Use of pulsed ultraviolet laser light for the cold pasteurization of bovine milk

Preclinical confirmation of UVC efficacy in treating infectious keratitis

PURPOSE

Preclinical evaluation of the therapeutic potential of antimicrobial 265 nm UVC for infectious keratitis.

METHODS

Four experiments explored UVC: 1) impact on bacterial and fungal lawns on agar, in individual or mixed culture, 2) bacterial inactivation dose in an in vitro deep corneal infection model, 3) dose validation in an ex vivo porcine keratitis model and 4) efficacy in a masked, randomised, controlled murine keratitis trial using bioluminescent Pseudomonas aeruginosa.

RESULTS

Minimum effective UVC exposures ranged between 2 s and 5 s for lawn bacteria and fungi in individual or mixed culture. Significant P. aeruginosa growth inhibition in the in vitro infection model was achieved with 15 s UVC, that resulted in a >3.5 log10 reduction of bacteria in a subsequent ex vivo keratitis model (p < 0.05). Bioluminescence fell below baseline levels in all treated animals, within 8 h of treatment (p < 0.05), in the in vivo study. Re-epithelialisation with corneal clarity occurred within 24 h in 75% of UVC-treated cases, with no relapse at 48 h. On plating, bacteria were recovered only from untreated controls.

CONCLUSIONS

UVC inhibited all tested bacteria and fungi, including mixed culture and strains linked to antibiotic resistance, in vitro, with exposures of ≤ 5 s. In vitro and ex vivo testing confirmed therapeutic potential of 15 s UVC. In vivo, 15 s UVC administered in two doses, 4 h apart, proved effective in treating murine bacterial keratitis.

Applications of Pulsed Light Decontamination Technology in Food Processing: An Overview

Consumers of the 21st century tend to be more aware and demand safe as well as nutritionally balanced food. Unfortunately, conventional thermal processing makes food safe at the cost of hampering nutritional value. The food industry is trying to develop non-thermal processes for food preservation. Pulsed light (PL) is one such emerging non-thermal food processing method that can decontaminate food products or food contact surfaces using white light. Exposure to intense light pulses (in infrared, visible, and ultraviolet (UV) regions) causes the death of microbial cells, rendering the food safe at room temperature. PL technology is an excellent and rapid method of disinfection of product surfaces and is increasingly being used for food surfaces and packaging decontamination, enabling the minimal processing of food. This paper aims to give an overview of the latest trends in pulsed light research, discuss principles of pulse generation, and review applications of various PL systems for the inactivation of microorganisms in vitro, in various food products, and on food contact surfaces. Effects of PL on food quality, challenges of the process, and its prospects are presented.

Overview of Some Recent Advances in Improving Water and Energy Efficiencies in Food Processing Factories

Rapid development of food factories in both developed and developing countries, owing to continued growth in the world population, plays a critical role in the food supply chain, including environmental issues such as pollution, emissions, energy and water consumption, and thus food system sustainability. The objective of this study was to briefly review various environmental aspects of food processing operations, including aquatic, atmospheric, and solid waste generation, and also to discuss several strategies that many companies are using to reduce these negative impacts as well as to improve water and energy efficiency. To obtain higher energy efficiencies in food processing factories, two key operations can play critical roles: non-thermal processing (e.g., high pressure processing) and membrane processes. For higher water efficiency, reconditioning treatments resulting in water reuse for other purposes can be conducted through chemical and/or physical treatments. With regards to reducing volumes of processing food waste, two approaches include value-added by-product applications (e.g., animal feed) and/or utilization of food waste for energy production. Finally, we present trends for lowering operational costs in food processing.

Effects of UV irradiation in a continuous turbulent flow UV reactor on microbiological and sensory characteristics of cow's milk

The dairy industry under current pasteurization conditions (15 s at 72°C) and sanitary standards achieves a safe product with excellent quality. In an ever-competitive market there is still a need to improve product quality and extend shelf life of dairy products to increase competitiveness and open up new markets. In an attempt to test the effect of UV irradiation on microbiota of fluid milk, a continuous flow UV system at 254 nm was used to treat 3.5 and 2% fat milk at two UV doses (880 and 1,760 J liter(-1)). Milk was obtained from three processors, and two lots from each processor were assessed. To assess the impact on the most descriptive native microbiota in pasteurized milk after UV illumination, the product was held at two storage temperatures (4 and 7°C) and tested weekly for 5 weeks for aerobic plate counts (psychrotrophic and mesophilic bacteria), laboratory pasteurization counts, aerobic sporeformers, coliform organisms, and titratable acidity. Microbial counts for all tested microorganisms were lower in UV-treated milk when compared with control throughout storage at 4 and 7°C in both 3.5 and 2% fat milk. Sensory analysis indicated that there is a sensory defect associated with UV treatment at the wavelength used.

Decontamination of sugar syrup by pulsed light

The pulsed light produced by xenon flash lamps was applied to 65 to 67 °Brix sugar syrups artificially contaminated with suspensions of Saccharomyces cerevisiae and with spores of Bacillus subtilis, Geobacillus stearothermophilus, Alicyclobacillus acidoterrestris, and Aspergillus niger. The emitted pulsed light contained 18.5 % UV radiation. At least 3-log reductions of S. cerevisiae, B. subtilis, G. stearothermophilus, and A. acidoterrestris suspended in 3-mm-deep volumes of sugar syrup were obtained with a fluence of the incident pulsed light equal to or less than 1.8 J/cm(2), and the same results were obtained for B. subtilis and A. acidoterrestris suspended in 10-mm-deep volumes of sugar syrup. A. niger spores would require a more intense treatment; for instance, the maximal log reduction was close to 1 with a fluence of the incident pulsed light of 1.2 J/cm(2). A flowthrough reactor with a flow rate of 320 ml/min and a flow gap of 2.15 mm was designed for pulsed light treatment of sugar syrup. Using this device, a 3-log reduction of A. acidoterrestris spores was obtained with 3 to 4 pulses of incident pulsed light at 0.91 J/cm(2) per sugar syrup volume.

Effects of ultraviolet light and ultrasound on microbial quality and aroma-active components of milk

BACKGROUND

Heat treatment is the most common way to extend the shelf life of milk. However, alternative technologies such as ultraviolet (UV) light and ultrasound (US), which are non-thermal methods for processing milk, have been developed to replace heat treatment. These technologies do not have any adverse effects on the quality of milk. The major purpose of this study was to investigate the effects of UV and US on different micro-organism groups and aroma compounds in milk.

RESULTS

Heat pasteurisation at 65 °C for 30 min was used as thermal control treatment. The growth of total coliform group bacteria, Escherichia coli and Staphylococcus spp. was completely reduced by UV treatment. Application of US was not sufficient to reduce the numbers of yeasts and moulds. In neutral/basic fractions, 3-methylthiophene (plastic), hexanal (grass) and 1-hexen-3-one (floral) were major volatiles in milk samples.

CONCLUSION

UV had a major effect on total coliforms, E. coli and Staphylococcus spp., but US was not as effective as UV and heat treatment in reducing certain groups of micro-organisms. No major differences were observed in terms of aroma-active compounds and flavour of milk following the different treatments. However, some new volatiles and change in rheological properties were generated by UV and US treatments.

Relevant factors affecting microbial surface decontamination by pulsed light

Pulsed Light (PL) uses intense flashes of white light rich in ultraviolet (UV) light for decontamination. A log-reduction higher than 5 was obtained in one flash and at fluences lower than 1.8J/cm(2) on spores of a range of spore-forming bacteria, of vegetative cells of non-spore-forming bacteria and on yeasts spread on agar media. Vegetative cells were more sensitive than spores. The inactivation by PL of Bacillus subtilis, B. atrophaeus, B. cereus, Geobacillus stearothermophilus, and Aspergillus niger spores sprayed on polystyrene was similar. The inactivation by PL of B. subtilis and A. niger spores sprayed on glass was slightly lower than on polystyrene. No alteration of the spore structures was detected by scanning electron microscopy for both PL treated B. subtilis and A. niger spores. The inactivation of spores of B. subtilis, B. atrophaeus, B. cereus and B. pumilus by PL or by continuous UV-C at identical fluences was not different, and was much higher by PL for A. niger spores. The increase in the input voltage of the lamps (which also increases the UV-C %) resulted in a higher inactivation. There was no correlation between the resistance to heat and the resistance to PL. The relative effect of UV-C radiations and light thermal energy on PL inactivation was discussed.

Efficacy and safety assessment of a novel ultraviolet C device for treating corneal bacterial infections

BACKGROUND

A prototype solid-state Ultraviolet-C (UVC) LED device may be useful in the treatment of corneal microbial infections, as UVC is commonly used for eradicating bacteria, fungi and viruses in other settings. This study assessed the efficacy of 265 nm UVC from this LED, on four different bacterial strains, and investigated the consequences of corresponding exposures on human corneal epithelial cells in vitro.

METHODS

Agar plate lawns of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Streptococcus pyogenes were exposed to a 4.5 mm diameter 265 nm UVC beam at a fixed intensity and distance, for 30, 5, 4, 2 and 1 seconds. Growth inhibition was assessed with a BioRad Gel imager, and the diameter of lucent areas of bacterial inhibition recorded. Human corneal epithelial cells cultured on glass cover-slips were exposed to corresponding doses of UVC from the same device. Live/dead staining was performed and the results quantified.

RESULTS

There was 100% inhibition of growth for all bacteria tested, at all exposure times. A 30-second exposure of human corneal epithelium to UVC gave no statistically significant decrease (P = 0.877) in the ratio of live to dead cells when compared to control cultures.

CONCLUSION

The results confirmed that a 1 second exposure to germicidal UVC from this LED source was sufficient to inhibit microbial proliferation in the four bacterial strains tested in vitro. The literature suggests UVC at this dose could potentially be beneficial in treating corneal surface infections, without causing significant adverse effects, supported by our findings in human corneal epithelium exposed to UVC.

Effect of pulsed-light treatment on milk proteins and lipids

Pulsed-light treatment offers the food industry a new technology for food preservation. It allows the inactivation of numerous micro-organisms including most infectious foodborne pathogens. In addition to microbial destruction, one can also question whether pulsed-light treatment induced conformational changes in food components. To investigate this question, the influence of pulsed-light treatment on protein components of milk was evaluated by using UV spectroscopy, spectrofluorometry, electrophoresis, and determination of amino acid composition. Pulsed-light treatment resulted in an increase of UV absorbance at 280 nm. The intrinsic tryptophan fluorescence of beta-lactoglobulin (BLG) showed a 7 nm red shift after 10 pulses. SDS-PAGE showed the formation of dimers after treatment of BLG by 5 pulses and more. No significant changes in the amino acid composition of proteins and lipid oxidation were observed after pulsed-light treatment. The obtained results indicated changes in the polarity of the tryptophanyl residue microenvironment of BLG solutions or changes in the tryptophan indole structure and some aggregation of studied proteins. Hence, pulsed-light treatment did not lead to very significant changes in protein components; consequently, it could be applied to process protein foods for their better preservation.

Pulsed-light system as a novel food decontamination technology: a review

In response to consumer preferences for high quality foods that are as close as possible to fresh products, athermal technologies are being developed to obtain products with high levels of organoleptic and nutritional quality but free of any health risks. Pulsed light is a novel technology that rapidly inactivates pathogenic and food spoilage microorganisms. It appears to constitute a good alternative or a complement to conventional thermal or chemical decontamination processes. This food preservation method involves the use of intense, short-duration pulses of broad-spectrum light. The germicidal effect appears to be due to both photochemical and photothermal effects. Several high intensity flashes of broad spectrum light pulsed per second can inactivate microbes rapidly and effectively. However, the efficacy of pulsed light may be limited by its low degree of penetration, as microorganisms are only inactivated on the surface of foods or in transparent media such as water. Examples of applications to foods are presented, including microbial inactivation and effects on food matrices.

Development of pulsed UV light processes for surface fungal disinfection of fresh fruits

Pulsed UV (PUV) power techniques were studied as a nonthermal, residue-free alternative to contact pesticides and to evaluate the surface disinfection of fresh fruits using this type of extremely rapid, high-peak power UV beams. Coherent 248-nm beams from excimer lasers were used to simulate a variety of pulsed light sources now commercially available. Surface disinfection on a series of fresh fruits (i.e., apples, kiwi, lemon, nectarines, oranges, peaches, pears, raspberries, and grapes), representing economically important commodities, were studied and evaluated. Plant (fungal) pathogens were rapidly (<10 s), efficiently (>5 log), and reproducibly killed on fruit surfaces. However, in naturally infected or inoculated (sprayed) fruits, a fraction of the inoculum may penetrate into the epidermis or locate in injured tissue in crevices or in surface irregularities. Under these conditions, only partial disinfection was obtained due to UV shielding (shadowing) effects, which prevent the highly directional, coherent PUV beam from reaching its target. For maximum disinfection efficiency, coherent PUV sources must be combined with dispersing reflectors, and fruits must be handled to ensure uniform exposure to multidirectional incident beams. New, existing, noncoherent, broadband, pulsed light beams (high in UV emission) from arc lamps appear to provide adequate PUV light sources capable of meeting the conditions for commercial applications in slight-modified conveyorized operations. Therefore, PUV techniques may provide effective, commercial-scale, reliable, and viable residue-free alternatives to chemical (contact) pesticides.

Inactivation of Staphylococcus aureus by pulsed UV-light sterilization

Pulsed UV light is a novel technology to inactivate pathogenic and spoilage microorganisms in a short time. The efficacy of pulsed UV light (5.6 J/cm2 per pulse) for the inactivation of Staphylococcus aureus as suspended or agar seeded cells was investigated. A 12-, 24-, or 48-ml cell suspension in buffer was treated under pulsed UV light for up to 30 s, and 0.1 ml of sample was surface plated on Baird-Parker agar and incubated at 37 degrees C for 24 h to determine log reductions. Also, 0.1 ml of cell suspension in peptone water was surface plated on Baird-Parker agar plates, and the plates were treated under pulsed UV light for up to 30 s. The treated and untreated plates were incubated in the conditions described above. A 7- to 8-log CFU/ml reduction was observed for suspended and agar-seeded cells treated for 5 s or longer. In the case of suspended cells, the sample depth, time, treatment, and interaction were significant (P < 0.05). In the case of agar-seeded cells, the treatment time was significant (P < 0.05). Our results clearly indicate that pulsed UV technology has potential for the inactivation of pathogenic microorganisms.