Effect of H2O2-assisted ultrasonic bath on the degradation and physicochemical properties of pectin.

The effects of H2O2-assisted ultrasonic bath degradation technology on pectin were investigated. The degradation efficiency with different pectin concentrations, H2O2 concentrations, ultrasonic power, and ultrasonic time was analyzed. The results showed that pectin concentration was negatively correlated with the degradation efficiency of pectin, while, H2O2 concentration, ultrasonic power, and ultrasonic time were positive correlated with the degradation efficiency. Besides, the apparent viscosity and viscoelasticity of the degraded pectin decreased significantly. The antioxidant activity increased after the H2O2-assisted ultrasonic bath treatment. The results of FTIR, NMR, laser particle size, SEM, XRD, and AFM analysis indicated that the degradation treatment did not destroy the main structure of pectin. The average particle size and crystallinity of pectin decreased. The degree of aggregation and the height of the molecular chain decreased significantly. In conclusion, the H2O2-assisted ultrasonic bath degradation technique could effectively degrade pectin. This study provided a comprehensive analysis of the degradation of pectin under H2O2-assisted ultrasonic bath, which will be beneficial to further develop H2O2-assisted ultrasonic bath techniques for pectin degradation.

Mechanistic insights into nitrogen-induced changes in pasting characteristics of rice during storage based on proteomics analysis.

Nitrogen application delays rice quality deterioration due to changes in its pasting characteristics; however, the underlying mechanisms remain unclear. Using a label-free quantitative proteomics approach, we identified differentially expressed proteins (DEPs) during storage in paddy rice treated with different nitrogen levels. On combining the changes in physiological indicators, high-nitrogen treatment was found to downregulate ß-1,3-glucanase, reduce the decomposition of cell wall components, downregulate three proteins involved in starch metabolism, decrease the range of the amylose content and increase the range of the amylopectin, upregulate three proteins related to the lysosomal pathway, and enhance glutelin degradation. In addition, it upregulated three proteins related to flavonoid synthesis, which enhanced the stress response ability of rice, thereby contributing to the stability of biological macromolecules. The discovery of these key DEPs provides potential targets for further control over the deterioration of crop seed storage quality.

Synergistic effect of discrete ultrasonic and H2O2 on physicochemical properties of chitosan.

Synergistic degradation of chitosan by discrete ultrasonic and H2O2 was investigated. The effects of ultrasonic time, ultrasonic power, chitosan concentration, and H2O2 concentration were evaluated. The results revealed that ultrasonic power, H2O2 concentration and ultrasonic time were positively correlated with degradation rate, while chitosan concentration was negative. The results of degradation kinetics revealed that the synergistic degradation process was consistent with the first-order reaction. Changes of characterization of chitosan were analyzed by FTIR, 13C NMR, XRD, SEM, and AFM analysis. The results indicated that the synergistic degradation did not destroy the pyranose ring. The crystal structure of degraded chitosan was destroyed, and the molecular conformation changed significantly. The antioxidant activity of the original and degraded chitosan was determined by DPPH and reducing power assays. The degraded chitosan had higher antioxidant activity. All results showed that the synergistic degradation of discrete ultrasound and H2O2 was a feasible method for large-scale low molecular weight chitosan production.

Nitrogen fertilizer application rate impacts eating and cooking quality of rice after storage.

The effect of nitrogen fertilizer application on the quality of rice post-storage is not well understood. The eating and cooking quality (ECQ) of rice treated with 0 (CK, control), 160 (IN, insufficient nitrogen), 260 (AN, adequate nitrogen), and 420 (EN, excessive nitrogen) kg N/ha was analyzed over 12 months of storage. Results showed that the rate of nitrogen fertilizer application had no significant impact on the changes in taste value during storage. However, EN application significantly increased the hardness (p < 0.05), reduced the gumminess (p < 0.05), and delayed the decline in the viscosity of rice paste by two months after one-year storage, compared with other treatments. In conclusion, although EN application resulted in an inferior texture of rice, it delayed the quality change by two months during storage. It was demonstrated that a rational nitrogen application rate (0-260 kg N/ha) for rice cultivation is particularly important to obtain high ECQ; however, EN may be beneficial for the stability of the ECQ during storage.

Investigation on the role of the free radicals and the controlled degradation of chitosan under solution plasma process based on radical scavengers.

This study investigated the role of various active species (OH, O, and H2O2) under solution plasma process (SPP) degradation based on the influence of different radical scavengers on the degradation effect and ESR spectra. The structures of oligochitosan with different radical scavengers were characterized by FT-IR, 1H NMR, and XRD analysis. The results indicated that OH, O, and H2O2 played important roles in SPP degradation. The degradation effect of the O was even higher than that of the OH. The physical effects (e.g. UV light and shockwaves) of SPP method or Fenton's reaction might contribute to the degradation treatment. Furthermore, the different scavengers could adjust the degradation effect of the corresponding free radicals. FT-IR, 1H NMR, and XRD analysis revealed that the primary chemical structure of chitosan was not changed by the scavengers. This study found that the controlled degradation by addition of a radical scavenger is feasible. Therefore, this study provided a straightforward analysis of the role of the free radicals and the controlled degradation of chitosan under SPP treatment, which will be beneficial to further develop SPP techniques for chitosan degradation.

Determination of allosteric and active sites responsible for catalytic activity of delta 12 fatty acid desaturase from Geotrichum candidum and Mortierella alpina by domain swapping.

Cheese lacks essential fatty acids (EFAs). Delta 12 fatty acid desaturase (FADS12) is a critical enzyme required for EFA biosynthesis in fermentation of the predominant strains of cheese. Previously, we identified the FADS12 gene and characterized its function for the first time in Geotrichum candidum, a dominant strain used to manufacture soft cheese with white rind. In this study, we analyzed the molecular mechanism of FADS12 function by swapping domains from Mortierella alpina and G. candidum that had, respectively, high and low oleic acid conversion rates. The results revealed three regions that are essential to this process, including regions from the end of the second transmembrane domain to the beginning of the third transmembrane domain, from the end of the third transmembrane domain to the beginning of the fourth transmembrane domain, and from the 30-amino acid from the end of the sixth transmembrane domain to the C-terminal end region. Based on our domain swapping analyses, nine pairs of amino acids including H112, S118, H156, Q161, K301, R306, E307, A309 and S323 in MaFADS12 (K123, A129, N167, M172, T302, D307, I308, E310 and D324 in GcFADS12) were identified as having a significantly effect on FADS12 catalytic efficiency, and linoleic acid and its analogues (12,13-cyclopropenoid fatty acid) were found to inhibit the catalytic activity of FADS12 and related recombinant enzymes. Furthermore, the molecular mechanism of FADS12 inhibition was analyzed. The results revealed two allosteric domains, including one domain from the N-terminal region to the beginning of the first transmembrane domain and another from the 31st amino acid from the end of the sixth transmembrane domain to the C terminus. Y4 and F398 amino acid residues from MaFADS12 and eight pairs of amino acids including G56, L60, L344, G10, Q13, S24, K326 and L344 in MaFADS12 (while Y66, F70, F345, F20, Y23, Y34, F327 and F345 in GcFADS12) played a pivotal role in FADS12 inhibition. Finally, we found that both allosteric and active sites were responsible for the catalytic activity of FADS12 at various temperatures, pH, and times. This study offers a solid theoretical basis to develop preconditioning methods to increase the rate at which GcFADS12 converts oleic and linoleic acids to produce higher levels of EFAs in cheese.

Label-Free Quantitative Proteomics Reveals the Multitargeted Antibacterial Mechanisms of Lactobionic Acid against Methicillin-Resistant Staphylococcus aureus (MRSA) using SWATH-MS Technology.

The objective of the present study was to reveal the antibacterial mechanism of lactobionic acid (LBA) against methicillin-resistant Staphylococcus aureus (MRSA) using quantitative proteomics by sequential window acquisition of all theoretical mass spectra (SWATH-MS) to analyze 100 differentially expressed proteins after LBA treatment. Furthermore, multiple experiments were conducted to validate the results of the proteomic analysis including reactive oxygen species (ROS), virulence-associated gene expression, and the relative quantification of target proteins and genes by parallel reaction monitoring and quantitative real-time PCR. Combining the ultrastructure observations, proteomic analysis, and our previous research, the mode of LBA action against MRSA was speculated as cell wall damage and loss of membrane integrity; inhibition of DNA repair and protein synthesis; inhibition of virulence factors and biofilm production; induction of oxidative stress; and inhibition of metabolic pathways. These results suggest potential applications for LBA in food safety and pharmaceuticals, considering its multitarget effects against MRSA.

Reduction of Escherichia coli O157:H7, Listeria monocytogenes, and Naturally Present Microbe Counts on Lettuce using an Acid Mixture of Acetic and Lactic Acid.

Lactic acid (LA) and acetic acid (AA) are independently used to disinfect fresh leaf vegetables. LA has a higher efficacy but costs more than AA. Herein, we compared the disinfection efficacy of LA, AA, and their mixture on lettuce to determine whether the cheaper acid mixture shows similar or more efficacy than LA. Quality analysis indicated that the acid mixture and individual acids did not cause additional loss of instrument color and polyphenolic content compared with that of the control; however, visible defects were observed at AA concentrations exceeding 0.8%. Analysis of Escherichia coli O157:H7, Listeria monocytogenes, and naturally present microbes (aerobic mesophilic and psychrotrophic bacteria, coliforms, molds, and yeasts) showed that the acid mixture led to the highest reduction in microbial count during storage. 16S rRNA sequencing was further employed to understand the effects of the acid mixture and individual acids on lettuce microbial ecology. During storage, the acid mixture and individual acids significantly decreased the abundance of Massilia spp. and Alkanindiges spp. but there was a marked increase in Escherichia-Shigella abundance (LA: 0.003-58.82%; AA: 0.01-55.34%; acid mixture: undetected to 50.71%; control: 0.007-33.09%), indicating that acid disinfection altered the microbial ecology to stimulate Escherichia-Shigella growth. These results enhance our understanding of the relationship between lettuce disinfection and ecological changes.

An integrated metagenomic/metaproteomic investigation of microbiota in dajiang-meju, a traditional fermented soybean product in Northeast China.

Dajiang-meju have been used as major ingredients for the preparation of traditional spontaneously fermented soybean paste in Northeast China. In this work, we sequenced and analyzed the metagenome of 12 dajiang-meju samples. To complement the metagenome analysis, we analyzed the taxonomic and functional diversity of the microbiota by metaproteomics (LC-MS/MS). The analysis of metagenomic data revealed that the communities were primarily dominated by Enterobacter, Enterococcus, Leuconostoc, Lactobacillus, Citrobacter and Leclercia. Moreover, changes in the functional levels were monitored, and metaproteomic analysis revealed that most of the proteins were mainly expressed by members of Rhizopus, Penicillium and Geotrichum. The number of sequences allocated to fungi in the fermentation process decreased, whereas the number of sequences assigned to bacteria increased with time of fermentation. In addition, functional metagenomic profiling indicated that a series of sequences related to carbohydrates and amino acids metabolism were enriched. Additionally, enzymes associated with glycolysis metabolic pathways were presumed to contribute to the generation of flavor in dajiang-meju. Proteins from different dajiang-meju samples involved in global and overview maps, carbohydrate metabolism, nucleic acid metabolism and energy metabolism were differentially expressed. This information improves the understanding of microbial metabolic patterns with respect to the metaproteomes of dajiang-meju and provides a powerful tool for studying the fermentation process of soybean products.

Disinfection of lettuce using organic acids: an ecological analysis using 16S rRNA sequencing.

Organic acid disinfection efficacy has been previously estimated by analyzing microbial reduction on fresh produce. However, the effects of organic acids on the fresh produce microbiome are not considered for the evaluation of disinfection efficacy. Here, we studied the effects of seven generally recognized as safe organic acids (lactic, tartaric, acetic, propionic, malic, succinic, and citric acid), on the microbial counts and community on the surface of lettuce. The community was dominated by the following genera: Xanthomonas (24.73%), Sphingomonas (15.85%), Massilia (10.23%), Alkanindiges (9.00%), Acinetobacter (7.57%), and Pseudomonas (6.02%). Organic acid washing did not affect microbial diversity. Lactic acid was the most effective agent causing aerobic plate count reduction of 0.97 log CFU g-1; additionally, it increased the Escherichia-Shigella abundance from 0.77% to 3.29%. The relative abundance of Xanthomonas, a plant pathogen, was significantly increased by malic and propionic acid-propionic acid caused an increase from 24.73% to 47.53%. Microbial interaction analyses revealed the co-exclusion of Xanthomonas with the other core taxa, suggesting that the microbial distribution on the lettuce surface after disinfection carries a higher risk of quality loss. Therefore, the difference in disinfection efficacy of sanitizers was reflected in both microbial counts and bacterial community changes. We also propose a potential solution to control fresh produce safety and the rational use of sanitizers by collecting microbial diversity, composition, and count data from planting, transport, minimal processing, shelf and consumer storage, and gut digestion, and then using big data technology to develop a model to provide recommendations for sanitizer selection.

Characterization and comparison of whey N-glycoproteomes from human and bovine colostrum and mature milk.

Milk glycoproteins are crucial nutrients with a variety of functions. However, whey N-glycoproteomes in human and bovine milks have not been characterized during lactation. Herein, using lectin enrichment and liquid chromatography tandem mass spectrometry, 68, 58, 100, and 98 N-glycoproteins were identified in human colostrum and mature milk as well as bovine colostrum and mature milk whey. Gene Ontology and KEGG pathway analyses were used to elucidate the biological functions of whey N-glycoproteins in human and bovine colostrum and mature milks. Whey N-glycoproteomes differed dramatically between human and bovine milks and across lactation stages. The conserved and specific whey N-glycoproteins in all four sample types were also determined. Our results improve understanding of the properties and biological functions of whey N-glycoproteins in human and bovine milk and colostra, and provide insight into the potential application of some N-glycoproteins in infant formulae at different stages of development.

Effect of solution plasma process with hydrogen peroxide on the degradation of water-soluble polysaccharide from Auricularia auricula. II: Solution conformation and antioxidant activities in vitro.

Synergistic degradation of water-soluble Auricularia auricula polysaccharide (AAP) by solution plasma process (SPP) in the presence of hydrogen peroxide (H2O2) was investigated. The effects of H2O2 concentration, AAP concentration and the distance between the electrodes on the degradation of AAP were evaluated. The results showed that higher H2O2 concentration, lower AAP concentration and narrower distance between the electrodes were favorable for the degradation effect. Particle size, congo red (CR), scanning electron micrographs (SEM) and atomic force microscopy (AFM) results confirmed that SPP irradiation with H2O2 improved significantly the flexibility of the conformation. The degraded AAPs exhibited greater metal chelating effects and DPPH radical scavenging effect than the original AAP. It concluded that the combined SPP/ H2O2 method could be used for preparation of low-molecular-weight AAP.

The dynamic changes of chemical components and microbiota during the natural fermentation process in Da-Jiang, a Chinese popular traditional fermented condiment.

There is limited information on the chemical components and microbiota changes involved in da-jiang, a Chinese popular traditional fermented soybean condiment. Therefore, dynamic changes both in physicochemical quality and microbial community diversity of 20 samples of naturally fermented da-jiang collected over 95 days were measured, and we classified the samples into 5 groups (each containing 4 time points) according to the results. Based on OTUs analysis, Group 2 and Group 3 might represent the shift-stage between bacteria and fungi. Also, our results demonstrated that the formation of flavour, nutrient and quality of the traditional da-jiang were actually related to all of microbial community, especially the increased bacteria, including Staphylococcus and Leuconostoc. Correspondingly, 'Membrane Transport', 'Carbohydrate Metabolism', 'Amino Acid Metabolism' and 'Replication and Repair' were the top 4 KEGG pathways based on bacterial genes. The findings are expected to be helpful for us not only to understand the formation of flavour, taste and quality of traditional fermented da-jiang, but also to improve the industrialised fermented da-jiang.

Effect of solution plasma process with hydrogen peroxide on the degradation and antioxidant activity of polysaccharide from Auricularia auricula.

Solution plasma process (SPP) in combination with hydrogen peroxide (H2O2) were adopted to the degradation of Auricularia auricula polysaccharide (AAP). The results showed that SPP irradiation with H2O2 was effective for the AAP degradation. The intrinsic viscosity ([η]) of AAP solution decreased exponentially with increase in irradiation time. The degradation reaction closely fitted to the first order kinetics. The degradation rate constant after SPP irradiation with H2O2 was approximately 4.2 times that with SPP irradiation alone. GPC analysis showed that the molecular weight distribution of AAP was narrowed during degradation. FTIR and 13C NMR analysis revealed that primary structure of APP was not changed by the combination method. In vitro antioxidant activity of the polysaccharides was evaluated by determining their reducing power and radical (ABTS radical and superoxide radical) scavenging abilities. It was found that the degraded AAP possessed the higher antioxidant activity. The results suggested that SPP with H2O2 was an effective means for AAP degradation.

Quantitative analysis of amino acids in human and bovine colostrum milk samples through iTRAQ labeling.

BACKGROUND: The types and quantity of proteins vary widely between bovine and human milk, with corresponding differences in free and hydrolytic amino acids. In this study, the free and hydrolytic amino acids of bovine and human colostrum were for the first time qualitatively and quantitatively determined using isobaric tags for relative and absolute quantification technology combined with liquid chromatography tandem mass spectrometry detection. RESULTS: Total free amino acid content was 0.32 g L-1 and 0.63 g L-1 in bovine and human colostrum respectively, with free amino acid content in human colostrum twice that of bovine colostrum. However, total hydrolytic amino acid content was 4.2 g L-1 and 2.2 g L-1 in bovine and human colostrum respectively. We found that the hydrolytic amino acid content in bovine colostrum was higher than that in human colostrum; however, the amount of free amino acids and the overall amino acid content in human colostrum were respectively substantially higher and more varied than in bovine colostrum. CONCLUSION: Our findings revealed differences between bovine and human colostrum, with these data providing the basis for further research into amino acid metabolomics and infant formula. © 2018 Society of Chemical Industry.

Effects of methyl jasmonate and melatonin treatments on the sensory quality and bioactive compounds of harvested broccoli.

Harvested broccoli is prone to decline in quality with regard to its appearance and nutrition. In this study, freshly harvested broccoli was treated with methyl jasmonate (MeJA) and melatonin (MT) and stored at 20 °C and the changes in sensory qualities and bioactive compounds were analyzed. The control samples began yellowing on day 2, whereas MeJA and MT treatments delayed the yellowing by 2 and 4 days, respectively. Upon yellowing, sweetness and bitterness of control samples increased sharply, accompanied by the accumulation of bioactive compounds, except for sulforaphane; however, no significant change in volatile components was detected. When the samples started losing their green color, MeJA alleviated the bitterness while increasing the sweetness and sulforaphane content. The bitterness, astringency, umami level, and the content of sulfurous volatiles improved significantly in the MT-treated samples. Moreover, these samples showed high antioxidant activity; the protective effect on VC and carotenoids was extremely significant.

Comparative Analysis of Whey N-Glycoproteins in Human Colostrum and Mature Milk Using Quantitative Glycoproteomics.

Glycosylation is a ubiquitous post-translational protein modification that plays a substantial role in various processes. However, whey glycoproteins in human milk have not been completely profiled. Herein, we used quantitative glycoproteomics to quantify whey N-glycosylation sites and their alteration in human milk during lactation; 110 N-glycosylation sites on 63 proteins and 91 N-glycosylation sites on 53 proteins were quantified in colostrum and mature milk whey, respectively. Among these, 68 glycosylation sites on 38 proteins were differentially expressed in human colostrum and mature milk whey. These differentially expressed N-glycoproteins were highly enriched in "localization", "extracellular region part", and "modified amino acid binding" according to gene ontology annotation and mainly involved in complement and coagulation cascades pathway. These results shed light on the glycosylation sites, composition and biological functions of whey N-glycoproteins in human colostrum and mature milk, and provide substantial insight into the role of protein glycosylation during infant development.

Rhodamine B induces long nucleoplasmic bridges and other nuclear anomalies in Allium cepa root tip cells.

The cytogenetic toxicity of rhodamine B on root tip cells of Allium cepa was investigated. A. cepa were cultured in water (negative control), 10 ppm methyl methanesulfonate (positive control), and three concentrations of rhodamine B (200, 100, and 50 ppm) for 7 days. Rhodamine B inhibited mitotic activity; increased nuclear anomalies, including micronuclei, nuclear buds, and bridged nuclei; and induced oxidative stress in A. cepa root tissues. Furthermore, a substantial amount of long nucleoplasmic bridges were entangled together, and some nuclei were simultaneously linked to several other nuclei and to nuclear buds with nucleoplasmic bridges in rhodamine B-treated cells. In conclusion, rhodamine B induced cytogenetic effects in A. cepa root tip cells, which suggests that the A. cepa root is an ideal model system for detecting cellular interactions.