Crude oil bodies (COB) rich in exogenous proteins and purified oil bodies (POB) practically free from exogenous proteins were extracted from soybean by aqueous extraction followed by deionized water washing and alkaline washing, respectively. The physicochemical and rheological properties of COB and POB were analyzed and the effects of different environmental factors (pH, Na+ concentration and temperature) on the stability of COB and POB were determined. The results showed that the main protein components in soybean POB were oleosins, while COB contained a large number of exogenous proteins deside oleosins, mainly including glycinin and β-conglycinin. Compared with POB (whose average particle size and zeta-potential were (475.06 ± 4.49) nm, and (–14.00 ± 1.86) mV, respectively), the presence of exogenous proteins resulted in larger average particle size ((552.93 ± 9.40) nm) and lower zeta potential ((–35.03 ± 0.60) mV) of COB. The isoelectric point of COB was around pH 4.5, which was close to that of glycinin and β-conglycinin, while the isoelectric point of POB was around pH 5.5. At different pH and Na+ concentrations, POB exhibited better stability than COB, which might be due to the fact that the presence of exogenous proteins in COB makes it susceptible to the environment, causing changes in electrostatic and hydrophobic interactions and thus leading to its poor stability. However, thermal treatment had little effect on the stability of COB and POB. In addition, both COB and POB had shear thinning properties, but the viscosity of COB was higher than that of POB, which further proves the influence of the presence of exogenous proteins on the processing properties of soybean oil bodies, and provides an idea for the development of different oil body-based products.

Soybean lecithin was added to protect the phospholipid layer on the surface of homogenized milk fat globule (MFG), and the homogenized MFG was used to encapsulate three fat-soluble nutrients including fish oil, vitamin E, and β-carotene. The addition of phospholipids could result in the formation of oil droplets with complete structure, smaller diameters, and larger absolute value of surface potential. During accelerated storage, the primary and secondary oxidation of fish oil was slowed down in homogenized milk with simultaneous and sequential addition of phospholipids and fish oil, and the content of lipid hydroperoxide, produced at the primary oil oxidation stage, was 1.28 and 1.79 mmol/mL at the end of storage, respectively, and was significantly lower than that (2.81 mmol/mL) without exogenous phospholipids. The content of malonic dialdehyde (MDA), produced at the secondary oxidation stage, was 4.29 and 6.64 nmol/mL, respectively, and was significantly lower than that (15.87 nmol/mL) without the addition of exogenous phospholipids. The preservation rates of vitamin E and β-carotene in phospholipid fortified milk were as high as 90.80% and 71.02%, respectively, after 12 days of storage, and were significantly higher than those (80.63% and 64.54%) of homogenized milk without the addition of exogenous phospholipids. Accordingly, the addition of exogenous phospholipids could reduce the degradation of vitamin E and β-carotene.

To explore the effect of halogen substitution on the sweetness inhibition properties of 2-(4-methoxyphenoxy) propionic acid (HPMP), six halogenated derivatives of HPMP were synthesized through halogen (F, Cl or Br) substitution at the 2- or 3-position of the benzene ring of HPMP and characterized structurally, and their sweetness inhibition properties were evaluated by electronic tongue. The results showed that the six halogenated derivatives could competitively inhibit sweetness. In addition, a significant dose-effect relationship was observed for the derivatives with halogen atoms introduced at the 2-position of the benzene ring. All six derivatives exhibited inhibitory effects on sucrose, fructose, glucose, xylitol and erythritol. Furthermore, the fluorinated and chlorinated derivatives showed stronger inhibitory effect on the sweetness of the aforementioned sweeteners. Therefore, it was speculated that the size and electronegativity of halogen substituents may be the key factors causing different sweetness inhibitory activity. This study indicates the importance of halogen substitution in the sweetness inhibition effect of HPMP, and provide a reliable theoretical basis for the study of the structure-activity relationship of sweetness-inhibiting compounds.

The interaction mechanism of cyanidin-3-glucoside (C3G) with β-conglycinin and glycinin was investigated by multiple spectroscopies and molecular docking. The results showed that C3G quenched the intrinsic fluorescence of β-conglycinin/glycinin strongly in both static and dynamic modes and C3G had stronger binding affinity toward glycinin than β-conglycinin. However, the major interaction force involved in C3G binding to glycinin was different from that for β-conglycinin. As judged from the number of binding sites, a stable C3G-soy protein complex with a molar ratio of 1:1 was formed. C3G induced partial unfolding of the secondary structure of soy protein and a conformational switch from α-helix to β-sheet, thus resulting in conformational unfolding of soy protein. The addition of C3G could reduce the hydrophobicity of the microenvironment around tryptophan residues in β-conglycinin, but had no significant effect on the microenvironment around amino acid residues in glycinin. In addition, the majority of the phenolic hydroxyl groups in the C3G molecule were mainly involved in hydrogen bonds and hydrophobic interaction with soy protein. Compared with β-conglycinin, glycinin showed great potential as a biological carrier for the stabilization and delivery of C3G. However, it may be unfavorable for the biological activity of C3G.

The dynamic changes of biogenic amines in yak milk hard cheese with different salt content (1.0%, 1.3%, 1.8% and 2.3%) over a six-month ripening period were analyzed, and amine-producing microorganisms were selected. The results showed that the biogenic amines in yak milk hard cheese with different salt levels were mainly tryptamine, β-phenethylamine, cadaverine, tyramine and putrescine, but histamine was not detected, and the biogenic amines were mainly accumulated in the late stage of maturation. Tryptamine was the least abundant biogenic amine in all the cheeses, and there was little difference in tryptamine content between them in the late ripening stage. When the salt content was reduced from 2.3% to 1.0%, the β-phenethylamine content in the cheese decreased. The content of cadaverine in the cheeses with 1.0% and 1.3% salt content was lower, and putrescine was not detected. As the salt content increased from 1.8% to 2.3%, the content of cadaverine and putrescine in the cheese showed an increasing trend. The tyramine content was 3.13–49.81 mg/kg in the cheeses, and higher at a salt level of 1.3%. The total amount of biogenic amines in the cheeses with different salt levels was up to 304.18 mg/kg. An amine-producing microorganism was selected using a chromogenic medium and identified as Enterococcus durans by molecular biology techniques.

The digestive characteristics of micro/nano-sized colloidal particles (MNCPs) in bighead carp head soup and the effects of processing conditions on them was investigated using an in vitro digestion model. The results showed that salt addition and homogenization did not change the overall trend of MNCPs in the soup during digestion. During gastric digestion, proteins adsorbed to the membrane of MNCPs were degraded, and lipid droplets were released and aggregated for raw, salt-incorporated and homogenized fish soup. During intestinal digestion, the lipid droplets were dispersed and the MNCPs aggregates were cleaved. After salt addition, the average particle size of MNCPs decreased, but a local demulsification phenomenon appeared, thereby reducing the release rate of fatty acids. After subsequent homogenization, the average particle size of MNCPs was further reduced and MNCPs were rearranged; the membrane structure was changed, and the number of contact sites between lipids and enzymes in MNCPs was increased, promoting the release of fatty acids and consequently compensating for the decrease in the release rate of some fatty acids in bighead carp head soup after adding salt. Therefore, the changes in the composition and microstructure of MNCPs induced by salt and homogenization may be the major cause of the differences in the digestion properties of MNCPs.

Using high-amylose maize starch G50 and G70 as raw material, type III resistant starch was obtained by successive steps of acid hydrolysis, pasting, debranching and recrystallization, and annealing and autoclaving treatments were used to improve the yield of resistant starch. Scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), rapid viscosity analysis (RVA) were used to evaluate the morphology, crystalline structure, thermal properties and pasting properties of starch granules, and the digestion properties of starch were tested by the Englyst method. The results showed that the yields of type III resistant starch from high-amylose maize starch G50 and G70 after acid hydrolysis were 77.9% and 84.5%, respectively, and were reduced to 54.4% and 70.2% after recrystallization, respectively. For G50 and G70, the morphology of starch granules was destroyed after modification, and aggregates with different sizes and irregular shapes were formed. The crystalline type of starch changed from B + V to A + V, and the crystallinity increased. The pasting temperature of starch increased, and the viscosity almost disappeared after heating. The solubility of G50 and G70 significantly increased after acid hydrolysis, pasting, debranching and recrystallization, while the solubility and swelling power of type III resistant starch decreased after annealing and autoclaving treatments. In vitro digestion tests showed that the modified G50 and G70 had stronger resistance to digestion than the raw ones, and the resistant starch content of G70-derived type III resistant starch autoclaved after addition of 20% water was the highest (80.5%). In conclusion, the modification treatment can effectively increase the content of resistant starch in high-amylose maize starch G50 and G70, and the content of resistant starch is significantly positively correlated with the crystallinity and pasting temperature.

Objective: To develop a time-temperature indicator (TTI) with amylase nanoflowers based on protein hybrid nanotechnology and enzyme reaction and to determine the activation energy for TTI and its suitability for different food types. Methods: Based on the interaction between amylase and copper ions, amylase was immobilized to form amylase@Cu nanoflowers. The amylase concentration for nanoflowers with the best shape was selected, and the biological activity and stability of amylase in the nanoflowers were tested. Six formulations of TTI were prepared by adding 10, 20, 30, 40, 50 mg and 60 mg of amylase@Cu nanoflowers and using 15 mL of 40 g/L soluble starch solution as the substrate and 4.5 mL of 1 g/L iodine solution as the indicator. At constant temperatures of 5, 15, 25 and 35 ℃, the discoloration process was observed, the kinetic parameters were measured, and the activation energy for the reaction was calculated. Results: When the amylase concentration was 0.5 mg/mL, the flower-like shape of amylase@Cu nanoflower was the most complete, the amylase activity increased by 3.42 times, and the storage stability was significantly improved. The six TTIs showed a change process from dark blue to colorless, and the activation energy values were 14.84, 21.00, 28.85, 33.03, 32.55 and 32.83 kJ/mol, respectively. Conclusion: The amylase nanoflower-based TTI was simple to operate and had good indication performance. According to the matching principle between TTIs and foods, this series of TTIs were suitable for monitoring food deterioration and spoilage caused by diffusion control, enzymatic reaction, fat oxidation or other reasons.

In this study, Hericium erinaceus polysaccharide (HEPS, with a purity of more than 92%) was modified using a redox system consisting of Na2SeO3 and ascorbic acid (VC) to obtain selenized HEPS (HEPS-Se). The structural and physiochemical properties of HEPS-Se were investigated by atomic absorption spectrometry (AAS), Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and nano-zetasizer analysis. The anti-proliferation activity of HEPS-Se on A549 human lung cancer cells and DU145 human prostate cancer cells was evaluated. Results showed that HEPS-Se had a regular spherical shape and four elements C, O, Se and Pt at a ratio of 32.92:24.74:30.46:11.87 were determined in HEPS-Se. Its selenium content was 481.79 μg/g. FTIR analysis showed that HEPS could bind to selenium nanoparticles mainly through –OH and –C=O groups. Compared with HEPS, the particle size of HEPS-Se decreased significantly and the absolute potential increased by 69.12%. Meanwhile, HEPS-Se exhibited significantly anti-proliferative effects on DU145 cells and A549 cells in a dose-dependent manner. This study provides a theoretical basis for the development of organic selenium supplements.

A-type and B-type starch separated from waxy wheat starch were separately mixed with high-amylose corn starch and treated with pullulanase and/or branching enzymes. The granular morphology, crystalline structure, apparent amylose content, solubility, swelling power and other physicochemical properties of the modified starch were determined, and their digestion characteristics were also investigated. The results showed that the predicted glycemic index (pGI) of waxy wheat A- and B-type starch were significantly reduced by the dual-enzymatic modification, and the content of apparent amylose was increased significantly. The solubility increased with temperature, while the swelling power remained basically unchanged. Under a scanning electron microscope (SEM), the microstructure of the enzymatically modified starch granules exhibited holes. The relative crystallinity (RC) and the ratio between the intensities of the peaks at 1 047 and 1 022 cm-1 were obtained by X-ray diffraction and Fourier infrared spectroscopy, respectively, revealing that the long-range and the short-range ordered structures of starch were significantly improved by the dual-enzymatic modification. Furthermore, sequential treatment with pullulanase and branching enzymes could significantly improve the digestion characteristics of waxy wheat A-type and B-type starch.

The stability of powdered formulae for young children of different age groups packaged in atmospheres with different residual oxygen levels (0.2%, 2%, 3% and 5%, V/V) was investigated, and the effect of residual oxygen levels inside the package on the nutritional value and flavor of young child formulae was evaluated. The results showed that during accelerated storage for 24 weeks at 37 ℃ and relative humidity of 75%, the nutritional and sensory characteristics of young child formulae were susceptible to the residual oxygen inside the package. With the increase of residual oxygen inside the package, the content of VA, VE, VC and lutein decreased generally, while the content of all volatile lipid oxidation products except propanal increased, and the content of propanal in young child formula with a residual oxygen percentage of 3% inside the package was the highest. Therefore, the residual oxygen inside the package is crucial to the quality of young child formula, and low levels of residual oxygen are conducive to the stability of young child formula during storage.

This study attempted to investigate the effects of reducing sodium content and adding Lactobacillus paracasei M3, with high angiotensin-converting enzyme (ACE) inhibitory activity in skimmed milk, as an adjunct starter culture on the physicochemical properties and in vitro antihypertensive potential of Cheddar cheese. One control group (100% NaCl) and three experimental groups, 50% NaCl + 50% KCl, 100% NaCl + 0.5% L. paracasei M3, and 50% NaCl + 50% KCl + 0.5% L. paracasei M3 were set up. The major chemical components, microbial load, proteolysis, texture, flavor and ACE inhibitory activity of these four groups were evaluated. The results showed that there was no significant difference in the principal chemical components among the four groups (P > 0.05). The number of lactic acid bacteria, pH 4.6 soluble nitrogen and total free amino acid content were significantly higher in the experimental groups than the control?group (P < 0.05), while hardness and pH were lower in the experimental groups (P < 0.05) and bitterness was higher. The inhibition percentages of the three experimental groups toward ACE were 65.2%, 74.3% and 78.7% after six months of ripening, which were 19.6%, 36.2% and 44.4% higher than that of the control group, respectively. We concluded that potassium salt substitution and use of L. paracasei could contribute to the production of ACE inhibitory peptides with antihypertensive potential in cheese, but further research is needed to understand their effect on the flavor of cheese.

The effect of different inoculum levels of Lactobacillus plantarum (105, 106 and 107 CFU/g) on the quality characteristics and flavor profile of low-sodium dry sausage were explored in this study. The uninoculated sausage with 1.75% NaCl was regarded as a control. The pH, moisture content, water activity, shear force, lactic acid bacteria (LAB) count and Enterobacteria count of the four samples were measured on days 0, 3, 6 and 9 of fermentation and the flavor profiles were analyzed on the 9th day by electronic nose (EN) and gas chromatography-mass spectrometry (GC-MS). The results showed that the moisture content and water activity of all treatments decreased gradually as the fermentation progressed; at the end of fermentation (day 9), the moisture contents and water activity of the LP6 and LP7 treatments were higher than those of the other treatments and the Enterobacteriaceae count of the LP7 treatment was the lowest among all treatments, while there was no significant difference in shear force among all treatments (P > 0.05). The pH of all treatments decreased gradually (except for day 0 of fermentation) with an increase in the inoculum level, and the LAB count increased gradually (except for day 6 of fermentation). Inoculation with L. plantarum increased the contents of acids and esters. The volatile compound contents of low-sodium dry sausages with different inoculum levels of L. plantarum were significantly different. Finally, sensory evaluation indicated that the overall acceptability of low-sodium dry sausage with an inoculum level of 106 CFU/g was the highest, and its saltiness and sourness were moderate.

IgE-mediated rat basophilic leukemia (RBL)-2H3 cells were used to construct a cell model of anaphylaxis. RNA sequencing was used to analyze differentially expressed genes between unactivated and activated RBL-2H3 cells, and the related signaling pathways were enriched. The activation of IgE-mediated RBL-2H3 cells significantly increased the secretion of allergenic mediators and cytokines. Totally 232 differentially expressed genes were obtained by RNA sequencing, of which 127 (54.74%) could be annotated for gene function. Meanwhile, the activation of RBL-2H3 could affect the tumor necrosis factor, mitogen-activated protein kinase, janus kinase-signal transducer and activator of transcription, and Toll-like receptor signaling pathways. The transcription factors involved in these signaling pathways included MAP3K8, Nfkbia, Junb, Jun and Fos. In conclusion, the findings of this study may provide a theoretical foundation for the prevention and treatment of allergic diseases.

In this study, site-directed mutagenesis of non-conserved amino acid residues in the conserved regions of thermoacidophilic type III pullulan hydrolase TK-PUL was performed, and the effect of key amino acid residues in the conserved regions on its catalytic properties was determined by comparing the enzymatic properties of TK-PUL with those of its mutants. The I500W mutation in the conserved sequence region II of TK-PUL did not affect the optimum pH, pH stability, optimum temperature or thermal stability of TK-PUL, but significantly decreased the α-amylase and pullulanase activity. The kinetic parameters of TK-PUL and the mutant I500W TK-PUL were determined. The kcat/Km value of the mutant I500W for maltotriose was basically unchanged, and the kcat/Km value of the mutant I500W for isopanose was about 64.78% of TK-PUL. The results showed that Ile at residue 500 was important for the preference for α-1,4- and α-1,6-glycosidic linkages of TK-PUL. The I500W mutation did not affect the α-1,4-activity of TK-PUL, but significantly reduced the α-1,6-activity. This study is helpful for an in-depth understanding of the bifunctional catalytic mechanism of TK-PUL, and can also provide a theoretical basis and design ideas for the molecular modification of TK-PUL.

31P nuclear magnetic resonance (NMR) spectroscopy was used to compare the composition of egg yolk phospholipids before and after enzymatic oxidation. 1H NMR spectroscopy was used to monitor and compare the changes in the molar percentage of fatty acyl groups and the concentrations of primary and secondary oxidation compounds between the unoxidized control, lipoxygenase-catalyzed oxidation and thermal oxidation (in water bath at 95 ℃) groups. The results showed that phosphatidylcholine and phosphatidylethanolamine were the major components of egg yolk phospholipids. After oxidation of egg yolk phospholipids, the contents of phosphatidylcholine and phosphatidylethanolamine decreased, while the content of hemolytic phospholipids increased. The molar percentage of total unsaturated fatty acids in both oxidized samples decreased, while the molar percentage of saturated fatty acids increased. The degradation rate of linoleic acid was the fastest with the enzyme at pH 6, and more hydroperoxide was formed from the enzymatic oxidation of egg yolk phospholipids. (Z,E)-2,4-dienal was mainly produced after heating. At pH 9, hydroperoxide was produced and rapidly degraded and more n-alkaldehyde was generated after heating. Therefore, lipoxygenase can be used to catalyze the oxidation of egg yolk phospholipids at pH 6 to produce more flavor compounds such as 2,4-diene aldehydes.

Based on the composition of odor and taste substances and amino acids, this study evaluated the elimination efficiency of the yeasty flavor from yeast extract by fermentation with single and mixed cultures of Lactococcus lactis, Streptococcus lactis and Lactobacillus plantarum. The results showed that lactic acid bacterial fermentation reduced the yeasty odor (propionic acid and isovaleric acid) from yeast extract, but the overall flavor profiles of yeast extracts fermented with different cultures were significantly different. The effect of mixed culture fermentation was more pronounced than that of single culture fermentation, and the effect of the mixed culture of L. lactis and S. lactis was the best. After fermentation by the mixed culture of L. lactis and S. lactis, the level of the yeasty odorant isovaleric acid in yeast extract was decreased by 86.73%, the concentration of alcohols with fruity and flowery aroma was increased from 0.77 to 10.73 ng/mL, the lactic acid concentration was 10.60 g/L, the concentration of the flavor precursor amino acid phenylalanine was increased by 112.91 mg/L, and the concentration of umami taste substances (inosinate and guanylate) was increased by 0.02 g/L. The fermented sample had a well-balanced flavor and taste.

DNA was extracted from an exopolysaccharide (EPS)-producing strain of Streptococcus thermophilus IMAU20551, and was sequenced on an Illumina HiSeq platform and the filtrated reads were assembled using the SOAPdenovo software. Functional genes were annotated to the RAST, the Clusters of Orthologous Groups (COG), the Gene Ontology (GO), and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The genome of S. thermophilus IMAU20551 was found to be 1 725 107 bp in length, and 1 884 functional genes were annotated, including a complete eps gene cluster of 19 376 bp in length. In total 18 genes related to EPS synthesis were contained in the gene cluster, including epsA, epsB, epsC, epsD, epsE, eps1F, eps2F, epsJ, wzx, epsP and epsX. These genes regulate the synthesis, assembly and transport of exopolysaccharides. Furthermore, real-time PCR was used to verify the expression of the eps gene cluster from S. thermophilus IMAU20551, and it was found that all genes could be expressed. Except for a few glycosyltransferase genes, most of the genes showed maximum expression levels at 6 h. This study lays a foundation for further studies on the interaction between gene clusters and the structures of EPS from S. thermophilus.

In order to compare the conversion efficiencies of hesperidin into hesperitin-7-O-glucoside by single- and mixed-strain at 30 ℃ and 160 r/min, hesperidin was transformed by submerged fermentation using single and mixed (1:1) cultures of Fusarium nivale and Aspergillus sojae, and the fermentation products and the α-L-rhamnosidase activity of the fermentation broth the at different time points during fermentation were determined by high performance liquid chromatography (HPLC) and ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) and the pH of the fermentation broth was measured as well. The results showed that there was a significant difference between the mixed- and single-strain fermentations in the transformation of hesperidin to hesperitin-7-O-glucoside (P < 0.05). The mixed-strain fermentation gave a higher α-L-rhamnosidase activity (104.81 U/mL) than the single-strain fermentations (24.73 and 26.17 U/mL), and the fermentation of both strains was completed under acidic condition (pH 4–6). Mixed-strain fermentation could provide another way for the comprehensive development of orange peel, which could make full use of citrus by-products and at the same time avoid environmental pollution.

A total of seven lactic acid bacteria strains with bioprotective potential were isolated and characterized from vacuum-packaged chilled beef. By morphological observation, physiological and biochemical identification and 16S rDNA sequencing, they were determined as Lactobacillus sakei. All isolates grew well at 25?35 ℃, and RS-16 and RS-25 grew better and had a stronger acid-producing ability. Antibiotic resistance and virulence genes were detected in RS-33 and RS-41 but not any of the other strains. The results of agar diffusion test showed that the seven isolates had antagonistic effect on all indicator strains, and the antagonistic effect of strains RS-16 and RS-25 on Salmonella typhimurium was better than that of the other strains (P < 0.05). Organic acids secreted by the isolated strains were found to have antibacterial activity.

This study aimed to improve the thermostability of κ-carrageenase from Pseudoalteromonas sp. JMUZ2 by rational design. A total of 10 single-site mutants were chosen using the PoPMuSiC program to analyze the sequence of the κ-carrageenase gene. A mutant gene was obtained by site-directed mutagenesis. The mutant enzyme was expressed under induced conditions, purified and identified. The mutant K155A could maintain the specific enzyme activity and had improved thermostability. After treatment at 50, 55, and 60 ℃ for 40 min, the thermal stability of the mutant K155A was 1.8, 2.7, and 4.5 times higher than that of the wild-type enzyme (WT), respectively. The structure and molecular dynamic simulation analysis showed that the increase in hydrophobic interactions and structural rigidity may be the cause of the improved thermal stability of K155A. This study is of great significance for improving the properties of κ-carrageenase, expanding its application scope, and studying its structural-functional relationship.

Objective: The purpose of this research was to explore the global transcriptome response of Salmonella typhimurium under acid stress and non-acid stress conditions, analyze the expression levels of differentially expressed genes (DEGs), and elucidate the metabolic pathways related to the acid tolerance response (ATR) of S. typhimurium. Methods: Transcriptome sequencing and bioinformatics were used to select the ATR-related DEGs, whcih were then verified by real-time polymerase chain reaction (real-time PCR). Results: In response to acid stress, a total of 683 DEGs were identified in S. typhimurium, including 343 up-regulated and 340 down-regulated ones. The DEGs involved in cell movements, amino acid metabolism, and cell membrane composition were up-regulated, thus making S. typhimurium adapt to the acidic environment quickly. The up-regulation of the genes associated with carbohydrate metabolism could provide more energy for S. typhimurium to adapt to the acidic environment rapidly. Meanwhile, the down-regulation of the genes involved in energy metabolism pathways such as pyrimidine metabolism could reduce the energy consumption of S. typhimurium to maintain these essential metabolic processes. The up-regulation of the genes related to stress reponse response could enhance the cross-protective resistance of S. typhimurium, and the up-regulation of the virulence-related genes such as flagella, outer membrane protein, and lipopolysaccharide could strengthen the virulence of acid-adpted S. typhimurium. Additionally, the results of real-time PCR were consistent with these transcriptomic data. Conclusion: Acid stress can significantly enhance the acid tolerance of S. typhimurium, and the signaling pathways related to metabolism and cellular processes may play major roles in this effect. This study provides a theoretical basis for further understanding the ATR of S. typhimurium and better controlling its contamination in foods.

The changes in the microbial community structure and the synthesis of volatile flavor compounds in fermented grains (Jiupei) for nongxiangxing baijiu in the presence of Bacillus velezensis was analyzed to understand the effect of microorganisms in Daqu, a traditional fermentation starter for the production of baijiu, on microorganisms in Jiupei and their metabolism. Fermentation experiments were carried out by inoculating a strain of B. velezensis isolated from medium- and high-temperature Daqu into Jiupei. Headspace solid phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to detect the volatile flavor compounds of the control and experimental Jiupei, and the microbial community structure of the control and experimental Jiupei was studied by amplicon sequencing. Partial least squares-discriminant analysis (PLS-DA) was used to explore the differential volatile flavor compounds between the control and experimental samples, and Spearman correlation analysis was used to analyze the correlation between the dominant microbial community and the differential volatile flavor compounds in Jiupei. The results showed that the abundance and uniformity of microorganisms in the experimental group did not change significantly compared with the control group, and there was no significant difference in the microbial community structure during the whole fermentation process. The contents of volatile flavor substances such as acids, esters, and alcohols in the experimental group were significantly increased compared with the control group. A total of 15 significantly differential volatile flavor compounds were identified between the control and experimental groups. The contents of caproic acid and ethyl caproate in the experimental group increased significantly. Caproic acid had a significantly positive correlation with Lactobacillus, and ethyl caproate was positively correlated with Pichia and Wickerhamomyces, but negatively correlated with Thermoascus, Bacillus and Weissella. The results of this study can help to understand the perturbation effect of Daqu microorganisms on Jiupei microorganisms and the changes of metabolites.

In this study, the population structure and evolutionary relationships of 59 Enterococcus faecalis strains isolated from breast milk, cheese, camel milk, mare milk and cold water fish from Xinjiang were analyzed by multilocus sequence typing (MLST). All the isolates were allocated into 12 sequence types, including three clonal complexes and three singletons. None of the sequence types were found to belong to high risk clonal complexes. Housekeeping gene split decomposition analysis indicated that gene recombination could be a major driving force in the evolution of E. faecalis. The results of minimum spanning tree indicated these E. faecalis strains were relatively weakly related to their geographical origin. Although eBURST and phylogenetic analysis demonstrated that the isolates from breast milk and cold water fish exhibited host specificity, E. faecalis clones closely related to them were still detected in breast milk, cheese, mare milk and camel milk. Taken together, E. faecalis from different hosts can adapt to new niches and spread via production practice and the food chain. Continuous monitoring is necessary to reduce the potential risk of zoonotic diseases

In order to explore the differences in the metabolite profiles of industrially long-term fermented kohlrabi with different fermentation periods and the major metabolic pathways involved, the metabolite profiles of kohlrabi fermented for 0, 5 and 10 years were analyzed and compared by using liquid chromatography-tandem mass spectrometry (LC-MS/MS) combined with multivariate statistical analysis. The results showed that a total of 53, 113 and 174 differential metabolites were identified in years 0 versus 5, 5 versus 10, and 0 versus 10 of fermentation, respectively (variable importance in the projection (VIP) > 1.3, P < 0.05), including organic acids, amino acids, nucleic acids and their derivatives. Nineteen differential metabolites were common to the three fermentation time points, including L-phenylalanine, and β-D-fructose-6-phosphate. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of the differential metabolites showed that phenylalanine metabolism, the pentose phosphate pathway, and the fructose and mannose metabolic pathways were the most significantly correlated with the major differential metabolites. The present study provides a theoretical basis for targeted regulation of the biosynthesis of the characteristic metabolites in fermented kohlrabi.

The fungal strain M6-5 capable of producing aroma compounds was identified by morphology and molecular biology techniques (ITS sequence and tef1 sequence analysis), and the antifungal activity of volatile compounds from M6-5 at different growth stages against Alternaria alternata was tested. The volatile compounds were analyzed by headspace solid phase microextraction coupled with gas chromatography-tandem mass spectrometry (HPME-GC-MS). Antimicrobial properties of purified compounds were evaluated. A desiccator was used to analyze the inhibitory effect of volatile substances produced by strain M6-5 on postharvest black spot of Korla fragrant pear. The results showed that this strain was identified as Trichoderma erinaceum, and the antifungal activity of volatile substances produced by it against A. alternata reached a maximum on the fifth day of growth with an inhibition percentage of (82.48 ± 1.17)%, and was maintained until the 20th day. A total of 65 components were detected from strain M6-5 on the fifth day of growth, including 6-pentyl-2H-pyran-2-ketone, 3-hydroxybutyrate ethyl ester, phenylethanol, 2-allylfuran, and methyl palmitate, accounting for 40.12%, 6.49%, 4.38%, 4.13% and 3.48% of the total volatile substances, respectively. The inhibition percentages of 6-pentyl-2H-pyran-2-ketone, 3-hydroxy-ethyl butyrate and phenylethanol purified from a culture of strain M6-5 on A. alternata were (21.27 ± 0.60)%, (41.43 ± 2.36)% and (50.23 ± 1.07)%, respectively at a concentration of 714.28 μL/L. The volatile substances produced by strain M6-5 reduced the diameter of black spot in Korla fragrant pear by 42.46% compared with the control group. This study can provide useful information for the control of postharvest black spot in Korla fragrant pear.

To uncover the origin of the microbial community in strong-flavor Daqu, this study investigated the traceability of the microbial communities in Daqu and environmental samples from old and new production bases of one distillery. The production environment was thought to play a key role in the manufacturing process of Daqu. The results of SourceTracker showed that the major microbial sources of the raw starter brick before incubation from the old base were the raw materials and the production tools, and the environment in the old base contributed more to the bacterial communities in the raw starter brick and mature Daqu (Daqu just transferred to the storeroom). However, the fungal community was relatively stable and less affected by the environmental microbiota. As powdered aged Daqu (above three months old) was used to improve the quality of fresh Daqu, the microbial sources of the raw starter brick and mature Daqu from the new production base were the aged Daqu. A suitable environment for the production of Daqu could be created by proper fortification methods, which is of great significance to maintain the quality of Daqu.

Two short peptides PF1 and PF2 with isoelectric points of 12.01 and 3.18, respectively, were designed and synthesized artificially, with full gene length of 309 bp. Each gene was amplified with two primers, cloned into the pET-30a (+) vector and expressed. The expressed products were purified by Ni-NTA column affinity chromatography. SDS-PAGE and Western blot analysis showed that the expressed target protein was consistent with the expected size. The purified short peptides PF1 and PF2 increased and decreased glucose oxidase (GOD) activity by 8.34% and 6.88%, respectively. Therefore, it could be concluded that artificially designed short peptides with different charges PF1 and PF2 can promote or inhibit the catalytic effect of GOD, and further broaden the application scope of GOD in food fermentation and food preservation.

In this study, the difference in the chemical composition among the representative types of Yunnan white tea, Yun Baihao, Yueguangbai grade I and II of Baimudan and Yun Shou were investigated by metabolomics based on ultra-high performance liquid chromatography-quadrupole orbitrap mass spectrometry (UPLC-Q-Orbitrap-MS). A total of 120 compounds were identified, including catechins, dimeric catechins, amino acids, alkaloids, phenolic acids, organic acids, aroma glycosides, flavonoid glycosides, N-ethyl-2-pyrrolidinone-substituted flavan-3-ols, and lipids. Partial least squares-discriminant analysis (PLS-DA) and heatmap analysis showed that there were distinct differences in the chemical components among the different types of Yunnan white tea. A total of 76 significantly differential compounds were among these types (P < 0.05). The contents of catechins, dimeric catechins, alkaloids, phenolic acids, and theanine were higher in white tea from younger tea leaves; some amino acids and myricetin glycosides were richer in Baimudan, while the contents of apigenin glycoside, kaempferol glycoside, quercetin glycoside and lipid compounds were relatively high in Yunshou. This study can provide a theoretical basis for the studies of sensory quality, nutritional value and grade discrimination of Yunnan white tea.

Umami peptides from an aqueous extract of Wuding chicken meat were separated and purified by sequential ultrafiltration, gel filtration chromatography (GPC) and reversed-phase high performance liquid chromatography (RP-HPLC). Sensory evaluation was performed to find the fractions with the strongest umami taste, and then the umami peptides were identified by nano-high performance liquid chromatography-tandem gas chromatography (Nano-HPLC-MS/MS) and synthesized by and solid phase synthesis. Moreover, the sequence and taste characteristics of the umami peptides were further analyzed. The results showed that eight peptides with molecular masses ranging from 365.20 to 1 735.92 Da were isolated and identified. Among them, LDF, FVT and DLAGRDLTDYLMKIL exhibited significant umami intensity, with thresholds ranging from 0.062 to 0.250 mg/mL, indicating that they are the key umami components of Wuding chicken meat.

In this study, the volatile composition and characteristic flavor compounds of Changsha stinky tofu brine during fermentation were analyzed and identified by headspace solid phase microextraction coupled to gas chromatography-mass spectrometry (HS-SPME-GC-MS) with internal standards based on odor activity values (OAV). The dominant microbiota was investigated by shotgun metagenomic sequencing, and the correlation between the dominant microbiota and the characteristic flavor substances was analyzed by calculating Pearson’s correlation coefficients. Results showed that a total of 75 volatile flavor compounds were identified during the 120-day fermentation period, including phenols, indoles, alcohols, acids, aldehydes, ketones, esters, and ethers. Phenol, p-cresol, indole, 3-methylindole, butyric acid, isovaleric acid, 4-ethylphenol, trimethylamine, 3-methyl-1-butanol, 2-heptanol, 1-hexanol, 3-octanol, 1-octen-3-ol, 2-undecanol, phenethyl alcohol, (E,E)-farnesol, ethyl 3-phenylpropionate, 4-dodecanolide and 1-nonanal were identified as the characteristic flavor substances in the whole fermentation process. The predominant microorganisms identified were Clostridium bacterium SYSU GA17129, Clostridiales unclassified, Clostridium ultunense, Sporanaeromonas acetenes, Keratinibaculum paraultunense, Massiilibacterium senegalense, Aneurinibacillus aneurinilyticus, Pseudogracilibacillus auburnensis, Paencaligenes hominis, Ignatzschineria sp. F8392, and Ignatzschineria indica. Moreover, C. bacterium SYSU GA17129, A. aneurinilyticus, and S. acetigenes had significant correlations with 12 characteristic flavor components (P < 0.05), which were the major microbiota associated with the flavor of Changsha stinky tofu brine. This study provides a theoretical basis for promoting the stability of the flavor quality of Changsha stinky tofu.

An analytical method for simultaneous determination of phenolic acid compounds (free phenolic acids, free phenolic acid esters, bound phenolic acids, soluble phenolic acid glycosides and insoluble phenolic acid glycosides) in tea samples was established by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The free phenolic acids in samples were extracted with 70% methanol, and the extract was hydrolyzed with 2 mol/L NaOH solution (containing 1 g/100 mL ascorbic acid and 10 mmol/L EDTA) and 1 mol/L HCl solution, separately, to release free phenolic acid esters and soluble phenolic acid glycosides, respectively. The reside after extraction was hydrolyzed by alkali and acid, separately, to release bound phenolic acid and insoluble phenolic acid glycosides. The calibration curves for the 23 phenolic acid compounds showed good linearity in the range of 50–1 000 μg/L, with correlation coefficients (r) higher than 0.996, and the relative standard deviation was less than 8.84%. The recoveries of free phenolic acids in tea samples were 71.14%–105.43%, and the recoveries of free phenolic acid esters and soluble phenolic acid glycosides were 82.81%–108.93% and 39.09%–102.25%, respectively. Fourteen phenolic acid compounds were identified in tea, with a total content ranging from 7.84 to 12.90 mg/g.

In this study, fresh tea leaves produced in Chongqing were used to made Chongqing tuo tea. We explored the effect of four drying processes, oven drying at 60 ℃ (1), oven drying at 80 ℃ (2), sun drying for 3 h followed by oven drying at 60 ℃ (3), and sun drying for 3 h followed by oven drying at 80 ℃ (4), on the flavor quality of Chongqing tuo tea and crude tea for making it. Results showed that the tuo tea and crude tea samples prepared by the former two drying methods had better sensory quality than those prepared by the latter two. The content of polyphenols was lower and only 31.3% in the crude tea prepared by the third drying process, while its contents of amino acids, water extract and aroma substances were as high as 2.2%, 43.9% and 182.57 μg/L, respectively, and 16 alkenes and 7 alcohols were identified from it. Both the number and amount of aroma compounds in the crude tea prepared by the first drying process were the highest and 54 and 190.27 μg/L, respectively, but the aroma contents in the crude tea samples prepared by the second and fourth drying methods were lower. After being compacted to obtain tuo tea, the contents of amino acids, alcohols, aldehydes, alkenes and acids in all crude tea samples decreased, while the content of caffeine increased. The contents of tea polyphenols, amino acids and water extract did not significantly change in the tuo tea sample prepared by the third drying process compared to the crude tea processed by this process, and its number and amount of aroma substances were the highest and 50 and 252.11 μg/L, respectively. In addition, its contents of ketones and esters increased by 64.6% and 113%. Two new ketones were detected in the tuo tea sample prepared by the first drying process; however, the number and amount of aroma substances in tuo tea were reduced by the second and fourth drying processes. Eleven differential aroma substances were identified by orthogonal partial least squares-discriminant analysis (OPLS-DA), which included five alkenes. The first and third drying processes provided more differential aroma substances from crude tea, and the content of n-heneicosane was high in the tuo cha prepared by the two processes. The odor activity value (OAV) of β-ionone was above 10 in all tea samples, and the OAV of linalool was above one in the tuo tea and crude tea prepared by the first and third drying processes. In summary, the quality of crude tea and tuo tea prepared by the first and third drying processes was better, and so the drying processes were more suitable for Chongqing tuo tea processing.

In this study, non-targeted metabolomics based on ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) was used to explore the change in the metabolite profile in giant salamander meat during cold storage at 4 ℃ (0, 2, 4 and 8 days). The differences within each group and between the 0- and 2-day storage groups were small, while the intra- and inter-group differences between days 4 and 8 of storage were large. As the storage time increased, the number of differential metabolites between adjacent groups increased gradually. Using the variable importance in the projection (VIP) value of the first principal component in the partial least squares discriminant analysis (PLS-DA) model greater than or equal to two, and the P-value of t-test less than or equal to 0.001 as criteria, a total of 125 differential metabolites were selected, including organic acids and their derivatives (17), esters and their derivatives (53), amino acids and their derivatives (25), nucleotides and their derivatives (13), alcohols (3) and other compounds (14). The abundance of most of the metabolites decreased significantly on 8 day of storage (P < 0.05). The cumulative change in the abundance of the organic acids and their derivatives (A1) had a similar trend to that of the amino acids and their derivatives (A3), that is, there was a small increase from days 0 to 2, a small decrease from days 2 to 4, and a rapid decrease from days 4 to 8. The cumulative changes in the abundance of the esters and their derivatives (A2) as well as the nucleotides and their derivatives (A4) showed a downward trend, but the abundance of the esters and their derivatives (A2) decreased slowly from days 0 to 4 and rapidly from days 4 to 8, while the abundance of the nucleotides and their derivatives (A4) showed a linear downward trend. The results of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis and Pearson correlation analysis showed that histidine metabolism, arginine and proline metabolism, arginine biosynthesis, lysine degradation, taurine and sub taurine metabolism, valine, leucine and isoleucine biosynthesis, and aminoacyl-tRNA biosynthesis and other metabolic pathways had a good correlation with the changes of giant salamander meat quality; at the same time, creatine, L-histidinol, L-glutamate, histidine, ornithine, L-arginine and phytosphingosine could be used as potential markers for evaluating the quality change of giant salamander meat during cold storage. The results of this study provide a theoretical basis for understanding postmortem metabolism in giant salamander muscle and for quality control of giant salamander meat during cold storage.

The composition and content of anthocyanins in a superior strain of ‘Tarocco’ blood orange and the ordinary variety were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and differential metabolites were selected. The results indicated that a total of 33 anthocyanin-related metabolites belonging to seven classes: cyanidin, delphinidin, peonidin, pelargonidin, malyidin, petunidin and flavonoid precursors of anthocyanin synthesis were identified in the superior strain. Furthermore, the number and kinds of anthocyanin metabolites in bore and peripheral fruits from the superior strain were identical, with no differential metabolites being found between them. In contrast, 27 and 30 metabolites were detected in bore and peripheral fruits from the control variety, and nine differential metabolites including cyanidin, delphinidin, peonidin and flavonoids were identified between bore and peripheral fruits. For both the superior strain and the ordinary variety, the main anthocyanin components were cyanidin-3-O-(6-O-malonyl)-glucoside and cyanidin-3-O-glucoside, accounting for 42.3% and 41.0% of the total anthocyanin content in the inner bore fruit and 40.6% and 41.4% of the total anthocyanin content in peripheral fruit from the superior line; and accounting for 39.5% and 41.0% of the total anthocyanin content in inner bore fruit and 36.8% and 40.6% of the total anthocyanin content in peripheral fruit from the common variety, respectively. Compared with the control variety, the amount of cyanidin and the proportion of total anthocyanins in the superior strain were significantly increased, and the total cyanidin contents in inner and peripheral fruits from the superior strain were 48.68 (91.90%) and 62.16 μg/g (92.28%), respectively. In addition, the percentage of delphinidin, peonidin and flavonoids in relation to the total anthocyanin content were similar between inner and peripheral fruits, suggesting that temperature may have little effect on anthocyanin synthesis in the superior strain. We concluded that the superior strain of ‘Tarocco’ blood orange has higher anthocyanin content than that the common variety and contains more kinds of metabolites. This study can provide a theoretical basis for genetic improvement and utilization of ‘Tarocco’ blood orange.

In order to clarify the significance of the division of small wine production regions in the eastern foothill of Helan Mountain in Ningxia, the free and bound aroma substances in the mature fruits of two wine grape varieties from four vineyards in the eastern foothill of Helan Mountain were determined by gas chromatography-mass spectrometry (GC-MS), and the influence of different parcels on the aroma composition of wine grapes was analyzed. The results showed that the soils of these four parcels were all sandy loam. The soil of the Gaojiazha parcel contained more clay, the Zhihui parcel was close to sandy soil, and the soil texture of the Huaxi and Jinshan parcels was between the Zhihui and Gaojiazha parcels. The 100-berry mass, 100-berry volume and titratable acid content of Chardonnay grapes from the Zhihui parcel were significantly higher than those of Chardonnay grapes from the Gaojiazha parcel. No significant variation in the 100-berry mass or 100-berry volume of ‘Cabernet Sauvignon’ berries was found among the different parcels. However, ‘Cabernet Sauvignon’ berries from the Jinshan parcel had higher soluble solids content but lower titratable acid content. The types and contents of aroma substances in ‘Cabernet Sauvignon’ and ‘Chardonnay’ berries were significantly different among these four parcels, mainly in terms of the amounts of C6/C9, norisoprenoids, esters and terpenes. ‘Chardonnay’ grapes from the Zhihui parcel contained more free (E)-2-hexenal, β-damasone and bound octanoic acid ethyl ester, and had stronger floral, fruity and green aromas based on odor activity values (OAVs). ‘Cabernet Sauvignon’ grapes from the Jinshan parcel contained more free (E)-2-hexenal and (Z)-3-hexen-1-ol, and had a stronger green aroma based on OAVs.

The difference in the volatile composition of Toona sinensis from eight production areas was evaluated by gas chromatography-ion mobility spectrometry (GC-IMS). A total of 56 compounds were identified, the major ones being alcohols and aldehydes. Using principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA), T. sinensis samples from the eight production areas were well distinguished. A total of 12 volatile compounds with a variable importance in projection (VIP) score greater than one were selected as marker compounds, among which, (E)-2-hexenal-D, ethyl acetate-D, p-ethylphenol, furfural and benzeneethanol were found to be the major differential metabolites. The volatile composition of T. sinensis from different production areas was significantly different. GC-IMS could allow for the rapid identification of the differential volatile organic compounds in T. sinensis from different production regions, which provides a useful basis for the study of the difference in the volatile aroma composition of T. sinensis from different production areas.

In order to elucidate the difference in the composition of milk fat globule membrane proteins (MFGMP) in bactrian camel milk and bovine milk, the high-abundance MFGMP in the two milks were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional electrophoresis (2-DE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The experimental results showed that the most abundant protein fractions in bactrian camel and bovine MFGMPs were, in decreasing order, lactophilic lipoprotein (BTN), xanthine oxidoreductase/dehydrogenase (XO/XDH), milk agglutinin (MFG-E8 or PAS6/7), and adipocyte differentiation-related protein (ADRP or perilipin-2). The results of SDS-PAGE, 2-DE and LC-MS/MS were consistent for the high-abundance MFGMP fractions from bactrian camel milk and cow milk. The bactrian camel MFGMP identified by LC-MS/MS were subjected to Gene Ontology (GO) functional annotation analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, revealing that these proteins are mainly cell membrane, mitochondria and endoplasmic reticulum membrane components, involved in biological pathways such as translation and translation initiation, redox process, intracellular protein translocation, protein folding, and cellular redox homeostasis, and they have molecular functions such as binding activity and molecular catalysis.

An innovative strategy for the preparation of Zr-based metal-organic framework (MOF, UIO-67) anchored three-dimensional carboxymethyl cellulose (CMC) aerogels was developed as a flexible and efficient absorbent for the removal of the bitter compounds from ponkan wine. Field emission scanning electron microscopy (FESEM) was carried out to investigate the morphology and hierarchical structure of CMC and UIO-67/CMC aerogels. Results showed that UIO-67 was found to be uniformly distributed on CMC. UIO-67/CMC aerogels maintained the three-dimensional porous structure of CMC. The adsorption experiments showed that the adsorption equilibrium time of UIO-67/CMC aerogels was 10 min for limonin and 20 min for naringin with adsorption efficiency of 83% and 56%, respectively. The adsorption behaviors followed the pseudo-second-order kinetic and Langmuir isotherm models, indicating that the adsorption rate is governed by chemical adsorption and the adsorption process is single-layer adsorption. Treatment with UIO-67/CMC aerogels retained most of the flavor compounds in ponkan wine while improving its physicochemical properties.

The metabolites and lipids in donkey milk from Xinjiang and Shandong were studied by non-targeted metabolomics and lipidomics. The results showed that there were significant differences in metabolites and lipids between the two groups of samples. With variable importance in the projection (VIP) > 1, P < 0.05 and fold change (FC) ≥ 2 or < 0.5 as the threshold, 12 and 34 differential metabolites were selected in the positive and negative ion modes, respectively, including some important compounds such as morphiceptin, madlongiside C, valyl-hydroxyproline. Further analysis revealed that these compounds could be related to proteolysis and microbial metabolism. With VIP ≥ 3.0, P < 0.001 and FC ≥ 2 or < 0.5 as the threshold, 50 and 36 differential lipids were selected in negative and positive ion modes, respectively. The differential lipids and metabolites found in this study can be used as potential markers for geographic origin identification, while will provide a theoretical basis for intensive processing of donkey milk.

An analytical method for the determination of manganese dioxide (KMnO4) consumption for migrants from food contact rubber by ultraviolet-visible (UV-Vis) spectrophotometry was established. The reaction time, and the concentration of sulfuric acid (H2SO4) and KMnO4 were optimized, and the analytical figures of merit of the method were evaluated. Results showed that the concentrations of H2SO4 and KMnO4 in migrant aqueous solution with KMnO4 consumption of 1 mg/kg should exceed 0.1 and 0.005 74 mmol/L, respectively, and the optimal reaction time was 6 min. The detection wavelength was set at 525 nm. The KMnO4 standard solution exhibited good linearity in the range of 0.014–0.280 mmol/L, with a correlation coefficient (R2) of 0.998 91. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 6.8 × 10-4 and 2.0 × 10-3 mmol/L, respectively. F test and t test showed that the results of this method were not significantly different from those of the official redox titration method, and the relative standard deviation (RSD) was between 1.7% and 7.8%. The proposed method is useful for the analysis of KMnO4 consumption for migrants from food contact rubber in food quality control.

Driven by the urgent market demand for milk traceability technologies, a microdroplet digital polymerase chain reaction (PCR) assay was developed to accurately identify the milk source in goat milk powder. This method overcame the shortcomings of complex ingredients and long time required for identifying the source of milk, and could detect it more accurately and reduce the possibility of misjudgment. In this study, a model equation for describing the relationship between the number of DNA copies per μL from goat milk powder (C) and its mass (M, mg) was proposed as follows: M = (C?4.75)/3.56.

A simple, novel, and sensitive biosensor for the colorimetric detection of Sudan dyes was successfully prepared using Sudan III aptamer as a recognition element, hemin/G-quadruplex DNAzyme as a signal indicator, and hybridization chain reaction as a signal amplification strategy. Under optimized conditions, the sensitivity, accuracy and specificity of the method were evaluated.?Finally, the developed method was applied to detect Sudan III in food samples, and was validated by comparing it with the national standard method (GB/T 19681-2005). A good linear relationship was obtained between the absorbance at 450 nm and the concentration of Sudan III in the range of 0.5 to 250 ng/mL with correlation coefficient of 0.995, and the detection limit was 0.09 ng/mL. Specificity analysis demonstrated that this method could be used to detect Sudan I–IV. The recoveries of Sudan III from spiked real samples ranged from 84.3% to 101.6%, with relative standard deviations of 4.13%–8.36%. There was no significant difference in the spiked recoveries between the proposed method and the national standard method (P > 0.05). This method was simple, reliable, sensitive, and suitable for the detection of Sudan dyes in food samples.

In order to quickly and effectively identify the slight damage of white button mushroom (Agaricus bisporus), the near-infrared hyperspectral images (400?1 000 nm) of the intact mushroom and the mushroom with different degrees of damage caused by vibration for 60 and 120 s were recorded. It was found that the spectra of the three types of samples in the wavelength range 450?750 nm were obviously different. Compared to standard normal variable transformation and multivariate scattering correction, Savitzky Golay (SG) smoothing was determined as a better pretreatment method. The successive projection algorithm (SPA) and competitive adaptive reweighted sampling (CARS) were applied to extract the vibration-specific wavelengths. Based on the gray-level co-occurrence matrix, the texture features of the region of interest of the feature image at 500 nm were extracted. A model to discriminate the degree of damage of mushrooms was established using partial least square discriminant analysis (PLS-DA), BP neural network and extreme learning machine (ELM) based on the spectral information and the texture feature information, separately. The results showed that the PLS-DA model with each of the two feature sets as input had better performance than the other two models. With the spectral information as input, the average recognition accuracies for the training set and the test set were 93.33% and 91.11%, while those with the texture feature information as input were 88.89% and 86.67%, respectively. Finally, a PLS-DA classification model was established based on the spectrum-texture fusion information, whose overall classification accuracies for the training set and the test set were 97.78% and 95.56%, respectively. The predictive performance of the model based on the spectrum-texture fusion information was better than the model based on the single information. Therefore, the application of spectrum-texture fusion information-based modeling can improve the detection accuracy of white button mushrooms with different degrees of damage, which provides theoretical support for the storage and classification of white button mushrooms.

In this study, the effect of treatment with plasma-activated water (PAW) on the biogenic amine content and sensory quality of air-dried pork tenderloin was investigated with the aim of exploring the feasibility of applying cold plasma technology in dried meat products. PAW was prepared using a dielectric barrier discharge (DBD) system at voltages of 50, 60 and 70 kV. Dried meat products were prepared by curing pork tenderloin with NaCl dissolved in PAW or pure water, followed by drying and maturation. The pH, nitrite residue and biogenic amine content of the products were analyzed. The flavor composition was studied using an electronic nose combined with principal component analysis (PCA) and loading analysis (LA). Finally, sensory evaluation was carried out. The results showed that (1) the amount of residual nitrite in the 50, 60 and 70 kV treatment groups were 8.12, 10.11 and 15.24 mg/kg, respectively, which were all lower than the national maximum allowable limit; (2) PAW treatment significantly inhibited the formation of biogenic amines in products, at 50, 60 and 70 kV voltages decreasing cadaverine content by 8.21%, 11.29% and 19.49% and spermine content by 9.64%, 16.54% and 27.56%, respectively (P < 0.05); (3) electronic nose analysis showed that the overall flavor difference between the PAW and control groups was not significant; and (4) sensory evaluation results showed that there was no significant difference in the flavor, taste, texture or acceptability between the PAW and control groups, while high-intensity PAW treatment could impart a better color to products.