In this study, a ferritin-hesperetin covalent complex was prepared from apoferritin and hesperetin at pH 9. The effect of covalent interaction on the structural and physicochemical properties of ferritin was explored. The results showed that the covalent interaction with hesperetin reduced the fluorescence intensity of ferritin and resulted in a red shift in the fluorescence spectrum, changing ferritin structure. After binding with hesperetin, the solubility of ferritin was changed, and the isoelectric point was decreased. The oxidative deposition of iron was enhanced and the reductive release of iron from ferritin was decreased. Additionally, the thermal stability of the covalent complex was enhanced compared with that of ferritin. In conclusion, covalent modification with hesperetin can endow ferritin with new functional properties, which is of great significance to the development of ferritin-based foods or drugs.

In this study, we fabricated shea butter solid lipid nanoparticles (SLNs) by a high-speed shear homogenization method with Tween 20 or Tween 80 as the emulsifier. SLNs were obtained by cooling down to 4 ℃. The particle size range of SLNs with oil to water ratio of 5:5 to 1:9, as determined by dynamic light scattering, was 30.43–278.13 nm. The transmission electron microscopic (TEM) images showed that the particle morphology was spherical. The thermal peak temperature of SLNs ranged from 19.05 to 28.96 ℃ as measured by a differential scanning calorimeter, which was lower than that of shea butter (35.84 ℃). In addition, α-tocopherol, a lipophilic bioactive ingredient, was loaded into SLNs with encapsulation efficiency as high as 95.11%. Therefore, SLNs has great potential for application as a carrier for liposoluble bioactive materials.

This study investigated changes in the quality characteristics of Solenocera crassicornis as a result of protein oxidation after treatment with hydroxyl radical oxidation systems, and it observed the degradation of protein by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Peeled shrimps were oxidized in systems containing 0.01 mmol/L FeCl3, 0.1 mmol/L ascorbic acid and 0.5, 1.0, 2.0 or 4.0 mmol/L hydrogen peroxide and the quality characteristics were evaluated after 1, 3, 5, and 7 h. The results showed that the quality characteristics of shrimp were changed after the oxidative treatment. Specifically, the pH rose, the water activity and water content showed an upward and then downward trend, and the chewiness, elasticity and a* value kept declining. As oxidant concentration and oxidation time increased, the L* value and total volatile basic nitrogen (TVB-N) content showed an upward trend (P < 0.05). After oxidation, the space between muscle fibers in shrimps was widened, muscle fibers were broken and the arrangement of muscle fibers became loose. At different oxidant concentrations, protein degradation and aggregation occurred to varying extents. It can be concluded that free radical oxidation can significantly affect the quality characteristics of shrimps and the degree of protein degradation. Therefore, this study provides a reference for the control of protein oxidation in processed shrimps.

Ovalbumin (OVA) was used to improve the gel strength of minced meat products added with soybean protein isolate (SPI). The effect of OVA-SPI mixtures at different ratios on the physicochemical properties and microstructure of minced meat gels was examined. The results showed that OVA-SPI mixtures significantly improved the hardness, springiness, cooking loss, and water-holding capacity (WHC) of sausages (P < 0.05). The smallest fat aggregates were formed in the product added with their 1:1 mixture, which had improved hardness as well as the highest and stable springiness. Besides, it had the best consumer acceptance.

In this study, high internal phase Pickering emulsions (HIPEs) stabilized by β-lactoglobulin nanoparticles (β-LGNPs) were used to replace animal fat in minced meat products in order to improve product quality and reduce saturated fatty acid intake. The experimental results showed that with increasing level of emulsion replacement, the quality of pork patties was gradually improved. When the replacement ratio was 100%, the cooking yield was increased from 75.53% to 89.47%, and the texture characteristics hardness, elasticity and chewiness were improved. Addition of HIPEs reduced the thiobarbituric acid reactive substances (TBARS) value of the patties after heating, indicating the emulsion system’s ability to suppress the oxidation of lipids, and improved the color and water and oil retention. Microstructural studies showed that all samples formed a sponge-like (honeycomb-like) structure due to protein aggregation after heating. The distribution of lipids droplets in all fat replacement groups was relatively uniform, indicating that HIPEs maintained good stability during heating. The protein digestion rate was also increased with increasing level of HIPEs. This study provides a theoretical basis for the application of HIPEs as a fat substitute in minced meat products.

The main purpose of this study is to explore the effects of amino acids on the growth and bacteriocin synthesis of Lactobacillus plantarum. L. plantarum KLDS1.0391 was cultured in chemically?defined?medium with predetermined concentrations of amino acids. The content of lactic acid in the culture supernatant was determined by high performance liquid chromatography (HPLC). The expression of the genes associated with bacteriocin and amino acid synthesis was analyzed by real-time polymerase chain reaction (real-time PCR). The results showed that the deficiency of Asp, His, Ile, Leu, Pro, Thr, Tyr, Asn, and Gln significantly reduced the growth capacity and bacteriocin production of the strain (P < 0.05). The deficiency of Glu, Gly, Ala, Cys, Arg, Phe, Ser, Trp and Val affected only the growth of the bacterium, but had no obvious effect on the synthesis of bacteriocin. Lys stress (deficiency or excess) had little effect on the growth of the strain, but significantly affected the synthesis of bacteriocin by it. The chromatographic results showed that single deficiency of Lys, Tyr, Ile, Leu, Met, Asp, Asn, Pro or Thr increased the lactic acid content. Real-time-PCR showed that the genes related to bacteriocin synthesis plnEF, plnD and plNC8HK were significantly down-regulated in the absence of Lys (P < 0.05), while they were up-regulated more significantly with increasing exogenous Lys up to 2.0 g/L. The key genes involved in amino acid synthesis dapG and yclM were significantly up-regulated in the absence of Lys, but down-regulated in the presence of 2.0 g/L Lys (P < 0.05). Therefore, it can be speculated that in the absence of Lys, the expression of genes such as dapG and yclM is up-regulated to synthesize a variety of proteins essential to the growth and metabolism of bacteria. Lysine can positively induce bacteriocin synthesis, which may play an important role as a substrate for bacteriocin synthesis.

The effect of sodium chloride (NaCl) on pullulan biosynthesis by Aureobasidium pullulans CCTCC M 2012259 in shaking flasks was investigated. NaCl was found to be conducive to pullulan production, but was unfavorable to maintain the molecular mass of pullulan at a high level. The results of batch fermentation showed that pullulan production increased by 17.6% in the experimental group (3 g/L NaCl), while the molecular mass of pullulan finally obtained decreased by 55.8%, as compared to the control group (0 g/L NaCl). Based on the RNA sequencing (RNA-Seq) analysis of A. pullulans, a total of 659 significantly differentially expressed genes (DEGs) were identified between the two groups, of which 227 genes were up-regulated while the remaining 432 were down-regulated in the experimental group. Gene Ontology (GO) functional annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of these DEGs indicated that NaCl regulated the expression of genes encoding certain hydrolases as well as ion and small molecule-binding proteins. These genes participated in carbohydrate, starch and sucrose metabolism, and glycolysis/gluconeogenesis, resulting in significant changes in the production and molecular mass of pullulan.

The growth of Streptomyces alboflavus TD-1 in Gauze’s modified medium with different concentrations of glucose was evaluated by double-dish buckle, and the volatile organic compounds (VOCs) produced by it including 1-octen-3-ol were determined by gas chromatography-mass spectrometry (GC-MS). The antimicrobial mechanism of 1-octen-3-ol against Aspergillus flavus was determined by fluorescence microscopy (FM), scanning electron microscopy (SEM) and high performance liquid chromatography (HPLC). The results showed that the initial growth rate and VOCs production capacity of S. alboflavus TD-1 were severely inhibited by high concentration of glucose (500 mmol/L), but when the glucose concentration was decreased to 50 mmol/L, this inhibition was removed. The antibacterial VOCs produced by S. alboflavus TD-1 included hexanal, 1-octen-3-ol, 2-pentylfuran, and 2-methylisobornyl and acetophenone. Food-grade 1-octen-3-ol completely inhibited the growth of A. flavus at a concentration of 15 μL/L, which had an obvious teratogenic effect on the mycelium and spore morphology of A. flavus, seriously damaged the mitochondrial membrane, and significantly reduced the synthesis rate of AFB1 to 31.98%. Therefore, the concentration of glucose in the medium can affect the growth of S. alboflavus TD-1 and the production of VOCs; 1-octen-3-ol can effectively inhibit the growth of A. flavus and the synthesis of AFB1.

To explore the diversity of lactic acid bacteria (LAB) during the pile fermentation process of Liupao tea and screen for cholesterol-reducing strains for use as probiotics in preventing hyperlipidemia caused by unbalanced diets, high-throughput sequencing combined with pure culture was used to analyze the bacterial diversity at different stages of fermentation, and the cholesterol-lowering capability and gastrointestinal tolerance in vitro of vigorously growing strains were evaluated. The results showed that four genera (Lactobacillus, Weissella, Lactococcus and Enterococcus) and five species of LAB were detected from 25 samples with Lactobacillus being the single dominant genus. A total of 76 strains were isolated, including 55 Lactobacillus pentosus, 3 Enterococcus casseliflavus, 5 Weissella paramesenteroides, 8 Weissella hellenica and 5 Lactococcus taiwanensis. In addition, the rate of cholesterol removal by the selected strains ranged from 0% to 30%, and Lactobacillus pentosus strain L131 gave the highest removal rate of (29.56 ± 0.37) %. The survival rate of this strain was (92.70 ± 0.71) % and (77.54 ± 4.81) % in artificial gastric juice (pH 3.0) and artificial pancreatic juice (pH 8.0), respectively, significantly higher than that of other strains (P < 0.05). The results of this study will provide a theoretical basis for the development of healthy dark tea products and probiotics from tea.

In this study, a thermophilic fungus, designated GZFH7, that can produce thermophilic mannanase was isolated from Maotai-flavor Daqu, a traditional fermentation starter for the production of Maotai-flavor Baijiu. The fungus was identified as Rhizomucor pusillus, and the optimal reaction temperature of mannanase produced from konjac gum by this strain was 70 ℃. At temperatures ranging from 50 to 80 ℃, the enzyme retained more than 50% of its activity, and kept its activity almost unchanged for 1 h at the optimal reaction temperature. The optimal reaction pH of the enzyme was 5.0, and it was tolerant to pH 2.0 to 12.0. Transcriptomic analysis showed that 253 carbohydrate-active enzymes (CAZyme) genes such as chitinase, galactosidase, and mannosyltransferase were expressed. Among them, glycosyltransferase was most abundantly expressed, accounting for 41.1% of the total, followed by glycoside hydrolase, about 37.5%. The mannanase produced by R. pusillus GZFH7 had good thermal stability. Furthermore, this strain could efficiently produce CAZymes, proving its great potential for the development and application of enzyme preparations.

The purpose of this study is to isolate lactic acid bacteria (LAB) capable of producing γ-aminobutyric acid (GABA) from Yujiangsuan, a unique traditional fermented condiment in Qiandongnan, Guizhou Province, China, and analyze the fermentation characteristics of the strains. The GABA-producing strains were identified by thin-layer chromatography (TLC) and the Berthelot colorimetric method, and their fermentation characteristics such as acid tolerance, bile salt tolerance, amino acid decarboxylase activity, antibacterial activity, growth curve, pH, and acid production rate were evaluated. The results showed that a total of 387 strains were isolated from different stages of fermentation. Fifteen typical GABA-producing strains were selected from the 387 strains, including two strains of Weissella cibaria, one strain of Weissella bombi, 11 strains of Lactobacillus plantarum and one strain of L. spentosus. Among them, strain Y113 produced the highest amount of GABA (0.239 mg/mL). The GABA production ability and fermentation characteristics among the 15 strains were clearly separately by principal component analysis (PCA). Strains Y279 and Y64 were highly tolerant to acid and bile salt, exhibited good antibacterial activity, and had high growth rate and acid production rate but no amino acid decarboxylase activity. Due to its excellent fermentation characteristics, probiotic characteristics and GABA-producing capacity, strain Y279 shows great potential to be used as an excellent strain for industrial and standardized production of Yujiangsuan.

In this study, the diversity of microbial community during the fermentation of light-flavor Baijiu with mixed-strain Xiaoqu was analyzed by high-throughput sequencing. The results showed that a total of 35 bacterial phyla and 378 genera as well as four fungal phyla and 38 genera were detected. Firmicutes, Proteobacteria, Bacteroidetes, Ascomycota and Mucoromycota were the dominant phyla. The microbial community structure kept changing during the fermentation process. Unidentified Rickettsiales was the dominant genus over the first two days; Lactobacillus was the dominant genus from day 3 until the end of fermentation. The dominant fungal genera were Issatchenkia, Rhizopus, Saccharomyces and Aspergilus. The relative abundance of Rhizopus and Aspergilus decreased with the increase in fermentation time, while the relative abundance of Saccharomyces increased from day 2 onwards to become dominant. These results provide theoretical support for the brewing of Baijiu with mixed-strain Xiaoqu.

Fifteen strains of Bifidobacterium infantis were screened for their promoting effects on the proliferation of human fetal colon epithelial cells (CCD841 CoN) in this study. The biological properties of the selected strains such as morphological characteristics, growth characteristics, environmental tolerance, adhesion properties and safety were evaluated, and the optimal conditions for promoting cell proliferation were also determined. The effect of live and inactivated cell suspensions, culture supernatants, and lysates of each strain on the proliferation activity of CCD841 CoN cells was evaluated by CCK-8 method. The results of principal component analysis (PCA) showed that Bifidobacterium longum K2-21-4 had the best overall cell proliferation-promoting effect. The adhesion rate of K2-21-4 to CCD841 CoN cells was 6.6%, only slightly lower than that of the commercial strain Lactobacillus animalis BB12. However, the tolerance of K2-21-4 to acid and bile salt was poor. K2-21-4 had resistance to aminoglycosides and quinolones but was to a certain extent sensitive to penicillin and macrolide, and highly sensitive to amoxicillin, vancomycin, tetracycline, rifampicin and chloramphenicol. It had no hemolytic activity. The live cell suspension of B. longum K2-21-4 at 107 CFU/mL had the best effect on promoting cell proliferation when co-cultured for 24 h. To sum up, B. longum K2-21-4 can be potentially applied to promote the proliferation of CCD841 CoN cells.

The impact of Lactobacillus plantarum on the immunological activity of tropomyosin (TM) as the major shrimp allergen was investigated. TM enriched and purified from Penaeus vanname was hydrolyzed for durations between 12 and 48 h with the viable cells, broken cell contents, cell debris and intracellular enzyme extracts of L. plantarum, the cells from which protein, fat or lipoteichoic acid was removed, and those subjected to carboxyl esterification or aminomethylation, separately. The immunological activity was analyzed by SDS-PAGE, Western-blot and competitive enzyme linked immunosorbent assay (ELISA). In order to analyze the site of action of L. plantarum on TM for reduced immunological activity, epitope polyclonal antibodies combined with infrared spectroscopy was used to explore the influence of L. plantarum on the secondary structure and allergenic epitopes of TM. The immunological analysis results showed that the highest percentage reduction (76.9%) of its immunological activity was obtained when TM was treated with the viable cells for 48 h, and the lowest percentage reduction was observed with the cell debris and the aminomethylated cells (60.7% and 61.7%, respectively), indicating that L. plantarum reduced the immunological activity of TM. The infrared spectroscopy and ELISA results displayed that L. plantarum could greatly change the secondary structure and allergenic epitopes of TM, while the aminomethylated cells and cell debris caused the least damage to the α-helical structure and allergenic epitopes of TM, resulting in less folded structure and thus exerting the worst effect on reducing the immunological activity of TM. Additionally, it was found that amino groups may be an important site of action for L. plantarum to reduce the immunological activity of TM. The findings of this study will provide a theoretical reference to control the allergenicity of food allergens and for the development of hypoallergenic aquatic products.

Objective: To meet the requirements of laboratory quality control and proficiency testing in enteroaggregative Escherichia coli (EAEC) detection, homogenous and stable reference materials for enteroaggregative E. coli cells and genomic DNA (gDNA), with independent intellectual property rights, were developed. Methods: Next-generation sequencing (NGS) was used for whole genome sequencing of enteroaggregative E. coli (CMCC 44841). Bioinformatics analysis was performed on the sequencing results for species and virulence genes identification, serotyping, and multi-locus sequence typing (MLST). The characteristic genes of astA, aggR and pic were confirmed by PCR. Freeze-dried reference materials containing 103 CFU of cells and 20 ng of gDNA per sample were prepared. According to CNAS-GL017, homogeneity testing was performed on the 20 EAEC samples, and the results were statistically analyzed by one-way analysis of variance (ANOVA). The samples were stored at ?20, 4, 25 or 37 ℃ to evaluate their stability during storage and transportation. Then, three laboratories were organized for collaborative calibration and verification, and the applicability of the reference materials was tested on five different ready-to-eat food matrices according to the national standard method. Results: The genome size of CMCC44841 was 5.057 285 Mb, the GC content was 50.6%, and the genome contained 5 173 coding genes. The strain was identified as E. coli, serotyped as O127:H21, and typed as ST40 by MLST, carrying other virulence genes apart from aggR, astA and pic. The PCR fragments of astA, aggR and pic were 102, 400 and 1 111 bp in size, respectively. The result of homogeneity testing was F = 1.59, which meets the requirements for standard materials. The EAEC cell and gDNA samples were stable at ?20 and 4 ℃ for 60 days, at 25 ℃ for 7 days, and at 37 ℃ for 5 days. The collaborative interlaboratory calibration confirmed the EAEC cell reference material to contain 103 CFU of cells. The reference materials could be detected when they were added to 20 sample of different food matrices. Conclusion: The EAEC cell and gDNA reference materials, prepared from isolates obtained in the country, contain clear whole genome sequence information. They have good homogeneity, stability and applicability and can meet the requirements of quality control and proficiency testing in food testing laboratories.

In order to uncover the influence of various physicochemical indicators on the microbial community structure in Chinese liquor fermentation pit muds, the difference in the physicochemical properties of pit muds of different ages and their correlation with the prokaryotic community structure were studied. The results showed that the contents of moisture, pH, ammonium nitrogen, available phosphorus and available potassium in 20-year-old pit bottom and wall muds were significantly higher than those in the 2-year-old pit muds, while the calcium content was significantly lower than that in the 2-year-old pit muds. However, there was no significant difference in any physicochemical indexes except moisture and humus contents between the 30-year-old pit bottom and wall muds and those aged two years. The correlation analysis indicated that moisture content, pH and ammonium nitrogen content had the most prominent effect on the microbial flora, which were significantly negatively correlated with Lactobacillus (P < 0.01), and significantly positively correlated with six bacterial genera including Aminobacterium, Syntrophomonas and Sedimentibacter (P < 0.05). The various microbial floras in the young pit muds interacted with each other during long-term repeated fermentation; some microorganisms gradually became dominant and the microflora structure finally reached a dynamic balance, resulting in the formation of high-quality pit mud. The results of this study will provide theoretical support for the quality maintenance of pit mud and the production of high-quality pit mud.

In this study, 16S rRNA high-throughput sequencing was used to study the succession of microbial community during the natural fermentation of tilapia surimi. The results showed that Firmicutes and Proteobacteria were the major phyla in the whole fermentation process, especially Firmicutes, whose relative abundance gradually increased with fermentation time, reaching nearly 90% after 30 h. Lactococcus, Pediococcus, Enterococcus, and Lactobacillus could adapt to the fermentation environment of tilapia surimi, and rapidly grow during the fermentation process. Lactococcus was the most important genus in fermented tilapia surimi, whose relative abundance increased significantly from 12.6% to 64.9% after 18 h, followed by Pediococcus with a relative abundance of 13.2% after 30 h fermentation. The quality evaluation showed that the gel strength, whiteness, hardness, and total plate count progressively increased with fermentation time, while the pH, adhesiveness, springiness, chewiness, and cohesiveness decreased when compared with those observed before fermentation. The correlation between core genera and quality indices was analyzed using Pearson correlation analysis and principal component analysis (PCA). As results, the increase in acid-producing bacteria such as Lactococcus, Pediococcus, Enterococcus, Enterobacter, and Citrobacter was positively correlated with the decrease in pH, as well as the improvement in the key quality indexes such as gel strength, whiteness, and hardness. These results showed that lactic acid bacteria such as Lactococcus, Pediococcus and Enterococcus, especially Lactococcus, played an important role in the quality formation of fermented tilapia surimi, which will provide an important theoretical basis for directional screening for functional microorganisms suitable for tilapia surimi fermentation and targeted improvement of the quality of fermented tilapia surimi.

To explore the effect of mixed-culture fermentations on antioxidant properties of fermented milk, yogurts fermented with Bifidobacterium animalis subsp. lactis (Ba) and/or Lactobacillus plantarum (Lp) combined with a commercial direct?vat?set?(DVS)?yogurt?starter culture containing Sterptococcus thermophilus and L. bulgaricus (1:1) were evaluated for acidification characteristics (pH and titratable acidity), proteolytic activity, exopolysaccharide (EPS) content, peptide content, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, hydroxyl radical scavenging activity, Fe2+ chelating activity and reducing power. The results showed that the acidification activity and proteolytic activity of fermented milk increased (P < 0.05) during refrigerated storage. EPS was mainly produced by the commercial starter culture, and was not responsible for the difference in the antioxidant capacity of fermented milks made with different starter cultures. The peptide content and reducing power showed an upward and then downward trend, reaching maximum values on the 7th day. Y in conjunction with Ba and/or Lp enhanced the proteolytic activity, peptide content and antioxidant activity when compared with Y alone (P < 0.05). Yogurt fermented with Y-Ba/Lp showed the highest DPPH radical scavenging activity, hydroxyl radical scavenging activity, Fe2+ chelating activity and reducing power (P < 0.05). Yogurt fermented with Y-Lp showed higher hydroxyl radical scavenging activity, but lower DPPH radical scavenging activity, Fe2+ chelating activity and reducing power than that fermented with Y-Ba (P < 0.05). This study suggests that co-fermentation with probiotics improves the antioxidant activity of fermented milks, and this effect is mainly due to the higher proteolytic activity of probiotics.

The α-L-fucosidase from Pedobacter sp. was modified by direct evolution for improved 2’-fucosyllactose (2’-FL) synthesis. A mutation library of α-L-fucosidase (PbFuc29A1) was constructed by error-prone PCR, and one mutant (mPbFuc29A1) capable of providing improved conversion ratio of 2’-FL was identified and characterized. The modified enzyme (mPbFuc29A1) showed the highest activity at pH 5.0 and 40 ℃ (compared to 35 ℃ for the wild-type PbFuc29A1), respectively. In comparison with PbFuc29A1, the specific activity of mPbFuc29A1 towards 2’-FL was increased by three folds, while that towards 4-nitrophenyl-α-L-fucopyranoside (pNP-FUC) and 3’-fucosyllactose were decreased by 22.8% and 52.5%, respectively. Using pNP-FUC and lactose as the substrates, mPbFuc29A1 catalyzed the synthesis of 2’-FL and 3’-FL with conversion ratios of 23.6% (9.1% higher than that with PbFuc29A1) and 56.4%, respectively. Sequence and mutation analysis revealed that there were two mutation sites (Asp21Val and Glu266Lys) in mPbFuc29A1, and Glu266Lys (located in the loop area) may play a key role in changing the specific activity and transglycosylation property of the mutant. The excellent properties of mPbFuc29A1 may make it a great candidate in industrial synthesis of 2’-FL.

This study attempted to investigate the effect of Lactobacillus helveticus on proteolysis and angiotensin-converting enzyme (ACE) inhibitory activity in Cheddar cheese during ripening. Those inoculated with L. casei, L. rhamnosus or nothing were used as controls for comparison. The digestion stability of cheese was evaluated at the time of the maximum ACE inhibitory activity. The results showed that during ripening, there was no significant difference (P > 0.05) in the number of viable bacteria among cheeses supplemented with probiotic bacteria, but they were all higher than that in the control cheese samples. The degree of proteolysis and ACE inhibitory activity in probiotic cheeses were higher than those in the control cheese samples significantly (P < 0.05). L. helveticus cheese had the strongest proteolysis degree and ACE inhibitory activity (79.71%). After simulated digestion, the viable bacterial count of L. helveticus cheese decreased by 14.30%, the ACE inhibitory activity increased significantly up to 86.06% (P < 0.05), and the polypeptide concentration increased to 2.81 mg/mL. Furthermore, it was found that the ACE inhibitory activity of peptides above 10 kDa increased while the ACE inhibitory activity of peptides below 10 kDa decreased after digestion. In addition, addition of L. helveticus did not influence the overall acceptance of cheese. Therefore, L. helveticus can promote the production of ACE inhibitory peptide and enhance its activity. The increased activity after digestion is mainly related to the degradation of macromolecular peptides.

In this study, high-throughput sequencing was used in combination with mathematical statistical analysis to analyze the succession of bacterial community structure during the mechanized fermentation of Maotai-flavor Daqu. The results showed that the dominant bacteria during the fermentation process were Firmicutes, Proteobacteria, Actinobacteria and Cyanobacteria. As fermentation progressed, Firmicutes became the single dominant phylum. A total of 84 bacterial genera were detected during the mechanized fermentation process, and 82 bacterial genera during the traditional fermentation process. Of the 84 genera, 14 were dominant, including Pantoea, Rhizobium, Lactobacillus, Weissella, Bacillus, Oceanobacillus, Lentibacillus, Kroppenstedtia, Thermoactinomyces, Staphylococcus, Enterobacter, Saccharopolyspora, Leuconostoc and Pseudomonas, of which Pantoea, Rhizobium, Lactobacillus, Weissella, Bacillus, Oceanobacillus, Lentibacillus, Kroppenstedtia, Thermoactinomyces, Staphylococcus, Enterobacter, Saccharopolyspora, Pediococcus and Tepidimicrobium. Pediococcus and Tepidimicrobium were dominant exclusively during the mechanical fermentation process, while Leuconostoc and Pseudomonas were dominant exclusively during the traditional fermentation process. Accordingly, there was a high similarity in the dominant bacteria between the mechanized and traditional fermentation processes. The correlation analysis of the dominant bacteria and environmental factors indicated that the major functional genera Bacillus, Lactobacillus and Weissella were positively correlated with Daqu fermentation temperature and acidity, indicating that during the mechanized fermentation process, the temperature and acidity should be controlled reasonably and scientifically to promote the growth of the major functional bacteria and simultaneously inhibit the multiplication of heat-resistant and acid-tolerant bacteria. This study corroborates that the mechanized fermentation process can be an alternative to the manual fermentation process from the perspective of the structure of bacterial community, which will lay the scientific foundation for the theoretical research and industrial application of the mechanized Maotai-flavor Daqu-making process.

In order to efficiently utilize shrimp and crab shells for the production of chitosan with chitin deacetylase, genomic sequencing of a Rhodococcus strain with high productivity of chitin deacetylase, designed 11-3 was conducted using Illumina high-throughput sequencing in this study. Subsequently, bioinformatics analysis was performed, including Gene Ontology (GO), Cluster of Orthologous Group (COG), Kyoto Encyclopedia of Genes and Genomes (KEGG) function annotation of genes, carbohydrate-active enzyme annotation, and bioinformatics analysis of chitin degradation enzyme genes. It was found that the genome of Rhodococcus 11-3 was 6 089 866 bp in length including a total of 5 904 coding genes with a GC content of 70.514%. A total of 165 genes were identified by carbohydrate-active enzyme annotation, including 59 carbohydrate esterase genes, 42 glycosyltransferase genes, 36 glycoside hydrolase genes and 28 auxiliary oxidoreductase genes. Among these, one chitin deacetylase gene (gene 4907), four chitinase (EC 3.2.1.14) genes (genes 1286, 1287, 3810, and 4754) and two chitinase (EC 3.2.1.132) genes (genes 4921 and 5362) were identified. The sequence similarity between gene 4907 and the reported chitin deacetylase genes was 26.60%–32.43%, suggesting that gene 4907 was a new chitin deacetylase. Therefore, Rhodococcus 11-3 has great potential in the utilization of chitin resources.

In this study, high-throughput sequencing combined with mathematical statistical software analysis was used to systematically investigate the structure and characteristics of fungal flora in environmental samples from different fermentation rounds of Maotai-flavor liquor in Maotai town. A total of 4 fungal phyla and 212 fungal genera were detected in seven fermentation rounds. According to their relative abundance, Ascomycota and Basidiomycota were the dominant phyla in each round, and Wallemia and Saccharomycopsis were the absolute dominant fungal genera. The fungal compositions in the seven rounds were highly similar to each other, but there were fungal genera characteristic of each round. A total of 56 fungal genera were found to be common to the seven rounds, which were dominant in each round; the number of fungal genera characteristic of each round was great, but their relative abundance was small. The strongest node of Ascomycota was Debaryomyces and the strongest node of Basidiomycota was Rhodotorula. The results of this study can lay a scientific foundation for further studies on the mechanism behind the brewing of Maotai-flavor liquor and on microorganisms in the brewing environment.

The relationships between total hydrogen content, dominant microbial genera and lactic acid content in bottom pit muds (BPMs) from old and young mud pits used for the production of strong-flavor Baijiu were analyzed in this study. It was found that the total hydrogen content decreased with the increase in pit depth and pH and lactic acid content in various layers of young and old BPM, this decrease being greater in old BPM. The copy numbers of dominant genera in old BPM were generally higher than those in young BPM. The correlation coefficients between lactic acid content and total copy numbers of dominant genera were significantly different between young and old BPMs (?0.665 2 vs 0.025 6), and a strong negative correlation existed in young BPM. Fifteen dominant genera showed a strong negative correlation with lactic acid content in young BPM (< ?0.5); while in old BPM, small correlation coefficients (half positive and half negative) were observed between most dominant genera and lactic acid content and only two dominant genera (Caproiciproducens and Hydrogenispora) showed strong correlation with lactic acid content. It was indicated that the metabolic profile of dominant genera was different between young and old BPMs. The dominant genera in young BPM were mainly involved in the degradation of lactic acid. In conclusion, the reduction of lactic acid content in BPM was related to microbial total hydrogen metabolism, which was beneficial to increase the pH of BPM thereby improving its quality.

The aim of this study was to analyze and discriminate the volatile profiles of the kernel oils of 10 Korean pine varieties by headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and electronic nose (E-nose). Totally 163 volatile compounds were identified from the 10 oils, including hydrocarbons, alcohols, aldehydes, esters, ketones and acids, with hydrocarbons, aldehydes, alcohols and esters being the predominant ones. The main flavor contributors were aldehydes, alcohols and esters. By cluster analysis (CA) and principal component analysis (PCA), the pine nut oils could be divided into three groups. There were significant differences in volatile contents among these groups. When the E-nose data were processed by PCA and CA, the cumulative contribution rates of the first two principal components were 97.17% and 88.82%, respectively, indicating that the sensors had a high degree of recognition and good discrimination between the samples. Moreover, the signal sensors were correlated with different volatile components. This study confirmed the feasibility of applying HS-SPME-GC-MS combined with E-nose to analyze and discriminate the volatile profiles of the 10 pine nut oils.

A rapid and precise method to identify the phytochemicals in the fruit of Lycium ruthenicum Murray (LRM) was established using ultra-high performance liquid chromatography coupled to triple time of flight mass spectrometry (UPLC-Triple TOF/MS) with multistage fragment ions data, the natural compounds mass spectral database and related data reported in the literature. Total anthocyanins in LRM were quantitatively analyzed by UPLC equipped with an Acquity UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 μm). Gradient elution was carried out using 0.1% trifluoroacetic acid-10% formic acid aqueous solution as mobile phase A and formic acid:water:methanol:acetonitrile (1:5:2:2, V/V) as mobile phase B. The detection wavelength was 530 nm. The total content of anthocyanins was calculated as cyanidin-3-O-glucoside. Thirty compounds were identified from LRM, including 13 alkaloids and 13 anthocyanins. The concentration of cyanidin-3-O-glucoside in the range of 0.005–0.08 mg/mL had good linear relationship with the peak area (R = 0.999 9). The average recovery for spiked samples was 95.45%, with a relative standard deviation (RSD) of 2.62%. The chemical constituents of LRM were identified rapidly and efficiently by UPLC-Triple TOF/MS, and the UPLC method for the determination of total anthocyanins was highly repeatable and accurate and could be used for the quality evaluation and control of LRM.

The major taste compounds and volatile flavor compounds in samples of honey-roasted duck legs at different stages (curing and roasting) during processing were analyzed and identi?ed by electronic tongue, high performance liquid chromatography (HPLC), amino acid analyzer and headspace solid phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results showed that the key taste compounds in the product were 5’-inosine acid, 5’-adenosine phosphate, aspartic acid and glutamic acid. A total of 61 volatile flavor compounds were identified. Among them, seven aldehydes, two esters, one alcohol and one heterocyclic compound were determined as the key volatile flavor compounds. During the curing stage, the contents of 5’-inosine acid, 5’-adenosine phosphate, aspartic acid and glutamate decreased significantly, and the number of volatile flavor compounds increased from 29 to 40. During the roasting stage, the contents of 5’-inosine, 5’-adenosine phosphate and aspartic acid increased significantly, and the number of volatile flavor compounds increased from 40 to 50, mainly including aldehydes and esters. The contents of volatile flavor compounds increased sharply at the middle stage of roasting, and then decreased significantly at the late stage. To sum up, the curing and middle-late roasting stages are the critical periods for the formation of the flavor of honey-roasted duck legs.

In this study, the flavor composition of typical base liquors for Maotai-flavor Baijiu from different mechanized brewing rounds was analyzed by liquid-liquid extraction (LLE) combined with gas chromatography-mass spectrometry (GC-MS) based on retention index. The characteristic aroma compounds were determined by their odor activity values, and their relationship with sensory properties was evaluated. The results showed that a total of 37 characteristic aroma compounds were identified. The contribution of each class of volatile compounds to the aroma of typical base liquors from each brewing round was consistent with the sensory evaluation results. The aroma of the base liquors from the first and second rounds was clean with the fruity and fruity notes being superior to the soy?sauce-like note. The base liquors from the third, fourth and fifth rounds had a more prominent soy?sauce-like note, the base liquor from the sixth round had stronger roasted and caramellic notes, and the base liquor from the sixth round exhibited a stronger burnt note together with weakening of other notes. Nineteen compounds including ethyl valerate, ethyl isovalerate, ethyl hexanoate, butyl hexanoate and ethyl octanoate were found to be the main contributors to the fruity, floral and sweet aromas, and the contributors to the roasted and nutty aromas included isobutanol, 2,6-dimethylpyrazine, 2,3,5-trimethylpyrazine and 2-ethyl-6-methyl pyrazine. Furfuryl alcohol and furfural were identified as major caramel-like aroma compounds, and acids as major cheese-like aroma compounds.

A new method for quickly detecting the content of amino acid nitrogen in brewed soy sauce has been established for grade identification. Several Chinese brands of soy sauce were tested using natural food colorants as chromogenic agents according to the national standard GB 18186-2000 Fermented Soy Sauce. According to the law of conservation of mass, the concentration of NaOH and the amount of substances needed to detect all grades of soy sauce products were systematically investigated. The results showed that the purple sweet potato colorant exhibited red, orange-red or orange-gray colors for qualified soy sauce. The developed method was simple, convenient, intuitive, accurate, and practical, and took a few minutes to give results consistent with those from the national standard method GB 2009.235-2016 Detection of Amino Acid Nitrogen in Food.

In this study, the influence of different molar extinction coefficients and reference substances on the determination of total anthocyanins in black chokeberry by the pH differential method and high performance liquid chromatography (HPLC), respectively was investigated. The results obtained by the optimized pH differential method were compared with those obtained by the HPLC method using t-test. Results showed that the selection of molar extinction coefficient and reference substance had a significant impact on the results of the two methods. Moreover, the pH differential method with cyanidin-3-O-galactoside, which is abundant in black chokeberry as the reference substance, and HPLC with a mixed reference standard were superior to the traditional method with cyanidin-3-O-glucoside as the reference substance (P < 0.05). There was no significant difference between the results of HPLC with cyanidin-3-O-galactoside as the reference substance and those with the mixed reference standard (P > 0.05). The results of HPLC were higher than those of the pH differential method. Collectively, despite its low cost, HPLC with the mixed reference standard was the most accurate method for the determination of total anthocyanins in black chokeberry. HPLC with cyanidin-3-O-galactoside as the reference substance was simple, accurate and economical and also suitable for this purpose.

The chemical and nutritional composition of red millet produced in Nanyang, Henan in different years were analyzed by blender extraction, purification through silica gel chromatography combined with crystallization precipitation, and conventional analyses. Using apigenin as a reference standard, the total flavonoid content in red millet was measured by the sodium nitrite-aluminum nitrate-sodium hydroxide colorimetric method. Vanillin, vanillic acid, β-sitosterol, dibutyl phthalate and apigenin were isolated from red millet for the first time to our knowledge; the total flavonoid content was determined to be 4.91%. Moreover, red millet was found to contain a variety of amino acids; the ratios of essential to total amino acids (EAA/TAA) and essential to non-essential amino acids (EAA/NEAA) were 39.49% and 60.51%, respectively, close to the Food and Agriculture Organization/World Health Organization (FAO/WHO) recommended pattern. The major fatty acids were palmitic acid and linoleic acid, oleic acid, and stearic acid, with linoleic acid being the single dominant fatty acid (64.60%). γ-Vitamin E was the most abundant vitamin (2.24 mg/100 g). Mg and P were the most abundant microelements (2 160 and 3 470 mg/kg, respectively).

To rapidly and non-destructively detect beer quality, olfactory visualization technology was used to qualitatively distinguish among eight kinds of Tsingtao beer (namely Premium, 1903, Augerta, Weiss, Stout, Pilsner, IPA and Strong), and quantitatively determine their key quality indicators (namely alcohol content, original gravity and diacetyl concentration). A 4 × 4 colorimetric sensor array (CSA) was used to react with volatile compounds of beer, and the color difference images obtained were analyzed by chemometric methods. The results showed that the linear discriminant analysis (LDA) model was able to qualitatively distinguish among these eight kinds of beer with a 100% recognition rate for both the calibration and prediction sets, while the least square-support vector machine (LS-SVM) model was able to quantitatively predict alcohol, original gravity and diacetyl concentration with correlation coefficients over 0.98 for the calibration and prediction sets. Hence, olfactory visualization technology has good potential for application in the rapid and non-destructive detection of beer quality.

A machine vision-based method for the non-destructive firmness detection and grading of whole bunches of Red Globe grapes was proposed in this study. Red, green and blue (RGB) and near infrared images of the samples were acquired with an industrial camera. The three color channels in the RGB images were extracted, and the normalized GB color difference method was applied to locate the fruit stems based on the RGB images. Meanwhile, the center of mass of each fruit in a bunch was located by morphological reconstruction based on local maximum brightness and the center of mass of the whole bunch was extracted. The area of the fruit stalk, the ratio of the number of grapes to the area of the whole bunch of grapes, and the ratio between the sum of distance from the surface of each grape to the center of mass of the whole bunch of grapes and the number of grapes were selected as characteristic parameters to establish a classification model for predicting the firmness of grape bunches using linear discriminant analysis (LDA), integrated learning algorithm (ILA) or support vector machine (SVM). The results of validation showed that the SVM model had the best classification performance. This model was applied to 130 bunches of Red Globe grapes with a grading accuracy of 94.6%. These results will contribute to predicting grape quality and yield in the future.

The purpose of this study is to evaluate the feasibility of the feasibility of identifying the geographical origin of Korla fragrant pear (KFP) by the strontium (Sr) content and 87Sr/86Sr isotopic ratio. Sr contents in Xinjiang KFPs, Shaanxi Hongxiangsu pears and Gansu fragrant pears as well as orchard soils for each fruit were analyzed by inductively coupled plasma mass spectrometry (ICP-MS), and 87Sr/86Sr isotopic ratios in the peel and pulp of KFP were determined by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The difference in Sr contents among the peel and pulp of the three fruits as well as the orchard soils, among the peel and pulp of KFP from different regions in Xinjiang, and among KFP orchard soils collected in different years was investigated by analyses of variance (ANOVA). The correlation between Sr contents in fruits and soils was analyzed and the distribution characteristics of 87Sr/86Sr isotope ratio and Sr contents in pear fruits from different geographical origins were discussed. The results showed that there were significant differences in the contents of Sr in pear orchard soils from Xinjiang, Gansu and Shaanxi Provinces (P < 0.05), but not in KFP orchard soils collected in different years. The contents of Sr in peel and pulp were significantly correlated with each other (P < 0.01), but not with soil Sr content. There was a significant difference in 87Sr/86Sr isotopic ratio (P < 0.05) but not Sr content in the pulp and peel of the three fruits. To sum up, KFP peel is more suitable for geographical origin identification by Sr isotope technique. It is feasible to identify the geographical origin of KFP based on Sr isotopic ratio.

In the present study, we examined the potential of non-targeted metabolomics based on ultra-high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) for the authentication of sea buckthorn oil. Chemometric analysis showed that sea buckthorn oil could be discriminated from other edible oils including sunflower seed oil, rapeseed oil and soybean oil by orthogonal partial least squares-discrimination analysis (OPLS-DA). Furthermore, 14 characteristic marker compounds in the oils were identified by their ion abundance and mass number, including organic acids and alcohols. Out of these compounds, six were found in sea buckthorn oil, three in sunflower seed oil, four in rapeseed oil and one in soybean oil. Our results suggest that non-targeted metabolomics based on UPLC-QTOF-MS has great potential for the rapid identification of adulterated sea buckthorn oil.

Totally 75 samples of 12 brands of food flavors commonly used in dairy products were analyzed qualitatively for their compositions by n-hexane extraction and gas chromatography-mass spectrometry (GC-MS) based on retention indices. A total of 148 compounds were identified, of which 19 were determined as flavor components of concern by median lethal doses (LD50), detection rates and relative contents. A quantitative analytical method for the 19 flavor substances of concern in 110 samples of fermented dairy products was established, optimized, and evaluated using headspace-solid phase microextraction-gas chromatography-tandem mass spectrometry (HS-SPME-GC-MS/MS) operated in the multiple reactions monitoring (MRM) mode. 2,3-Butanedione, benzaldehyde, maltol, ethyl maltol, and vanillin were detected at high prevalence and average levels. Based on the quantitative results and the consumption of dairy products in China, exposure risk assessment of the 19 flavor substances was carried out using the threshold of toxicological concern (TTC) approach, which indicated that the intake of ethyl maltol in all age groups of consumers exceeded the TTC, suggesting high exposure risks. The risk of dietary exposure to most of these flavor substances in children aged 1–3 years was higher than in other age groups, which needs to be further explored.

A modified QuEChERS coupled with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the determination of 18 succinate dehydrogenase inhibitor (SDHI) fungicides in fruits and vegetables. Samples were extracted with acetonitrile and salted out with anhydrous magnesium sulfate and sodium acetate, and then the supernatant was purified with primary secondary amine (PSA). The 18 compounds were separated on a C18 column by gradient elution using acetonitrile-0.1% (V/V) formic acid in water as the mobile phase, detected by MS/MS in both positive ion and negative ion mode using multiple reaction monitoring (MRM), and finally quantified by the external standard method. The calibration curves for all analytes showed good linearity with correlation coefficients (r) of above 0.99 in the concentration range of 0.5–200 μg/L. The limits of detection (LOD) and the limits of quantification (LOQ) of the developed method were 0.5–2.0 and 1.5–6.0 μg/kg, respectively. The recoveries of the analytes in four different matrixes each spiked at three levels (10, 50 and 150 μg/kg) ranged from 83.6% to 109.4% with relative standard deviations (RSD) of 1.2%–8.4% (n = 6). This method was easy to operate and showed good purification efficiency, and thus it could be applied to the rapid determination of SDHI fungicides in fruits and vegetables.

The peptide mass fingerprints of actin from Siniperca chuatsi, Trachinotus ovatus and Acipenser sinensis were analyzed by Orbitrap Fusion Lumos mass spectrometry. The differences in the amino acid sequence and the signature peptides of actin from the three fishes were clarified. Results showed that the signature peptides were identified in the enzymatic hydrolysate of skeletal muscle α-actin for S. chuatsi, while the signature peptides were derived from β-actin for both T. ovatus and A. sinensis. Totally 29 peptides were detected in S. chuatsi actin, 24 peptides in T. ovatus actin, all being the signature peptides, and 13 peptides in A. sinensis actin. Compared with the actin fingerprints of the two other fishes, 10 differential peptides were identified in skeletal muscle α-actin of S. chuatsi, five differential peptides in β-actin of T. ovatus, and only three differential peptides in β-actin of A. sinensis. According to the arrangement of amino acid sequences, there were 21 amino acid substitutions between S. chuatsi skeletal muscle α-actin and T. ovatus β-actin, starting from the similar sequences, and 17 amino acid substitutions between S. chuatsi skeletal muscle α-actin and A. sinensis β-actin. The amino acid sequences of A. sinensis and T. ovatus β-actin showed high homology to each other with only three amino acid substitutions. The results of this study will lay a foundation for the identification of quality properties of rare fish and the development of fish actin standards, and provide a theoretical basis for the development, utilization and rapid quantitative detection of functional fish protein products.

In this study, a ratiometric fluorescence sensor based on silicon-doped carbon quantum dots (Si-CDs) and lysozyme (Lys) functionalized gold nanoclusters (Lys-AuNCs) was developed for the rapid detection of mercury (II) ion (Hg2+). In the method, Si-CDs emitted a blue light as a reference fluorescence signal, and Lys-AuNCs emitted a red light as a response fluorescence signal. Hg2+could efficiently quench the fluorescence of Lys-AuNC at 670 nm (I670) by virtue of gold affinity between Au+ and Hg2+, while the fluorescence intensity of Si-CDs at 470 nm (I470) remains unchanged. The ratio of the fluorescence intensity at 670 nm and 470 nm (I670/I470) showed a good linear relationship with the concentration of Hg2+ in the range of 0–0.016 mg/L, which was fitted as follows: I670/I470 = 1.35–64.18C (Hg2+). The recoveries of Hg2+ spiked in lake water, mineral water and running tap water were in the range of 94.3%–115.0%. The detection limit of this sensor was 0.001 mg/L (3σ) with a variation coefficient not more than 10.3%. Other metal ions exhibited no interference for this sensor.

An impedimetric aptasensor based on reduced graphene oxide (rGO)/carbon nanotube (CNT)-gold nanoparticles (AuNPs) nanocomposite was prepared for the detection of Pseudomonas aeruginosa. The GO/CNT was modified on the surface of the electrode by electrodeposition, followed by electrochemicalreduction of GO. Then, electrodeposition was used to deposit AuNPs on the surface of the electrode. The working electrode was prepared by bonding thiol-modified aptamer specific for P. aeruginosa to the AuNPs composite via Au-S bonds. The morphology of the rGO/CNT-AuNPs nanocomposite was characterized by scanning electron microscopy. Cyclic voltammetry was used to monitor each assembly step. When exposed to samples containing P. aeruginosa, the anti-P. aeruginosa aptamer on the electrode could capture its target, blocking electron transport and consequently resulting in a great increase in impedance. P. aeruginosa could be quantified by the change in impedance. The linear range of this method was 10–106 CFU/mL and the detection limit was 4 CFU/mL. To the best of our knowledge, the developed electrochemical biosensor may be the most sensitive detection method for P. aeruginosa.

A novel absorption spectrometric method for the rapid and accurate determination of the colorants tartrazine and sunset yellow in beverages was established. In Tris-HCl medium with a certain acidity, ethyl violet could react with tartrazine (pH 5.69) and sunset yellow (pH 8.68) to form an ion association complex. At 506 and 646 nm, tartrazine and sunset yellow exhibited characteristic absorption, respectively, allowing their quantitative analysis. Their apparent molar absorption coefficients were 1.37 × 105 and 7.68 × 104 L/(mol·cm), respectively. There was a linear relationship between the concentration of tartrazine in the range of 0.04–9.6 mg/L and the absolute value of absorbance, and the detection limit and the quantitation limit were 0.024 mg/L and 1.29 mg/kg, respectively. There was a linear relationship between the concentration of sunset yellow in the range of 0.04–6.3 mg/L and the absorbance, the detection limit and the quantitation limit were 0.031 mg/L and 1.68 mg/kg, respectively. The spiked recoveries of tartrazine and sunset yellow in real samples were 97.0%–104% and 97.3%–103%, respectively, with relative standard deviations (n = 5) of 1.5%–2.6% and 1.2%–2.6%, respectively. The method was simple and rapid, and it could be used for the determination of tartrazine and sunset yellow in beverages with satisfactory results.

A rapid, sensitive real-time method for the detection of guanine in fish flesh was developed by impurity removal using microporous resin adsorption combined with surface-enhanced Raman spectroscopy (SERS). The percentage adsorption of protein onto a column packed with D152 resin (20?cm × 1?cm, i.d.) was 83%–92% and the recovery of guanine was higher than 95%. Using one-factor-at-a-time and orthogonal array design methods, the optimum adsorption and desorption conditions were established as follows: sample loading flow rate 3 mL/min, eluent pH 4.0, and elution flow rate 0.5?mL/min. Silver-coated gold nanoparticles (Au@Ag NPs) were used as a substrate for SERS. Guanine concentration in the range from 0.001 to 100?mg/L had a linear relationship with its Raman intensity, with a correlation coefficient (R2) of 0.969 9 and the detection limit of the method was 0.1?mg/L. The entire detection process took only 10 minutes without the requirement for any complicated sample preparation. These results show that the chromatographic column filled with D152 resin could effectively eliminate the interference of impurities such as proteins in fish flesh, and the SERS method could rapidly and sensitively detect trace purines in fish flesh with a detection limit lower than that of the existing HPLC method.

To study the diversity and seasonal variation of bacteria contaminating duck eggshell surfaces, fresh duck eggs collected in different seasons were cleaned by ultrasonic washing to prepare bacterial samples. The diversity of bacterial flora in the samples was analyzed by Illumina MiSeq high-throughput sequencing. The results showed that a total of 697 244 optimal sequences were obtained and assigned to 650 operational taxonomic units (OTU), covering 35 phyla, 298 genera, and 447 species. For each seasonal samples, the dominant bacteria with a high relative abundance were Bacillus and Enterococcus (17.78% and 17.16%) of the phylum Firmicutes, and Escherichia-Shigella (17.14%) of Enterobacteriaceae in Proteobacteria. However, there was a significant difference in the microbial community structure and species richness among these samples. The maximum Chao and ACE were observed for winter samples (n = 4), with averages of 596.5 ± 22.29 and 587.5 ± 17.82, respectively, as well as maximum Shannon’s index and minimum Simpson’s index, 3.52 ± 1.02 and 0.1 ± 0.07 on average, respectively, indicating that the species complexity was highest. A total of 35 OTUs were common to the spring, summer, autumn and winter samples, accounting for 0.06%–70.00% of the total number of OTUs in each sample; and 9, 0, 17 and 496 OTUs were unique to these samples respectively. There were great differences in the composition of the microflora on the surface of eggshells among seasons. Vibrio, Pseudomonas_caeni, Enterobacter, Lysinibacillus, Clostridium_sensu_stricto_1 existed in different seasons. Some pathogenic floras were obviously affected by temperature. These results will provide a theoretical basis for further studies on the major spoilage bacteria of duck eggs and for controlling them.

For ultrasensitive detection of Escherichia coli O157:H7, the target bacteria were enriched effectively by immunomagnetic separation. Then, colloidal gold nanoprobes simultaneously with a large amount of antibodies and β-lactamase were used as the mediators. β-Lactamase was employed to hydrolyze penicillin efficiently for the transduction and amplification of detection signals. Immunochromatography was applied for detecting the variation in penicillin concentration. The sensitivity of the developed method was 2 × 102 CFU/mL, which was 570 folds higher than that of traditional immunochromatography. In addition, this method avoided the Hook effect in sandwich immunochromatography, which provides a new tool for immunochromatographic detection of macromolecular analytes with high sensitivity and accuracy.

In order to improve the safety and efficiency of spectrophotometry in the determination of nitrite and its applicability to pickles, the spectrophotometric method specified in the Chinese national standard was modified by using three new diazo-coupling reagents: p-aminobenzene sulfonic acid/N-(1-naphthyl) ethylenediamine dihydrochloride (ASA-NED), p-aminoacetophenone/N-(1-naphthyl) ethylenediamine dihydrochloride (AAP-NED) and sulphanilamide/N-(1-naphthyl) ethylenediamine dihydrochloride (SN-NED) to replace the two-step reaction. For each diazo-coupling reagent, the operating conditions were optimized using an orthogonal array design, and the detection performance and storage stability of the diazo-coupling reagents were compared. The results showed that in the optimized ASA-NED, AAP-NED and SN-NED methods, succinic acid, tartaric acid, and malic acid respectively could replace concentrated hydrochloric acid as the acid medium, shortening the detection time by 5–14 min, and improving the safety and detection efficiency. The linear detection ranges of the ASA-NED, AAP-NED and SN-NED methods were 0.02–3, 0.02–3 and 0.02–3.4 μg/mL, and the detection limits were 0.82, 0.51 and 0.76 mg/kg respectively, compared to 1 mg/kg for the traditional method. The AAP-NED method had comparable anti-interference capacity to that of the traditional method, and the AAP-NED and SN-NED methods were more resistant to interference than the traditional method. When the levels of nitrite in 15 kinds of pickle were detected by the four methods, except for high iodine kelp samples, the accuracy decreased as follows: AAP-NED (96.01%–99.60%) > SN-NED (93.82%–96.24%) > traditional (88.61%–92.66%) > ASA-NED (84.04%–87.00%), and the relative standard deviation (RSD) values were all less than 5%. SN-NED at all temperatures investigated and AAP-NED only at 4 ℃ were stable for 40 days, having better detection applicability than ASA-NED. In conclusion, the efficiency and safety of spectrophotometry could be improved by using AAP-NED and SN-NED, which could be suitable for the rapid determination of nitrite in pickles.