Yali Tang

Investigation of the Protein−Protein Aggregation of Egg White Proteins under Pulsed Electric Fields

Egg whites were exposed to pulsed electric fields (PEFs) to investigate the protein-protein aggregation. No insoluble protein aggregate was found when egg whites were exposed to PEFs at 25, 30, and 35 kV/cm for 400 micros. However, atomic force microscopy showed that the sizes of the protein particles increased. Native polyacrylamide gel electrophoresis (PAGE) demonstrated the existence of aggregates under PEFs at 35 kV/cm for 400 micros. Sodium dodecyl sulfate (SDS)-PAGE in the presence and absence of 2-mercaptoethanol further indicated that sulfhydryl-disulfide interchange reactions occurred under PEFs. Differential scanning calorimetry scans showed 400 micros of PEF treatment at 35 kV/cm denatured 16.5% proteins. Insoluble egg white protein aggregates were induced by PEF (35 kV/cm, 800 micros) and heat (60 degrees C, 3.5 min) treatments. Disulfide bonds were the dominant binding forces in the formation of protein aggregates. However, the weakly noncovalent bonds play a much more important role in the protein aggregation forming in heat treatment (60 degrees C, 3.5 min) than that in PEF treatment (35 kV/cm, 800 micros).

The membrane action mechanism of analogs of the antimicrobial peptide Buforin 2

Previously, the antimicrobial peptides BF2-A and BF2-B, two analogs of Buforin 2 that was hypothesized to kill bacteria by entering cells and binding nucleic acids, had been designed based on the structure-activity analysis of Buforin 2. In the present study, BF2-A and BF2-B were chemically synthesized and their activities and lipopolysaccharide affinity were assayed. To elucidate the mechanism of action with cytoplasmic membranes, we subsequently examined the membrane permeability of both peptides in detail. Both peptides showed stronger antimicrobial activities against a broad spectrum of microorganisms than their parent peptide. Interestingly, BF2-A did not cause significant membrane permeabilization for influx of ONPG into cells, and hardly caused the leakage of intracellular macromolecules, probably BF2-A slightly disturbed cell membrane causing the K(+) leakage during peptide crossing phospholipids bilayer. Electron micrographs indicated that the cell membrane treated by BF2-A was still intact within 20min. On the contrary, BF2-B obviously increased the outer and inner membrane permeability, even induced the slight leakage of macromolecules in the cytoplasm. The leakage of cytoplasmic contents was also demonstrated by the electron micrographs. The increase of membrane permeabilization explained why BF2-B displayed better antimicrobial activity and rapid killing kinetics than BF2-A.

Review: Pulsed Electric Fields Processing of Protein-Based Foods

Pulsed electric fields (PEF) processing is a promising nonthermal food preservation technology, which is ongoing from laboratory and pilot plant scale level to the industrial level. Application of PEF processing may be a good alternative treatment to thermal methods in protein-based foods. A large number of literatures have fully demonstrated that small molecule compounds in plant-based foods, mainly aroma compounds and health-related phytochemicals, were not significantly affected by PEF. However, there was a lack of knowledge on the effects of PEF on proteins and qualities of protein-based foods. This review focuses on effects of PEF processing on endogenous enzymes, safety, and quality of protein-based foods. Finally, the ways to achieve food quality assurance and food safety in PEF processing of protein-based foods are proposed.

Insertion mode of a novel anionic antimicrobial peptide MDpep5 (Val-Glu-Ser-Trp-Val) from Chinese traditional edible larvae of housefly and its effect on surface potential of bacterial membrane

Antimicrobial molecules from insects may serve as a potentially significant group of antibiotics. To identify the effect of antimicrobial peptides (AMPs) on bacterial membrane and obtain further insight in the mechanism of membrane transport of AMPs, the interaction of surface potential and permeation of a novel antimicrobial peptide MDpep5 (Val-Glu-Ser-Trp-Val) from Chinese traditional edible larvae of housefly was examined using liposomes from bacterial lipids extract. Compared with the cationic AMPs, MDpep5 cannot completely disrupt membrane. The uptake of MDpep5 by bacterial liposomes was dependent on the membrane surface potential. The mutual inhibition of the transport of MDpep5 through the cell membrane was caused by the change in surface potential due to the binding of MDpep5 to the membrane. Furthermore, formation of MDpep5-enriched lipid aggregates could lead to the disorder of the bilayer structure. Based on our experimental data, we propose that MDpep5 initiated its antimicrobial activity by profoundly disordering the structure and affecting physical properties of bacterial membrane when binding to the phospholipid which accounts for its bactericidal activity.

The intracellular mechanism of action on Escherichia coli of BF2-A/C, two analogues of the antimicrobial peptide Buforin 2

In the present study, the antimicrobial peptides BF2-A and BF2-C, two analogues of Buforin 2, were chemically synthesized and the activities were assayed. To elucidate the bactericidal mechanism of BF2-A/C and their different antimicrobial activities, the influence of peptides to E. coli cell membrane and targets of intracellular action were researched. Obviously, BF2-A and BF2-C did not induce the influx of PI into the E. coli cells, indicating nonmemebrane permeabilizing killing action. The FITC-labeled BF2-A/C could penetrate the E. coli cell membrane and BF2-C penetrated the cells more efficiently. Furthermore, BF2-A/C could bind to DNA and RNA respectively, and the affinity of BF2-C to DNA was powerful at least over 4 times than that of BF2-A. The present results implied that BF2-A and BF2-C inhibited the cellular functions by binding to DNA and RNA of cells after penetrating the cell membranes, resulting in the rapid cell death. The structure-activity relationship analysis of BF2-A/C revealed that the cell-penetrating efficiency and the affinity ability to DNA were critical factors for determining the antimicrobial potency of both peptides. The more efficient cell-penetrating and stronger affinity to DNA caused that BF2-C displayed more excellent antimicrobial activity and rapid killing kinetics than BF2-A.

Combined Effects of Heat and PEF on Microbial Inactivation and Quality of Liquid Egg Whites

Combined effects of heat and pulsed electric fields treatment (20 and 40oC, 0-800 µs at 30 kV/cm) on microbial inactivation inoculated in egg whites were studied. Pulsed electric fields treatment time and processing temperature had profound effects on microbial inactivation. Pulsed electric fields treatment with a bipolar pulse (2 µs wide), an intensity of 30 kV/cm, a frequency of 100 Hz, the processing temperature of 40 oC and treatment time for 800 µs, was sufficient to achieve pasteurization conditions using S. enteritidis , E. coli and S. aureus, common spoilage and pathogenic micro-organisms in egg products. This treatment produced a non-significant (p>0.05) increase in foaming capacity and stability and an increase (p<0.05) in emulsifying capacity and stability. Surface free sulfhydryls and hydrophobicity of egg white proteins increased with the increment of the PEF treatment time due to the partial unfolding of egg white proteins. Almost 50 % of trypsin inhibitory activity of ovomucoid in liquid egg white was decreased when the treatment time extended to 800 µs. These results suggested that combined treatment of heat and pulsed electric fields could be applied to process liquid egg whites to get desired products.

Electrochemical reaction and oxidation of lecithin under pulsed electric fields (PEF) processing.

Pulsed electric fields (PEF) processing is a promising nonthermal food preservation technology, which is ongoing from laboratory and pilot plant scale levels to the industrial level. Currently, greater attention has been paid to side effects occurring during PEF treatment and the influences on food qualities and food components. The present study investigated the electrochemical reaction and oxidation of lecithin under PEF processing. Results showed that electrochemical reaction of NaCl solutions at different pH values occurred during PEF processing. Active chlorine, reactive oxygen, and free radicals were detected, which were related to the PEF parameters and pH values of the solution. Lecithin extracted from yolk was further selected to investigate the oxidation of food lipids under PEF processing, confirming the occurrence of oxidation of lecithin under PEF treatment. The oxidative agents induced by PEF might be responsible for the oxidation of extracted yolk lecithin. Moreover, this study found that vitamin C as a natural antioxidant could effectively quench free radicals and inhibit the oxidation of lipid in NaCl and lecithin solutions as model systems under PEF processing, representing a way to minimize the impact of PEF treatment on food qualities.

Rapid detection techniques for biological and chemical contamination in food: a review.

The contamination problem in food safety is still a major concern not only for developing countries but also for the industrialized world. To guarantee the food safety, the advanced examination technique is needed urgently. However, the traditional methods have some typical drawbacks which include: high costs of implementation, long time of analysis and low samples throughput, and the need for high qualified manpower. The availability of fast, reliable and simple to use detecting tools for food products is therefore a target both for the safeguard of customers health and production improvement. This article overviews the progress of the rapid detection methods for biological and chemical contamination in food.

Inactivation of lipoxygenase in soybean by radio frequency treatment

1 State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu 214122, China 2 National Engineering Research Center for Functional Food, Jiangnan University, Wuxi, Jiangsu 214122, China 3 Collaborative Innovation Center of Food Safety and Quality Control in Jiangsu Province, Jiangnan University, Wuxi, Jiangsu 214122, China 4 School of Internet of Things Engineering, Jiangnan University, Wuxi, Jiangsu 214122, China

Comparative Effects of Microwave and Water Bath on the Packing Films of Milk

Milk is heated by microwave or conventional water bath in our daily lives. To investigate the influence of heating modes on food package safety, the present work is designed to compare the changes to packaging materials of milk subjected to microwave treatment and water bath. The mechanical properties of milk package materials were compared, and the migration of harmful substances from the films was analyzed. The results showed that the microwave and water-bath treatments could both influence the mechanical properties of the film. For the heat-sealing strength, the susceptibility of the package materials from different manufacturers was varied. For the tensile strength, the changes were obvious after treatment. Both treatments could induce migration, but the amounts of migrating materials were within the limit permitted by the national standard.