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Effect of Combining Infrared Heating with Ultraviolet Irradiation on Inactivation of Mold Spores
Abstract
Combining effect of infrared radiation (IR) heating with ultraviolet (UV) irradiation on the inactivation of mold spores isolated from citrus fruits was investigated. Fruit-related molds (Penicillium, Aspergillus, Cladosporium, Rhizopus, and Byssochlamys) were inoculated on stainless steel Petri dish and inactivated by IR heating, UV irradiation, and combined treatments with different sequence orders. Three isolates (Penicillium, Aspergillus and Cladosporium) were sensitive to IR heating, while Rhizopus and Byssochlamys spores were relatively sensitive to UV irradiation rather than IR heating. Combinations of IR heating with UV irradiation were effective in the inactivation of all mold spores. Considerable reductions in the survival of all mold spores were achievable by the combined treatment regardless of the treatment order.
... Until a few years ago, HRM were only occasionally searched in food and beverage packaging devices, thus being isolated from PET bottles, laminated paperboard, stretch wraps or slip sheets (Delgado et al., 2012;Rico-Munoz et al., 2007;Rico-Munoz, 2017;Rico-Munoz and dos Santos, 2019;Sato and Takano, 2000). Consequently, the UV-C resistance of these microorganisms has been scarcely documented in literature, and the effect of UV-C on HRM was actually limited to papers by Begum et al. (2009) on Aspergillus ruber (≡Eurotium rubrum) in liquid medium, by Hamanaka et al. (2010) on Paecilomyces (≡Byssochlamys) sp. in stainless steel Petri dishes, and by Manns et al. (2015) on Paecilomyces fulvus (≡Byssochlamys fulva) in apple cider or juice. ...
In food industries UV-C irradiation is used to achieve decontamination of some packaging devices, such as plastic caps or laminated foils, and of those smooth surfaces that can be directly irradiated. Since its effectiveness can be checked by microbial validation tests, some ascospore-forming molds (Aspergillus hiratsukae, Talaromyces bacillisporus, Aspergillus montevidensis, and Chaetomium globosum) were compared with one of the target microorganisms actually used in industrial bio-validations (Aspergillus brasiliensis ATCC 16404) to find the species most resistant to UV-C. Tests were carried out with an UV-C lamp (irradiance = 127 μV/cm2; emission peak = 253.7 nm) by inoculating HDPE caps with one or more layers of spores. Inactivation kinetics of each strain were studied and both the corresponding 1D-values and the number of Logarithmic Count Reductions (LCR) achieved were calculated. Our results showed the important role played by the type of inoculum (one or more layers) and by the differences in cell structure (thickness, presence of protective solutes, pigmentation, etc.) of the strains tested. With a single-layer inoculum, Chaetomium globosum showed the highest resistance to UV-C irradiation (1D-value = 100 s). With a multi-layer inoculum, Aspergillus brasiliensis ATCC 16404 was the most resistant fungus (1D-value = 188 s), even if it reached a number of logarithmic reductions that was higher than those of some ascospore-forming mycetes (Aspergillus montevidensis, Talaromyces bacillisporus) tested.
... These results are in harmony with results obtained by Kader et al. (1989). As to the tested pre-harvest treatments during storage period, data in Table (9) indicate clearly that fruits using IR lamb with using 100% water requirement during pre-harvest gave the lowest score of decay followed by fruits using IR lamb with using 85% water requirement during pre-harvest then control treatments in both seasons, maybe increasing infrared radiation delay ripening (Hamanaka et al., 2005(Hamanaka et al., , 2006(Hamanaka et al., , 2010. It is clear from data presented that the decay of fruits were significantly increased with prolongation of the storage period. ...
Two field experiments were carried out at Experimental Station, Central Lab. for Agricultural climate, A.R.C, Dokki, during the two successive winter seasons in (2015/2016 and 2016/2017). This study was performed in four single type plastic houses to investigate the effect of infrared light and different water requirements (70, 85 and 100% of water requirements) and their interaction on climatic factors, vegetative growth, as well as fruit yield and quality of cucumber plants Parcoeda grown under clay soil condition. Obtained results revealed that infrared light increasing both minimum and maximum air temperature in general and especially at night. Infrared light and irrigated with any of used irrigation regimes (70, 85 and 100% of water requirements) enhanced all vegetative growth measurements (plant height, leaves number per plant, fresh and dry weight, whole plant) and increased all assayed chemical constituents of plant leaves i.e. chlorophyll, total nitrogen, phosphorus and potassium. Also it increased the total fruit yield and its components i.e., number of fruits per plant and fruit yield as well as total produced fruit yield. Economically, using infrared lamp with 100% water requirement was increasing the cucumber yield nearly 40%. While, using infrared with 85% water requirement was increasing yield nearly 25% and saving 15% of water irrigation. For the pos-tharvest experiment, which aims to estimate the effect of all pre-harvest treatments on the quality of cucumber fruits during storage at 10˚C and 85-90% relative humidity for 28 days, the results showed that infrared and irrigated with used irrigation regimes 100% of water requirements reduced weight loss% and decay score. Also maintained total soluble solids and color measurement (L*, a* and b* value) compared to other treatments.
... Heat-resistant ascospores of P. niveus survive thermal processing and it grows in products stored across a wide range of temperatures (4-38°C) as a facultative anaerobe, even when there is as little as 0.5% oxygen in the head-space (Splittstoesser, Kuss, Harrison, & Prest, 1971;Taniwaki, Hocking, Pitt, & Fleet, 2009). P. niveus ascospores withstand temperatures > 85°C, irradiation, and high pressure (Evelyn & Silva, 2015;Gumus, Gecgel, Demirci, & Arici, 2008;Hamanaka, Atungulu, Tanaka, & Uchino, 2010;Hatcher et al., 1979;Houbraken, Dijksterhuis, & Samson, 2012;Smelt & Brul, 2014). Little is known about the ecology of this species. ...
... En este caso, la sinergia de los tratamientos físicos contribuyó en la disminución de la intensidad requerida por cada uno de ellos, además el grado de susceptibilidad celular se afectó en función de la secuencia de aplicación, por ejemplo, B. Cinerea fue más lábil cuando el tratamiento térmico estuvo precedido de la dosis lumínica, resultado contrario al de M. Fructigena. En estudios desarrollados por Hamanaka et al. (2010), no fue claro si la secuencia calentamiento con infrarrojo (IR) seguida por UVC presentaron mayor eficiencia que la serie UVC-IR, pues, no se observaron diferencias sobre el grado de inactivación de esporas de los hongos Penicillium sp., Aspergillus sp., Cladosporium sp., Rhizopus sp. Y Byssochlamys sp. ...
In light of the impact that involves the microbial contamination on the surface of fruits and vegetables, researchers and industry have focused their interest in the study and applications of short wave ultraviolet radiation by their deleterious effect against the pathogens, relatively low cost, versatility and zero residual. Recent findings have revealed that non-ionizing radiation, acts as an elicitor that at low doses stimulates the expression of genes involved in photomorphogenic responses which are in charge of triggering the
tissue resilience. Considering aforesaid, this paper summarizes varied and recent studies that analyzed the responses of different fresh and minimally processed products subjected to photochemical treatments (UVC), constrains, benefits and adverse effects.
Keywords: ultraviolet radiation, postharvest, photochemistry, antioxidant activity, agroindustry.
... UV-C exposure of 60 s reduced the survival of tested fungi (Alternaria alternata, Aspergillus carbonarius, A. niger, Cladosporium herbarum, and Penicillium janthinellum) isolated from grapes and raisins by more than 90% in plates inoculated by spreading the inoculum onto the surface of agar (32). Hamanaka et al. (13) reported that Penicillium spp. isolated from citrus fruits were reduced about 3 log by a UV-C treatment of 6 kJ m 22 in vitro. ...
In this study, the effects of UV-C on two of the main wound pathogens of citrus fruits, Penicillium digitatum and Penicillium italicum, were investigated with different inoculation methods in vitro and on oranges. P. digitatum and P. italicum spores were inoculated onto the surface of potato dextrose agar or oranges using spread, spot, wound, and piercing inoculation methods. UV-C treatment for 1 min from a working distance of 8 cm reduced the numbers of P. italicum and P. digitatum by about 3.9 and 5.3 log units, respectively, following spread inoculation under in vitro conditions. Significant reductions were obtained after 1-min UV-C treatments of the tested fungi following inoculation using the spread and spot methods. With inoculation by the wound and piercing methods, the tested spores were not inactivated completely even after 10- and 20-min treatment times, respectively. The application of UV-C (7.92 kJ m(-2)) on oranges reduced the percentage of oranges infected at least threefold compared with the rate of infection in the untreated control samples. UV-C irradiation could effectively inactivate spores of P. italicum and P. digitatum inoculated by the spread plate and spot inoculation methods under in vitro and in vivo conditions. On the other hand, because of the low penetration ability of UV-C light, the tested fungi were not completely inactivated following inoculation with the wound and piercing methods. UV-C treatment has potential for use in surface decontamination of citrus fruits.
It is important to prevent contamination inside the incubator as a method of preventing microbial infections during the embryo culture. In the present study, we examined the effects of ultraviolet-C (UV-C) irradiation, used for microorganism inactivation, on embryo development and the growth of bacteria, including Escherichia coli and Staphylococcus aureus, and the fungus Cladosporium cladosporioides. In the embryo irradiation experiment, we examined the effects of the plastic lid of the culture dish, irradiation distances (10, 20, and 25 cm), and different irradiation wavelengths (228 and 260 nm) during embryo culture for 7 days on the development and quality of porcine in vitro-fertilized embryos. None of the embryos cultured in dishes without plastic lids developed into blastocysts after irradiation with 228 nm UV-C. When porcine embryos were cultured in a culture dish with lids, the 228 nm UV-C irradiation decreased blastocyst formation rates of the embryos but not their quality, irrespective of the UV-C irradiation distance. Moreover, irradiation with 260 nm UV-C, even with plastic lids, had more detrimental effects on embryo development than irradiation with 228 nm UV-C. Investigation of the inactivating effects of UV-C irradiation at 228 nm and 260 nm on the growth of the bacteria and fungus showed that 260 nm UV-C reduced the viability to a greater extent than 228 nm UV-C. Moreover, the disinfection efficacy for the bacteria increased when the irradiation duration increased and the distance decreased. In conclusion, porcine embryos can develop into blastocysts without loss of quality even after continuous long-duration irradiation (7 days) with 228 nm UV-C, which can inactivate the growth of bacteria and the tested fungus; however, the development rate of the embryo is reduced.
Food processing technologies are concerned with ensuring maximum nutrient retention and enhancing shelf life while avoiding microbial degradation. Conventional food processing techniques are slow and prone to quality deterioration. Researchers are working on incorporating new food processing techniques to overcome the mentioned shortcomings of conventional food processing and preservation techniques. One such alternative food processing technique is utilizing infrared (IR) technology. IR heating offers many advantages over conventional heating. Moreover, the integration of IR with conventional drying techniques has shown promising results in terms of energy throughput, uniform heating, reduced heating time, and product quality. Despite the huge potential of infrared (IR) technology, it is not widely used due to a lack of proper knowledge and misconception regarding IR heating. This chapter provides insight into IR technology while mentioning its novel and diverse application in food processing.
Aflatoxin B1 (AFB1) is a highly toxic substance produced mainly by Aspergillus spp., which are known to contaminate a wide variety of foods and feeds. The objective of this study was to understand the growth and AFB1 production rate of Aspergillus flavus NRRL 3357 and investigate the impact of different infrared (IR) heat intensities on the growth and aflatoxin-producing potential of A. flavus. Thirty healthy corn kernels were inoculated with 1 × 10⁶ spores/mL of A. flavus spores and incubated at 25 °C. Then, A. flavus plate count, ergosterol, and AFB1 were measured every 24 h. In another experiment, inoculated corn incubated for 24 h was exposed to different IR heat intensities and heating durations. Afterward, the IR-exposed A. flavus were incubated for additional 3 and 6 days (4 and 7 days of incubation in total), and the ergosterol and AFB1 concentrations were measured. For non-IR exposed A. flavus, the highest AFB1 concentration (32.2 μg/g) was observed after 6 days of incubation. Treatment at high IR heat intensities and heating duration resulted in low AFB1 and ergosterol concentrations. However, IR heat treatment at low intensities (e.g., 1.86 kW/m²) for 20 s resulted in high AFB1 and ergosterol concentrations (97.83 and 34.84 μg/g, respectively). The sublethal IR heat intensity may have increased the potential of the exposed A. flavus NRRL 3357 to grow and produce AFB1. The outcome of this study will contribute to and enhance the continual efforts of mitigating AFB1 contamination of economically important grains.
This study investigated the impacts of selected and broadband infrared (IR) wavelength treatments with tempering step on inactivation of aflatoxigenic molds and the treatments’ effects on head rice yield (HRY). Rough rice was treated with different IR intensities, product‐to‐emitter gaps, and heating durations. Afterward, the samples were tempered at 60°C for 4 h. Selected IR wavelength treatment at intensities of 15.71 and 10.08 kW/m2 for 20 and 30 s resulted in complete aflatoxigenic mold inactivation; broadband IR wavelength treatment with intensity of 10.84 kW/m2 for 30 s resulted in 1.09 log (CFU/g) reduction in aflatoxigenic mold load. Selected IR wavelength treatment (15.71 kW/m2 for 30 s) resulted in 7 percentage points reduction in the mean HRY. Incorporating a tempering step into treatments at IR intensities of 15.71, 10.08, 7.27 and 4.13 kW/m2 resulted in a complete aflatoxigenic mold inactivation. Also, tempering increased the mean HRY of the treated samples.
Background and objectives
Mycotoxigenic fungi pose a severe threat to humans’ health and cause economic losses to crop growers. This study investigated the impact of selected wavelengths of infrared (IR), as a novel technique, followed by a tempering step to inactivate the fungi on shelled corn.
Findings
Ascomycota was found to be the most dominant phylum (95.6 and 93.2%, respectively) on corn treated with only IR and IR followed by a tempering. Among fungal genera, Aspergillus was the primary genus found on corn treated with only IR heat. However, a significant reduction in relative abundance of Aspergillus (22%) was obtained when corn with 16% moisture content (wet basis) was treated with the following set up: IR wavelength of 3.2 µm at product‐to‐emitter gap of 110 mm, and 60 s duration.
Conclusion
The use of selected IR wavelengths is effective in inactivating mycotoxigenic fungi such as Aspergillus flavus. The further significant suppression of the mycotoxigenic fungi is feasible with incorporating a tempering step into the IR heat treatment.
Significance and novelty
The selected IR system is scalable for large scale industrial application, offering promises of reliable and rapid mycotoxigenic fungal inactivation on corn and other cereals.
This study investigated the effects of broadband and selected infrared (IR) wavelength treatments of rough rice on microbial inactivation. Rough rice was treated at different IR wavelengths and product‐to‐emitter distances (110, 275, and 440 mm) followed by tempering at 60°C for 4 hr. The total mold and aerobic plate counts (APC) on non‐treated and treated samples were determined. Significant total mold reductions of 1.14 and 3.11 log CFU/g were obtained after IR heating using broadband and selected wavelengths, respectively (p < .05). The most significant reduction of APC using selected IR wavelength was 1.09 log CFU/g; the broadband IR wavelength had no effect on the mean APC. The IR treatments followed by tempering step resulted in greater reductions of total mold counts and APC (4.03 and 3.50 log CFU/g) in comparison to IR treatments without tempering (3.11 and 1.09 log CFU/g). Overall, bacteria showed more resistance to IR treatments than molds. Infrared (IR) heat treatment was effective in inactivating mold and bacterial contaminants of rough rice. Selected IR wavelengths treatment had a greater significance on mold and bacterial reduction when compared to broadband IR wavelengths treatment. However, adding a tempering step after both broadband and selected IR wavelength treatments resulted in further mold and bacterial inactivation. Infrared heat had more effect on mold than bacteria.
Ultraviolet (UV–C) is one of the alternative non-thermal technologies used for the surface decontamination of many foods. The aim of this study was to evaluate the effects of UV-C treatment on molds isolated from dried persimmons and also to determine the inactivation kinetics of selected UV-C resistant mold cultures. UV-C resistant fungal strains identified by using molecular methods were Rhizopus oryzae, Aspergillus niger and Alternaria tenuissima. UV-C resistant fungal spore suspensions were subjected to UV-C at doses of 0.6–18 kJ/m² under in vitro conditions to characterize the inactivation kinetics. UV-C treatment at 0.6 kJ/m² significantly reduced the numbers of test molds (P < 0.05). Results revealed that R. oryzae was the most sensitive microorganism among the selected strains, whereas higher UV-C doses of 6 and 18 kJ/m² were required to eliminate A. niger and A. tenuissima, respectively. The inactivation kinetics of R. oryzae, A. niger and A. tenuissima were best described by Biphasic + shoulder, Biphasic and Log lineer + tail models, respectively. Predicted values were in close agreement with the experimental values with R² of higher than 0.98 and RMSE lower than 0.12. In the present study, UV-C resistant molds, that can be used as target microorganisms for the establishment of UV-C process schedule for dried persimmons, were selected and identified.
In the past few decades, there has been an increasing awareness of the importance of consuming a diet high in fresh fruits and vegetables, which has led to substantial changes in food habits and consumption of humans. To accommodate this awareness, novel postharvest technologies are needed for extending the shelf-life of fresh produce. High-, hyperbaric, and hypobaric pressure methods have been introduced to reduce microbial growth, preserve nutritional quality, and enhance antioxidant enzyme activity in fresh produce. The high-pressure method is the most practical for use in food industry, to inactivate microorganisms in processed products; however, excessive pressure causes physical cell damage when applied to fresh produce. The hypobaric and hyperbaric methods are two emerging techniques highly capable of prolonging the shelf-life of fresh produce. Both hypobaric and hyperbaric methods prevent cellular damage and reduce respiration rates, ethylene production, and microbial growth. However, the mechanism of quality preservation underlying these methods needs to be explored in future studies.
Significance and impact of the study:
Microbial contamination is one of the most serious problems for foods, fruit and sugar thick juices. UV light is suitable for the nonthermal decontamination of food products by inactivating the contaminating micro-organisms. However, UV-A exposure is insufficient for disinfection. This study demonstrates that the combination of UV-A LED light (350-385 nm), which is not hazardous to human eyes and skin, and ferulic acid (FA), a known phytochemical and food additive, provides synergistic antimicrobial activity against foodborne pathogenic and spoilage micro-organisms. Therefore, FA addition to UV-A light treatment may be useful for improvement of UV-A disinfection technology to prevent food deterioration.
The influence of a combination of ultraviolet (UV) irradiation with infrared radiation heating (IRH) and conductive heating (CH) on the inactivation of bacterial spores (Bacillus subtilis) was investigated at 20, 30, 40, and 50°C on the surface of agar plates. The survival curves of B. subtilis spores were convex downward. Generally, the inactivation efficiency of UV irradiation with IRH was greater than that with CH for B. subtilis spores. A 4.1 log reduction of B. subtilis spores was obtained by 60 sec of UV irradiation with IRH at 50°C. The highest decimal reduction time was obtained at around 30°C of IRH. These variations in the inactivation characteristics of UV irradiation might be caused by differences in the UV and IR absorption characteristics of spores exposed at different temperatures.
Inactivation effects of infrared radiation (IR) heating (1.87 μW/cm 2/nm) and ultraviolet (UV) irradiation (0.455 mW/cm 2) on two mold spores (Penicillium, Cladosporium) were investigated before and after germination on potato dextrose agar. Penicillium was more resistant to IR heating than Cladosporium both before and after germination. Over 90% of Cladosporium was inactivated by 120 sec of IR heating after germination for up to 36 hours. The inactivation ratio of Cladosporium was temporarily increased for periods of 6 to 12 hours after 60 sec of IR heating and decreased to < 10 % by 30 sec of UV irradiation at 18 hours. In contrast, about 75% of Penicillium was inactivated by 30 sec of UV irradiation at 36 hours. These findings indicate that the ability of IR heating and UV irradiation to inactivate germinated molds is affected by mold type and growth stage.
Cumin seeds might be exposed to a high level of natural bacterial contamination, and this could potentially create a public health risk besides leading to problems in exportation. Ultraviolet (UVC) and far infrared (FIR) radiation has low penetration power, and due to that, there might be no detrimental defects to the products during a possible decontamination process. Therefore, the objective of this study was to determine the effect of UVC and FIR treatment on microbial decontamination and quality of cumin seeds. For this purpose, FIR treatment at different exposure times and temperatures were applied followed by constant UVC treatment with an intensity of 10.5 mW/cm2 for 2 h. Total mesophilic aerobic bacteria of the cumin seeds were decreased to the target level of 104 CFU/g after 1.57, 2.8, and 4.8 min FIR treatment at 300, 250, and 200 °C, respectively, following a 2 h UVC treatment. Under the given conditions, a complete elimination for total yeast and molds were obtained while there were no significant changes in volatile oil content and color of the cumin seeds. Consequently, combined UVC and FIR treatment was determined to be a promising method for decontamination of the cumin seeds.
Practical Application: This research attempts to apply UVC and far infrared (FIR) radiation for pasteurization of cumin seeds. The data suggested that combined UVC and FIR radiation treatments can become a promising new method for pasteurization of cumin seeds without causing any detrimental defect to the quality parameters. The results of this industry partnered (Kadioglu Baharat, Mersin, Turkey—http://www.kadioglubaharat.com) study were already applied in industrial scale production lines.
Mango fruit (Mangifera indica L. cv. Zill) were dipped in 5 mM oxalic acid solution for 10 min at 25 °C to investigate effects on ripening and decay incidence during storage at room temperature (25 °C). The results showed that oxalic acid treatment delayed fruit ripening and reduced fruit decay incidence compared to the control. It was suggested that the physiological effect of oxalic acid in decreasing ethylene production was an important contributor to delaying the ripening process. Oxalic acid treatment might be a promising method for postharvest storage of mango fruit.
To examine how UVC affects the different genera of fungi commonly isolated from grapes, with the aim of understanding changes in mycobiota during grape ripening and possible applications for preventing grape decay during storage.
Spores of Aspergillus carbonarius, Aspergillus niger, Cladosporium herbarum, Penicillium janthinellum and Alternaria alternata (between 100-250 spores/plate agar) were UVC irradiated for 0 (control), 10, 20, 30, 60, 300 and 600 s. Plates were incubated at 25 degrees C and colonies were counted daily up to 7 days. Alternaria alternata and Aspergillus carbonarius were the most resistant fungi. Conidial germination in these species was reduced by approx. 25% after 10 s of exposure, compared with greater than 70% reduction for the remaining species tested. Penicillium janthinellum spores were the most susceptible at this wavelength. UVC exposures of 300 s prevented growth of all isolates studied, except for Alternaria alternata.
UVC irradiation plays a major role in selecting for particular fungi that dominate the mycobiota of drying grapes.
The UVC irradiation of harvested grapes could prevent germination of contaminant fungi during storage or further dehydration.
Bacillus subtilis spores pretreated at various water activities (aw, from 0.005 to 0.996) were inactivated by infrared radiation heating (IRH) at 0.5 and 1.0 kW of electric power under dry conditions in an open system. The resistance of B. subtilis spores to IRH was greater in the range of 0.25 to 0.874 aw, and had the maximum value when aw was 0.796 at 0.5 kW and 0.688 at 1.0 kW. Markedly lower IRH resistance of B. subtilis spores was observed at the lower or higher levels of aw.
Single table grape berries (Vitis vinifera L. cv. Italia) were irradiated with ultraviolet-C (UV-C) doses ranging from 0.125 to 4 kJ m−2 and inoculated with Botrytis cinerea. The pathogen was inoculated on artificial wounds at different times (0, 24, 48, 72, 96 and 144 h) after irradiation and the berries were stored either at 21 or 3°C. To check the influence of UV-C irradiation on the wound-healing processes, trials using berries wounded just before the UV-C irradiation and inoculated at different times were also performed. Significantly lower numbers of infected berries and lesion diameter were found in berries treated with UV-C doses ranging from 0.125 to 0.5 kJ m−2. There was also a significantly lower level of disease in berries inoculated after 24–48 h than in those inoculated just after (10–15 min) the UV-C treatment. Thus, pretreatment with low UV-C doses followed by artificial inoculation with B. cinerea reduces postharvest grey mould of table grapes, suggesting induced resistance to the disease, both in berries wounded before and after irradiation. The microbial epiphytic population on UV-C-treated berries was also monitored. Results showed a significantly higher increase in the population of yeasts (including yeast-like fungi) and bacteria on berries irradiated with 0.25 and 0.5 kJ m−2 than on unirradiated control berries.
We investigated the effect of pre-storage exposure to shortwave ultra-violet (UV-C) light on the decay and quality of fresh strawberries. Fresh strawberries (cv. Kent, 25% to 50% red) were exposed to UV-C at doses of 0.25 and 1.0 kJ/m2 and stored at 4 °C or 13 °C. UV treatment controlled the decay caused by Botrytis cinerea at both temperatures and extended the shelf-life of the fruits by 4 to 5 d. UV-treated fruits had a lower respiration rate, higher titratable acidity and anthocyanin content, and were firmer than the untreated fruits. The percentage of free sugars increased faster in UV-treated fruits at the beginning of the storage period. A lower electrical conductivity in fruits treated with 0.25 kJ/m2 suggests a slower rate of senescence compared to the control. A higher electrical conductivity observed with 1.0 kJ/m2suggests damage to the fruits. Overall, UV treatment at 0.25 kJ/m2 appears to slow down the ripening and senescence of strawberry fruits stored at 4 °C.
Fludioxonil is a newly registered and classified as reduced-risk fungicide by the US EPA for citrus fruit postharvest treatments. The efficacy of fludioxonil for the control of diplodia stem-end rot caused by Lasiodiplodia theobromae and green mold (Penicillium digitatum) on Florida citrus fruit was evaluated. The ED50 values of fludioxonil against L. theobromae and P. digitatum in potato dextrose agar were 0.012 and 0.020 mg/L, respectively. Application of fludioxonil at 250–1200 mg/L on oranges using a simulated commercial drench system before fruit ethylene degreening reduced diploda stem-end rot incidence by 75.7–88.6%, and fludioxonil at 500–1200 mg/L performed similarly to the commercial postharvest fungicide imazalil or thiabendazole (TBZ) at 1000 mg/L. Fludioxonil was compatible with chlorine in drench suspension as measured by the efficacy of fludioxonil for diplodia stem-end rot control. Fludioxonil also effectively reduced both diplodia stem-end rot and green mold when applied through a simulated commercial packingline system. Fludioxonil was more effective for diplodia stem-end rot control on non-ethylene-treated oranges than on ethylene-treated fruit. Fludioxonil was also effective for the control of TBZ-resistant P. digitatum isolates on oranges. An active suppression of P. digitatum sporulation by fludioxonil on citrus fruit was observed. However, fludioxonil showed a much less activity for P. digitatum sporulation control compared to postharvest fungicide imazalil. The registration of fludioxonil has provided a new alternative, reduced-risk compound for citrus postharvest disease control and fungicide resistance management in Florida.
The effect of UV-C (lambda = 254 nm) and heat treatment was investigated on the inactivation of conidia of Botrytis cinerea and Monilinia fructigena, two major postharvest spoilage fungi of strawberries and cherries, respectively. Both fungi were grown at 21 degrees C in the dark and conidia were isolated after 1 week by washing the mycelium with a mild detergent solution. After filtration and resuspension in phosphate buffer to a titer of 10(5) to 10(6) cfu/ml, the conidia were subjected to different treatments. The applied UV-C doses varied from 0.01 to 1.50 J/cm2, and the conditions for the thermal treatment were 3, 5, 10, 15 and 20 min at temperatures ranging from 35 to 48 degrees C. Both techniques were applied individually and in combination. Spore inactivation increased with increasing intensity of single treatments. No surviving spores of B. cinerea were observed after 15 min at 45 degrees C or an UV-C treatment of 1.00 J/cm2. M. fructigena was more sensitive and a thermal treatment of 3 min at 45 degrees C or an UV-C treatment of 0.50 J/cm2 resulted in complete spore inactivation. Combination of both techniques reduced the required intensity of the treatment for inactivation of both fungi. The order of the applications had a significant effect on the degree of inactivation. The inactivation of B. cinerea conidia was greater when the heat treatment came first, and for M. fructigena, most inactivation was achieved when the heat treatment was preceded with an UV-C irradiation.
The multiple histidine-aspartate phosphorelay system plays a crucial role in cellular adaptation to environments in microorganisms and plants. Like kinase-phosphatase systems in higher eukaryotes, the multiple steps provide additional regulatory checkpoints with phosphatases. The Escherichia coli phosphatase SixA exhibits protein phosphatase activity against the histidine-containing phosphotransfer (HPt) domain located in the C-terminus of the histidine kinase ArcB engaged in anaerobic responses. We have determined the crystal structures of the free and tungstate-bound forms of SixA at 2.06 A and 1.90 A resolution, respectively. The results provide the first three-dimensional view of a bacterial protein histidine phosphatase, revealing a compact alpha/beta architecture related to a family of phosphatases containing the arginine-histidine-glycine (RHG) motif at their active sites. Compared with these RHG phosphatases, SixA lacks an extra alpha-helical subdomain as a lid over the active site, thereby forming a relatively shallow groove important for the accommodation of the HPt domain of ArcB. The tungstate ion, which mimics the substrate phosphate group, is located at the centre of the active site where the active residue, His8, points to the tungsten atom in the mode of in-line nucleophilic attack.
Fresh fruits are prone to fungal contamination in the field, during harvest, transport, marketing, and with the consumer. It is important to identify fungal contaminants in fresh fruits because some moulds can grow and produce mycotoxins on these commodities while certain yeasts and moulds can cause infections or allergies. In this study, 251 fresh fruit samples including several varieties of grapes, strawberries, blueberries, raspberries, blackberries, and various citrus fruits were surface-disinfected, incubated at room temperature for up to 14 days without supplemental media, and subsequently examined for mould and yeast growth. The level of contamination (percent of contaminated items/sample) varied depending on the type of fruit. All raspberry and blackberry samples were contaminated at levels ranging from 33% to 100%, whereas 95% of the blueberry samples supported mould growth at levels between 10% and 100% of the tested berries, and 97% of strawberry samples showed fungal growth on 33-100% of tested berries. The most common moulds isolated from these commodities were Botrytis cinerea, Rhizopus (in strawberries), Alternaria, Penicillium, Cladosporium and Fusarium followed by yeasts, Trichoderma and Aureobasidium. Thirty-five percent of the grape samples tested were contaminated and supported fungal growth; the levels of contamination ranged from 9% to 80%. The most common fungi spoiling grapes were Alternaria, B. cinerea and Cladosporium. Eighty-three percent of the citrus fruit samples showed fungal growth at levels ranging from 25% to 100% of tested fruits. The most common fungi in citrus fruits were Alternaria, Cladosporium, Penicillium, Fusarium and yeasts. Less common were Trichoderma, Geotrichum and Rhizopus.
Bacterial spores (Bacillus subtilis subsp. subtilis NBRC 16183) inoculated onto a stainless steel Petri dish and treated at nine levels of water activity (a(w)) for 2 days were inactivated by infrared radiation heating (IRH) using three kinds of infrared heaters with different radiation spectra. The peak wavelengths used were 950, 1,100 and 1,150 nm. In general, the inactivating efficacy of IRH treatment against bacterial spores with shorter wavelength heater (950 nm) was greater than that with other heaters. The decimal reduction times (D value) calculated using the linear portion of survival curves were affected by both the initial a(w) values and the spectra of the infrared rays. Spores at approximately 0.9, 0.7 and 0.6 a(w) were most resistant to IRH at wavelengths of 950, 1,100 and 1,150 nm, respectively. The a(w) values that led to maximum D values for bacterial spores increased as the wavelength was shortened. Optimum a(w) values were identified for the inactivation of bacterial spores by IRH. Spore resistance to IRH could also be affected by the spectral characteristics of the infrared absorption, which varied with the a(w) of bacterial spores.
The effect of the natural volatile hexanal was studied as an antifungal agent on the major postharvest fungal pathogens Botrytis cinerea, Monilinia fructicola, Sclerotinia sclerotiorum, Alternaria alternata, and Colletotrichum gloeosporioides. The antifungal effect of hexanal vapor was dependent on concentration and treatment duration, but sensitivity of the pathogens varied. All spores of B. cinerea and M. fructicola were killed after exposure to 900 microL/L for 12 h at 20 degrees C, and almost all were killed after a 24-h exposure to 450 microL/L. Only moderate numbers of spores were killed at a concentration of 200 microL/L. Mycelial growth of S. sclerotiorum on agar was completely inhibited after a 12-h exposure to 900 microL/L, but only slight inhibition occurred at 450 microL/L and none at 200 microL/L. Mycelium of A. alternata and C. gloeosporioides appeared more sensitive, with strong inhibition occurring after a 12-h exposure at 450 microL/L. Similar trends in spore viability and mycelial growth were observed at 7 degrees C. The antifungal effect of hexanal vapor was further tested on raspberry fruit naturally infected with B. cinerea and on peach fruit inoculated with spores of M. fructicola. Decay was markedly reduced in raspberry and almost completely controlled in peach after exposure to 900 microL/L hexanal vapor for 24 h. The potential of hexanal for postharvest decay control is discussed.
This study was performed to evaluate the inactivation efficiency or synergy of combined ozone and UV processes (combined ozone/UV process) or sequential processes (ozone-UV, UV-ozone) compared with individual unit processes and to investigate the specific roles of ozone, UV and the hydroxyl radical, which is formed as an intermediate in the combined ozone/UV process. The Bacillus subtilis spore, which has often been used as a surrogate microorganism for Cryptosporidium parvum oocysts, was used as a target microorganism. Compared to individual unit processes with ozone or UV, the inactivation of B. subtilis spores by the combined ozone/UV process was enhanced under identical conditions. To investigate the specific roles of ozone and UV in the combined ozone/UV process, sequential ozone-UV and UV-ozone processes were tested for degrees of inactivation. Additionally, the experiment was performed in the presence and absence of tert-butyl alcohol, which acted as a hydroxyl radical scavenger to assess the role of inactivation by the hydroxyl radical in the combined ozone/UV process. Among the five candidate processes, the greatest synergistic effect was observed in the combined ozone/UV process. From the comparison of five candidate processes, the hydroxyl radical and ozone were each determined to significantly enhance the overall inactivation efficiency in the combined ozone/UV process.
To evaluate the efficacy of ultraviolet (UV) light (254 nm) combined with hydrogen peroxide (H(2)O(2)) to inactivate bacteria on and within fresh produce.
The produce was steep inoculated in bacterial cell suspension followed by vacuum infiltration. The inoculated samples were sprayed with H(2)O(2) under constant UV illumination. The log count reduction (LCR) of Salmonella on and within lettuce was dependent on the H(2)O(2) concentration, temperature and treatment time with UV intensity being less significant. By using the optimized parameters (1.5% H(2)O(2) at 50 degrees C, UV dose of 37.8 mJ cm(-2)), the surface Salmonella were reduced by 4.12 +/- 0.45 and internal counts by 2.84 +/- 0.34 log CFU, which was significantly higher compared with H(2)O(2) or UV alone. Higher LCR of Escherichia coli O157:H7, Pectobacterium carotovora, Pseudomonas fluorescens and Salmonella were achieved on leafy vegetables compared with produce, such as cauliflower. In all cases, the surface LCR were significantly higher compared with the samples treated with 200 ppm hypochlorite. UV-H(2)O(2)-treated lettuce did not develop brown discolouration during storage but growth of residual survivors occurred with samples held at 25 degrees C.
UV-H(2)O(2) reduce the bacterial populations on and within fresh produce without affecting the shelf-life stability.
UV-H(2)O(2) represent an alternative to hypochlorite washes to decontaminate fresh produce.