Preparation of gelatin-chitosan bilayer film loaded citral nanoemulsion as pH and enzyme stimuli-responsive antibacterial material for food packaging.

The responsive release of enzymes, pH, temperature, light and other stimuli is an effective means to reduce the loss of volatile active substances and control the release of active ingredients. The purpose of this study is to design a simple and rapid method to synthesize a multifunctional bilayer membrane, which has good mechanical properties, long-lasting pH and enzyme dual sensitive sustained release properties, and excellent antibacterial activity. The citral nanoemulsion was prepared by ultrasonic method, then the chitosan solution loaded with nanoemulsion was assembled on the gelatin film, and the uniform and smooth gelatin-chitosan bilayer film was successfully prepared. Compared with the control group, the bilayer film loaded with nanoemulsion showed better barrier performance, mechanical properties and antibacterial activity.

Utilizing Imine Bonds to Create a Self-Gated Mesoporous Silica Material with Controlled Release and Antimicrobial Properties.

In recent years, silica nanomaterials have been widely studied as carriers in the field of antibacterial activity in food. Therefore, it is a promising but challenging proposition to construct responsive antibacterial materials with food safety and controllable release capabilities using silica nanomaterials. In this paper, a pH-responsive self-gated antibacterial material is reported, which uses mesoporous silica nanomaterials as a carrier and achieves self-gating of the antibacterial agent through pH-sensitive imine bonds. This is the first study in the field of food antibacterial materials to achieve self-gating through the chemical bond of the antibacterial material itself. The prepared antibacterial material can effectively sense changes in pH values caused by the growth of foodborne pathogens and choose whether to release antibacterial substances and at what rate. The development of this antibacterial material does not introduce other components, ensuring food safety. In addition, carrying mesoporous silica nanomaterials can also effectively enhance the inhibitory ability of the active substance.

Purification, Identification and Molecular Docking of Immunomodulatory Peptides from the Heads of Litopenaeus vannamei.

In order to realize the high-value utilization of Litopenaeus vannamei (L. vannamei) heads, immunomodulatory peptides were prepared from the enzymatic hydrolysate of L. vannamei heads, and the action mechanism of immunomodulatory peptides was determined by molecular docking. The results showed that six proteases were used to hydrolyze L. vannamei head proteins, with the animal protease hydrolysate exhibiting the highest macrophage relative proliferation rate (MRPR). The enzymatic products were then sequentially purified by ultrafiltration, Sephadex G-15 gel chromatography, identified by liquid chromatography-mass spectrometry (LC-MS/MS), and finally selected for six immunomodulatory peptides (PSPFPYFT, SAGFPEGF, GPQGPPGH, QGF, PGMR, and WQR). These peptides maintained good immune activity under heat treatment, pH treatment, and in vitro gastrointestinal digestion. Molecular docking analysis indicated that these peptides showed great binding to both toll-like receptor 2 and 4 (TLR2 and TLR4/MD-2), leading to immunomodulation. The discarded L. vannamei heads in this article are considered to be promising food-borne immunomodulators that contribute to enhancing the immune function of the body.

Purification, identification and molecular mechanism of dipeptidyl peptidase IV inhibitory peptides from discarded shrimp (Penaeus vannamei) head.

DPP-IV plays a key role for regulation of glucose metabolism in the body. The object of this study was to obtain DPP-IV inhibitors from discarded but protein-rich Penaeus vannamei (P. vannamei) head, and to explore the potential mechanism between DPP-IV and its inhibitors. P. vannamei head protein was hydrolyzed by five food grade proteases, respectively. The animal protease hydrolysate showed the highest inhibitory active. Then the hydrolysate was sequentially separated by ultrafiltration, gel filtration chromatography and reversed phase high-performance liquid chromatography (RP-HPLC), the peptides sequences were identified by LC-MS/MS and four potential peptides YPGE, VPW, HPLY, YATP showed superior DPP-IV inhibitory activity. Meanwhile, molecular docking effectively explored their mechanism through formed hydrogen bonds and hydrophobic regions. The four peptides showed better DPP-IV inhibitory activity stability with heating treatment, pH (1-10) treatment, and in vitro gastrointestinal digestion. Our results demonstrated that the protein hydrolysate from discarded P. vannamei head can be considered as a promising natural source of DPP-IV inhibitor for helping to improve glycaemic control in Type 2 diabetes.

Purification, identification, and molecular mechanism of DPP-IV inhibitory peptides from defatted Antarctic krill powder.

Dipeptidyl peptidase-IV (DPP-IV) inhibitors can reduce the blood sugar levels of diabetic patients by preventing the rapid decomposition of incretin hormone and prolonging its physiological effects. In this study, DPP-IV inhibitory peptides FAGDDAPR and LAPPRGSL were isolated from defatted Antarctic krill powder (DAKP) protein by the sequential purification of ultrafiltration, gel filtration chromatography, and RP-HPLC, and IC50 values of the two peptides were 349.70 ± 3.66 µM and 461.14 ± 0.87 µM, respectively. The FAGDDAPR and LAPPRGSL were identified by LC-MS/MS method, and the molecular models of DPP-IV and the two peptides were further constructed by AutoDock Vina software, the results revealed that the inhibition activity of FAGDDAPR and LAPPRGSL was mainly attributed to the formation of strong hydrophobic interactions and hydrogen bonds with amino acids of DPP-IV. PRACTICAL APPLICATIONS: DAKP is an economical by-product produced in the production of krill oil and contains high-quality protein, but these products were mainly used as fish feed and had low utility value in the past. DPP-IV inhibitors are an efficacious drug employed in the treatment of hyperglycemia processes. However, these drugs can cause undesirable side effects. Thus, the development of new natural hypoglycemic drugs with low side effects is a valuable strategy to be applied in therapeutic interventions.

Microevolution of Vibrio parahaemolyticus Isolated from Clinical, Acute Hepatopancreatic Necrosis Disease Infecting Shrimps, and Aquatic Production in China.

Vibrio parahaemolyticus is the leading cause of bacteria-associated foodborne diarrheal diseases and specifically causes early mortality syndrome (EMS), which is technically known as acute hepatopancreatic necrosis disease (AHPND), a serious threat to shrimp aquaculture. To investigate the genetic and evolutionary relationships of V. parahaemolyticus in China, 184 isolates from clinical samples (VPC, n=40), AHPND-infected shrimp (VPE, n=10), and various aquatic production sources (VPF, n=134) were collected and evaluated by a multilocus sequence analysis (MLST). Furthermore, the presence of potential virulence factors (tlh, tdh, and trh) and single nucleotide polymorphisms (SNPs) in V. parahaemolyticus isolates was assessed using genomic sequencing. Analyses of virulence factors revealed that the majority of VPC isolates (97.5%) possessed the tdh and/or trh genes, while most of the VPF isolates (83.58%) did not encode hemolysin genes. Therefore, we hypothesized that the environment is a potential reservoir that promotes horizontal DNA transfer, which drives evolutionary change that, in turn, leads to the emergence of novel, potentially pathogenic strains. Phylogenetic analyses identified VPF-112 as a non-pathogenic maternal strain isolated from aquatic products and showed that it had a relatively high evolutionary status. All VPE strains and some VPC strains were grouped into several small subgroups and evenly distributed on phylogenetic trees. Anthropogenic activities and environmental selective pressure may be important factors influencing the process of transforming strains from non-pathogenic to pathogenic bacteria.

Pepper fragrant essential oil (PFEO) and functionalized MCM-41 nanoparticles: formation, characterization, and bactericidal activity.

BACKGROUND: It is well known that plant essential oils have good antimicrobial activity. However, their strong volatility and intense odor limit their application. Mesoporous silica (MCM-41), a non-toxic mesoporous material with excellent loading capability, is a promising delivery system for different types of food ingredients in the food industry. RESULTS: In this study, we first performed component analysis of pepper fragrant essential oil (PFEO) by gas chromatography - mass spectrometry (GC-MS), then the MCM-41 host was prepared, and the essential oil functionalized nanoparticles (EONs) were formed by embedding PFEO into mesoporous silica particles. Further analysis indicated that the particle size and zeta potential of EONs were 717 ± 13.38 nm and - 43.90 ± 0.67 mV, respectively. Transmission electron microscopy (TEM) images showed that EONs had an inerratic morphology and stable structure. The bactericidal activities of PFEO and EONs against Escherichia coli (E. coli), Salmonella enterica (S. enterica), Staphylococcus aureus (S. aureus) and Listeria monocytogenes (L. monocytogenes) were subsequently tested using the twofold dilution method. Results indicated that, after 48 h incubation, minimum bactericidal concentrations (MBC) of EONs used against gram-negative bacteria were decreased to a greater degree than those of PFEO, suggesting that nanoencapsulation by MCM-41 can improve antimicrobial activity. Atomic force microscopy (AFM) observation also confirmed that EONs showed a notable inhibitory effect against E. coli by disrupting cell membrane structure. CONCLUSION: Pepper fragrant essential oil nanoencapsulation could be a very promising organic delivery system in food industry for antimicrobial activity enhancement. © 2019 Society of Chemical Industry.

Enzymatic hydrolysis of Grass Carp fish skin hydrolysates able to promote the proliferation of Streptococcus thermophilus.

BACKGROUND: The promotion effect on proliferation of Streptococcus thermophilus by enzymatic hydrolysates of aquatic products was firstly studied. The effect of influencing factors of the hydrolysis on the growth of S. thermophilus was investigated. RESULT: Grass Carp fish skin was hydrolysed to peptides by enzymatic hydrolysis using protease ProteAX, and for the S. thermophilus growth, the optimal enzymatic hydrolysis conditions were temperature of 60 °C, initial pH of 9.0, enzyme concentration of 10 g kg-1 , hydrolysis time of 80 min, and ratio of material to liquid of 1:2. The Grass Carp fish skin hydrolysate (GCFSH) prepared under the optimum conditions was fractionated to five fragments (GCFSH 1, GCFSH 2, GCFSH 3, GCFSH 4, GCFSH 5) according to molecular weight sizes, in which the fragments GCFSH 4 and GCFSH 5, with molecular weights of less than 1000 Da, significantly promoted the growth of S. thermophilus. CONCLUSION: The hydrolysis process of Grass Carp fish skin can be simplified, and the peptides with molecular weights below 1000 Da in the hydrolysates are the best nitrogen source for proliferation of S. thermophilus. This work can provide a fundamental theoretical basis for the production of multi-component functional foods, especially in milk drinks or yogurt. © 2017 Society of Chemical Industry.

Photophysical properties of praseodymium complexes with aromatic carboxylic acids: double light conversion both in ultraviolet and visible region.

A series of luminescent praseodymium complexes with different aromatic carboxylic acids have been synthesized and characterized. The photophysical properties of these complexes have been studied with ultraviolet spectra, phosphorescence spectra and fluorescence spectra. Ultraviolet absorption spectra show that the praseodymium complexes systems with aromatic carboxylate form the more extensive conjugated systems to be suitable for the distribution of electron in the whole coordination environment, resulting in the energy decrease and red-shifts of ultraviolet spectral bands. Phosphorescence spectra suggest that excited triplet state of aromatic carboxylic acids, which can indicate the energy match and intermolecular energy transfer process between the excited triplet state of ligands and the resonant emissive energy level of Pr ions. The emission spectra of all praseodymium complexes show two emission peaks under the excitation band of 245 nm at about 395 and 595 nm, respectively, while one peak at about 595 nm under 415 nm excitation, which attributed to be 1S0-->1I6 (395 nm) transition and the characteristic emission 1D2-->3H4 (595 nm) transition of Pr3+ ion. The 1S0-->1I6 transition can be speculated to belong to the transition of charge transfer state, and the 1D2-->3H4 can be further proved that there exists an antenna effect in the luminescence of praseodymium with aromatic carboxylic acids. In conclusion, the praseodymium complexes systems can realize the double proton light conversion both in the ultraviolet and visible region, which can be further studied to have potential application.

Double fluorescence conversion in ultraviolet and visible region for some praseodymium complexes of aromatic carboxylates.

Four praseodymium complexes of aromatic carboxylates (benzoate, 4-tert-butylbenzoate, 2-benzoylbe-noate, and benzimidazole-5-carboxylate) have been synthesized and characterized, whose photophysical properties have been studied with ultraviolet spectra, phosphorescence spectra, and fluorescence spectra. The fluorescent emission spectra of all praseodymium complexes show two emission peaks under the excitation band of 245 nm at about 395 and 595 nm respectively, while one peak under 415 nm at about 595 nm, which attributed to be 1S0 --> 1I6 (395 nm) transition and the characteristic emission 1D2 --> 3H4 (595 nm) transition of Pr3+ ion. The 1S0 --> 1I6 transition can be ascribed as the transition of charge transfer state, and the 1D2 --> 3H4 can be further proved that there exists an antenna effect in the fluorescence of praseodymium with aromatic carboxylic acids. In conclusion, the praseodymium complexes systems can realize the double fluorescent conversion in both ultraviolet and visible region and can be further studied the application of this conversion.