Postharvest Pest Control Research Articles

Effects of sulfur dioxide fumigation on mortality of confused flour beetle (Coleoptera: Tenebrionidae) and rice weevil (Coleoptera: Curculionidae).

Sulfur dioxide (SO2) fumigation was studied in laboratory to determine its potential as an alternative treatment for postharvest control of stored product insects, confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), and rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae). Three-hour fumigations with 0.1%-2.0% SO2 were conducted against eggs, immature stages, and adults of the 2 insects at 20 °C. Effective control of both insects was achieved. However, there were considerable variations between the 2 insects and among different life stages. Confused flour beetle was more susceptible to SO2 fumigation than rice weevil. Complete control of adults and all life stages of confused flour beetle was achieved in 3-h fumigations with 0.5% and 2.0% SO2, respectively. For rice weevil, 3-h fumigation with 1.5% SO2 resulted in 96.5% adult mortality and the fumigation with 2.0% SO2 resulted in 99.27% mortality of adults and 87.5% mortality of immature stages. Three-hour fumigations with 1% SO2 resulted in <5% egg survival to adults. The study demonstrated high efficacy of SO2 fumigation against the insects and suggested that SO2 fumigation has good potential for postharvest pest control on stored products.

Evaluation of fumigant toxicity of cyclohexanone to 5 species of insect pests.

Cyclohexanone is a major precursor for nylon production and is also used as a pesticide solvent. In this study, cyclohexanone was evaluated as a fumigant against rice weevil adults, confused flour beetle adults, western flower thrips larvae and adults, spotted wing drosophila adults, and subterranean termite workers. Cyclohexanone fumigation was effective against all 5 insects, and there were considerable variations in susceptibility to cyclohexanone fumigation among the 5 species. At 20 °C, complete control of spotted wing drosophila adults was achieved in 1-h fumigation with 25 μl/l of cyclohexanone and complete control of eastern subterranean termite workers was achieved in 3-h fumigations with 50 μl/l dose of cyclohexanone. Stored-product insects confused flour beetle, and rice weevil adults were more tolerant to cyclohexanone fumigation. Fumigations of 24 h with 75 μl/l dose of cyclohexanone caused 100% mortality of rice weevil adults and 98% mortality of confused flower beetle adults. Even at a 100 μl/l dose, the 24-h fumigations did not achieve 100% mortality of confused flour beetle adults. At 5 °C, complete control of western flower thrips was achieved in 3- and 6-h fumigations with 100 and 50 μl/l doses of cyclohexanone, respectively. Cyclohexanone vapor concentrations were measured using cyclohexanone detector tubes. Vapor concentrations were far below the expected saturation concentration indicating that most cyclohexanone did not exist as vapor in fumigation chambers. The results of effective control of all 5 insect species suggest that cyclohexanone has the potential to be used as a fumigant for postharvest pest control.

Effectiveness of bagasse and rice straw ashes against postharvest pest, Sitophilus zeamais on maize seed

Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) is the main pest on maize seed in the storage. In general, postharvest pest control uses synthetic insecticides. However, the use of these synthetic insecticides causes insect resistance and negative impact on human health. This study aimed to determine the effectiveness of rice straw and bagasse ashes as inert dust in postharvest pest management of S. zeamais. This study was conducted at the Laboratory of Entomology, Faculty of Agriculture, Universitas Hasanuddin. This study used two treatments with four different doses i.e., 2, 4, 6, 8 g, and untreated (control). The results showed that complete (100%) of adult mortality at highest dose (8 g/kg seed) of bagasse ash in three days after infestation, while in the higher doses (6 and 8 g/kg seed) of rice straw ash killed 99.15%. The use of inert dust also causes typical symptoms in mortality in the form of wings coming out of the elytra, which is different from adult mortality without treatment.

Insight into the molecular mechanism of phosphine toxicity provided by functional analysis of cytochrome b5 fatty acid desaturase and dihydrolipoamide dehydrogenase in the red flour beetle, Tribolium castaneum

Phosphine is the dominant chemical used in postharvest pest control. Widespread and highly frequent use of phosphine has been selected for pest insects, including Tribolium castaneum, which is highly resistant. Lipid peroxidation and reactive oxygen species (ROS) are two major factors determining phosphine toxicity; however, the mechanisms of production of these two factors in phosphine toxicity are still unknown. Here, we first determined the time course of phosphine-induced lipid peroxidation and ROS production in T. castaneum. Our results showed that lipid peroxidation occurs before ROS in the process of phosphine toxicity, and fumigated beetles with higher resistance levels were associated with weaker activity on lipid peroxidation and ROS. A significant decline in lipid peroxidation was observed in fumigated individuals after knockdown of cytochrome b5 fatty acid desaturase (Cyt-b5-r) via RNA interference (RNAi), indicating that Cyt-b5-r is critical for triggering phosphine-induced lipid peroxidation. Moreover, significant decreases in both ROS and mortality were detected in fumigated T. castaneum adults fed melatonin for 7 days, an inhibitor of lipid peroxidation. Cyt-b5-r RNAi also inhibited ROS production and mortality in phosphine-treated beetles. Meanwhile, a significant decrease in ROS production (68.4%) was detected in dihydrolipoamide dehydrogenase (DLD) knockdown individuals with phenotypes susceptible to phosphine, suggesting that lipid peroxidation initiates ROS with the expression of DLD. However, a significant increase in ROS (122.1%) was detected in the DLD knockdown beetles with strongly resistant phenotypes, indicating that the DLD-involved pathway may not be the only mechanism of ROS generation in phosphine toxicity and the existence of a moonlighting role in downregulating ROS in strongly resistant T. castaneum.

A potential role of nitric oxide in postharvest pest control: A review

Novel methods of stored-product pest control are essential to greater success against a wide variety of pest species worldwide, especially in tropical regions. Modern methods such as ozonation and organic pesticides have ensured grain preservation without loss of quality and without the accumulation of residues; these properties are considered fundamental to food safety. Thereby, nitric oxide (NO) is a newly discovered fumigant that has shown the potential to control stored product pests. It has also been described as a substitute for phosphine and sulfuryl fluoride. In this regard, NO has the potential to become an alternative method of postharvest pest control, primarily due to its high pest mortality rate from a broader range of pests and products. However, research is needed to reduce the impact of NO on food quality due to the high reactive power of NO. Potentially toxic residues, such as the primary forms of NO oxidation, NO2− and NO3−, can accumulate in treated products and damage consumers' health. Further research is needed into the possible use of NO fumigation as an alternative practice in controlling stored grain pests.

Essential Oil-Based Nano-Biopesticides: Formulation and Bioactivity against the Confused Flour Beetle Tribolium confusum

Post-harvest pest control can rely on few approved pesticides and tools; hence, there is a rising interest in new sustainable, eco-friendly approaches. In this study, eight commercial essential oils (EOs) (anise Pimpinella anisum, artemisia Artemisia vulgaris, fennel Foenicum vulgare, garlic Allium sativum, lavender Lavandula angustifolia, mint Mentha piperita, rosemary Rosmarinus officinalis, and sage Salvia officinalis) were selected for their bioactivity and commercial availability, and then formulated in nano-emulsions. Repellency and acute toxicity of the developed nano-formulations were tested against a key stored product pest, Tribolium confusum (Coleoptera: Tenebrionidae). All the developed nano-emulsions presented optimal physical characteristics (droplet dimension = 95.01–144.30 nm; PDI = 0.146–0.248). All the formulations were repellent over time tested against adult beetles, in area preference bioassays. The best repellent was the anise EO-based formulation (RC50 = 0.033 mg). Mortality values from cold aerosol trials showed that the majority of tested EOs caused immediate acute toxicity, and garlic EO nano-emulsion caused the highest mortality of T. confusum adults (LC50 = 0.486 mg/L of air). EO-based nano-insecticides, used as cold aerosol and gel, are promising control methods against stored product pests, which can be integrated and combined with other sustainable biorational approaches.

Anisole is an environmentally friendly fumigant for postharvest pest control

Plant essential oils have demonstrated insecticidal effects but not many are as effective as currently used fumigants. We evaluated anisole, a volatile compound extracted from aniseed, for control of four insect pests including adult rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae), and confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), and a fresh produce product pest, western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in the laboratory tests. Anisole fumigations were effective against all four pests. At a dose of 100 μL/L, anisole fumigation completely controlled S. granarius and S. oryzae in 24 and 16 h, respectively. At a dose of 150 μL/L, complete control of the two weevils was achieved in 16 and 8 h, respectively. T. confusum was completely controlled in 16 and 8 h with anisole fumigations at 400 μL/L and 600 μL/L respectively. F. occidentalis was 100% controlled in 8 and 6 h treatments with anisole at doses of 150 μL/L and 300 μL/L, respectively. The median lethal times (LT50) of anisole fumigation at 50 μL/L were 0.6 and 0.5 h for S. granarius and S. oryzae, respectively. LT50 for T. confusum at 600 μL/L was 2.9 h. In a 16 h confirmatory test in a mini silo, anisole fumigation achieved 100% control of rice weevil at different depth of stored corn. This study demonstrated that anisole fumigation was effective against insects. Therefore, anisole fumigation has potential as an environmentally friendly, alternative fumigant for postharvest pest control.

Effects of Nitric Oxide Fumigation on Mortality of Light Brown Apple Moth, &amp;lt;i&amp;gt;Epiphyas postvittana&amp;lt;/i&amp;gt; (Lepidoptera: Tortricidae)*

Light brown apple moth, Epiphyas postvittana, is a quarantine pest in most countries and has established in California and, therefore, has potential to affect export of fresh products from infested areas. There is currently lack of effective treatment especially against eggs. Nitric oxide is a recently discovered fumigant for postharvest pest control and is evaluated in laboratory fumigations to determine its efficacy against different life stages of this pest. Small scale fumigations with nitric oxide at 1.0%, 2.0%, 3.0%, and 5.0% concentrations were conducted under ultralow oxygen conditions at 2?C against larvae, pupae, and eggs of light brown apple moth. Treatment times ranged from 4 to 24 h depending on nitric oxide concentration and life stage. Complete control of larvae and pupae was achieved in 8 h fumigation with 2.0% NO. Eggs were successfully controlled in 6, 12, and 24 h fumigations with 5.0%, 3.0%, and 2.0% NO respectively. The study demonstrated that nitric oxide fumigation was effective against all life stages of light brown apple moth and, therefore, has potential to be an alternative treatment to methyl bromide fumigation for postharvest control of light brown apple moth.

Use of essential oil for post-harvest pest control

Abstract Since past few decades, application of essential oils (EOs) was explored experimentally for the management of postharvest pests and diseases. However, uses of essential oils face a series of problems, including regulatory obstruction to commercialization (such as cost of toxicological and environmental assessments) or the way that efficiency of essential oils toward pests and diseases is not as evident or clear as that seen with the present available forms. This review highlights several issues extending from EOs chemistry to their bioactivity potential. The mechanism of action of EOs is also discussed to provide better understanding about their functions and improve the scope for the establishment of commercial opportunities in the form of natural biocontrol agents/botanical pesticides.

Comparison of efficacy of nitric oxide fumigation under nitrogen and carbon dioxide atmospheres in controlling granary weevil (Sitophilus granaries) and confused flour beetle (Tribolium confusum)

Nitric oxide (NO) was a recently discovered fumigant for postharvest pest control. Because NO reacts with oxygen (O2) spontaneously to form nitrogen dioxide (NO2), NO fumigation must be conducted under ultralow oxygen (ULO) atmospheres to preserve NO and nitrogen (N2) has been used to establish ULO atmospheres in NO fumigation studies in the past. However, carbon dioxide (CO2) can also be used to ULO atmospheres and CO2 fumigation was also reported to be effective in controlling certain insect pests and enhancing toxicity of some fumigants. In the present study, NO fumigations under ULO conditions established with N2 and CO2 were compared for effects against granary weevil, Sitophilus granaries, and confused flour beetle, Tribolium confusum. All life stages of the two insects were subjected to 12 h fumigation treatments with 0.5–1.0% NO at 25 °C under ULO established with CO2 (NO–CO2 treatments) and N2 (NO–N2 treatments). The most tolerant life stage for each species in each fumigation treatment was then fumigated with NO for 24 h fumigation at 25 °C to determine an effective treatment. There were no significant differences in mortalities of adults, larvae, and pupae at all NO concentrations between ULO conditions established with CO2 and N2 for either insect. NO–CO2 was, however, significantly less effective than NO–N2 against eggs of both species. Granary weevil pupae and confused flour beetle eggs were the most tolerant stages for each respective species to NO fumigation: >99% mortality of granary weevil pupae and confused flour beetle eggs were, however, achieved in the 24 h fumigation with 2% and 1% NO, respectively. This study showed that CO2 can be used to establish ULO atmospheres for NO fumigation, but did not significantly contribute to insect mortality.

Effectiveness of Nitrogen Dioxide Fumigation for Microbial Control on Stored Almonds

Quality of stored almonds is compromised by insect infestations and microbial contamination. Nitric oxide (NO) is a potent fumigant for postharvest pest control on fresh and stored products. NO fumigation must be conducted under ultralow oxygen conditions, and it always produces nitrogen dioxide (NO2), depending on the O2 level in the fumigation chamber. NO and NO2 have proven antimicrobial effects but have not been tested for efficacy against microbes in almonds. We evaluated, in this study, fumigation of unpasteurized almonds with NO2 at different levels for inhibition of bacteria and fungi. Almonds were fumigated with 0.1, 0.3, or 1.0% NO under ambient O2 to generate 0.1, 0.3, or 1.0% NO2 conditions; the fumigation treatments lasted 1 or 3 days at 25°C. GreenLight rapid enumeration tests on diluted wash-off almond samples from NO2 fumigation treatments showed either greatly reduced microbial loads or complete control of microorganisms, depending on NO2 concentration and treatment duration. NO2 fumigation was more effective against fungi than against bacteria. These results suggest that postharvest NO fumigation with proper levels of NO and NO2 can be used for insect and microorganism control on stored almonds.

Oil Characterization and Aflatoxin Profile of Peanut Kernel Subjected to Gamma Irradiation

Peanuts are nutritious foods, however, following harvest and storage, these nuts are prone to mycotoxin contamination. Gamma irradiation is an effective technique in postharvest pest control to kill insects and inhibit mycotoxin biosynthesis. Thus, this study aimed to investigate the effect of doses of gamma ray on oil properties and mycotoxin profile of raw peanut seeds. Seeds were exposure to gamma radiation at 10 and 25 kGy and stored at ambient temperature for 6 months compared to non-treated seeds before storage. Color, hardness, oil content, total sugar, total protein content, peroxide value (PV), malonaldehyde (MDA) and aflatoxin analysis were assessed. According to this finding, no significant differences of color, hardness, oil content, PV, MDA were found among treatments. Aflatoxin inhibition and total sugars of treated gamma irradiation peanuts at 10 kGy were higher than treated peanuts at 25 kGy.

Nitrogen Dioxide Fumigation for Microbial Control on Unshelled Peanuts

Stored peanuts often need treatments to control microbial infections as well as insects to maintain postharvest quality. Nitric oxide (NO) is a recently discovered fumigant for postharvest pest control. NO fumigation must be conducted under ultralow oxygen condition to preserve NO and always contains NO2 due to NO reaction with oxygen and NO2 has antimicrobial property. Therefore, NO fumigation has potential to control both pests and pathogens. In this study, we evaluated antimicrobial effects of NO2 fumigation on unpasteurized unshelled peanuts. Peanuts were fumigated with 0.3%, 1.0%, and 3.0% NO2 for three days at 25˚C by injecting NO gas into glass jars to react with O2 in the atmosphere. After fumigation, wash-off microbial samples were collected from intact peanut samples and, then, cracked open peanut samples with non-selective tryptic soy broth medium. The wash-off samples were then diluted with both the non-selective medium and a fungal-selective potato dextrose broth medium and were tested on GreenLight™ rapid enumeration test based on oxygen depletion on culture medium. All three NO2 fumigation treatments showed significant antibacterial and antifungal effects on intact peanuts as well as on cracked peanuts with complete inhibition with 3.0% NO2. Fumigation did not have obvious effects on appearance of skinned peanut kernels. These results suggested that NO2 fumigation has potential to control microbes on stored products, and NO fumigation with the combination of NO and NO2 has potential to control both insects and microbes on stored products.

Residue analysis of nitric oxide fumigation in nine stored grain and nut products

Nitric oxide (NO) is a recently discovered fumigant for postharvest pest control on fresh and stored products. Nitric oxide fumigation also does not leave residues on fresh fruit and vegetables when conducted properly. In this study, we analyzed nitrate (NO3−) and nitrite (NO2−) levels in liquid extracts and nitrogen dioxide (NO2) desorption rates as residues of NO fumigation at various times after fumigation on nine stored grain and nut products. Each product was fumigated separately with 3.0% NO for 24 h in two treatments: one treatment (NO–N2) was terminated with nitrogen gas (N2) flush and the other (NO-Air) was terminated with normal air flush. For NO–N2, NO3− concentrations of all fumigated products were not significantly higher than those of untreated controls at 1, 7, and 14 d after fumigation. NO2− concentrations of all fumigated products from N2 gas flush were not significantly higher than those of control products at 14 d after fumigation. NO2 desorption rates for most products from NO–N2 treatment showed no significant difference from those for the controls 1 d after NO fumigation, except for beans and wheat, which showed no significant difference at ≥7 d after fumigation. All products from NO-Air treatment, however, had significant higher NO3− and NO2− ion concentrations in liquid extracts at 14 d after fumigation than those from NO–N2 treatment and the control. NO2 desorption rates in all products from NO-Air treatment were also significantly higher than those from NO–N2 treatment and the control at 21 d after fumigation. Therefore, when terminated properly with N2 flush, NO fumigation did not result in significant increases of NO3−, NO2−, or NO2 as residue in nut and grain products.

Response of Aspergillus flavus spores to nitric oxide fumigations in atmospheres with different oxygen concentrations

Nitric oxide (NO) is a newly discovered fumigant for postharvest pest control. NO fumigation must be conducted under ultralow oxygen conditions because NO reacts with O2 to produce nitrogen dioxide (NO2). In this study, NO fumigations under different O2 concentrations were conducted on Aspergillus flavus spores to determine effectiveness of NO and NO2 in inactivating spores. Spores on gridded cellulose filter discs in Petri dishes were subjected to six fumigation treatments including a control with varying levels of NO under different O2 conditions for 3 h at 15 °C. The discs with spores were then cultured on Aspergillus Differentiation medium plates after fumigation for four days at 25 °C to count A. flavus colonies. Untreated control discs each had over 50 A. flavus colonies. Three fumigation treatments with 0.1% NO2 or 1.0% NO caused complete inactivation of A. flavus spores. The study demonstrated that NO fumigation with certain levels of NO2 can effectively inactivate A. flavus spores. The results suggest that NO fumigation has potential to be an alternative treatment to control both pests and microbes on stored products.

Nitric oxide fumigation for postharvest pest control on lettuce.

The lettuce aphid, Nasonovia ribisnigri, and western flower thrips, Frankliniella occidentalis, are quarantine pests of lettuce in Asian markets and, therefore, require treatments on lettuce exported from USA to Japan and Taiwan, respectively. Nitric oxide (NO) is a newly discovered fumigant for postharvest pest control and has been demonstrated as safe to fresh fruit and vegetables. In this study, small-scale NO fumigations were conducted to determine effective treatments and large-scale confirmatory tests were conducted to determine the efficacy against N. ribisnigri and F. occidentalis on commercially packed lettuce. The safety of NO fumigation to postharvest quality of lettuce was also evaluated. In small-scale experiments, complete control of N. ribisnigri was achieved in 3, 8, and 16 h fumigations with 2.0%, 1.0%, and 0.5% NO, respectively, at 2°C on both iceberg and romaine lettuce. In a large-scale experiment, complete control of both N. ribisnigri and F. occidentalis was achieved in a 16 h fumigation with 0.5% NO at 2°C. The fumigation treatment had no effect on either external or internal postharvest quality of lettuce at 14 days after treatment. Nitric oxide fumigation was demonstrated to be effective against both N. ribisnigri and F. occidentalis and safe to lettuce quality in large-scale fumigations of commercially packed lettuce. The study suggests that NO fumigation has the potential to be an alternative treatment to methyl bromide for postharvest pest control on harvested lettuce. © 2018 Society of Chemical Industry.

Procedures of Laboratory Fumigation for Pest Control with Nitric Oxide Gas

Nitric oxide (NO) is a newly discovered fumigant for postharvest pest control. This paper provides detailed protocols for conducting NO fumigation on fresh products and procedures for residue analysis and product quality evaluation. An airtight fumigation chamber containing fresh fruit and vegetables is first flushed with nitrogen (N2) to establish an ultralow oxygen (ULO) environment followed by injection of NO. The fumigation chamber is then kept at a low temperature of 2 - 5 °C for a specified time period necessary to kill a target pest to complete a fumigation treatment. At the end of a fumigation treatment, the fumigation chamber is flushed with N2 to dilute NO prior to opening the chamber to ambient air to prevent the reaction between NO and O2, which produces NO2 and may damage delicate fresh products. At different times after NO fumigation, NO2 in headspace and nitrate and nitrite in liquid samples were measured as residues. Product quality was evaluated after 2 weeks of post-treatment cold storage to determine effects of NO fumigation on product quality. Keeping O2 from reacting with NO is critical to NO fumigation and is an important part of the protocols. Measuring NO levels is challenging and a practical solution is provided. Possible protocol modifications are also suggested for measuring NO levels in the fumigation chambers as well as residues. NO fumigation has the potential to be a practical alternative to methyl bromide fumigation for postharvest pest control on fresh and stored products. This publication is intended to assist other researchers in conducting NO fumigation research for postharvest pest control and accelerating the development of NO fumigation for practical applications.

Procedures of Laboratory Fumigation for Pest Control with Nitric Oxide Gas

Nitric oxide (NO) is a newly discovered fumigant for postharvest pest control. This paper provides detailed protocols for conducting NO fumigation on fresh products and procedures for residue analysis and product quality evaluation. An airtight fumigation chamber containing fresh fruit and vegetables is first flushed with nitrogen (N2) to establish an ultralow oxygen (ULO) environment followed by injection of NO. The fumigation chamber is then kept at a low temperature of 2 - 5 °C for a specified time period necessary to kill a target pest to complete a fumigation treatment. At the end of a fumigation treatment, the fumigation chamber is flushed with N2 to dilute NO prior to opening the chamber to ambient air to prevent the reaction between NO and O2, which produces NO2 and may damage delicate fresh products. At different times after NO fumigation, NO2 in headspace and nitrate and nitrite in liquid samples were measured as residues. Product quality was evaluated after 2 weeks of post-treatment cold storage to determine effects of NO fumigation on product quality. Keeping O2 from reacting with NO is critical to NO fumigation and is an important part of the protocols. Measuring NO levels is challenging and a practical solution is provided. Possible protocol modifications are also suggested for measuring NO levels in the fumigation chambers as well as residues. NO fumigation has the potential to be a practical alternative to methyl bromide fumigation for postharvest pest control on fresh and stored products. This publication is intended to assist other researchers in conducting NO fumigation research for postharvest pest control and accelerating the development of NO fumigation for practical applications.

Critical success factors and organizational performance: A study on citrus industry

Quality management of citrus fruits is the top priority as the demand for the fruits is increasing tremendously. In order to investigate the effect of critical success factors (CSF,s) or predictors on the performance measurement factors of citrus industry, an exploratory type of study was conducted with 100 valid responses collected from citrus stake holders. Specially prepared questionnaire consisted of 102 items clubbed in to ten groups for performance improvement Input factors and 24 items clubbed in to four groups for performance measures. The questionnaire is prepared in consultation with experts of industry and 1-5 Likert scale is being used for data collection. The data obtained is tested for normality, validity and reliability then, ANOVA and multiple regression analysis is performed. The ANOVA test revealed that the perceptions associated with the findings were in conformity with the hypothesis. Quality improvement frame work or model is derived from the current study. The study revealed that business environment and resources leads to Economic, Quality, Non-financial and Innovation/ technology performance of the citrus industry. Post harvest process control and post harvest pest and disease control measures improved economic performance and technology and innovation performance. Critical factors like marketing and distribution contributed to non-financial performance. It is further seen that socio economic aspects lead to innovation and technology performance.

Computer simulation analyses to improve radio frequency (RF) heating uniformity in dried fruits for insect control

Abstract In recent years, radio frequency (RF) heating has been explored as a new postharvest pest and pathogen control procedure for agricultural commodities and dry food ingredients. Non-uniform heating and, sometimes runaway heating, have been the major challenges with implementation of this technology. In this study, an experimentally validated computer simulation model was developed to predict the effects of different package geometries, electrode configurations, and use of forced air (60 °C) on improving the heating uniformity of raisins treated with RF for insect control. Higher temperatures (60–76 °C) were observed in the areas between the edges and corners on the top and bottom layers of the RF treated raisins held in rectangular and cylinder shaped containers, with lower temperatures (40–52 °C) observed in the central areas of each layer. The heating uniformity was improved by rounding the corners of the containers and reducing sharp edges on the packages, modifying electrode configurations, and applying forced air after RF heating. These modifications reduced the maximum temperature difference throughout a container of heated raisins to about 5 °C. Approximately 356 min were needed to raise the raisin temperature in a rectangular container from 23 °C to 55–60 °C using only forced air at 60 °C. In contrast, only 6 min of RF heating followed by 10 min of forced air treatment at 60 °C was needed for a similar filled container to reach a temperature of 55–60 °C. Shortening the electrodes length to 4 cm shorter than the horizontal dimensions of the rectangular containers also improved heating uniformity. This technique can be easily implemented to improve the uniformity of RF heating in the food industry for the control of insects in packaged dried fruits. Industrial relevance The results in this study provide essential information about the non-uniform heating inside the RF heated materials packed in containers with sharp areas, edges and corners, such as rectangular and cylindrical shaped containers. Rounding the edges and corners in the containers or bending the top and bottom electrodes is key parameters to control the electrical field inside the RF system. This technique can be easily implemented to improve the uniformity of RF heating in the food industry for the control of insects in packaged dried fruits.