Ozone as a management alternative against phosphine-resistant insect pests of stored products

This study was carried out to assess ozone toxicity to 16 populations of Tribolium castaneum (Herbst), 11 populations of Rhyzopertha dominica (F.) and nine populations of Oryzaephilus surinamensis (L.) collected from six regions of Brazil. These populations were also used to test if there is cross-resistance to ozone and phosphine. The relationship between susceptibility to ozone and respiration rate, and associated fitness costs were also evaluated. The instantaneous population growth rate (r_i), CO₂ production and mean insect body mass of each population were measured. Ozone toxicity was determined using time-response bioassays at the dosage rate of 150 ppm ozone in a continuous flow of 2 L min⁻¹. All of the populations were susceptible to ozone and there was no cross-resistance to ozone and phosphine. The populations of each species differed in respiration rate and body mass, but there was no significant association between respiration rate or body mass and susceptibility to ozone, as was also the case for the instantaneous rate of population increase (r_i). As none of the populations showed resistance to ozone, regardless of their susceptibility to phosphine, ozone is a potential alternative for phosphine resistance management in the insect species evaluated in this study.     

A study on the feasibility of quantifying the population density of stored product insects in air-tight grain storage using CO2 concentration measurements

This study was aimed at estimating the number of insects per 1 kg of paddy (IPK) in an air-tight mock-up silo by CO₂ concentration monitoring. The first experiment was to determine the respiration rates of adult Sitophilus zeamais, Rhyzopertha dominica, and Tribolium castaneum. CO₂ concentrations were recorded from groups of 50, 100 and 200 insects with and without 125 g of brown rice. The respiration rate was calculated from the slope of the CO₂ concentration curve. A sample size of at least 100 insects was recommended. In 100-insect group, with the presence of food the respiration rates of S. zeamais, R. dominica, and T. castaneum were 9.57–14.13, 1.96–3.93 and 4.59–11.76 μl_CO2/insect−h, respectively. In the second experiment, S. zeamais populations at actual IPK = 2, 0.5, 0.25, 0.125 and 0.0625 in a 1.618 m³ silo filled with paddy were quantitatively determined. Similarly, R. dominica and T. castaneum populations at actual IPK = 0.5, 0.25, 0.125 and 0.0625 in 0.064 m³ silos were estimated in the third experiment. In each trial, small containers filled with a known number of adult insects along with brown rice were buried in the silo. Additionally, a control silo containing only disinfested paddy was set up in parallel. The insect population density was calculated from the difference in the slopes of the CO₂ curves between the infested and control silos divided by the respiration rate of one insect. On average, for each species and each infestation level the estimated population density was not greater than twice of the actual ones. Although several assumptions (e.g., silos being completely sealed, only one species and one life stage of infesting insects) had to be made, monitoring CO₂ concentrations could potentially be an effective tool for determining insect population density during grain storage.     

Modelling respiration rate of soybean seeds (Glycine max (L.)) in hermetic storage

The dynamic of oxygen (O₂) and carbon dioxide (CO₂) concentration was characterized in soybean (Glycine max (L.)) samples hermetically stored in glass jars at 15, 25 and 35 °C and 13, 15 and 17% moisture content (m.c., wet base). Two correlations were used for smoothing gas concentration in time: linear and exponential. Then, the respiration rate at each temperature and m.c. combination was calculated as storage time progressed and oxygen was consumed and two predictive models for respiration were proposed: Model I (temperature and m.c. dependent) and Model II (temperature, m.c. and oxygen dependent). It was observed that respiration rate increased with storage m.c. and temperature. However, respiration rate was not mainly affected by O₂ until a critical concentration limit of about 2% was reached. Respiration rates were from 0.341 to 22.684 mg O₂/(kgDM d) and from 0.130 to 20.272 mg CO₂/(kgDM d) for a range of storage condition of 13–17% m.c. and 15–35 °C temperature. The respiration rate of soybean seeds obtained in this study resulted significantly lower than the rates reported in the literature for other grains at similar temperature and a_w (water activity) storage condition. For hermetic storage simulations in which O₂ concentration is not expected to drop below 2%, the simplest model (Model I) could be used, but if the O₂ concentration of the hermetic system is expected to be depleted, Model I would under estimate the time at which O₂ is consumed, and thus a model with O₂ dependency is recommended instead (Model II).     

Modeling the effect of storage temperature on the respiration rate and texture of fresh cut pineapple

The effect of temperature on the respiration rate and texture of fresh cut pineapple was studied over the course of 10 days of storage. The thermal exchange between the pineapple trays and the cooling environment was simulated using the finite element method and tested at 6 °C. The temperatures on pineapple wedges differed between the cold point and points near the surface, indicating that the respiration rate may be affected in pineapple subjected to temperature abuse. The experimental respiration rates obtained were used to develop a model relating respiration to O₂ and CO₂ concentrations at different temperatures using the closed system method. The O₂ consumption and CO₂ production of pineapple wedges was accurately modeled using Michaelis–Menten kinetics. The texture degradation of pineapple wedges follows a zero-order kinetic reaction at different temperatures and the thermal dependence of the model’s parameters for both respiration rate and texture degradation was described by Arrhenius-type equations.     

Modeling of Respiration Rate of Litchi Fruit under Aerobic Conditions

Respiration of the produce and permeation of gas through the packaging films are the processes involved in creating a modified atmosphere inside a package that will extend shelf life of agricultural perishables. Thus modeling respiration rate of the selected produce is crucial to the design of a successful modified atmosphere packaging system. Two different models based on regression analysis and enzyme kinetics were developed with the help of respiration data generated at temperatures 0, 5, 10, 15, 20, 25, and 30 °C for litchi fruit using the closed system method. Temperature was found to influence the model parameters. In the model, based on enzyme kinetics, the dependence of respiration rate on O₂ and CO₂ was found to follow the uncompetitive inhibition. The enzyme kinetic model parameters, calculated from the respiration rate at different O₂ and CO₂ concentration were used to fit the Arrhenius equation against different storage temperature. The regression coefficients values were used for the prediction of respiration rate using regression model. The activation energy and respiration pre-exponential factor were used to predict the model parameters of enzyme kinetics at any storage temperature. The developed models were tested for its validity at 2 °C. The models showed good agreement with the experimentally estimated respiration rate.     

Toxicological and physiological effects of allyl isothiocyanate upon Callosobruchus maculatus

This study aimed at evaluating the toxicity of allyl isothiocyanate (AITC) to adults of Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae) and its effects upon oviposition rate, population development, respiration rate, and dry mass loss in cowpea beans. The toxicity of AITC was determined by applying lethal concentrations (LC) of the compound, whereas the mortality curves were drawn by utilizing increasing concentrations of AITC (from 5.0 to 13.33 mL m⁻³ of grains). Population development was assessed through oviposition, progeny and both daily and accumulated emergence at sublethal concentrations (LC₁ = 3.81 mL m⁻³, LC ₁₀ = 5.71 mL m⁻³, LC ₃₀ = 7.67 mL m⁻³, and LC ₅₀ = 9.41 mL m⁻³). Furthermore, the loss of dry mass in grains and the respiration rate of adults when exposed to AITC (LC₁, LC₁₀, LC₃₀, and LC₅₀) were withal appraised. The values of LC ₅₀ and LC ₉₅ to adults of C. maculatus were of 9.41 and 17.85 mL m⁻³ of grains, respectively. At sublethal concentrations of AITC, the respiration oviposition, and emergence rates declined. The fumigant agent also prevented mass loss in cowpea beans. On account of that, it is safe to say that the compound has significant potential for controlling C. maculatus, inhibiting its development in storage conditions.     

Measurement and Modeling of Respiration Rate of Guava (CV. Baruipur) for Modified Atmosphere Packaging

Several experiments were conducted at different storage temperatures for generating respiration data using close system method for respiration. A respiration rate model, based on enzyme kinetics and the Arrhenius equation was proposed for predicting the respiration rates of Guava as a function of O₂ and CO₂ concentrations and storage temperature. Temperature was found to influence the model parameters. In this model, the dependence of respiration rate on O₂ and CO₂ was found to follow the uncompetitive inhibition. The enzyme kinetic model parameters, calculated from the respiration rate at different O₂ and CO₂ concentration were used to fit the Arrhenius equation against different storage temperature. The activation energy and respiration pre-exponential factor were used to predict the model parameters of enzyme kinetics at any storage temperature between 0–30°C. The developed models were tested for its validity at 12°C and it was found to be in good agreement (the mean relative deviation moduli between the predicted and experimental respiration rates were found to be 8.95% and 8.02% for O₂ consumption and CO₂ evolution, respectively) with the experimentally estimated respiration rates.     

Modelling the respiration rate of minimally processed broccoli (Brassica rapa var. sylvestris) for modified atmosphere package design

In this work, the effect of temperature, oxygen and carbon dioxide on the respiration rate of minimally processed broccoli was studied to develop suitable modified atmosphere packaging. Respiration rate was measured at 3, 5, 7, 10, 15 and 20 °C under different gas compositions of O₂ and CO₂ (1%, 5%, 10%, 15% and 21% of O₂ with the balance N₂, a mixture of 10% and 20% of carbon dioxide with the balance air and a mixture at 3% of O₂ and 15% of CO₂ with the balance N₂). As expected, temperature was the most influential factor on respiration rate, for all atmospheres tested: increasing the temperature from 3 to 20 °C resulted, for air‐stored samples, in a 84% change in oxygen respiration rate, whereas at constant temperature, the respiration rate decreased by 35% with lowering the O₂ concentration from 21% to 1% and by 44% with increasing the CO₂ concentration from 0% to 20%. The Michaelis and Menten competitive model with maximum respiration rate varying against temperature with an Arrhenius equation accurately described the influence of gas composition and temperature on the respiration rate of minimally processed broccoli, and it was used to design a suitable package.     

Effects of heat treatment on atmospheric composition and color of peeled white asparagus in modified atmosphere packaging

Freshly harvested spears of white asparagus were subjected or not to heat treatment by immersion in a hot water bath at 55 °C for 3 min, then left unpeeled or were peeled before wrapping in 16 µm stretch film and stored at 3 °C for 6 days. During storage, the atmosphere within the packages was sampled for O₂, CO₂ and C₂H₄ determination, while spear fresh weight, color and anthocyanin content at the 3 cm apical peel segments were determined before and after storage. The results showed that CO₂ concentration in packages of white asparagus spears was not greatly influenced by peeling or heat treatment. On the other hand, a higher package O₂ depletion of treated (peeled or heated) spears was observed. Peeling also resulted in an increase of ethylene peak concentration, indicating wound-induced ethylene production, which was suppressed by heat treatment. The initial color of the whole spear was retained, while the appearance of a violet coloration on the spear tip was prevented by heat treatment in both unpeeled and peeled spears.Industrial relevancePeeled white asparagus has drawn the attention of industry as a novel lightly processed product. The combination of heat treatment with modified atmosphere packaging (MAP) could be used to improve the storage life of this product. Moreover, both peeling and heat treatment cause changes in ethylene production and respiration rate of asparagus spears and this information could be useful for development of novel application to MAP design for lightly processed (peeled) white asparagus.     

Oxidative enzymes and functional quality of minimally processed grape berries sanitised with ozonated water

Thompson Seedless (TS) and Black (BS) grapes sanitised with 2, 4, 6, 8 mg L^?1 O₃ or NaOCl (100 mg L^?1) were stored 21 days at 5 °C. Ozonated water stimulated the respiration rate, especially after 5 days of storage, and increased superoxide dismutase and catalase activity compared to NaOCl‐sanitised grapes. Total polyphenol content (TPC) was 23–50% higher in TS and 18.5–28% higher in BS samples sanitised with ozonated water. Twofold higher total antioxidant capacity (TAC) was registered in TS at all of the evaluated O₃ doses while the doses of 6 and 8 mg L^?1 increased TAC by 19–30% in BS. The use of ozonated water as a sanitising method, especially at 6 and 8 mg L^?1 doses, improved the functional quality and maintained low microbial counts on fresh‐cut grapes being a good alternative for the industry.     

Respiration Rate of a Dry Coleslaw Mix Affected by Storage Temperature and Respiratory Gas Concentrations

The respiration rate of dry coleslaw mix at different concentrations of O₂ and CO₂ was determined in an open flow-through respirometer at 5°C. Product O₂ consumption rate fitted an enzyme kinetics model. V_m and K_m values of 22.72 mlkg^-1h^-1 and 1.083 %O₂, respectively were calculated. CO₂ had an inhibitory effect on respiration rate. The effect of CO₂ on respiration gave a good fit with an uncompetitive inhibition enzyme kinetics model (E = 5.11%). Product respiration rate increased with temperature by an Arrhenius type relationship. Activation energies for O₂ consumption and CO₂ evolution were 74.8 kJ/kg and 84.2 kJ/kg respectively. These results provide information essential for the design and optimization of modified atmosphere packs for this product.     

Allyl isothiocyanate actions on populations of Sitophilus zeamais resistant to phosphine: Toxicity,emergence inhibition and repellency

The risks associated with the use of synthetic insecticides have caused increased interest in the research of essential oils and their main constituents for use in the pest management of stored products. Allyl isothiocyanate (AITC) is the main component of mustard essential oil and has been reported as a potential replacement pesticide for conventional insecticides that control stored product insect pests. Here, we assessed the toxicity (including emergence inhibition) and repellent actions of AITC on Brazilian populations of the maize weevil Sitophilus zeamais (Coleoptera: Curculionidae) resistant to conventional insecticides (e.g., phosphine). We also evaluated physiological (e.g., respiration) and behavioral (e.g., walking and flight) traits of AITC-exposed insects. The AITC showed consistent insecticidal activity against the populations resistant to phosphine and other synthetic insecticides, with LC₅₀ values ranging from 1.5 to 2.9 μL L⁻¹. Significant inhibition of the offspring emergence was achieved after the exposure of parental adults to sublethal levels (i.e., LC₁ and LC₅) of AITC. Reductions in respiration rates were also registered in all the populations sublethally exposed to AITC. In all five populations, a high number of insects avoided AITC-treated (1.5 μL L⁻¹) grain masses, and although individuals of a phosphine-susceptible (i.e., Abre Campo) population increased walking and reduced flight activities, individuals of another phosphine-susceptible (i.e., Tunápolis) population exhibited higher flight activity under AITC exposure. Thus, our findings suggest that AITC is a potential tool that may be integrated into the control strategies of maize weevils where resistance to phosphine and other conventional insecticides is a problem.     

Modelling the effect of gas composition on the gas exchange rate in Perforation-Mediated Modified Atmosphere Packaging

Modified Atmosphere Packaging (MAP) relies on modification of the atmosphere inside a package, achieved by the natural interplay between the respiration of the product and the transfer of gases through the package. Polymeric films are the most usual packaging material but because of the increase in the consumption of fresh-cut products with a higher respiration rate and higher tolerance to CO₂, alternative materials are being investigated. The perforation-mediated package is one of those alternatives, where the regulation of the gas exchange is achieved by single or multiple tubes that perforate an otherwise impermeable packaging material. From an engineering point of view, the transport of gases through perforations is a complex phenomenon that involves diffusion gradients together with co-current transport of multiple species, with oxygen entering the package and carbon dioxide leaving it. The influence of one species transport in the other has not been studied so far. The objective of this work was to analyse the effect of initial concentration of CO₂ on the effective mass transfer coefficients of O₂ (K_O2) and CO₂ (K_CO2) in perforation-mediated MAP. K_O2 ranged from (6.99 ± 0.05) × 10⁻⁸ (m³ s⁻¹) to (28.50 ± 0.01) × 10⁻⁸ (m³ s⁻¹) and for K_CO2 from (6.45 ± 0.04) × 10⁻⁸ (m³ s⁻¹) to (28.32 ± 0.01) × 10⁻⁸ (m³ s⁻¹). On average K_O2 decreased by approximately 15% with an increase of CO₂ initial concentration from 25% to 100%. K_CO2 was insensitive to the composition of the gas mix. The permeability ratio (β) varied from 0.73 ± 0.01 to 1.34 ± 0.01. A mathematical model considering the co-current effect of CO₂ flux on the gas exchange rate for O₂ was developed. These results suggest that there is a significant drag effect in the gas exchange process that should be taken into consideration when designing perforation-mediated MAP.     

Effect of osmotic dehydration and vacuum impregnation on respiration rate of cut strawberries

Respiration rate in terms of O₂ consumption and CO₂ production was determined in strawberry halves, both fresh-cut and vacuum impregnated with an isotonic solution. The experimental measurements were also carried out in osmodehydrated samples for different concentration levels (to 30 °Brix) at atmospheric pressure and by applying a vacuum pulse. Changes throughout time of O₂ and CO₂ concentration in the headspace of chambers containing the samples were analysed to determine respiration rates. The effect of temperature on respiration rate in fresh-cut and impregnated samples showed sigmoid behaviour where a sharp increase in respiration levels occurred between 5 and 10 °C. Osmodehydration treatments resulted in a great decrease in O₂ consumption but no notable changes in CO₂ generation, which suggests that anaerobic biochemical pathway became dominant respiration mode due to the treatments. Production of ethanol and acetaldehyde was detected in these cases in agreement with the anaerobic process.     

Influence of γ-irradiation on the reactive-oxygen metabolism of blueberry fruit during cold storage

To explore a safe, environmentally friendly, and efficient preservation technology for blueberry (Semen trigonellae), “Bluecrop” blueberry fruits were treated with different irradiation doses. During cold storage at 0 ± 5 °C, the decay rate, fruit firmness, and indices relating to respiration and reactive-oxygen metabolism were detected regularly. Results showed that irradiation treatment with 1.0 kGy to 2.5 kGy doses was able to inhibit the respiration intensity, ethylene production, and the improvement of lipoxygenase (LOX) activity, thus reducing the increase of malondialdehyde (MDA) content and the permeability of cell membranes. In addition, irradiation treatment can improve the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) to eliminate, on a continual basis, the constantly generated superoxide anions (O₂⁻) and hydrogen peroxide (H₂O₂), keeping them at a low level: ultimately, this effectively guaranteed the storage quality and postponed the senescence process in the blueberry fruits. Meanwhile, those irradiated at 2.5 kGy presented optimal preservation effects as the respiration was inhibited to the utmost extent and the anti-oxidisation effect was enhanced. The results prove that the ⁶⁰Co γ-irradiation treatment at proper doses is an effective method of storing post-harvest blueberry fruits at low temperatures.     

Efficacy and cytotoxic potential of deltamethrin,essential oils of Cymbopogon citratus and Cinnamonum camphora and their synergistic combinations against stored product pest,Trogoderma granarium (Everts)

Residual film method was followed to analyze the toxicity of deltamethrin, essential oils (EOs) of Cymbopogon citratus and Cinnamonum camphora in separate and form of various combinations against LHR1 and LHR2 populations of fifth instar larvae of Trogoderma granarium. The cytotoxic potential of LC_50s of both EOs, deltamethrin and their various combinations was as well investigated. The LHR2 population showed 23.73 fold deltamethrin resistance with respect to LHR1 population. Both EOs had high insecticidal activity than deltamethrin but C. citratus EO was less toxic than C. camphora EO against both populations. Based on strength of synergism and dose reduction index, the order of insecticidal activity of combinations in LHR1 population was: C. citratus EO: deltamethrin < C. camphora EO: deltamethrin < C. citratus EO: C. camphora EO < C. citratus EO: C. camphora EO: deltamethrin. In LHR2 population the order was: C. citratus EO: C. camphora EO < C. citratus EO: deltamethrin < C. camphora EO: deltamethrin < C. citratus EO: C. camphora EO: deltamethrin. Following to exposure of LC₅₀ of each treatment various markers of cytotoxicity viz., haemocyte viability, cell proliferation rate and mitochondrial dehydrogenase activity were decreased significantly with respect to control in both populations. Except for deltamethrin, each treatment significantly increased the lactate dehydrogenase activity. Phenoloxidase activity was reduced significantly in LHR1 population following to exposure of each treatment. Likewise, LHR2 population also showed significantly reduced activity of phenoloxidase following to exposure of each treatment except deltamethrin as it increased the activity. Furthermore, each marker of cytotoxicity was fluctuated in relation to the toxicity of LC₅₀ of treatments and combination contained both EOs and deltamethrin produced highest cytotoxicity. Findings of this study should be used in granaries for the effective control of insecticide resistance in T. granarium¹.     

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.     

Phosphine resistance in Brazilian populations of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Phosphine resistance was assessed in adults of 22 Brazilian populations of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). The concentration-mortality bioassays for the detection of phosphine resistance followed the FAO standard method. Twenty populations of S. zeamais were resistant to phosphine and the resistance ratios at the LC₅₀ ranged from 1.1- to 86.6-fold. This is the first report of phosphine resistance in populations of S. zeamais in Brazil, where previous surveys did not detect resistance in this species. There was significant variation in respiration rate (CO₂ production) among the populations (P < 0.05). Respiration rate was significantly inversely correlated with phosphine resistance for this species (P < 0.05). The populations with lower respiration rates showed higher levels of phosphine resistance, suggesting that the lower respiration rate is associated with the physiological basis of phosphine resistance due to reduced fumigant uptake.     

Achillea millefolium L. s.l. herb extract: Antioxidant activity and effect on the rat heart mitochondrial functions

An extract of Achillea millefolium herb (YE) was investigated for antioxidant activity using chemical and biological assays. Qualitative and quantitative analysis of some major phenolics was carried out by HPLC. An on-line HPLC-DPPH assay showed that YE possesses significant antiradical activity which is due to the presence of active components amongst phenolic compounds. Furthermore, direct effects of YE and a mixture of its identified phenolic compounds (MPC) on isolated rat heart mitochondrial function were investigated. We found that YE in concentration-dependent manner induce a decrease in State 3 respiration rate without any changes in the integrity of inner mitochondrial membrane. Thus, pyruvate oxidation was affected only by the highest used YE concentrations; meanwhile succinate oxidation was reduced even at lower YE concentrations. MPC had no effect on mitochondrial State 3 respiration rate. Fluorimetric measurements demonstrated that YE at concentrations that had no effect on the State 3 respiration rate significantly decreased H₂O₂ production in mitochondria.