ultraviolet-C Treatment Research Articles

Comparison of UV-C treatment and thermal pasteurization on quality of Chokanan mango (Mangifera indica L.) juice

Ultraviolet-c treatment is an emerging food processing technology for health-conscious consumers. Freshly squeezed Chokanan mango juice was exposed to UV-C light (for 15, 30 and 60min at 25°C) and thermally pasteurized (at 90°C for 60s) to compare the effect on microbial inactivation, physicochemical properties, antioxidant activities and other quality parameters. In addition, shelf life study of juice samples stored at 4±1°C was conducted for 5 weeks. After UV-C treatment and thermal pasteurization, no significant changes occurred in physicochemical properties. A significant increase in extractability of carotenoids (6%), polyphenols (31%), and flavonoids (3%) were observed in juice exposed to UV-C light for 15 and 30min, when compared to freshly squeezed juice. Besides that, enhancement of antioxidant activity was observed after UV-C treatment. Thermal pasteurization and UV-C treatment exhibited significant reduction in microbial load and prolonged shelf-life of juice. The results obtained support the use of UV-C light to improve the quality of Chokanan mango juice along with safety standards as an alternative to thermal pasteurization.

Respiratory activity and mitochondrial membrane associated with fruit senescence in postharvest peaches in response to UV-C treatment

The effect of 3.0kJ/m2 ultraviolet-C (UV-C) treatment on respiratory activity and mitochondrial membrane associated with fruit senescence in peach fruit stored at 20°C for 8days was investigated. UV-C treatment could reduce senescence development, as evidenced by higher fruit firmness due to inhibition of respiration rate via reducing succinic dehydrogenase and cytochrome C oxidase activity. Meanwhile, the activities of superoxide dismutase, catalase and ascorbate peroxidase in the UV-C-treated fruit were much higher than those in control fruit, resulting in lower levels of superoxide radicals (O2−) and hydrogen peroxide (H2O2). In addition, this treatment maintained a higher level of mitochondrial membrane fluidity and inhibited opening of mitochondrial permeability transition pore. Our results suggest that the induction of antioxidant enzymes to scavenge O2− and H2O2 by UV-C treatment was associated with the maintenance of mitochondrial membrane integrity, which also played an important role in senescence retardation in peach fruit.

Effects of UV-C treatment on inactivation of Salmonella enterica and Escherichia coli O157:H7 on grape tomato surface and stem scars, microbial loads, and quality

The purpose of this study was to investigate the effectiveness of ultraviolet-C (UV-C) light inactivation as affected by the location of pathogens on the surface and at stem scars of whole grape tomatoes. A mixed bacterial cocktail containing a three strain mixture of Escherichia coli O157:H7 (C9490, E02128 and F00475) and a three serotype mixture of Salmonella enterica (S. Montevideo G4639, S. Newport H1275, and S. Stanley H0558) were used. Tomatoes were spot inoculated using approximately 100 μL of inocula to achieve a population of about 107±1 CFU/tomato. Additionally, the effects of treatment on color, texture, lycopene content, and background microbial loads during post UV-C storage at 4 °C for 21 days were determined. Results showed that UV-C doses of 0.60–6.0 kJ/m2 resulted in 2.3–3.5 log CFU per fruit reduction of E. coli O157:H7 compared to 2.15–3.1 log CFU per fruit reduction for Salmonella on the surfaces. Under the same conditions, log reductions achieved at stem scar were 1.7–3.2 logs CFU for E. coli O157:H7 and 1.9–2.8 logs CFU for Salmonella. The treatment was effective in controlling native microbial loads during storage at 4 °C as the total aerobic mesophilic organisms (PCA) and anaerobic lactic acid bacteria (LAB) counts of treated tomatoes were significantly (p < 0.05) lower during storage compared to the control group and the yeast and mold populations were reduced significantly below the detection limit. Furthermore, the firmness of tomato and its color was not affected by the UV-C doses during storage. UV-C radiation could potentially be used for sanitizing fresh tomatoes and extending shelf-life. The results of this study indicate that the specific location of pathogens on the produce influences the effectiveness of UV-C treatment, which should be taken into consideration for the design of UV-C systems for produce sanitization.

Reduction of spiked porcine circovirus during the manufacture of a Vero cell-derived vaccine

Porcine circovirus-1 (PCV1) was recently identified as a contaminant in live Rotavirus vaccines, which was likely caused by contaminated porcine trypsin. The event triggered the development of new regulatory guidance on the use of porcine trypsin which shall ensure that cell lines and porcine trypsin in use are free from PCV1. In addition, manufacturing processes of biologicals other than live vaccines include virus clearance steps that may prevent and mitigate any potential virus contamination of product. In this work, artificial spiking of down-scaled models for the manufacturing process of an inactivated pandemic influenza virus vaccine were used to investigate inactivation of PCV1 and the physico-chemically related porcine parvovirus (PPV) by formalin and ultraviolet-C (UV-C) treatment as well as removal by the purification step sucrose gradient ultracentrifugation. A PCV1 infectivity assay, using a real-time PCR infectivity readout was established. The formalin treatment (0.05% for 48h) showed substantial inactivation for both PCV1 and PPV with reduction factors of 3.0log10 and 6.8log10, respectively, whereas UV-C treatment resulted in complete PPV (≥5.9log10) inactivation already at a dose of 13mJ/cm but merely 1.7log10 at 24mJ/cm2 for PCV1. The UV-C inactivation results with PPV were confirmed using minute virus of mice (MVM), indicating that parvoviruses are far more sensitive to UV-C than PCV1. The sucrose density gradient ultracentrifugation also contributed to PCV1 clearance with a reduction factor of 2log10. The low pH treatment during the production of procine trypsin was investigated and showed effective inactivation for both PCV1 (4.5log10) and PPV (6.4log10). In conclusion, PCV1 in general appears to be more resistant to virus inactivation than PPV. Still, the inactivated pandemic influenza vaccine manufacturing process provides for robust virus reduction, in addition to the already implemented testing for PCV1 to avoid any contaminations.

Competitive interactions inside mixed-culture biofilms of Salmonella Typhimurium and cultivable indigenous microorganisms on lettuce enhance microbial resistance of their sessile cells to ultraviolet C (UV-C) irradiation

Salmonella Typhimurium (ST) is one of the leading causes of foodborne diseases in fresh produce, such as lettuce. Despite this, the role of the possible interactions between lettuce indigenous microorganisms and ST on their ability to form biofilm on lettuce and subsequently on the sensitivity of their sessile cells to ultraviolet C (UV-C) irradiation, remains relatively unexplored. Here, the interaction of a mixed-culture of ST and cultivable indigenous microorganisms (CIMs) was examined, as well as the efficacy of UV-C. Initially, the CIMs were isolated and cultured with ST at 15°C either planktonically or left to form biofilms on stainless steel (SS) and lettuce leaves. Microbial growth, biofilm formation, and survival following UV-C treatment were monitored using traditional plate count methods while biofilm formation, production of extracellular polymeric substance (EPS), and stomatal colonization were also observed by field emission scanning electron microscopy (FESEM). Internalization strength, color, and texture were analyzed by standard methods. Results revealed that the mixed-culture of ST and CIMs presented significantly (p<0.05) decreased biofilm formation on lettuce leaves compared to mono-cultures (i.e. ST or CIMs alone), which indicated competitive interaction between them, while no interactions were observed for biofilms on SS and for the planktonic cultures. It was also demonstrated that a mixed-culture biofilm on lettuce presented significantly higher resistance (p<0.05) to UV-C treatment compared to mono-culture biofilms, but such an effect was not observed for biofilms formed on SS and for the planktonic cultures. The Weibull model fitted well to microbial inactivation curves with R2 values that ranged from 0.90 to 0.97. Regarding the mixed-culture conditions, a UV-C fluency of 35mJ/cm2 was required to achieve a 5.0logCFU/mL or cm2 reduction in planktonic and biofilms on the SS for the mixed-culture, while 360mJ/cm2 was required to reduce biofilm cell number by approximately 2.0logCFU/cm2 on lettuce. Furthermore, FESEM analysis indicated higher EPS production, and greater stomatal colonization on lettuce mixed-cultures compared to mono-cultures. Finally, internalization strength was significantly higher (p<0.05) for the mixed-culture on lettuce, thus supporting the notion that internalization in lettuce is a factor that contributes to microbial UV-C resistance. The absence of adverse effects of UV-C on the color and texture of the lettuce suggests it as an alternative means of eliminating ST.

Postharvest ultraviolet-C irradiation suppressed Psy 1 and Lcy-β expression and altered color phenotype in tomato (Solanum lycopersicum) fruit

Mature green cherry tomato fruit were harvested and treated with ultraviolet-C (UV-C) irradiation at a predetermined dose of 4.2kJm−2, and stored at 18°C for 35 days. The effects of UV-C treatment on color change, pigment contents, and the expression of major genes involved in carotenoid metabolism, including Psy 1, Pds, Lcy-β, and Lcy-ɛ, encoding phytoene synthase, phytoene desaturase, lycopene β-cyclase and lycopene ɛ-cyclase, respectively, were examined. The UV-C treated fruit developed a pink red color in contrast to the normal orange red color of control fruit. Lycopene accumulation during ripening in UV-C treated fruit was significantly inhibited but its final content was not affected. However, both accumulation and final content of β-carotene were significantly suppressed in UV-C treated fruit. The lower content of β-carotene, leading to a higher lycopene to β-carotene ratio, is probably responsible for the altered color phenotype in UV-C treated fruit. Psy 1, a major gene involved in lycopene synthesis was inhibited by UV-C irradiation. Significantly suppressed expression of Lcy-β gene was also observed in UV-C treated fruit. Thus it is possible that the lower transformation from lycopene to carotenes contributed to the relatively stable content of lycopene.

Postharvest UV-C irradiation inhibits the production of ethylene and the activity of cell wall-degrading enzymes during softening of tomato (Lycopersicon esculentum L.) fruit

Mature green cherry tomato fruit were harvested and treated with ultraviolet-C (UV-C) irradiation at a predetermined dose of 4.2kJm−2 and stored at 18°C for 35 days. The effects of UV-C treatment on firmness, cell wall compositions (pectin and cellulose), cell wall ultra-structure, levels of ethylene production, and activities of cell wall degrading enzymes in the fruit were investigated during storage. Major genes involved in cell wall degradation (PME 2.1, Cel 1, PG cat and Exp 1) were also checked. Fruit firmness was better maintained in UV-C treated fruit corresponding with higher contents of cellulose and acid-soluble pectin. Transmission electron microscopy indicated that UV-C irradiation retarded cell wall disassembly in the pericarp. Ethylene production was significantly inhibited by UV-C treatment. The UV-C treatment also suppressed the transcriptional expression of PME2.1, Cel1, PGcat and Exp1 genes, and inhibited pectin methylesterase (PME; EC 3.1.1.11), polygalacturonase (PG; EC3.2.1.15) and cellulase (EC3.2.1.4) activities during storage. These results suggested that the inhibition of ethylene production, which in turn down-regulated expression of genes encoding cell wall degrading enzymes, might be one of the possible mechanisms of UV-C delaying tomato fruit softening.

Terroir and variety: Two key factors for obtaining stilbene-enriched grapes

Grapes and wine are among the main sources of bioactive stilbenes in the diet. The stilbene composition of grapes depends on both variety and terroir. The effect of terroir on grape stilbenes has not been widely studied. In this research the study of the stilbene content (resveratrol, piceatannol and viniferins) in four different red grape varieties (Syrah, Merlot, Cabernet sauvignon and Pinot noir) and from four different Andalusian terroirs (Jerez, Cabra, Cadiar and Ronda) was carried out during the 2009 vintage. In addition, stilbene induction capacity was studied in each terroir and variety after ultraviolet-C (UVC) postharvest treatment. Data were analysed by multivariate statistical methods. Principal component analysis applied to the oenological parameters and stilbene data classified varieties into two terroir groups satisfactorily: Jerez and Cabra on the one hand, and Ronda and Cadiar on the other hand. Terroir effect is stronger than variety on stilbene induction capacity after UVC treatment. Syrah from Cabra stood out due to both the high basal (13.07mg/kg fw) and induced (33.14mg/kg fw) stilbene concentration attained. Therefore, it can be affirmed that Cabra and Syrah are the most suitable terroir and variety, respectively, for obtaining a stilbene-enriched wine.

Fate of E. coli O157:H7, Salmonella spp. and potential surrogate bacteria on apricot fruit, following exposure to UV-C light

Some soft fruit, such as tree-ripened apricots, cannot be washed with aqueous sanitizers, due to their innate softness and delicate surfaces. In this study, ultraviolet-C (UV-C) light was investigated for its efficacy in inactivating 4–5 individual strains of Escherichia coli O157:H7 and Salmonella spp. on apricots, in addition to a four-strain composite of Shiga toxin-negative E. coli O157:H7 and a cocktail of three attenuated strains of Salmonella Typhimurium and Salmonella Typhimurium LT2. Also, the survival of E. coli O157:H7 and Salmonella spp. after exposure to 74 and 442mJ/cm2 of UV-C was evaluated during post-UV storage at 2 and 20°C. The fruit was spot inoculated and the areas (ca. 1.5cm2) of fruit surface with the inoculated bacteria were exposed to UV-C at 7.4mW/cm2. E. coli O157:H7 and Salmonella spp. populations decreased rapidly (1–2 logs) (P<0.05) with increasing UV-C doses of 0 to 74mJ/cm2. Further increases in UV-C dosage achieved only limited additional reductions in bacterial populations. Shiga toxin-negative bacteria and attenuated S. Typhimurium strains, along with S. Typhimurium LT2, responded similarly to corresponding pathogenic E. coli O157:H7 and Salmonella spp. During storage at 2 or 20°C, populations of pathogenic E. coli O157:H7 and Salmonella spp. on untreated fruit decreased slowly; however, populations on fruit treated with 442mJ/cm2 decreased rapidly at both temperatures. After 8days at 20°C or 21days at 2°C, E. coli O157:H7 and Salmonella spp. populations on UV-C treated fruit were at least 2logCFU/g lower than on non-treated controls. Our results suggest that surface-inoculated bacteria survived poorly following UV-C treatment of apricots.

The combined effects of aqueous chlorine dioxide, fumaric acid, and ultraviolet-C with modified atmosphere packaging enriched in CO2 for inactivating preexisting microorganisms and Escherichia coli O157:H7 and Salmonella typhimurium inoculated on buckwheat sprouts

The combined effects of a sanitizer mixture, ultraviolet-C (UV-C), and modified atmosphere packaging (MAP) on the quality of non-inoculated and inoculated (Escherichia coli O157:H7 and Salmonella typhimurium) buckwheat sprouts were examined. Buckwheat sprouts were treated with a sanitizer mixture (comprising 100mgL−1 aqueous ClO2 and 0.3% fumaric acid) and 2kJm−2 UV-C, packaged under two different conditions (air and CO2 gas) and storage for 8d at 4°C. The combination of the sanitizer mixture and UV-C treatment reduced the initial counts of preexisting microorganisms in the buckwheat sprouts by 1.9logCFUg−1 and reduced the initial inoculated counts of E. coli O157:H7 and S. typhimurium on buckwheat sprouts by 3.0 and 2.3logCFUg−1, respectively. The preexisting microorganisms and inoculated pathogens in buckwheat sprouts packaged under CO2 gas were significantly reduced during storage following the combined treatment compared to those of the control by above 95%. Differences in Hunter L*, a*, and b* values among the treatments were negligible. The combined sanitizer mixture and UV-C treatment increased the sprout rutin content by 147%, but there was no significant difference in 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity between treatments during storage. Therefore, the combination of sanitizer mixture made from aqueous ClO2 and fumaric acid, UV-C irradiation, and MAP can improve the microbial safety and quality of buckwheat sprouts.

Effects of electron beam and ultraviolet-C irradiation on quality and microbial populations of leafy vegetables during storage

Effects of ultraviolet-C (UV-C) and electron beam irradiation on the quality and microbial populations of leafy vegetables were compared as a microbial decontamination method. Tatsoi and red chard leaves were treated with UV-C at a dose of 5 kJ/m2 or by electron beam irradiation at doses of 0.5, 1, and 3 kGy. After UV-C or electron beam irradiation treatment, the samples were stored at 4 ± 1°C for 11 days. Populations of total aerobic bacteria in leafy vegetables decreased by 0.8–1.1 log CFU/g after treatment with UV-C irradiation, and those of yeast and molds decreased by 1.0–1.8 log CFU/g. On the contrary, electron beam irradiation at 0.5 or 1 kGy reduced the microbial populations by 2.0–2.5 log CFU/g. Electron beam irradiation at 3 kGy eliminated the microorganisms in the samples. These results suggest that electron beam irradiation at low dose below 3 kGy can be more effective than UV-C treatment for the inactivation of microorganisms in Tatsoi and red chard leaves.

Effects of ultraviolet-C treatment in Teflon®-coil on microbial populations and physico-chemical characteristics of watermelon juice

Abstract The efficacy of UVC radiation for inactivation of bacteria (aerobic, coliform) and yeast/mold in watermelon juice using helix Teflon®-coil was investigated. Changes in microbial load, pH, °brix, color (L*, a*, and b*), lycopene, and phenolics in juice, after UVC treatment were evaluated for 37 days of storage at 5 ± 1 °C. Microbial inactivation was dependent on the UVC intensity between 2.7 and 37.5 J/mL. UVC treatment inactivated all (2.6 log CFU/mL) coliform bacteria. UVC (37.5 J/mL) reduced total aerobes and yeast/mold by 1.47 and 0.99 log CFU/mL, respectively. The microbial load in treated juice remained lower than 6.0 log CFU/mL until the 31st day of storage. UVC treatment resulted in no-significant effects on pH, °brix, color change, lycopene, and phenolics, the values of which remained consistent with those of a control until 25th day of storage. UVC treated juice had lower b* (yellowness) and higher a* (redness) colors than untreated juice. Industrial relevance Watermelon juice is a potential health food and strategies to increase its shelf-life with minimal or no damage to nutritional components are crucial for obtaining more commercial benefits. Our study suggests that a Teflon®-coil UVC system can be effectively used as a non-thermal method for microbial inactivation in watermelon juice and to improve the product shelf-life with no significant effects on different physico-chemical and nutritional characteristics.

Hot water, UV‐C and superatmospheric oxygen packaging as hurdle techniques for maintaining overall quality of fresh‐cut pomegranate arils

In recent years there has been increasing consumer pressure to avoid the use of agrochemicals such as chlorine on fresh plant products for extending their shelf life. The combined use of eco-sustainable techniques may be an alternative. The effect of hot water (HW), ultraviolet-C (UV-C) light and high oxygen packaging (HO) on the overall quality of fresh-cut pomegranate arils stored under modified atmosphere packaging (MAP) for up to 14 days at 5 °C was studied. Arils extracted manually, washed with chlorine (100 µL L⁻¹ NaClO, pH 6.5, 5 °C water), rinsed and drained were exposed to single or combined (double and triple) hurdle techniques. The HW treatment consisted of a 30 s immersion in water at 55 °C followed by air surface drying. A 4.54 kJ m⁻² dose was used for the UV-C treatment before packaging. Active MAP with initial 90 kPa O₂ was used in the HO treatment. The respiration rate remained relatively constant throughout shelf life, with no differences among treatments. CO₂ accumulation was higher within HO packages. HW induced a slight reduction in total soluble solids, while no changes in titratable acidity were found. HO-treated arils had the highest phenolic content, while the lowest was found in HW-treated arils. The lowest antioxidant activity was found in HW + UV-C + HO and the highest in UV-C + HO and HO treatments. HW alone or in combination with UV-C and HO inhibited mesophile, mould and yeast growth, while UV-C + HO was most effective for controlling yeast and mould growth. UV-C and HO either alone or in combination are promising techniques to preserve the quality of pomegranate arils for up to 14 days at 5 °C.

Contact-free cold atmospheric plasma treatment of Deinococcus radiodurans

In this study we investigated the sensitivity of Deinococcus radiodurans to contact-free cold atmospheric plasma treatment as part of a project to establish new efficient procedures for disinfection of inanimate surfaces. The Gram-positive D. radiodurans is one of the most resistant microorganisms worldwide. Stationary phases of D. radiodurans were exposed to cold atmospheric plasma for different time intervals or to ultraviolet C (UVC) radiation at dose rates of 0.001-0.0656 J cm⁻², respectively. A methicillin-resistant Staphylococcus aureus strain (MRSA) served as control for Gram-positive bacteria. The surface microdischarge plasma technology was used for generation of cold atmospheric plasma. A plasma discharge was ignited using ambient air. Surprisingly, D. radiodurans was sensitive to the cold atmospheric plasma treatment in the same range as the MRSA strain. Survival of both bacteria decreased with increasing plasma exposure times up to 6 log₁₀ cycles (>99.999 %) within 20 s of plasma treatment. In contrast, UVC radiation of both bacteria demonstrated that D. radiodurans was more resistant to UVC treatment than MRSA. Cold atmospheric plasma seems to be a promising tool for industrial and clinical purposes where time-saving is a critical point to achieve efficient disinfection of inanimate surfaces and where protection from corrosive materials is needed.

Combination of the biocontrol yeast Cryptococcus laurentii with UV-C treatment for control of postharvest diseases of tomato fruit

Integrated management that combines different methods is being actively pursued in the control of postharvest disease. In this study, the biocontrol yeast Cryptococcus laurentii and ultraviolet-C (UV-C) treatment were evaluated for controlling infection following artificial inoculation with Botrytis cinerea or Alternaria alternata, and natural infection in tomato fruit. Applied separately, C. laurentii and UV-C (4 kJ m−2) effectively inhibited decay caused by B. cinerea or A. alternata, and natural infection. The combination of C. laurentii and UV-C showed better control efficiency. UV-C treatment did not affect yeast growth in fruit wounds, while the treatment induced the transcript expression of β-1,3-glucanase, phenylalanine ammonia-lyase, peroxidase and superoxide dismutase based on real-time PCR analysis, as well as increased the activity of these enzymes in tomato fruit. Results indicate that the mechanism by which UV-C enhanced the biocontrol efficacy of C. laurentii may be associated with the elicitation of defense response in tomato fruit.

Use of UV‐C Treatments to Maintain Quality and Extend the Shelf Life of Green Fresh‐cut Bell Pepper (Capsicum annuum L.)

The objective of this work was to select a Ultraviolet-C (UV-C) treatment for fresh-cut mature green bell pepper, and to evaluate the effect of its combination with refrigeration on quality maintenance. Bell pepper sticks were treated with 0, 3, 10, or 20 kJ/m² UV-C in the outer (O), inner (I), or both sides of the pericarp (I/O) and stored for 8 d at 10 °C. During the first 5 d of storage, all UV-C treatments reduced deterioration as compared to the control. The treatment with 20 kJ/m² I/O was the most effective to reduce deterioration, and was used for further evaluations. In a second group of experiments, mature green bell pepper sticks were treated with 20 kJ/m² I/O, stored at 5 °C for 7 or 12 d and assessed for physical and chemical analysis, and microbiological quality. UV-C-treated fruit showed lower exudates and shriveling than the control. UV exposure also reduced decay, tissue damage, and electrolyte leakage. After 12 d at 5 °C, UV-C irradiated peppers remained firmer and had higher resistance to deformation than the control. The UV-C treatments also reduced weight loss and pectin solubilization. UV-C exposure decreased the counts of mesophile bacteria and molds, and did not affect acidity or sugars. UV-C-treated fruit stored for 0 or 7 d at 5 °C did not show major differences in antioxidants from the control as measured against DPPH(•) or ABTS(•)⁺ radicals. Results suggest that UV-C exposure is useful to maintain quality of refrigerated fresh-cut green pepper. Exposure to UV-C radiation before packing and refrigeration could be a useful nonchemical alternative to maintain quality and reduce postharvest losses in the fresh-cut industry.

Ultraviolet-C Light Effect on Pitaya (Stenocereus griseus) Juice

Pitaya (Stenocereus griseus) juice, obtained from fresh pitayas, was processed using a continuous ultraviolet-C (UV-C) light (57 µW/cm 2 ) system. Juice was processed at five flow rates (0.46, 3.28, 6.57, 16.49 and 30.33 mL/s) and five treatment times (5, 10, 15, 20, and 25 min). Fresh juice was used as control. Some physicochemical (pH, total soluble solids, color, and betalains), antioxidant (total phenolic compounds and antioxidant activity), and microbiological (aerobic mesophylls bacteria and yeasts plus molds) characteristics were assessed in fresh and UV-C processed juices. It was observed that the UV-C treatments did not affect pH and total soluble solids in juice. The total change in color (E) increased as treatment times increased; however, E values were reduced at high flow rates. The betalains and total phenolic compounds contents were reduced as flow rates and treatment times increased; consequently, the antioxidant activity lessened in juice. A maximum reduction of 2.11 and 1.14 log cycles was observed for mesophylls and yeasts plus molds, respectively, in the UV-C light treated pitaya juice.

Physico-chemical changes in tomato with modified atmosphere storage and UV treatment.

Physico-chemical changes in ripe tomato (Lycopersicon esculentum Mill.) were analyzed on day 0 and 2weeks after ultraviolet-C (UV-C) light treatment or modified atmosphere (MA) storage and combined UV-C + MA storage at 10°C. Modified atmosphere packaging (MAP) film was used to create MA conditions. The tomatoes were evaluated for surface colour, mass loss, firmness, respiration rate, total soluble solids and antioxidant capacity. The tomatoes treated with UV-C and MA storage underwent least changes in their physico-chemical properties, indicating that combination of UV-C and MA storage was successful in retaining the attributes of the fresh product. The increase in antioxidant capacity of the tomatoes during UV-C treatment suggested that UV treatment during post harvest handling may be successfully combined with MA storage, resulting in a product with better nutritive value.

Effects of UV-C Light Processing on Some Quality Characteristics of Grape Juices

White and red grape juices (GJs) were subjected to ultraviolet C (UV-C) light as a non-thermal preservation technology using a coiled tube UV-C reactor with nine lamps. The effects of UV-C light on microbial (total aerobic count and yeast and mould count) and some chemical quality characteristics (total phenolics, antioxidant capacity, anthocyanin and polymeric colour, etc.) of white and red GJs were investigated. The results were compared with control (untreated) and heat-treated juice samples. Single-pass UV-C treatment (12.6 J/mL) of white and red GJs resulted in 3.51 and 3.59 log reductions in total aerobic count and, 2.71 and 2.89 log reductions in yeast and mould counts, respectively. The microbial loads of both GJs were completely eliminated after two passes through the reactor (25.2 J/mL). After UV-C and heat treatments, there were no significant changes in antioxidant capacity, total phenolics, titratable acidity, soluble solids and pH of white and red GJs (P > 0.05). The losses in monomeric anthocyanins were 6.1% and 8.7% after UV-C treatment of 12.6 and 25.2 J/mL doses, respectively. However, anthocyanin level of red GJ was significantly affected by the heat treatment with an 11.8% loss (P < 0.05). The percent polymeric colour of the red GJ with heat treatment was significantly higher compared to the colour with the UV-C treatment.

Effects of UV-C treatment on inactivation of Escherichia coli O157:H7, microbial loads, and quality of button mushrooms

This study investigated the effects of ultraviolet-C (UV-C) light applied to both sides of mushrooms on microbial loads and product quality during storage for 21 d at 4 °C. Microflora populations, color, antioxidant activity, total phenolics, and ascorbic acid were measured at 1, 7, 14 and 21 d of storage. Additionally, the inactivation of Escherichia coli O157:H7 by UV-C was determined. Results showed that UV-C doses of 0.45–3.15 kJ m −2 resulted in 0.67–1.13 log CFU g −1 reduction of E. coli O157:H7 inoculated on mushroom cap surfaces. UV-C radiation also reduced total aerobic plate counts by 0.63–0.89 log CFU g −1 on the surface of mushrooms. Although mushrooms treated with UV-C had more severe browning with increasing dosage after initial treatment, the control mushrooms also browned as indicted by lower L* and higher a* values after 21 d of storage at 4 °C. In addition, the UV-C treatments apparently inhibited lesion development on the mushroom surface. During the first 7 d, irradiated mushrooms had lower antioxidant activity, total phenolics, and ascorbic acid content compared to non-radiated samples. However, irradiated mushrooms reached similar amounts of these nutrients as the control after 14 d of storage at 4 °C. In summary, UV-C radiation could potentially be used for sanitizing fresh button mushrooms and extending shelf-life.