1. Introduction
Risks to food security happen during all phases of food preparation, storage, transportation, distribution, and sale, under any condition: raw, cooked, chilled, at room temperature, or kept warm – whether exposed or not – for consumption [1].
Chemical, physical, or biological aspects can alter the organoleptic properties of food, often causing the appearance of lethal substances for allergic individuals, or even producing bacteria, viruses, fungi, protozoa, and toxins, which are often pathogenic, making food unfit for consumption [2].
The relative number of microorganisms or even the presence of pathogenic strains in food affects microbiological quality, which is a factor causing infectious diseases and pertains to the importance of controlling contamination – as described – in order to guarantee food security. Figure 1 shows the most common microbial agents that cause foodborne diseases. Microbial resistance to existing antimicrobials is a growing food security problem – serotypes of Salmonella typhimurium, Campylobacter spp., Shigella spp., Vibrio spp., E. coli can be cited in this context. The severity of these diseases in humans can vary from mild symptoms to health risk conditions [3].
Considering the cumulative effects on humans, the use of chemical substances used in hygiene, disinfection or decontamination to control microbial contamination in food can threaten the population, exposing it to the danger of cellular mutations that cause cancer [4].
2. Alternative optical-based technologies for the food loss problem
2.1 Ultraviolet illumination
Ranges of ultraviolet (UV) radiation from 100 to 400 nm are variable for the inactivation of each microbial type and species. UV light induces damage to DNA molecules that can lead to mutations or cell death. Viruses and bacteria are more easily affected by UV-C radiation at 254 nm. Higher doses of UV-C used for inactive protozoa such as in the case of helminth eggs, are overdoses. The absorption of UV-C photons in the nitrogenous bases of DNA results in the reduction of the dimerization of the pyrimidine bases [5].
Thermal and acidic inactivation of microorganisms are options used to decontaminate fresh vegetables. These acidic pH solutions are effective in achieving a reduction in the number of pathogens. However, they cause an environmental pollution problem. Food geometry can be a problem for penetration of UV-C rays if these cannot reach the entire surface where the microorganisms are attached. The circulation of water in a reactor with the volume passing at a precise distance from UV-C light may inactivate microorganisms.
The Optics and Photonics Research Center (CEPOF) in São Carlos, São Paulo, Brazil, described the construction of a reactor in Oliveira et al. [6] with several UV-C emitters distributed to improve homogeneous lighting of fresh broccoli and increase their microbiological quality (Figure 2). The circulation of UV-water in this system, in addition to removing the microorganisms contained in the vegetables, can destroy microorganisms in food when it passes through the light. Water volume in this system is reduced, causing no problems to the environment and not even the accumulation of toxic substances in food. Microbial inactivation in fresh broccoli by this system was effective without resorting to standard use, which is the solution using chemical substances.
In another study, Corrêa et al. [7] demonstrated the decontamination of meat and fruit using a new device with UV-C lamps distributed above and below the food. UV-C radiation eliminated part of the microorganisms on the surface of these foods, and the most effective result was achieved in apples, with reductions of 3.2 ± 0.4 and 3.8 ± 0.2 log CFU/mL after 5 and 10 min of UV-C irradiation, respectively. Moreover, since UV-C irradiation only takes a few minutes to reduce microbial contamination, the physicochemical and nutritional qualities of the foods were preserved.
2.2 Ozone
Ozone gas is well known for its antibacterial activity and, although toxic, it quickly dissociates into oxygen. Ozone is widely used to inactivate microorganisms in solution. The mechanism of action in bacterial cells occurs through the oxidation of unsaturated lipids in the cytoplasmic membrane that overflows the contents of the cell in addition to oxidizing proteins, enzymes, and nucleic acids.
Among the techniques most used today to preserve food for sale, only refrigeration paralyzes the growth of microorganisms, decreasing their metabolism.
Concerning food safety with minimal processing for the commercial valorization of the product, CEPOF has been developing new equipment with designs capable of delivering ozone in gaseous and liquid form, in addition to acting in conjunction with UV to reduce the microbial load of meat, thus ensuring that this food reaches consumers with quality intact.
The efficiency of ozone gas in concentrations of 11-15 ppm was tested in steel and meat samples, the microbial inactivations were significantly different (p <0.05), obtaining for steel samples reductions about 3,9 Log of E.coli in 30 minutes (Figure 3A) and for meat samples 2 Log of in natura contaminations (Figure 3B). These results showed the potential of ozone for microbial inactivation in different types of samples.
2.3 Photodynamic inactivation
Photodynamic inactivation (PDI) is a technique based on the simultaneous interaction of photosensitizer (PS), considering its non-toxic concentration of light at a specific wavelength for its absorption by PS, and oxygen (O2), generating reactive oxygen species capable of disrupting pathogenic microorganisms of various species and strains. PDI has been introduced as a promising approach to food decontamination.
CEPOF has studied curcumin, used as a food additive, as a PS in the decontamination of different types of meat and fruits. An article by Corrêa et al. [7] describes protocols using curcumin, capable of reducing pathogenic microorganisms in food. PDI reduced microorganisms in beef and chicken by 1.5 ± 0.2 and 1.4 ± 0.2 log CFU/mL, respectively, using 40 μM curcumin and 15 J/cm2 of light dose at 450 nm (Figure 4A). The most effective result was achieved in apples, with a reduction of 2.0 ± 0.4 log CFU/mL, using 80μM curcumin and 10 J/cm2 of light dose (Figure 4B).
PDI showed antimicrobial effect in food, being useful to reduce bacterial contamination levels on the surface of meats and fruits. The surface properties of the food may influence the decontamination success, since microorganisms occurring in crevices on the surface of the food are shielded from the light. However, one strategy to maintain the effectiveness of PDI would be use a light array that spreads evenly over the entire surface of the food to be decontaminated.
3. Conclusion
In general, finding solutions for food decontamination using new optical technologies is a new and very promising area. Both the use of ultraviolet light and the use of visible light with photodynamic action are techniques based on photo-reactions that inactivate biological contaminants in food quite adequately. The most important feature of these techniques is that they do not modify the basic characteristics of the food or offer risks to those who consume it. These techniques are inexpensive, and highly secure. On the other hand, the use of ozone is quite efficient and constitutes an already established clean method, which is minimally aggressive to the environment and quite efficient in combating contaminants. These modern, more technological techniques are an encouragement to solve the current situation of food losses caused by contamination.
References
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2. Húngaro, H.M. et al. Food Microbiology, in Encyclopedia of Agriculture and Food Systems (2014). doi:10.1016/B978-0-444-52512-3.00059-0
3. World Health Organization. WHO estimates of the global burden of diseases. World Heal. Organ. 46, 1-15 (2014).
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6. Oliveira, B.P., Lara, S., Chianfrone, D., Blanco, K.C., Bagnato, V.S. Perimetric Distributed UV Reactor and Its Validation and the Decontamination of Fresh Broccolis. American Journal of Applied Chemistry 7, 161-167 (2019).doi: 10.11648/j.ajac.20190706.12
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