Antimicrobial activity of 405 nm light-emitting diode (LED) in the presence of riboflavin against Listeria monocytogenes on the surface of smoked salmon

Antifungal effect and mechanism of 405 nm light-emitting diodes combined with riboflavin on Penicillium digitatum and Penicillium italicum

AIMS

This study was designed to evaluate the antifungal effect of a 405 nm light-emitting diode (LED) combined with an exogenous photosensitizer against Penicillium digitatum and Penicillium italicum and elucidate the antifungal mechanism.

METHODS AND RESULTS

The results showed that riboflavin significantly enhanced the antifungal effect of 405 nm LED illumination among the three photosensitizers tested (chlorogenic acid, chlorophyllin, and riboflavin). Riboflavin inactivated mold spores below the detection limit (∼6.0 log reduction) at a lower dose (1.9-2.6 kJ cm-2) compared to the others and LED alone. Mycelial growth and sporulation were completely suppressed by LED illumination with or without riboflavin. Adding ascorbic acid required a similar dose (3.9 kJ cm-2) for spore inactivation, suggesting reactive oxygen species (ROS) generation as the primary mechanism. Transmission electron microscopy revealed intracellular organelle damage without morphological changes in spores. Lipid peroxidation, indicated by a 6- to 8-fold increase in malondialdehyde concentration, likely caused the organelle damage.

CONCLUSIONS

This study confirmed that riboflavin-mediated 405 nm LED illumination was more effective in controlling both molds than LED illumination alone, and that its antifungal effect might be due to the ROS generated by the photoinactivation of riboflavin during LED illumination, which oxidizes the membranes of intracellular organelles.

Preparation of a biodegradable packaging film by konjac glucomannan/sodium alginate reinforced with nitrogen-doped carbon quantum dots from crayfish shell for crayfish meat preservation

The development of biomass material is an important approach to alleviating the excessive using of plastic packaging, by which the product could be more environmentally friendly and lower toxicity. In this study, we developed a biodegradable photodynamic antibacterial food packaging film using nitrogen-doped carbon quantum dots (N-CQDs) synthesized from crayfish shells, combined with konjac glucomannan (KGM) and sodium alginate (SA). Casting method was used to prepare the composite film and results indicated that incorporation of N-CQDs significantly enhanced the mechanical and barrier properties of the film by reducing the number of micropores. The N-CQDs endowed the film with strong antioxidant activity and UV resistance. The DPPH scavenging rate of the composite film reached 77.92 %, while the transmittance of ultraviolet (300 nm) was reduced to 16.97 %. Furthermore, under blue light irradiation, the film exhibited excellent photodynamic antibacterial effects against Shewanella putrefaciens and Staphylococcus aureus, achieving inhibition rates of 99.2 % and 98.99 %, respectively. The film solution demonstrated no cytotoxicity, and the composite film preserved crayfish meat for up to 8 days at 4 °C. Furthermore, the film almost completely degrading in soil within 14 days. These findings suggest that the KGM/SA/N-CQD film is a promising degradable antimicrobial material for food packaging applications.

Microbial Control in the Processing of Low-Temperature Meat Products: Non-Thermal Sterilization and Natural Antimicrobials

The safety and health of food have been persistent concerns, particularly about meat products. Low-temperature meat products refer to those that are processed at lower temperatures. Meat, rich in proteins and other nutrients, is highly susceptible to microbial contamination, leading to spoilage, particularly when processed at lower temperatures that increase storage and transportation requirements. In response to the limitations of conventional preservation methods, such as heat treatment and chemical bacteriostats, emerging preservation technologies are increasingly being adopted. These technologies aim to mitigate the negative effects of microorganisms on meat products. Non-thermal technologies and biotechnological approaches, which are low in energy consumption and energy efficiency, are becoming more prevalent. Non-thermal sterilization technology is widely applied in various food products. It maintains the original quality of food, enhances food safety, reduces energy consumption, and improves production efficiency. Biocides are extensively used in the antibacterial field owing to their high efficiency, low toxicity, and long-lasting properties. Both non-thermal sterilization technology and biocides can ensure food safety, extend the shelf life of food products, improve food quality, meet consumers' demand for natural and healthy food, enhance market competitiveness, and play a positive role in promoting the sustainable development of the food industry. This paper provides a comprehensive review of the specific applications of biocides and non-thermal sterilization methods in food, highlighting the control parameters and their effects on microbes during low-temperature meat processing, to supply pertinent researchers with theoretical references.

Inactivation of Listeria monocytogenes, Escherichia coli O157:H7, and Staphylococcus aureus by sequential light-emitting diodes (LEDs) treatment at 365 nm and 420 nm

Frequent outbreaks caused by foodborne pathogens pose long-term risks to consumer health. To proactively reduce the load of pathogenic bacteria during food processing, a novel light-based antibacterial approach was developed by sequential application of 365 nm and 420 nm light-emitting diodes (LEDs). Results demonstrated that after treatment with 365 nm (480 J/cm2) followed by 420 nm (307.2 J/cm2), the reduction of Listeria monocytogenes reached 4.05 ± 0.31 log CFU/mL, significantly higher (an additional 1.8 log CFU/mL, P < 0.05) than cumulative reductions achieved by each 365 nm (2.25 ± 0.92 log CFU/mL) and 420 nm (0.02 ± 0.15 log CFU/mL) treatments. Further analysis revealed that the enhancement in bacterial reduction achieved through the sequential treatment with 365 nm and 420 nm was primarily driven by the exposure time to 365 nm. The inactivation mechanisms were investigated, considering possible photothermal, physical, and oxidative effects. Findings showed that the antibacterial effect of sequential treatment was mainly ascribed to intracellular oxidation generated by reactive oxidative species (ROS), namely hydrogen peroxide and superoxide anion. The antibacterial mechanism of two LEDs may result from the sensitization of bacterial cells to excessive ROS, as evidenced by fluorescent intensity measurements and chemical scavenger assays. This research provides new insight for improving the efficacy of UVA and blue light treatment to control food contamination by Listeria.

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.

Radical species generating technologies for decontamination of Listeria species in food: a recent review report

Foodborne illnesses occur due to the contamination of fresh, frozen, or processed food products by some pathogens. Among several pathogens responsible for the illnesses, Listeria monocytogenes is one of the lethal bacteria that endangers public health. Several preexisting and novel technologies, especially non-thermal technologies are being studied for their antimicrobial effects, particularly toward L. monocytogenes. Some noteworthy emerging technologies include ultraviolet (UV) or light-emitting diode (LED), pulsed light, cold plasma, and ozonation. These technologies are gaining popularity since no heat is employed and undesirable deterioration of food quality, especially texture, and taste is devoided. This review aims to summarize the most recent advances in non-thermal processing technologies and their effect on inactivating L. monocytogenes in food products and on sanitizing packaging materials. These technologies use varying mechanisms, such as photoinactivation, photosensitization, disruption of bacterial membrane and cytoplasm, etc. This review can help food processing industries select the appropriate processing techniques for optimal benefits, in which the structural integrity of food can be preserved while simultaneously destroying L. monocytogenes present in foods. To eliminate Listeria spp., different technologies possess varying mechanisms such as rupturing the cell wall, formation of pyrimidine dimers in the DNA through photochemical effect, excitation of endogenous porphyrins by photosensitizers, generating reactive species, causing leakage of cellular contents and oxidizing proteins and lipids. These technologies provide an alternative to heat-based sterilization technologies and further development is still required to minimize the drawbacks associated with some technologies.

Gelatin/carboxymethylcellulose composite film combined with photodynamic antibacterial: New prospect for fruit preservation

Plastic packaging causes environmental pollution, and the development of simple and effective biodegradable active packaging remains a challenge. In this study, gelatin (G) and sodium carboxymethylcellulose (CMC) were used as film materials, with the addition of curcumin (Cur), a photosensitive substance, to investigate the changes in the physical and chemical properties of the film and its application in fruit preservation. The results demonstrated that Cur was compatible with the film. With the addition of Cur, the thickness of the film increased up to 1.3 times, while the moisture content was reduced to 12.10 %. The tensile strength (TS) and elongation at break (EAB) of the film can reach 8.84 MPa and 19.33 %, respectively. The photodynamic antibacterial experiment revealed that the film containing 0.5 % Cur exhibited the highest antibacterial rate, reaching 99.99 % against Staphylococcus aureus (S. aureus) and 95 % against Escherichia coli (E. coli). During storage, the grapes remained unspoiled for up to 9 days after being phototreated with the film and the microbial content of the skin was much lower than that of the control group. In addition, Cur provided antioxidant activity for the film, with a scavenging activity of 39.54 % against the 2,2-diphenyl-1-picrind radical (DPPH). Bananas exposed to the film-forming solution for a short period of time remained fresh for up to 6 days. During preservation, the weight of the treated bananas decreased more slowly than that of the control group. In addition, the activity of SOD on the 7th day was approximately 20 U/g higher than that of the control group, which helped to reduce oxidative stress during banana preservation. In summary, G-CMC/Cur film is an optional fruit-cling film that can be used in food packaging.

Combined antibacterial effect of 460 nm light-emitting diode illumination and chitosan against Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes on fresh-cut melon, and the impact of combined treatment on fruit quality

This study evaluated the combined antibacterial effect of 460 nm LED illumination and chitosan on Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes on fresh-cut melon surface and its impact on the quality of melon at a total dose of 2.4 kJ/cm2 at 4 and 10 °C. Results showed that the antibacterial effect of LED illumination in combination with chitosan (0.5 and 1.0%) was much better than that of LED illumination alone, showing their synergistic effect. Among the pathogens, L. monocytogenes was the most susceptible pathogen to LED illumination. Although the color of melons became paler after LED illumination, there was little to no change in ascorbic acid content, total flavonoid content, or antioxidant capacity of the illuminated fruits compared with non-illuminated fruits. Thus, these results suggest that chitosan-mediated 460 nm LED illumination could be applied to inactivate foodborne pathogens on fresh-cut melons during storage at food establishments.

Chitosan enhances antibacterial efficacy of 405 nm light-emitting diode illumination against Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. on fresh-cut melon

This study aimed to evaluate the influence of chitosan on the antibacterial efficacy of 405 nm LED illumination against Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes on fresh-cut melons. The antibacterial efficacy of LED illumination (a total dose of 1.3 kJ/cm²) with or without chitosan (0.5 and 1.0 %) against these three pathogens was determined at 4 and 10 °C, respectively. Non-illuminated and chitosan-treated fruits were stored in the dark for 36 h under the same temperature. Color changes, ascorbic acid content, and total flavonoid content of illuminated and non-illuminated fruits were also analyzed. The results showed that the populations of all three pathogens on the non-illuminated and chitosan-treated fruits remained unchanged during storage. Regardless of bacterial species and chitosan concentrations, LED illumination in combination with chitosan greatly reduced the bacterial populations by 1.5 - 3.5 log/cm², which was greater than LED illumination alone. Among the three pathogens, L. monocytogenes was the most susceptible to chitosan-mediated LED illumination. However, the whiteness index of illuminated fruits significantly increased by 1.3-fold compared to that of non-illuminated fruits, regardless of the presence of chitosan. Unlike color, no significant difference was observed in ascorbic acid and total flavonoid contents between illuminated and non-illuminated fruits. Although the fruit color was changed by LED illumination, these results indicate that adding chitosan could enhance the antibacterial efficacy of 405 nm LED illumination against major foodborne pathogens on fresh-cut melons without changing nutritional quality.

A singlet state oxygen generation model based on the Monte Carlo method of visible antibacterial blue light inactivation

Visible antibacterial blue light (VABL) has received much attention recently as a nondestructive inactivation approach. However, due to the sparse distribution of bacteria, the light energy evaluation method used in existing studies is inaccurate. Thus, the sensitivity of microorganisms to VABL in different experiments cannot be compared. In this paper, a Monte Carlo-based photon transport model with the optimized scattering phase function was constructed. The model calculated the spatial light energy distribution and the temporal distribution of cumulative singlet state oxygen (CSO) under various cell and medium parameters. The simulation results show that when the cells are sparsely distributed, <30% of light energy from the light source is absorbed by microbes and participates in photochemical reactions. The CSO produced increases with cell density and cell size. Little light energy is available, and thus, the concentration of CSO produced is insufficient to inactivate microbes at deeper depths. As the light intensity and inactivation time increased, the production of singlet state oxygen tended to level off. The model proposed here can quantify the generation of singlet state oxygen and provide a more accurate light energy guide for the VABL inactivation process.

Antimicrobial Effect of Phytochemicals from Edible Plants

Current strategies of combating bacterial infections are limited and involve the use of antibiotics and preservatives. Each of these agents has generally inadequate efficacy and a number of serious adverse effects. Thus, there is an urgent need for new antimicrobial drugs and food preservatives with higher efficacy and lower toxicity. Edible plants have been used in medicine since ancient times and are well known for their successful antimicrobial activity. Often photosensitizers are present in many edible plants; they could be a promising source for a new generation of drugs and food preservatives. The use of photodynamic therapy allows enhancement of antimicrobial properties in plant photosensitizers. The purpose of this review is to present the verified data on the antimicrobial activities of photodynamic phytochemicals in edible species of the world’s flora, including the various mechanisms of their actions.

Photodynamic inactivation and its application in food preservation

Food incidents caused by various foodborne pathogenic bacteria are posing a major threat to human health. The traditional thermal and chemical-based procedures applied for microbial control in the food industry cause adverse effects on food quality and bacterial resistance. As a new means of innovative sterilization technology, photodynamic inactivation (PDI) has gained significant attention due to excellent sterilization effect, environmental friendliness, safety, and low cost. This review analyses new developments in recent years for PDI systems applied to the food preservation. The fundamentals of photosensitization mechanism, the development of photosensitizers and light source selection are discussed. The application of PDI in food preservation are presented, with the main emphasis on the natural photosensitizers and its application to inactivate in vitro and in vivo microorganisms in food matrixes such as fresh vegetable, fruits, seafood, and poultry. The challenges and future research directions facing the application of this technology to food systems have been proposed. This review will provide reference for combating microbial contamination in food industry.