Preservation effects of photodynamic inactivation-mediated antibacterial film on storage quality of salmon fillets: Insights into protein quality.

The preservation effects of a photodynamic inactivation (PDI)-mediated polylactic acid/5-aminolevulinic acid (PLA/ALA) film on the storage quality of salmon fillets were investigated. Results showed that the PDI-mediated PLA/ALA film could continuously generate reactive oxygen species by consuming oxygen to inactivate native pathogens and spoilage bacteria on salmon fillets. Meanwhile, the film maintained the content of muscle proteins and their secondary and tertiary structures, as well as the integrity of myosin by keeping the activity of Ca2+-ATPase, all of which protected the muscle proteins from degradation. Furthermore, the film retained the activity of total superoxide dismutase (T-SOD), suppressed the accumulation of lipid peroxides (e.g., MDA), which greatly inhibited four main types of protein oxidations. As a result, the content of flavor amino acids and essential amino acids in salmon fillets was preserved. Therefore, the PDI-mediated antimicrobial packaging film greatly preserves the storage quality of aquatic products by preserving the protein quality.

Stevia Polyphenols, Their Antimicrobial and Anti-Inflammatory Properties, and Inhibitory Effect on Digestive Enzymes.

Polyphenols from stevia leaves (PPSs) are abundant byproducts from steviol glycoside production, which have been often studied as raw extracts from stevia extracts for their bioactivities. Herein, the PPSs rich in isochlorogenic acids were studied for their antimicrobial and anti-inflammatory properties, as well as their inhibitory effects on digestive enzymes. The PPSs presented stronger antibacterial activity against E. coli, S. aureus, P. aeruginosa, and B. subtilis than their antifungal activity against M. furfur and A. niger. Meanwhile, the PPSs inhibited four cancer cells by more than 60% based on their viability, in a dose-dependent manner. The PPSs presented similar IC50 values on the inhibition of digestive enzyme activities compared to epigallocatechin gallate (EGCG), but had weaker anti-inflammatory activity. Therefore, PPSs could be a potential natural alternative to antimicrobial agents. This is the first report on the bioactivity of polyphenols from stevia rebaudiana (Bertoni) leaves excluding flavonoids, and will be of benefit for understanding the role of PPSs and their application.

Covalent Grafting of 5-Aminolevulinic Acid onto Polylactic Acid Films and Their Photodynamic Potency in Preserving Salmon.

A novel photodynamic inactivation (PDI)-mediated antimicrobial film of polylactic acid/5-aminolevulinic acid (PLA/ALA) was successfully fabricated by a covalent grafting method using low-temperature plasma. The chemical structure, surface morphology, hydrophilic ability, and mechanical and barrier properties of the films were characterized, and their antibacterial, anti-biofilm potency and preservation effects on ready-to-eat salmon were investigated during storage. Results showed that the amino group of ALA was covalently grafted with the carboxyl group on the surface of PLA after the plasma treatment, with the highest grafting rate reaching ∼50%. The fabricated PLA/ALA films displayed an enhanced barrier ability against water vapor and oxygen. Under blue light-emitting diode illumination, the PLA/ALA films generated massive reactive oxygen species from the endogenous porphyrins in cells induced by ALA and then fatally destroyed the cell wall of planktonic cells and the architectural structures of sessile biofilms of the pathogens (Listeria monocytogenes and Vibrio parahaemolyticus) and spoilage bacterium (Shewanella putrefaciens). More importantly, the PDI-mediated PLA/ALA films potently inhibited 99.9% native bacteria on ready-to-eat salmon and significantly suppressed the changes of its drip loss, pH, and lipid oxidation (MDA) during storage, and on this basis, the shelf life of salmon was extended by 4 days compared with that of the commercial polyethylene film. Therefore, the PDI-mediated PLA/ALA films are valid in inactivating harmful bacterial and preserving the quality of seafood.

Anti-tyrosinase, antioxidant and antibacterial activities of gallic acid-benzylidenehydrazine hybrids and their application in preservation of fresh-cut apples and shrimps.

A series of gallic acid-benzylidenehydrazine hybrids were synthesized and evaluated for their tyrosinase inhibitory activity. Thereinto, compounds 5d and 5f potently inhibited tyrosinase with IC50 of 15.3 and 3.3 µM, compared to kojic acid (44.4 µM). The inhibition mechanism suggested that 5d and 5f not only chelated with Cu2+, but also reduced Cu2+ to Cu1+ in the tyrosinase active site. Additionally, 5d and 5f exhibited strong DPPH scavenging and antibacterial activities against Vibrio parahaemolyticu and Staphylococcus aureus, which can be attributed to the function of gallic acid and hydrazone moiety. These compounds also exhibited capacity to preserve fresh-cut apples and shrimps. Finally, 5d and 5f exhibited low cytotoxic activity in a human cell line (HEK293). Therefore, these compounds possess anti-tyrosinase, antioxidant, and antibacterial activities, and can be used in the development of novel food preservatives.

Fenton reaction-assisted photodynamic inactivation of calcined melamine sponge against Salmonella and its application.

Photodynamic inactivation (PDI) is an effective alternative to traditional antibiotics to broadly kill bacteria. This study aimed to develop a potent PDI system by coupling calcinated melamine sponges (CMSs) with the Fenton reaction. The results showed that CMS calcined at 350 ℃ was successfully carbonized with intact and porous structures, and it possessed excellent hydrophilicity and photothermal conversion performance. When Fe2+ was added and internalized, the Fenton reaction in which Fe2+ reacted with H2O2 in cells occurred to produce reactive oxygen species (ROS) (OH, OOH, etc.) and O2, and notably, the O2 molecules could serve as a raw material to absorb the photothermal energy of CMS to generate highly reactive 1O2. Under synergistic effects, CMS-350 coupled with Fe2+ potently inactivated > 6 Log CFU/mL (>99.9999%) of Salmonella under 201.6 J/cm2 blue LED illumination by destroying Na+/K+-ATPase and Ca2+/Mg2+-ATPase, DNA synthesis-related enzymes, cell membranes, etc. Meanwhile, the composite photocatalyst was proven to be nontoxic and could inactivate Salmonella in various foods, including vegetables (Brassica chinensis L), eggs and fresh cucumber juice. As a result, CMS coupled with the Fenton reaction greatly improves the inactivation potency of PDI against harmful bacteria.

Novel 2,3-Dialdehyde Cellulose-Based Films with Photodynamic Inactivation Potency by Incorporating the ß-Cyclodextrin/Curcumin Inclusion Complex.

Antibacterial packaging film mediated by photodynamic inactivation (PDI) is a new concept in food industry. The objective of this study was to fabricate a green 2,3-dialdehyde cellulose (DAC)-based antimicrobial film with PDI potency by incorporating the ß-cyclodextrin/curcumin (ß-CD/Cur) complex as a photosensitizer. The PDI-mediated films were characterized by evaluating the surface morphology, chemical structure, light transmittance, mechanical properties, photochemical and thermal stability, and water solubility. The results showed that the DAC-CD/Cur films were soluble in water and mechanically strong with a tensile strength of 63.87 MPa and an elongation break of 1.32%, which was attributed to the formation of hydrogen bonds between DAC and ß-CD/Cur molecules. Meanwhile, the composite films possessed a good light transmittance but impeded the penetration of ultraviolet light and efficiently delayed the degradation of curcumin. More importantly, the PDI-mediated films exhibited a broad-spectrum ability to kill Listeria monocytogenes, Vibrio parahaemolyticus, and Shewanella putrefaciens in pure culture. Notably, they also potently inactivated these harmful bacteria on ready-to-eat salmon with a maximum of ∼4 Log CFU/g (99.99%) reduction after 60 min irradiation (13.68 J/cm2). Therefore, the PDI-mediated DAC-CD/Cur films are novel and promising antimicrobial food packaging films in food industry.