This study was conducted in order to investigate the mechanism of the effect of adding different concentrations of L-lysine (L-Lys) on the gelling properties of porcine myofibrillar protein (MP) damaged by repeated freeze-thaw cycles. The changes in the conformation, solubility and gelling properties were analyzed by means of circular dichroism (CD) spectroscopy, intrinsic tryptophan fluorescence spectroscopy, a rheometer, a texture analyzer and a scanning electron microscope. The results showed that the addition of L-Lys caused an increase in the α-helix content and intrinsic tryptophan fluorescence intensity of freezing-damaged MP. The solubility of freezing-damaged MP gradually increased with increasing L-Lys concentrations, the storage modulus (G’), gel strength, cooking loss and gel whiteness gradually decreased, and the gel microstructure became gradually more uniform. On the whole, the addition of L-Lys significantly reduced the gel strength and cooking loss of repeatedly frozen-thawed MP gel by changing the conformation, and could thus improve the water-holding capacity and tenderness of freezing-damaged meat.

This study investigated the non-covalent interactions between zein and each of three polyphenols, and the structure and antioxidant properties of zein-polyphenol complexes in ethanol-water solution using a fluorescence spectrophotometer and an ultraviolet (UV) spectrophotometer. The zein-polyphenols colloidal particles were characterized for their turbidity, particle sizes and microscopic morphology, and the effect of polyphenols on the self-assembly of zein colloidal particles was discussed. The results showed that the polyphenols could statically quench the fluorescence of zein. Zein bound to tannic acid (TA) and epigallocatechin gallate (EGCG) by hydrogen bonds, and the binding constants decreased with increasing temperature, thereby impairing the binding capacity. Zein and gallic acid (GA) were combined by hydrophobic interaction to form a complex, and increased temperature was conducive to the interaction between them. The molar binding ratios of the three polyphenols to zein were all nearly 1:1. In addition, after the combination of polyphenols and zein, the UV absorbance of the complexes was significantly increased, the mode of protein folding was changed, the hydrophobic group was buried, and the antioxidant activity and thermal stability of the non-covalently bound complexes was increased. The non-covalent interaction between zein and TA increased the particle size of the complex, and decreased the surface charge. The microstructure of the composite particles showed a regular spherical shape. TA could act as a cross-linking agent for the particles. Similarly, the surface characteristics and microstructure of the composite nanoparticles formed by zein with EGCG or GA were changed. However, the colloidal particles were not cross-linked obviously and still uniformly dispersed.

In this study, β-lactoglobulin (β-LG) nanoparticles loaded with three polyphenols were prepared by emulsification-evaporation method. Ferulic acid, quercetin and vanillic acid were combined with heat-treated β-LG to form a three-ligand complex, and then the emulsification-evaporation method was used to reduce the particle size of the complex. The structure and morphology were investigated by dynamic light scattering, circular dichroism (CD) spectroscopy, infrared spectroscopy, fluorescence spectroscopy, and transmission electron microscopy (TEM). The polyphenol loading efficiency and stability were studied by ultra-high performance liquid chromatography (UPLC). The results showed that the particle size of the β-lactoglobulin-polyphenol complex was reduced from the submicron level (100–200 nm) to the nanometer level (< 100 nm) by the emulsification-evaporation method. Fluorescence, infrared and CD spectra showed that the addition of polyphenols changed the microenvironment and secondary structure of β-LG. TEM images showed that the composite was approximately elliptical in shape and evenly distributed. The loading efficiencies of ferulic acid, quercetin and vanillic acid in the composite nanoparticles were 86.78%, 75.00% and 86.40%, respectively, which were 60.11%, 37.09% and 68.93% higher than those in the three-ligand complex, respectively and the former had better stability.

To identify the effects of fructo-oligosaccharides on retrogradation characteristics of rice starch, we determined the setback viscosity, syneresis rate, firmness, amylose leaching, and dynamic rheology of rice starch paste blended with fructo-oligosaccharides in contrast to the widely reported anti-retrogradation additive β-cyclodextrin. The retrogradation characteristics of rice starch were analyzed by Fourier transform infrared (FTIR) spectroscopy, low field nuclear magnetic resonance (LF-NMR), scanning electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, and confocal laser scanning microscopy (CLSM). The results showed that fructo-oligosaccharide treatment significantly decreased the peak viscosity, final viscosity and setback value of gelatinized rice starch paste. In addition, after short-time refrigeration, fructo-oligosaccharide-treated rice starch exhibited lower syneresis rate (21.82%), hardness (16.26%) and amylose leaching (17.25%), indicating that fructo-oligosaccharides could improve the water retention and stability of rice starch. Also, fructose-oligosaccharides decreased the storage modulus, water mobility, relative crystallinity, and ratio between transmittance at wavenumbers of 1 047 and 1 022 cm-1 of rice starch paste, and made the network structure become more compact, showing better anti-retrogradation efficiency. Therefore, fructo-oligosaccharides have excellent potential in delaying the retrogradation of rice starch-based foods.

In this study, heat-induced gels were made from mixtures of potato protein (PP) and egg white protein (EWP) at different ratios, and their texture properties, protein secondary structures, intermolecular forces, free sulfhydryl group contents and rheological properties were investigated. The results showed that with increasing level of PP, the water-holding capacity of mixed gels increased from (73.5 ± 0.71)% to (97.5 ± 0.71)% (P < 0.05) and the roughness gradually decreased. With increasing level of EWP, the hardness increased from (460.5 ± 4.4) g to (1 614.9 ± 126.4) g (P < 0.05). The two proteins complemented each other in water-holding capacity and hardness. When the ratio of PP to EWP approached 1, the secondary structure of mixed gels was transformed from β-sheet and α-helical to random coil, and the hydrogen bonds were gradually weakened. Hydrophobic interactions and free sulfhydryl contents increased with increasing level of EWP. The mixed gels with PP-EWP ratio of 1:0, 9:1 and 0:1 possessed higher elastic modulus. The gels strength was significantly positively correlated with hydrophobic interactions and free sulfhydryl group content (P < 0.01), and negatively correlated with water-holding capacity (P < 0.01), but had no significant correlation with storage modulus (P > 0.05).

Alkylpyrazines formed by the Maillard reaction between alanine (Ala) and 2,3-butanedione (2,3-BD) were identified and quantified by high performance liquid chromatography (HPLC). Kinetic models for six alkylpyrazines were established to understand the mechanism of the formation of pyrazines. A total of eight alkylpyrazines were identified, including five methylpyrazines and three ethylpyrazines. The results showed that the formation of alkylpyrazines had a good correlation with reaction temperature and time, and was favored by alkaline conditions. The formation of dimethyl pyrazines (DMPs) and ethylpyrazines (EP) followed a first-order kinetic model, while the formation of the other pyrazines fitted well to a zero-order kinetic model. Among the eight alkylpyrazines, the activation energy for the formation of 2-ethyl-5-methylpyrazine (EP-5-MP) was the lowest (3.310 6 kJ/mmol).

The effects of the amount of magnetic cellulose microcrystalline complex added, oil/water ratio and the number of homogenization cycles on properties of O/W Pickering emulsions stabilized by magnetic cellulose microcrystalline were studied. The results showed that the average size of Fe3O4 particles prepared was approximately 10 nm, and the average length of cellulose microcrystals modified by Fe3O4 was about 14.2 μm. The surface morphology of cellulose microcrystals was changed from smooth rod to rough morphology. The Fourier transform infrared (FTIR) spectra of cellulose microcrystals showed that the absorption peak of Fe–O bond appeared at 565 cm-1, and that the contact angles of Fe3O4, cellulose microcrystallites and magnetic cellulose microcrystalline complexes were 46.67°, 42.48° and 69.58°, respectively. The optimal conditions for stabilizing Pickering emulsion were determined as follows: addition of 1.5 g/100 mL of magnetic microcrystalline composite, oil/water ratio 3:7 and two homogenization cycles. The initial magnetization value of the magnetic microcrystalline composite was 56.8 emu/g, which was reduced to 4.2 emu/g after fifth repeated use.

The aim of the present work was to develop a novel method integrating two-step aqueous two-phase extraction and affinity adsorption for the separation and purification of horseradish peroxidase (HRP) from horseradish roots. Two-step aqueous two-phase extraction was used to remove sugars and pigments, and then “multivalent” phenylboronic acid affinity magnetic graphene composite (d-PBA-GO@Fe3O4@PEI) was to selectively isolate HRP from impurity proteins. The liquid-liquid equilibrium behaviors of 17R4-(NH4)2SO4, K3C6H5O7 or K2HPO4 aqueous two-phase systems (ATPSs) and the partition behaviors of nine model compounds in these R4-salt ATPSs were investigated, indicating that the optimum ATPS was 8% 17R4-13.2% (NH4)2SO4. The successful isolation of HRP from horseradish roots was achieved by the integrated method without negative effect on the structure of HRP, and the specific activity and purification factor of HRP were 28.93 U/mg and 1.92, respectively. The method has excellent separation and purification performance and thus holds great promise for application in the industrial production of plant glycoproteins.

The purpose of this study is to improve the catalytic activity of aspartate kinase (AK), the first key rate-limiting enzyme in aspartic acid metabolism pathway by site-directed random mutagenesis; reduce or remove the synergistic feedback inhibition of metabolites on it; and analyze its spatial structure using Discovery Studio (DS) software and the underlying mechanism through molecular dynamics simulation (MDS). First, the key residue sites around ATP were chosen for further construction of mutants based on the mutant obtained in our previous study, T379N/A380C/G171I. Then, through high-throughput screening, the mutant T379N/A380C/G171I/S227D with significantly increased AK activity was selected from the mutants. Kinetic analysis showed that the Vmax value of T379N/A380C/G171I/S227D was 242.05 U/(mg·min), which was 1.28 and 80.41 times higher than that of T379N/A380C/G171I (187.88 U/(mg·min)) and the wild-type (WT) strain (3.01 U/(mg·min)), respectively. The Km value decreased to 1.35 mmol/L, and the substrate affinity was increased. Through DS software and MDS analysis, it was found that the system became more stable after the mutation, the hydrogen bond occupancy rate with ATP was increased, and the substrate binding stability was enhanced, thereby favoring the catalytic reaction. The enzymatic properties showed that the optimal reaction temperature of T379N/A380C/G171I/S227D was 30 ℃, 5 and 2 ℃ higher than the wild-type strain and T379N/A380C/G171I, respectively; the optimal pH was 8.5 compared to 9.0 for T379N/A380C/G171I; the half-life was 3.9 h, which was 0.8 h longer than T379N/A380C/G171I. In addition, in the presence of different concentrations of the inhibitors Lys, Thr and Met as well as different combinations of Lys + Thr, Lys + Met, Thr + Met and Lys + Thr + Met, the mutant strain was activated by up to 143.35% rather than inhibited.

This study was executed in order to enrich the transcriptome information of flaxseeds and explore the reasons for the difference in the aroma of flaxseed oils from different cultivars at the molecular level. Two specialty flaxseed cultivars (Yiya-3 and Tianya-6) in Xinjiang were selected to perform transcriptome sequencing analysis using the Illumina high-throughput sequencing platform and a variety of bioinformatic methods. The results showed that a total of 61 995 756 high-quality clean reads were obtained. Further, a total of 33 218 unigenes were obtained after de novo assembling of the sequence data. Non-Redundant Protein (NR) database annotations revealed that the flaxseed transcriptome had the highest sequence similarity to Jatropha curcas, and 17 269 unigenes were annotated in the Cluster of Orthologous Group (COG) database, which were divided into 22 branches in three categories, including cellular processes and signals, information storage and processing, and metabolism. There were 1 658 significant differentially expressed genes (DEGs) identified between the two cultivars. Compared to Tianya-6, 825 genes were up-regulated and 833 genes were down-regulated in Yiya-3. The annotation of the DEGs in the Gene Ontology (GO) database showed that they were distributed in three categories: biological processes, cellular components and molecular functions. The 380 DEGs annotated in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database were mainly enriched in fatty acid metabolism and other metabolic pathways, and 17 DEGs could be annotated in the fatty acid metabolism pathway, with eight being annotated in the unsaturated fatty acid metabolism pathway. This study provides a theoretical basis and technical support for the analysis of the difference in the aroma of flaxseed oils from different cultivars in Xinjiang.

The effect of Tweens (Tween 40, Tween 80, and Tween 80 combined with oleic acid) on in the metabolism of Corynebacterium crenatum MT NAGK M4 ΔproBΔNcgl1221ΔdtsR1 (CCM01) for L-arginine production was investigated by determining biomass concentration, L-arginine concentration and residual sugar levels in the fermented broth. Real-time polymerase chain reaction was used to evaluate the transcription levels of genes related to L-arginine biosynthesis. The results showed that addition of Tween 40, Tween 80, and Tween 80 combined with oleic acid increased the supply of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) and consequently the production of L-arginine. Notably, when Tween 80 and oleic acid were added to the medium at a molar ratio of 1:0.1, NADPH accumulation increased by 2.56 folds and L-arginine production increased by 29.43%. Additionally, the transcription levels of tkt-tal-zwf-opcA-pgl and gnd involved in NADPH biosynthesis were up-regulated, and the transcription level of the fatty acyl-responsive regulator FarR, a negative regulatory factor of arginine biosynthetic pathway, was down-regulated; accordingly, the transcription levels of gdh, argB and argG were up-regulated. The above results suggest that Tween can increase arginine production in two ways.

The sequence of the 1 887 bp long α-L-arabinofuranosidase gene in Aspergillus niger was cloned by using gene recombination, and was expressed in Pichia pastoris SMD1168. The recombinant protein had a molecular mass of 85 kDa and a specific activity of 55.73 U/mg. The optimal temperature and pH for the enzyme were 65 ℃ and 5.0, respectively. The enzymatic activity was promoted by Mn2+, while it was significantly inhibited by K+. When p-nitrophenyl-α-L-arabinofuranoside (pNPA) was used as the substrate, the Km and Vmax values of α-L-arabinofuranosidase were 2.31 mmol/L and 625 μmol/(mL·min), respectively. More interestingly, the purified α-L-arabinofuranosidase showed a significant clarification effect on citrus juice. This study not only enriches the resource library of α-L-arabinofuranosidase, but also provides a reference for juice processing with α-L-arabinofuranosidase.

This study was performed in order to explore the regulatory mechanism of nitrogen catabolite repression (NCR) in Debaryomyces hansenii cultured under two different nitrogen levels: with (experimental group) and without (control group) L-histidine addition. The Illumina high-throughput sequencing platform was used for transcriptome sequencing of both groups, and various bioinformatics methods were used for data analysis and processing. A total of 42.921 6 and 41.415 4 M clean reads were obtained for the control and experimental groups. Furthermore, a total of 133 significantly differentially expressed genes were identified between the two groups, 78 of which were up-regulated, while 50 were down-regulated. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that most of the differentially expressed genes were involved in histamine metabolism-related coenzymes. This study provides a reference for further studies on histamine metabolism in D. hansenii.

In the present study, four key residues in aspartokinase were selected for site-directed saturation mutagenesis, namely, Thr 379 and Ala 380 (the binding sites of the inhibitor Lys), Thr 65 (the binding site of the substrate Asp) and Asp 173 (the catalytically active site of both substrates and ATP binding site). The mutant T379N/A380C/T65I/D173G was successfully constructed using high-throughput screening. Compared with the wild type (WT) enzyme, the activity of the mutant was increased by 75.83 times. In addition, the characterization of kinetics and enzymatic properties showed that the Km value of the mutant was reduced (1.34 versus 4.11 mmol/L) compared to the WT enzyme, indicating increased substrate affinity. The n value was reduced (1.07 versus 1.71), suggesting that the positive synergistic effect was weakened. Moreover, the optimal temperature, pH and half-life of the mutant were 30 ℃, 8.0 and 3.23 h compared to 25 ℃, 8.0 and 4.24 h for the WT enzyme, respectively. The inhibition effect of the inhibitors at 0.2–10 mmol/L on the mutant was weakened, especially for Lys and Lys + Thr. Through seamless cloning, it was transformed into Corynebacterium pekinense to construct an engineered bacterium. Compared with WT, the yields of lysine, threonine and methionine were increased by 83.05%, 29.36% and 30.77%, respectively. This work will provide a theoretical basis for optimizing the AK metabolic pathway and constructing strains capable of producing aspartate-family amino acids in high yield.

In order to clarify the effect of inoculated fermentation on the bioaccessibility of phenolic compounds and antioxidant activity in grape jiaosu (fermented grape juice), the changes in fermentation properties, phenolic composition and antioxidant activity during fermentation were studied, and the bioaccessibility of polyphenols was also evaluated by in vitro simulated gastrointestinal digestion. The results showed that the reducing sugar content decreased from 31.91 to 0.46 g/L and the pH decreased from 3.77 to 3.19 during fermentation. The ethanol content increased to 7.66% (V/V) on the sixth day, and then decreased to 0.47% on the 27th day. The release of phenolic compounds was promoted by inoculated fermentation. The contents of total phenols and flavonoids presented a fluctuant increasing trend during the fermentation process, and were increased by 2.16 and 1.83 folds at the end of fermentation. Compared with must, the contents of gallic acid, vanillic acid and myricetin were increased by 7.17, 5.18 folds and 60.29%, respectively. After in vitro gastrointestinal digestion, five phenolic acid showed higher bioaccessibility in the range from 39.11% to 57.77%. Among the tested flavonoids, myricetin and quercetin showed higher bioaccessibility of 35.78% and 42.34%, respectively. The antioxidant activity of grape jiaosu showed an overall increasing trend with fermentation time. Compared with must, the scavenging capacities against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical increased by 51.45% and 82.23%, respectively at the end of fermentation. In conclusion, inoculated fermentation can increase the concentrations of specific phenolic compounds, improve the bioaccessibility of some polyphenols, and enhance the antioxidant activity of grape jiaosu. These results indicate that inoculated fermentation can be used as an effective way to prepare grape jiaosu, which can improve the nutrition and function of grape jiaosu and provide a basis for the development of other functional jiaosu products.

To clarify the basic properties of the dehydroascorbate reductase (DHAR) gene in Hami melon and its expression level during cold stress, we investigated the basic information, multiple sequence alignment, phylogenetic relationship, collinearity and domain characteristics of two DHAR genes, protein three-dimensional (3D) models and protein-protein interaction, as well as ascorbic acid (AsA) contents, DHAR activities and DHAR gene expression levels under cold stress, and we performed gene set enrichment analysis (GSEA). The results showed that the lengths of the proteins encoded by the two CmDHAR genes consisted of 297 and 206 amino acids, respectively. Their isoelectric points were 8.67 and 5.99, respectively. Their molecular masses were 33 082.9 and 22 891.6 Da, respectively. Multiple sequence alignment analysis showed that the CmDHAR genes had a highly conserved glutathione S-transferase (GST) N-terminal functional domain. Gene structure analysis indicated that CmDHAR contained six exons, six conserved motifs and three types of cis-acting elements. Collinearity analysis indicated that Hami melon was evolutionarily closer to zucchini, winter squash and pumpkin. The 3D models revealed that the secondary structure of CmDHAR2 mainly included α-helix, random coil, extended strand and β-turn. Protein-protein interaction analysis showed that CmDHAR family members were closely related to other GST family members. The AsA content, DHAR activity and CmDHAR gene expression level in the cold-tolerant cultivar “Jiashi-310” (JS) were significantly higher than those in the cold-sensitive cultivar “Golden Empress-308” (GE) under cold stress. GSEA results revealed that the CmDHAR genes participated in the biological processes of ‘structural molecule activity’, ‘macromolecular complex’, ‘membrane-enclosed lumen’ and ‘antioxidant activity’. This study has proved that the CmDHAR genes play an important role in the resistance of Hami melon to cold stress.

The aim of this study was to explore a method for screening for proteases specifically hydrolyzing the epitopes of αs1-casein. First, the epitope aa 83–105 of αs1-casein was synthesized by solid-phase synthesis method. After purification and identification, the peptide was coupled to bovine serum albumin (BSA) to prepare a complete antigen, and then BALB/c mice were immunized to prepare monoclonal antibodies. In addition, an indirect competitive enzyme linked immunosorbent assay (ELISA) was established. The monoclonal antibody prepared with αs1-casein and the established method were regarded as controls. The results showed that the purity of the synthetic epitope was over 90%, and the coupling rate with BSA was 6.31. The monoclonal antibody belonged to IgG1, with a titer of 1:320 000, and it could react specifically with αs1-casein, but did not cross-react with soybean protein. The linear regression equation of the competitive inhibition curve was y = ? 9.22x + 100.78 (R2 = 0.989 1). The indirect competitive ELISA method showed good repeatability and accuracy, and its detection limit was lower than that of the monoclonal antibody method. The amounts of residual antigen in papain and alcalase hydrolysates were relatively small, which needs to be further verified by in vivo test. The successful preparation of G1 monoclonal antibody against αS1-casein epitope aa 83–105 provides a specialized tool for ELISA detection of antigen residues and for the development of hypoallergenic formula.

In this study, we screened and identified Pseudoalteromonas sp. HL9 with the capacity to produce phospholipase B from the mud of the Yellow Sea. The optimal growth medium for this strain consisted of rice bran, yeast powder, and 30 g/L NaCl at pH 8.0, and the optimal culture temperature was 25 ℃. The optimal fermentation conditions that provided maximum phospholipase B activity were found to be culture at 30 ℃ for 48 h in a medium containing rice bran 10 g/L, fish meal peptone 5 g/L, and NaCl 20 g/L at pH 8.5. Thin layer chromatography (TLC) and gas chromatography (GC) results showed that strain HL9 could produce phospholipase B, and that the hydrolysate of sn-2 acyl groups with the enzyme accounted for 70% of the total. The optimal temperature and pH of this enzyme were 45 ℃ and 7.5, respectively. Ca2+, Co2+ and Mn2+ could enhance the activity of phospholipase B, while Cu2+ had an inhibitory effect on the enzyme activity. The phospholipase B retained 80% of its activity in organic solvents. In summary, this enzyme has good catalytic properties at high temperature or alkaline conditions and thus has broad application prospects. The results of this study will lay the foundation for investigating its structure and function.

High-yield phytase-producing Pediococcus acidilactici (L-19) and β-glucosidase-producing Pediococcus pentosaceus (J-28) were singly used as a starter culture for black bean-wheat bran sourdough. During sourdough fermentation, lactic acid bacteria growth, acidification properties, enzyme production, and changes in the contents of phytic acid and dietary fiber were investigated. Hydration properties of sourdough gluten proteins were characterized by low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI), and physical and microstructural properties of different black bean-wheat bran sourdough-based doughs were compared. Furthermore, nutritional and baking properties of black bean-wheat bran sourdough bread were evaluated. The results showed that both strains grew well and had strong acidification capacity, but produced different enzymes during sourdough fermentation. After fermentation, the degradation rates of phytic acid in sourdoughs containing L-19 and J-28 were 81.08% and 59.79%, respectively, and the proportions of soluble dietary fiber to the total amount of dietary fiber increased from 22.49% to 31.47% and 44.15%, respectively in the sourdoughs. Black bean and wheat bran interfered with gluten hydration, being detrimental to the formation of a continuous network structure. The destructive effect on the gluten network was attenuated by lactic acid bacteria fermentation. Dietary fiber contents of the L-19 and J-28 based sourdough breads were both higher than 6%, and protein contents were 13.82% and 13.91%, respectively. The sourdough breads had better amino acid profiles and higher in vitro protein digestibility in comparison with wheat bread. In conclusion, both strains effectively improved the nutritional and baking properties of black bean-wheat bran sourdough bread. This suggested their potential applications in the baking industry.

In the present study, a method for enzymatically digesting N-glycolylneuraminic acid (Neu5Gc) in bovine immunoglobulin G (bIgG) and then ligating the IgG with human N-acetylneuraminic acid (Neu5Ac) was developed to transform bIgG into human IgG (hIgG), and conditions for preparing a crystallizable fragment (Fc) from hIgG were explored. Results showed that hIgG was prepared by digesting Neu5Gc in bIgG (4 mg/mL) with 170 U/mL neuraminidase and subsequently transferring 8.4 galactose (Gal) residues and 42 Neu5Ac residues into the digested IgG with β-1,4-galactosyltransferase (B4GALT1) and α-2,6-sialyltransferase (ST6GAL1), respectively. Further, a highly pure Fc fragment from hIgG was prepared under the conditions: hIgG concentration 10 mg/mL, papain/hIgG ratio 0.05 (m/m), cysteine concentration 10.0 mmol/L, EDTA concentration 2.0 mmol/L, pH 7.0, and hydrolysis time 3 h. The yields of glycosylated hIgG and Fc fragment were 71.7% and 20.8%, respectively. The results of the present study can provide a scientific basis for the development and nutritional evaluation of bIgG-based products.

In order to improve the production process of sour meat, a traditional fermented meat product of some ethnic minorities in China, this work studied the effect of commercial acidic protease on the microbial structure, physicochemical characteristics and flavor quality of sour meat during its fermentation. Using high-throughput sequencing, the bacterial and fungal community compositions were analyzed. The results showed that the addition of protease affected the relative abundance of Lactobacillus, Bacillus and Staphylococcus during the fermentation of sour meat, reduced fungal species richness, and promoted the release of free amino acids (FAAs). Gas chromatography-mass spectrometry (GC-MS) analysis showed that the addition of protease increased the number and contents of volatile compounds, such as alcohols, acids, esters, ketones and aldehydes in ripened sour meat. Correlation analysis showed that Staphylococcus was correlated positively with 3-hydroxy-2-butanone and Bacillus was correlated positively with 1-octen-3-ol. The sensory evaluation showed protease addition improved the taste, smell and overall acceptability of sour meat samples. Therefore, acidic protease has an important effect on the microbial community composition and flavor quality of sour meat, which provides a theoretical basis for improving the production process of sour meat.

Revealing the ecological roles of rare and abundant taxa in the whole bacterial community in a fermentation system can provide clues for understanding the bacterial community structure and its succession pattern during fermentation. In the present study, we investigated the roles and functions of the rare taxa (RT), conditionally rare taxa (CRT) and abundant taxa (AT) sub-communities in the whole bacterial community during the third round of stacking fermentation via high-throughput sequencing. In general, the results showed that the three sub-communities displayed distinct succession patterns. The high level of alpha diversity in the RT sub-community suggested its important role in maintaining the ecological stability of the whole bacterial community during fermentation. The species-time relationship (STR) model implied that the reduction in the number of species in the bacterial community was primarily attributable to the rapid decrease in the RT sub-community. The time-decay relationship (TDR) model combined with the results of Mantel test and β diversity contribution suggested that AT determined the strength and trend of succession of the whole bacterial community, and that CRT boosted them. RT microbes were located at the center of the co-occurrence network, thereby evidencing their roles in maintaining the ecological stability. The constrained correspondence analysis (CCA) showed that the succession patterns of the distinct sub-communities were significantly correlated with specific endogenous physicochemical factors. Moreover, the responses of CRT microbes to environmental changes were more sensitive than the other sub-communities, and structural variations in CRT could impact the whole community system.

In this study, the changes in the viable count of lactic acid bacteria and the contents of major organic acids in sourdough were explored during spontaneous and inoculated fermentations with the typical sourdough starter cultures Lactobacillus plantarum (Lp), Lactobacillus paralimentarius (Lpa) and Lactobacillus fermentum (Lf) separately and in combination: Lpa + Lp (1:1), Lp + Lf (1:1) and Lpa + Lf (1:1), and the effect of co-fermentation with yeast on bread quality was evaluated. The results demonstrated that Lf grew fastest in sourdough among the single cultures, while the highest number of bacterial colonies of 9.20 (lg(CFU/g)) was observed in sourdough fermented with Lpa + Lp + Lf for 10 h. From 16 h onward, the number of bacterial colonies remained stable. Furthermore, the rate of inoculated fermentation (for both single and mixed culture fermentation) was always faster than that of natural fermentation, and the sourdoughs fermented with Lf and Lpa + Lp + Lf reached the desired pH 4.0 after 16 h. Moreover, at this time, the maximum contents of lactic acid and acetic acid in sourdough were obtained (9.05 and 2.31 mg/g, respectively). Compared with ordinary dry yeast fermented bread (OFB), the specific volume of Lpa + Lp + Lf fermented sourdough bread increased by 19.43%, the hardness decreased by 38.21%, and the resilience rose by 29.17%. In the case of flavor quality, Lpa + Lp + Lf fermented sourdough bread contained the largest number (49) and amount (352.39 μg/kg) of flavor compounds including four unique esters, namely ethyl lactate, ethyl palmitate, phenethyl 2-methylpropionate and ethyl caproate. In addition, anti-aging properties of the bread were evaluated, revealing that after 7 days of storage, the quality did not remarkably deteriorate, the hardness increased by only 1.93 times, and the rate of water migration was slow during storage. In summary, Lpa + Lp + Lf fermented sourdough can significantly improve the taste of bread and extend its shelf life.

In this study, we analyzed the relative expression levels of the structural genes VcCHS, VcCHI, VcF3H, VcDFR and VcANS as well as the transcription factor MYB involved in the anthocyanin biosynthesis pathways in six cultivars of highbush blueberry including Emerald, Lanmei #1, Gulf Coast, Legacy, Biloxi, and O’neal and two cultivars of rabbiteye blueberry (i.e. Brightwell and Gardenblue) by real-time polymerase chain reaction (real-time PCR). The results showed that VcCHS, VcCHI, VcF3H, VcDFR and VcANS could up-regulate the synthesis of anthocyanins and promote the production of anthocyanins. However, VcANR had a down-regulatory effect on anthocyanin synthesis, reducing the content of anthocyanins in blueberries. The regulatory effect of the transcription factor MYB on anthocyanin synthesis was relatively complex, which was related to its expression level. The results of this study can provide a foundation for further research on high-quality blueberry cultivars with respect to anthocyanins and for the development of functional foods containing blueberry anthocyanins.

The microbial diversity and functional genes related to flavor formation in solid-state fermented jujube mash for jujube wine were analyzed by metagenomics. The results showed that 37 bacteria phyla, 1 247 genera and 3 937 species were identified, the core ones being Lactobacillus buchneri, L. plantarum and L. parabuchneri. A total of 6 269 and 238 860 genes were annotated in the Cluster of Orthologous Group (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, respectively, and the prominent pathways were carbohydrate metabolism and amino acid metabolism. According to the results of annotation in the Carbohydrate-Active Enzymes (CAZy) database, the number of glycoside hydrolases and glycosyltransferases accounted for the highest percentage (70%) of the active carbohydrate enzymes in the fermented mash. For carbohydrate metabolism, 442 genes controlling different carbohydrate transporter systems were found, including those encoding the key enzymes catalyzing intracellular D-1-phosphate fructose, 6-phosphate sucrose and gluconate into glycolysis intermediates. Meanwhile, 171 branch-chain amino transferase, 288 ketoacid invertase, 319 alcohol/aldehyde dehydrogenase and 144 acetylesterase-controlling genes were identified as the basis for the formation of rich flavor substances from amino acids.

In order to investigate how antioxidant enzymes inhibit the browning process of wampee fruit, we performed RNA sequencing using RNA-Seq technique on Clausena lansium fruit subjected to heat treatment (HT), low temperature conditioning (LTC) or no treatment (control) and then stored at 3 ℃ for 8 days. The results showed that compared with the control group, HT and LTC treatment could effectively postpone postharvest browning and water loss of wampee fruit, maintain higher activities of superoxide dismutase, peroxidase and catalase at the mid-to-late stage as well as higher 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging capacity. The antioxidant activity of LTC-treated fruit began to significantly increase starting from the sixth day of storage. RNA-Seq results showed that totally 35 421 transcripts were collected; 1 631 and 5 404 differentially expressed genes (DEGs) were obtained on day 6 after HT and LTC treatment, respectively, compared with the control group. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG)?enrichment analysis?showed that these DEGs were mainly involved in plant hormone signal transduction, flavonoid biosynthesis, and phenylpropanoid biosynthesis, which may be related to antioxidant activity or browning resistance. From the DEGs, antioxidant gene groups IX, V and X were selected, whose expression could be induced by HT or LTC, thus delaying browning. These results may provide a theoretical basis for mining key antioxidant genes associated with wampee fruit browning.

In this study, the probiotic properties of lactic acid bacteria (LAB) isolated from Tibetan kefir grain (TKG) were evaluated. Twenty LAB strains were screened for their tolerance to acid and simulated gastrointestinal fluid, 11 of which were tolerant to pH 3.0 and 2.5 in medium and eight of which showed viable counts of greater than 106 CFU/mL after culture in simulated gastrointestinal fluid. The results of hydrophobicity, self-aggregation, antioxidant capacity and bacteriostatic activity showed that Lactobacillus paracasei KF2-5 and Lactobacillus rhamnosus RG had high hydrophobicity and the highest bacteriostatic activity. Strain RG showed high self-aggregation and antioxidant capacity. The results of antibiotic resistance showed that KF2-5 and RG were susceptible to erythromycin, kanamycin, chloramphenicol and tetracycline, and resistant to cefotaxime and vancomycin. No hemolysis was observed in the two strains. It was concluded that both KF2-5 and RG had probiotic properties suggesting potential application in prebiotic products.

Nano-selenium synthesized by the probiotic bacterium Lactobacillus plantarum LP21 was analyzed by transmission electron microscopy (TEM) and energy spectroscopy, and its particle size was measured by a particle size analyzer. Additionally, biomolecule distribution on the surface of nano-selenium were analyzed by Fourier transform infrared (FTIR) spectroscopy, and the antibacterial activity of nano-selenium against Vibrio alginolyticus was tested. The results showed that the nano-selenium was spherical in shape and well dispersed; the average particle size of the purified nano-selenium was 184.6 nm, and its surface was covered with proteins, polysaccharides and other biological molecules, showing an amorphous form. The antibacterial activity of nano-selenium against V. alginolyticus and Escherichia coli was strong, and the minimum inhibitory concentration (MIC) against V. alginolyticus was 286 μg/mL. The growth, motility and biofilm of V. alginolyticus were significantly inhibited by the nano-selenium at sub-inhibitory doses, and the cell morphology was changed as well. The results of this study provide a basis for its application to control pathogenic infection in aquaculture.

Thirty-eight strains suspected of being lactic acid bacteria were isolated from 15 donkey milk samples collected in Hami, Xinjiang, of which seven strains were found to have obvious milk coagulation characteristics. The strains were identified by 16S rRNA gene sequencing as Pediococcus acidilactici HL12-21, Pediococcus pentosaceus HL29-5, Enterococcus mundtii HL30-3, Lactobacillus plantarum HL21-44, Lactobacillus coryniformis HL26-24, Lactobacillus curvatus HL29-1 and Leuconostoc lactis HL13-23. They were screened for their milk coagulation time, acid-producing capacity, post-acidification capacity, aroma-producing capacity, sensory characteristics and viable counts during cold storage, of which HL12-21, HL29-5, HL21-44 and HL29-1 possessed better acid-producing and aroma-producing capacity and weaker post-acidification capacity, and the single culture fermented milk had the highest comprehensive scores for color, texture and flavor. The number of viable bacteria still remained above 106 CFU/mL after storage at 4 ℃ for 20 days. In addition, the tolerance of the seven strains and the probiotic bacterium Lactobacillus rhamnosus GG to simulated gastrointestinal fluid, as well as their antimicrobial spectra, antibiotic resistances and antioxidant activities were compared. The results showed that HL29-5 and HL30-3 were superior to the other strains in terms of all above probiotic properties, with special reference to the highest scavenging rates against hydroxyl, 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide anion free radicals (over 30%). Based on our results, Pediococcus pentosaceus HL29-5 holds great potential as a probiotic starter culture for developing specialty yogurt.

To identify the green off-flavor compounds in Moutai-aroma type Baijiu, a method involving sensory-guided fractionation and metabolomics was developed for analyzing its characteristic off-flavor compounds. The samples were separated into volatile and non-volatile compounds by vacuum rotary evaporation. Liquid-liquid extraction and sensory analysis were performed on the volatile components with an intense green off-flavor, and the results showed that the green off-flavor compounds mainly existed in the neutral/alkaline components. A total of 94 flavor compounds were qualitatively and quantitatively identified in the volatile components by gas chromatography-mass spectrometry (GC-MS), the predominant ones being esters, alcohols and aromatic compounds. There were significant differences between normal and defective Baijiu as determined by Venn diagram and clustered heatmap analysis. Furthermore, a total of 15 major differential compounds with variable importance in the projection (VIP) > 1 were identified by orthogonal partial least-squares discriminant analysis. Among them, alcohol and ester compounds showed the most significant difference between the two Baijiu samples. Esters including ethyl lactate, ethyl 2-furoate and ethyl DL-2-hydroxycaproate, as well as higher alcohols including isoamyl alcohol, isobutanol and furfural were identified as the major green off-flavor compounds, and also important contributors to the bitterness and astringency of Baijiu. It is worth noting that ethyl 2-furoate and ethyl DL-2-hydroxycaproate were identified in Baijiu with green off-flavor for the first time; however, their flavor characteristics have yet to be further investigated. The results of this study provide a scientific basis for improving the quality of Moutai-aroma type Baijiu and also provide a reference for the analysis of characteristic flavor compounds in foods in the future.

A total of 99, 96 and 98 volatile aroma compounds were identified in three kinds of soy sauce aroma type Xi Baijiu, namely, Xijiulan, Xijiuyinxiangguizhou and Xijiuyinzhi by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame photometric detection (GC-FPD), respectively, each including 12 sulfur-containing compounds. As determined by gas chromatography-olfactometry (GC-O), ethyl hexanoate (OAVs of 1 720–1 992), ethyl butanoate (OAVs of 1 401–1 523), ethyl octanoate (OAVs of 218–327), ethyl 3-methylbutanoate (OAVs of 835–966), 2-butylfuran (OAVs of 464–719), ethyl 2-methylpropanoate (OAVs of 146–342), 3-hydroxy-2-butanone (OAVs of 90–117), butanoic acid (OAVs of 71–79), 2-methyl-3-furanethiol (OAVs of 33–72), butanol (OAVs of 19–37), ethyl phenylacetate (OAVs of 90–91), hexanal (OAVs of 29–33), 2-methylpropionic acid (OAVs of 13–33), phenylacetaldehyde (OAVs of 16–35) and furfuryl alcohol (OAVs of 7–13) exhibited much higher odor activity values (OAVs) and aroma intensities (AIs) than the other compounds, which suggested that these aroma compounds were the main characteristic aroma compounds of Xi Baijiu. The correlation between the key aroma compounds and sensory attributes was further verified and explained by aroma recombination combined with partial least squares regression (PLSR). Finally, the perceptual interactions between five sulfur compounds and six esters in Xijiuyinxiangguizhou Baijiu were studied using Feller’s additive model to verify the accuracy of aroma identification of Xi Baijiu. The results showed that propanethiol, dimethyl trisulfide, 2-methyl-3-furanethiol, 3-mercaptohexyl acetate and 3-mercaptohexanol all enhanced the aroma of ethyl hexanoate, but enhanced or masked the aroma of the other five esters. The experimental data partly explained the interaction mechanism between aroma compounds, which would be helpful to improve the aroma quality of soy sauce aroma type Xi Baijiu through directional operation.

In order to explore the relationship between altitude and the major quality components of tea, the contents of the major non-volatile chemical components tea polyphenols and amino acids, as well as the composition and content of aroma components in baked green tea samples made from tea plants from different altitudes were analyzed. Then, the key components that significantly differed among tea samples were identified by multivariate statistical analysis, and their correlation with altitude was evaluated. Results showed that there was a statistical significant difference in the total amount of free amino acids among tea samples (P < 0.05), and that the contents of theanine, glutamine, threonine, serine and arginine in the high-altitude group (650–1 102 m) were significantly higher than in the low-altitude group (400–600 m). A total of 298 aroma components were identified from all samples, including aldehydes, alcohols, alkenes, alkanes, ketones, aromatic hydrocarbons, organic acids, esters, lactones, phenols, alkynes, amines, ethers, oxygen heterocyclic compounds, nitrogen compounds and sulphur compounds, with aldehydes and alkanes being the most abundant ones. The results of partial least squares discriminant analysis (PLS-DA), cluster analysis and correlation analysis indicated that the contents of quality components significantly differed (P < 0.05) between the low- and high-altitude groups, and 26 differential aroma compounds such as 3-methylbutanenitrile, α-phellandrene and indole were identified. It was also shown that the contents of total free amino acids, theanine, glutamine, threonine, serine and arginine as well as 3-methylbutanenitrile were higher in the high-altitude group than in the low-altitude group, while the opposite was observed for the contents of 25 aroma compounds such as α-phellandrene and indole. Furthermore, correlation analysis indicated that the contents of theanine, serine, threonine and total free amino acids had a significantly positive correlation with sensory taste scores. Nine aroma compounds including (Z)-2-heptenal, 3-penten-2-one, 4-methyloctane, 3-ethyl-heptane, 1-octen-3-one, α-phellandrene, (E,E)-2,4-heptadienal, 3,4-dimethylfuran-2,5-dione and 4-methylindan had a significantly negative correlation with altitude. It was speculated that the formation and accumulation of aroma precursors may be related to altitude.

In order to explore the quality changes of frozen aquatic products during distribution in the cold chain, tilapia (Oreochromis niloticus) fillets were repeatedly frozen and thawed for up to seven cycles. The differences in the basic nutrients in eight samples (i.e., one frozen-thaw sample and seven repeatedly frozen-thawed samples) were evaluated. Then, the differences in overall taste profile were determined by electronic tongue, and the contents of free amino acids, flavor nucleotides and taste inorganic ions were also measured. In addition, the changes of flavor substances were analyzed by sensory evaluation. The results showed that the overall flavor profile of tilapia fillets could be effectively distinguished during freeze-thaw cycles. With the increase in the number of freeze-thaw cycles, the contents of umami and sweet amino acids and nucleotides decreased, while the contents of bitter amino acids and nucleotides increased, which was consistent with the trend of sensory scores. The total content of free amino acids showed a decreasing trend, and decreased significantly after the fourth freeze-thaw cycle (P < 0.05). The content of Na+, which had an adjunctive effect on umami taste, was also significantly decreased. The above results showed that the overall taste profile was gradually deteriorated as the number of freeze-thaw cycles increased. The results of this study may provide a theoretical basis for further research on quality control of frozen aquatic products.

In order to study the dynamic changes of major active substances and volatile components in Toona sinensis at different growth stages, the contents of total flavonoids, total polysaccharides, total saponins and total alkaloids in the leaves of T. sinensis collected from April to October, 2019 were determined by conventional methods, and the volatile compounds by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-ion mobility spectrometry (GC-IMS). Additionally, the volatile components in the leaves of T. sinensis in different growth periods were distinguished by cluster analysis (CA) and principal component analysis (PCA). The results showed that the major active substances in the leaves of T. sinensis exhibited an obvious accumulation tendency during the growth process; the contents of total flavonoids, total polysaccharides and total alkaloids reached the highest levels in October, while the content of total saponins reached the highest level in September. The volatile components changed significantly during the growth period, and 109 and 49 volatile components were identified by GC-MS and GC-IMS, respectively, mainly including terpenes, aldehydes, sulfur-containing compounds and alcohols. Most of the volatile components detected by GC-MS were larger molecules (C6–C20) at high levels, while most of the volatile components detected by GC-IMS were smaller molecules (C4–C10) at low levels. The combination of the two techniques can expand the scope of detection of volatile components in T. sinensis leaves. The results of this study can provide a scientific basis for the planting, quality evaluation, and comprehensive development and utilization of T. sinensis.

This study was carried out in order to explore the effect of second inoculation time on the volatile flavor components of fermented dry-cured meat. Fermented dry-cured meat samples were prepared by sequential inoculation of Staphylococcus xylosus MT, a dominant strain in traditional Longxi bacon, followed by a 1:1 mixture of Lactobacillus plantarum ZR and Leuconostoc mesenteroides CM, also dominant strains in traditional Longxi bacon. The second inoculation was performed on day 6 (F-6), 10 (F-10) or 14 (F-14) of fermentation. Besides, naturally fermented meat was prepared as a control. The volatile flavor components of fermented dry-cured meat were analyzed using solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) combined with relative odor activity value (ROAV) and principal component analysis (PCA). The results showed that 38, 51, 57, and 43 volatile flavor compounds were detected in the control, F-6, F-10 and F-14 samples, respectively. The number and amount of volatile flavor components in the inoculated groups were higher than those in the control group. The largest number of volatile flavor components were found in the F-10 group, and those with ROAV values greater than 0.1 accounted for a high proportion of the total. Nonanal, benzaldehyde, (E,E)-2,4-decadienal, ethyl caproate, ethyl octanoate and 1-octene-3-ol were the key flavor compounds in the inoculated groups. Meanwhile, the sensory evaluation results indicated that F-10 had the best flavor and the highest score. The findings revealed that sequentially inoculated fermentations could significantly increase the number and amount of volatile flavor substances in fermented dry-cured meat (P < 0.05), and that F-10 treatment was more favorable for the formation of the flavor, which provides a theoretical reference for the production of fermented dry-cured meat by inoculated fermentation.

The objectives of this study were to investigate the effects of pollinizer cultivars on the quality and aroma components of ‘Yali’ pear fruits and to explore the effect of xenia on fruit quality attributes in order to provide a reference for screening for ‘Yali’ pear pollinizer cultivars for improved fruit quality. Thirty-year-old ‘Yali’ pear trees were pollinated artificially with pollen from 18 pollinizer cultivars with different characteristics, and those pollinated with pollen from ‘Xuahuali’ pear was used as a control group. Fruit quality attributes including individual fruit mass, dot diameter, dot density, stone cell content, total soluble solid content, soluble sugar content, total organic acid content, and aroma compounds in mature pear fruit were measured. The effects of different pollinizer cultivars were comprehensively evaluated by principal component analysis (PCA). The results showed that different pollinizer cultivars affected the external and internal quality attributes and aroma components of ‘Yali’ pear fruit, resulting in 12.57%–96.10% changes in them. For pollination with pollen from ‘Nansui’, ‘Housui’ and ‘Korla’ pear, the contents of total soluble solids (TSS) and soluble sugars and TSS-to-acid ratio in ‘Yali’ pear fruit were increased significantly by 0.55%–0.76%, 7.53–16.54 mg/g and 1.96–4.54, respectively, compared with the control group, indicating improved nutritional quality. Using ‘Nansui’, ‘Korla pear’, ‘Crispel’, ‘Lvbaoshi’ and ‘Cuiyu’ pear as pollinizers, the relative contents of volatile esters in ‘Yali’ pear fruit were significantly increased by 8.77–18.85 times relative to the control group. Notably, the relative content of hexyl acetate was increased significantly by 3.76–15.86 times. Furthermore, six unique esters including ethyl acetate, hexanoic acid ethyl ester, butanoic acid ethyl ester, (E)-acetate-2-hexen-1-ol ester, acetic acid-2-phenylethyl ester and ethyl 2-trans-4-cis-decadienoate were detected, which could contribute to improving the aroma of ‘Yali’ pear fruit. Compared with the fruit quality attributes of the male parent, an obvious xenia effect was observed in pollinated pear fruit in terms of stone cell content, fruit texture, TSS content, soluble sugar content, and aroma components but not individual fruit mass, dot diameter, dot density or total organic acid content. The comprehensive evaluation results showed that ‘Nansui’ could be the most suitable pollinizer cultivar for ‘Yali’ pear production.

In order to identify the odor components of giant salamander meat and effectively remove its fishy smell, gas chromatography-ion mobility spectrometry (GC-IMS) was used to analyze the differences in the odor fingerprints of different edible parts (head, back, abdomen, tail, claw and liver) of giant salamander. The results showed that GC-IMS provided good separation of the odorants of different edible parts of giant salamander. A total of 34 volatile odorants were identified from six different edible parts, including nine esters, nine ketones, six aldehydes, seven alcohols, two acids and one pyrazine. Principal component analysis showed that there were some differences in volatile odor components among the six edible parts of giant salamander, and the first two principal components contributed cumulatively to 63% of the total variance, indicating that the edible parts of giant salamander could be discriminated by GC-IMS. The findings of this study could provide a reference for quality control of different edible parts of giant salamander, fishy smell removal, and product development in the future.

In order to evaluate the potential risks posed by N-nitrosamines, a group of emerging disinfection by-products in drinking water, to the food and beverage industry, a method based on ultra-high performance liquid chromatography-triple quadrupole mass spectrometry (UPLC-MS/MS) was developed for the simultaneous determination of nine N-nitrosamine disinfection by-products in drinking water. The samples were extracted by solid phase extraction. The chromatographic separation was accomplished on a RRHD-C18 column with gradient elution using a mobile phase consisting of 10 mmol/L ammonium bicarbonate aqueous solution containing 0.2% formic acid and methanol. The detection was carried out using an atmospheric pressure chemical ionization (APCI) source in a multi-reaction monitoring (MRM) mode. Under optimized conditions, the calibration curves for nine N-nitrosamines were linear in a certain concentration range, with correlation coefficient greater than 0.996, and the detection limit of the developed method was 0.10–0.33 ng/L. The spiked recoveries of the method were 62.1%–118.2%, with relative standard deviation (RSD) of 2.2%–10.0%. The analysis process took 6 min. Compared with the existing methods, this method is very sensitive, fast and highly applicable, and can meet the requirements for the detection of N-nitrosamine disinfection by-products in drinking water for food and beverage production.

A non-targeted metabolomics method for identifying the quality of Gougunao tea, Lu Mountain Clouds-Mist tea, and Wuyuan green tea was established by ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). The original data were screened by MassHunter Mass Profile, and 220 characteristic differential metabolites were obtained. The results of principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed that there was a clear discrimination among the three teas. Partial least squares discriminant analysis (PLS-DA) was used to establish a prediction model for identifying the quality of tea with an accuracy of 100%. Meanwhile, of the 220 characteristic differential metabolites, 22 were identified, mainly including flavonoids, glycoside derivatives and organic acids. Through heatmap analysis, it was found that their contents were significantly different among tea samples. This study is meaningful for guiding tea quality identification, which can be widely used in food analysis and characterization.

In this study, hyperspectral imaging was used to visualize the water content and springiness of preserved egg gels and to predict different quality grades. First, the hyperspectral information of qualified and high quality preserved eggs was collected, and their water content and springiness were measured. Then, the original spectral data were transformed by Savitzky-Golay (S-G), first derivative (FD) or Savitzky-Golay and first derivative (S-G-FD) to analyze their correlation with water content and springiness values. We identified and excluded outliers by Monte Carlo-partial least squares (MCPLS), and partitioned the sample sets by sample set partitioning based on joint X-Y distance (SPXY). The characteristic wavelengths were selected using successive projection algorithm (SPA) and the uninformative variable elimination (UVE) method, and a multiple stepwise regression model (MSR) was established to predict the water content and springiness of preserved eggs. The results showed that UVE-MSR was the optimal model for predicting water content. Its determination coefficient and root-mean-square error (RMSE) were 0.882 and 0.583, respectively, and its relative percent deviation (RPD) was 2.1. The optimal model for predicting springiness was SPA-MSR, whose determination coefficient and RMSE were 0.903 and 0.348, respectively, and whose RPD was 2.2. Then, the models were used to calculate the water content and springiness for each pixel in the hyperspectral image, and a visual distribution map was generated for the visual detection of the water content and springiness of preserved eggs. Finally, the competitive adaptive weight sampling method was used to select the characteristic wavelengths, and a back propagation (BP) neural network model was established for quality prediction. The total recognition accuracy of the model was 98.3%.

A triplex real-time polymerase chain reaction (real-time PCR) method for rapid simultaneous detection of Salmonella (SAL), Staphylococcus aureus (SA) and Bacillus cereus (BC) was established. Primers and TaqMan probes were designed targeting the invA gene of SAL, the Sa442 gene of SA, and the Cereolysin AB gene of BC. The performance indicators of the developed method were evaluated, and actual samples of ready-to-eat meat products were detected by it. The results showed that the real-time PCR method was highly reproducible, specific and sensitive. Fifteen non-target reference strains were tested by this method and the results were all negative. The standard curves for the three pathogenic bacteria were linear over the concentration range of 102–108 CFU/mL, and the intra-assay and inter-assay coefficients of variation (CVs) were less than 2% in the quantitative tests. Without bacterial enrichment, the limits of detection (LOD) for SAL, SA, and BC were 3.8 × 102, 4.9 × 102, and 5.7 × 102 CFU/mL, respectively. After 5 h enrichment, they increased to 3.8, 4.9, and 5.7 CFU/mL, respectively. The results of the real-time PCR method for 100 actual samples were consistent with those of the national standard method, indicating that the real-time PCR method can be used for the detection of the three pathogenic bacteria in bulk ready-to-eat meat products.

A method for detecting Staphylococcus aureus in foods was established by insulated isothermal polymerase chain reaction (iiPCR). In this study, specific primers and probes were designed based on the nuc gene, and the extraction of template DNA from S. aureus in food samples was explored. After optimizing the amount of primers, probes and templates, the specificity, sensitivity and stability of iiPCR were evaluated, and the application of iiPCR and traditional PCR was compared to detect S. aureus in artificially contaminated samples and actual food samples. The results showed that the water bath method was suitable for rapid extraction of template DNA due to its simple operation, short time consumption, and low instrument requirements. The iiPCR method had strong specificity, high sensitivity and good stability without cross-reaction with other bacteria. It took six hours to detect S. aureus in artificially contaminated pork samples and milk samples by the iiPCR method with a detection limit of 103 and 102 CFU/mL, respectively, while the traditional PCR method took eight hours with a detection limit of 105 CFU/mL. For actual food samples, the verification experiments showed that the results of the iiPCR method at 6 h were consistent with those of traditional PCR at 12 h and the traditional culture method at 16 h. It was proved that the iiPCR method could detect S. aureus in foods more quickly and accurately.

In this study, a time-resolved fluorescence immunochromatographic assay (TRFICA) for detecting aflatoxin B1 (AFB1) and ochratoxin A (OTA) simultaneously was developed. Europium-based time-resolved fluorescent microspheres were used to label anti-AFB1 monoclonal antibody and anti-OTA monoclonal antibody. Various factors such as pH for the activation of fluorescent microspheres, concentration of labeled antibodies, dosage of fluorescent probes, concentration of coating antigens for test line, concentration of goat anti-mouse IgG for quality control line, and sample pretreatment conditions were optimized. Under the optimal conditions, the assay showed half inhibition concentration (IC50) values of 1.58 and 3.91 μg/kg , linear ranges of 0.26–9.73 and 1.14–13.29 μg/kg, and visible limits of detection (vLOD) of 3.70 and 5.55 μg/kg for AFB1 and OTA, respectively. The cross-reactivity rates of this method with aflatoxin analogues and ochratoxin B were 12%–62% and 58%, respectively, without cross-reactivity with other mycotoxins. The recoveries of the two toxins spiked in corn samples were 92%–103%, with coefficients of variation (CV) less than 15%. The results of this method for real samples coincided with those of high performance liquid chromatography (HPLC) and commercial colloidal gold strip. The TRFICA strip was stored at 4 ℃ for more than 5 months with good stability. To sum up, this immunochromatographic strip is sensitive, accurate, rapid and easy to operate, and is very suitable for rapid screening of AFB1 and OTA in food and agricultural products.

A new enzyme-based electrochemical sensor NF/wPlaE-CS/AuNPs/MWNT/GCE was constructed using wheat esterase by taking advantage of the synergistic electro-catalytic amplification effect of gold nanoparticles (AuNPs) and multi-walled carbon nanotubes (MWNT) on the electrochemical signal. The sensor provided a simple and low-cost approach for the detection of dichlorvos with square wave voltammetry, and the detection limit was 4 μg/L (RSN = 3). The biosensor was used to measure dichlorvos spiked in lettuce and rice samples with recoveries ranging from 95.4% to 107.2%, indicating the biosensor was suitable for the detection of dichlorvos pesticides in actual samples. In addition, the biosensor exhibited good stability and inference resistance. This study can provide technical support for the application of plant esterase in pesticide detection.

This work was undertaken in order to demonstrate the feasibility of establishing a model based on fatty acid (FA) fingerprints to discriminate between beef from pasturing and barn feeding systems. A total of 91 samples of biceps femoris, longissimus dorsi, and costal subcutaneous fat from pastured and barn fed cattle from eight counties/banners in the dominant beef cattle farming belt of Inner Mongolia were collected for determination of fatty acids (FAs) by gas chromatography (GC), and principal component analysis (PCA) and descriptive statistics were conducted on the obtained data. Furthermore, soft independent modeling of class analogy (SIMCA) was used to establish a model to authenticate pastured and barn-fed beef. Results indicated that all samples were clustered into pasturing and barn feeding groups, that beef samples from grassland and agricultural areas were also clustered separately, that grassland beef samples from Hulun Buir and Xilingol could be separated, that barn-fed beef samples from Horqin Left Wing Rear Banner and Zhenglan Banner in the eastern region were grouped separately, and that barn-fed beef samples from Helingeer?county and Uxin Banner in the mid-western regions tended to be separated. The contents of n-3 polyunsaturated fatty acids (PUFAs), α-C18:3 n3 (α-linolenic acid), C18:0 and C14:0 in pastured beef were significantly higher than those in barn-feeding beef, and the contents of n-3 PUFAs and α-linolenic acid increased by 1.6 and 2.2 times, respectively. On the other hand, the contents of n-6 PUFAs, C18:1 n9c and C18:2 n6c (linoleic acid) in barn-fed beef were significantly higher than those in pastured beef. The ratio of n-6 to n-3 PUFAs in pastured beef was 3.6, closer to the ideal value. However, the paired t-test and blocked F test on means could not distinguish feeding systems or regions in terms of FA profiles, implying that the conventional statistics has limited ability to evaluate the overall pattern of indicator datasets. PCA performed on FA profiles of the three cuts showed better clustering effect on pastured and barn-fee beef than all samples. FAs of costal subcutaneous fat exhibited the farthest clustering distance for both pastured and barn-fee beef. The internal and external verification accuracy of the established SIMCA model were 100% and 92.6%, respectively. FA-based modeling is feasible to distinguish pastured from barn-fed beef. This study can provide innovative ideas and methods for further studies on meat authentication.