Gum tragacanth-sodium alginate active coatings containing epigallocatechin gallate reduce hydrogen peroxide content and inhibit lipid and protein oxidations of large yellow croaker (Larimichthys crocea) during superchilling storage.

The active coatings supplemented with epigallocatechin gallate (EGCG) (0.16 %, 0.32 %, and 0.64 %, respectively) combined with superchilling storage (-3 ± 0.2 °C) were used to reduce hydrogen peroxide (H2O2) content, and inhibit lipid and protein oxidations of large yellow croaker during 42 days of superchilling storage. EGCG coatings delayed lipid and protein oxidations by inhibiting the generation of H2O2, malondialdehyde (MDA) and carbonyl groups, and maintaining a higher Ca2+-ATPase activity and sulfhydryl content. We also observed that EGCG treatments maintained myofibrillar organized secondary structure by keeping higher α-helix content, and also stabilized tertiary structure during superchilling storage. Low-field nuclear magnetic resonance (LF-NMR) revealed that EGCG treatments might improve the association of water molecules with protein for fixed water. In addition, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and scanning electron microscope (SEM) images both showed that these treatments could delay the myofibrillar degradation of fresh fish. Overall, we report that the active coatings containing EGCG treatments protect the lipid and protein of large yellow croaker during superchilling storage.

Antimicrobial Effect of Epigallocatechin Gallate Against Shewanella putrefaciens ATCC 8071: A Study Based on Cell Membrane and Biofilm.

The study was to evaluate the antimicrobial impacts and biofilm influences on epigallocatechin gallate (EGCG) against Shewanella putrefaciens ATCC 8071. The minimum inhibitory concentration (MIC) of EGCG on S. putrefaciens was 160 µg mL-1. The growth curve exhibited that EGCG had a good antimicrobial activity. EGCG caused damages to the bacterial cell wall and membrane based the intracellular component leakage and cell viability analysis. The damage to the membrane integrity by EGCG has been confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM shows deformation of shape, TEM shows cell membrane and wall damage, and the leakage of cytoplasmic material. The treatment with EGCG at 0.25× and 0.5× MIC resulted in decreased motility and elevated levels of oxidative stress, leading to an increase in biofilm formation. These results demonstrated that EGCG may be used as a natural preservative to reduce S. putrefaciens in fish during cold storage.

The Antimicrobial Effect of Melissa officinalis L. Essential Oil on Vibrio parahaemolyticus: Insights Based on the Cell Membrane and External Structure.

The study was to evaluate the antimicrobial impacts on Melissa officinalis L. essential oil (MOEO) against Vibrio parahaemolyticus. The minimum inhibitory concentration (MIC) of MOEO on Vibrio parahaemolyticus was 1 µL⋅mL-1. The kill-time curve exhibited that MOEO had good antimicrobial activity. The analysis of cellular ingredients leakage and cell viability illustrated that MOEO has destruction to the morphology of the cell membrane. The damage to the membrane integrity by MOEO has been confirmed by transmission and scanning electron microscopy, obvious morphological and ultrastructural changes were observed in the treated bacterial cells. The MOEO at 0.5 µL⋅mL-1 can inhibit the biofilm formation, biofilm motility, and extracellular polysaccharide production. Meanwhile, the qPCR results exhibited MOEO inhibited the expression of virulence genes. The findings showed that MOEO exerted its antimicrobial effect mainly by destroying the membrane, which indicated its potential as a natural food preservative.

Effect of Gum Tragacanth-Sodium Alginate Active Coatings Incorporated With Epigallocatechin Gallate and Lysozyme on the Quality of Large Yellow Croaker at Superchilling Condition.

This research was done to investigate the synergistic interactions of the gum tragacanth (GT)-sodium alginate (SA) active coatings, incorporated with epigallocatechin gallate and lysozyme, on the quality of large yellow croaker (Larimichthys crocea) during superchilling storage at -3°C. Results showed that the GT-SA active coatings, containing epigallocatechin gallate [EGCG (E), 0.32% w/v], and lysozyme [LYS (L), 0.32% w/v] have reduced the total viable count, psychrophilic bacteria, and Pseudomonas spp. by about 1.55 log CFU/g, 0.49 log CFU/g, and 1.64 log CFU/g compared to the control at day 35. The GT-SA active coatings containing EGCG and LYS were effective in lowering the formations of off-odor compounds such as total volatile basic nitrogen (TVB-N), malondialdehyde (MDA), and off-favor amino acid (histidine). The solid phase microextraction gas chromatography-mass spectrometer (SPME-GC/MS) was applied to characterize and to quantify the volatile compounds of large yellow croaker samples during superchilling storage, while the relative content of the fishy flavor compounds (including 1-octen-3-ol and acetoin) was significantly reduced in the active coatings treated samples. Furthermore, the GT-SA active coatings containing EGCG and LYS treatments was found to be more effective in retarding the migration of water based on magnetic resonance imaging (MRI) results and in maintaining the organoleptic quality of large yellow croaker in superchilling storage at -3°C according to the sensory evaluation results. The results showed that the GT-SA active coating containing EGCG and LYS was effective to be used as a fish preservative to improve the quality and to prolong the shelf life of large yellow croaker in a superchilling storage for at least 7 days.