36 h) in adaptive evolution strategy. After 93 days of adaptive evolution, the tolerance pH value of S. albulus GS114 is reduced from 4.0 to 3.6. After a lot of strain screening in each selection pH (i.e. pH 4.0, 3.8, 3.6) in acid tolerance and ε-PL yield, we obtained S. albulus ALE4.0, S. albulus ALE3.8 and S. albulus ALE3.6. We chose spore plate coating and ε-PL shake flask fermentation to evaluate the characteristics of the strains after adaptive evolution. Combined with low pH tolerance and shaker fermentation experiments, it was determined that the optimal adaptive evolutionary strain is S. albulus ALE3.6. Further study investigated the influence of pH on the production of ε-PL by S. albulus ALE3.6. Results showed that S. albulus ALE3.6 had significant fermentation advantages under different pH values compared with parent strain S. albulus GS114. In terms of ε-PL production, dry cell weight, ε-PL yield, and ε-PL productivity, S. albulus ALE3.6 had different degrees of advantages. The ε-PL production of S. albulus ALE3.6 in batch fermentation at pH 4.0, 3.8, and 3.6 were reached 4.63, 6.14, and 7.2 g/L, respectively, which were enhanced by 13.5%, 8.9% and decreased by 7.7%, compared with the original strain S. albulus GS114. Meanwhile, the dry cell weight of S. albulus ALE3.6 was achieved by 16.8, 11.8, and 14.7 g/L, respectively, which were decreased to varying degrees compared to the original strain. After comparing the fermentation processes of different pH, we chose pH 4.0 for follow-up study from the point of view of the average specific synthesis rate of the product. Finally, the ε-PL production of S. albulus ALE3.6 in fed-batch fermentation at pH 4.0 were investigated. In a 5 L scale fermentor, ε-PL production of S. albulus ALE3.6 was reached by 43.7 g/L in 192 h, which is 63% higher than the original strain S. albulus GS114. The dry cell weight was attained by 39.8 g/L, which was 30% lower than the original strain. S. albulus ALE3.6 had higher ability of cell synthesis per unit and average specific synthesis rate of products in this fermentation process than the original strain. The acquisition of the S. albulus ALE3.6 provided an object for the analysis of the mechanism of acid tolerance. Furthermore, this result showed that the low-pH tolerance of S. albulus can be significantly improved through the adaptive evolution method, and enhancing the low-pH tolerance of S. albulus is an effective way to improve its ε-PL production.

Wine processing produces a large amount of waste, which is rich in bioenergy and bioactive substances. In recent years, disposal capacity of wine processing waste has been improving rapidly in our country, but the reuse rate of biological resources is low, and a comprehensive utilization and large-scale production system has not been formed. This paper provides a comprehensive overview on utilization of wine wastes from these four aspects: sources of wine processing wastes, material composition of wastes, industrial application, and graded utilization of waste. This paper aims to turn waste into treasure of wineries and to improve the added value of waste. It will provide a reference for the resource utilization of wine processing waste, and promote the low-carbon and sustainable development of wine industry.

In this study, an analytical method for the qualitative and quantitative determination of L/D-lactic acid in the fermentation broth of lactic acid bacteria was established by HPLC combined with chiral column. In this method, the concentration and detection results of L/D-lactic acid showed a good linear relationship in the range of 1.0-400.0 μg/mL. The limit of detection was 0.25 μg/mL, the limit of quantification was 0.80 μg/mL. The method was verified based on fermentation broth of two strains of lactic acid bacteria, the results showed that L/D-lactic acid in fermentation broth were well separated, and the method had good precision and repeatability, and the recovery rate was between 90.0% and 103.7%. The linear correlation coefficient R² were more than 0.999 in fermentation broth with different dilution degrees, and relative standard deviation of stability less than 5%. The production of L/D-lactic acid by 18 strains of lactic acid bacteria that can be used in food, including 8 species and 4 genera, was analyzed, the results showed that the content of L/D-lactic acid produced by lactic acid bacteria was different among strains, and the proportion of D-lactic acid had the same trend in species. The qualitative and quantitative determination of L/D-lactic acid in lactic acid bacteria fermentation broth by this method was accurate and stable. This study provides effective data support and practical reference for the detection of D-lactic acid, the metabolite of strains, in the safety evaluation of microbial food cultures.

The flavor structure of fermented bamboo shoots (FBS) in different areas of Guangxi was analyzed by gas-chromatography-olfactometry-mass spectrometry (GC-O-MS) and sensory evaluation. Results showed that the key aroma components of FBS were methyl salicylate, (E)-2-octenal, (E)-2-nonenal, nonanal, 1-octene-3-one, 1-octene-3-ol, phenylethyl alcohol, acetic acid, p-cresol, creosol, 4-ethyl guaiacol, and naphthalene. Among these, p-cresol and acetic acid contributed the most to the FBS flavor. The main aroma characteristics of FBS mainly included strong sour, sour smell, pungent, and fermented aroma. On this basis, the two-way orthogonal partial least squares method was used to analyze the correlation between sensory properties and key aroma compounds, and it was found that there was a good correlation between sour odor and the concentration of p-cresol and phenylethyl alcohol. A sour and irritating odor had a good correlation with p-ethyl guaiacol and 3-octanol, and fermentation flavor had a good correlation with two aldehydes and three esters. Therefore, this study analyzed the flavor structure characteristics of FBS in Guangxi and provided a reference basis for the evaluation and improvement of FBS flavor quality.

2′-Fucosyllactose (2′-FL) is one of the most abundant oligosaccharides found in human milk, which delivering many health benefits to the neonate. It is now available in some commercial infant formulas with great market potentials. In this study, salvage pathway was constructed by comparing α-1,2-fucosyltransferases from different sources, and choosing the co-expression of fucT2 from Helicobacter pylori and fkp. Then by over-expressing the substrate transporter LacY and product transporter Tpyb or SetA, the extracellular concentration of 2′-FL was greatly increased. Comparing the production capacity of BL21(DE3), C41(DE3), and JM109(DE3), the 2′-FL synthetic strain J2-V8 was obtained. Finally, through the optimization of fermentation conditions, the extracellular concentration of 2′-FL was 2.67 g/L in shaker for 48 h, which was 5 times higher than that of the initial strain, and the conversion rate was 0.82 mol/mol L-fucose, which provided a reference for the biological production technology of 2′-FL.

To investigate the quality differences of prepared dishes after reheating, three reheating methods (microwave reheating, steam reheating, and baking reheating) were used in the processing of pre-roasted fish. The effects of different reheating methods on the quality of pre-cooked fish were evaluated by analyzing shear force, color difference, thiobarbituric acid reaction substances value (TBARS), moisture content and distribution, volatile flavor substances, and sensory evaluation. Results showed that compared with steam reheating and baking reheating, fish after microwave reheating had the lowest shear force and the highest tenderness, and the shear force of the fish after baking reheating was about 3.16 times that of fish after microwave reheating. The moisture content of fish after microwave reheating was the highest, which was about 1.04 times that of fish after baking reheating. TBARS value of fish after microwave reheating was the highest, about 1.52 times that of fish after steam reheating. More kinds of volatile flavor substances were detected in fish of microwave reheating, with the highest content of aldehydes and sensory evaluation score. In terms of reheating time, microwave reheating time was the shortest. Based on various parameters, microwave reheating is a more suitable reheating method for pre-roasted fish. This study provides theoretical support for the reheating processing of prepared dishes.

As a lipid-soluble pigment, astaxanthin has low bioavailability due to its low solubility and low stability. This study aims to explore the effects of different formulation types of astaxanthin in in vitro digestion and absorption simulation model. A gastrointestinal digestion model in vitro was used to investigate the gastrointestinal release of astaxanthin oleoresin, microencapsulation powder, beadlets, and emulsion formulations. The final digestion products were further applied to the Caco-2 cell monolayer model to investigate the apparent permeability values (P_app), and to compare the bioavailability of different formulations of astaxanthin in vitro. In the digestion of various astaxanthin preparations in vitro, all dosage forms can form stable dispersion systems in the simulated digestive juice except for the oleoresin dosage form. The release rates of oleoresin, microencapsulation powder, beadlets, and emulsion were 14.73%, 93.71%, 89.07%, and 67.11%, respectively. The P_app in the Caco-2 cell monolayer model is 0.058×10^-6, 0.483×10^-6, 0.461×10^-6, and 0.656×10^-6 cm/s, respectively. Astaxanthin's microencapsulation powder, beadlets, and emulsion formulations significantly increased the release and penetration of astaxanthin, which effectively improved the bioavailability of astaxanthin.