Calorimetric evaluation of responses of Sitophilus oryzae and Tribolium confusum to elevated temperatures and controlled atmospheres

Metabolic heat rates, determined by microcalorimetry, were used to measure the effect of controlled atmospheres (CAs) and elevated temperatures on the stored-product insects Sitophilus oryzae (rice weevil) and Tribolium confusum (confused flour beetle). Results for larval and adult stages in air, and in a range of low O₂ and/or high CO₂ CAs, at temperatures from 15 to 45 °C, showed the general effectiveness of such atmospheres in lowering the lethal temperatures relative to those in air. Effects on adult S. oryzae at 25 °C were explored in more detail in experiments using the following conditions: exposure to anoxic CAs for extended times; exposure to hypoxic CAs; and simulated hermetic storage. A simple scanning calorimetric method was developed for determining lethal temperatures and a combined thermo-gravimetric and differential thermal-analysis method was used to interpret the thermal events, due to loss of water, occurring at and above these temperatures.     

Effect of relative humidity on the susceptibility of Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) to two modified atmospheres

It is known that modified atmospheres (MA) created in a storage environment, involving high carbon dioxide (CO₂) levels (hypercarbia) or low oxygen (O₂) levels (anoxia) are detrimental to bruchid pests of grain legumes. The possibility of enhancing MA action by increasing or decreasing the relative humidity (r.h.) conditions in storage at 25±2°C was investigated against Callosobruchus maculatus (F.), a major bruchid pest of stored cowpea seeds. Mortality of eggs and adults of the bruchid in 70% CO₂ in air and 1.0% O₂ in nitrogen (N₂) was higher at 10±3% and 34±2% than at 70±2% and 90±3% r.h. Mortality of larvae and pupae of the bruchid in the atmospheres was not affected by the r.h. in storage. Development period was longer for adults emerging from bruchid eggs exposed for 12 h to these atmospheres at the lower r.h. Freshly emerged adult bruchids from treated eggs also laid fewer eggs after 12 h of exposure to these atmospheres at the lower r.h.     

Suitability of Plastic Films for Modified Atmosphere Packaging of Fruits and Vegetables

Suitability of plastic films in standard configurations to maintain modified atmospheres was evaluated for common fruits and vegetables. Most films did not result in optimal O₂ and CO₂ atmospheres, especially when produce had high respiration. Produce with low and medium respiration could be matched with films considering O₂ permeability requirements alone. MA packaging systems designed to produce optimal oxygen at suitable temperatures could have complications from transient temperature increases during storage and/or transportation. Respiration rates of fruits and vegetables increase more with temperature than do gas permeabilities of films. Higher than optimum temperatures could cause anoxia and seriously damage produce. More permeable gas pathways and temperature compensation to equalize Q₁₀ values are needed for MA packaging systems to timction effectively.     

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.     

Optimum controlled atmospheres minimise respiration rate and quality losses while increase phenolic compounds of baby carrots

Baby carrot is a very perishable product mainly due to the abrasion of the cylindrical carrot root segments. The influence of four different controlled atmospheres (CA) (air, 2 kPa O₂ + 15 kPa CO₂, 5 kPa O₂ + 5 kPa CO₂ and 10 kPa O₂ + 10 kPa CO₂) was studied to maintain quality and prolong the shelf life of baby carrots. Respiration rate (RR), the content of vitamin C, carotenoids and phenolics by HPLC as well as the sensory quality of baby carrots during storage at 4 °C were evaluated. The lowest RR was observed in baby carrots stored under CA containing the lowest O₂ concentrations. Baby carrots under low O₂ atmospheres preserved the highest vitamin C content, as well as the individual carotenoids. The wound-induced phenolic compounds, mainly trans chlorogenic acid, increased two fold in baby carrots stored under 5 kPa O₂ + 5 kPa CO₂. In general, CA maintained the overall visual quality of baby carrots up to 8 days. Controlled atmosphere of 5 kPa O₂ + 5 kPa CO₂ can be recommended as an optimum atmosphere to maintain quality of baby carrots, increasing bioactive compounds such as chlorogenic acid and avoiding anaerobic fermentation in case of temperature abuse.     

Browning characteristics of fresh-cut ‘Tsugaru’ apples as affected by pre-slicing storage atmospheres

The change in browning characteristics of the slices processed from ‘Tsugaru’ apples stored at 0 °C for 5 months under controlled atmosphere (CA, 1 kPa O₂ + 1 kPa CO₂, 3 kPa O₂ + 3 kPa CO₂) or air has been investigated for 5 days at 20 °C. Respiration and ethylene production of the slices from apples stored in CA were retarded. Electrolyte leakage and browning index were lower in the slices from apples stored under CA than air. Vitamin C and phenolic contents in the slices from apples stored under air were maintained at higher level compared to the slices from apples stored under CA. Polyphenol oxidase activity in the slices was not affected by pre-slicing storage atmospheres. Therefore, the atmospheres of pre-slicing storage affected browning development in fresh-cut products of ‘Tsugaru’ apples and browning was found to be correlated with the levels of electrolyte leakage and phenolic compounds.     

EFFECT OF SOME GAS MIXTURES ON STORAGE QUALITY OF PLUMS1

Plums were stored in controlled atmospheres (CA) with five gas mixtures of the following O₂:CO₂ percentages; 1:1, 1:4, 4:4, 2:2 and 4:1, for 37 days at 2.5–3C. Fruit treated with CA displayed very low decay incidence at the end of the storage period plus 2 days ripening at 22C in air, in comparison with a very high decay incidence (88%) for control fruits. CA-treated fruit ripened normally, but slowly, after 2 days in ambient conditions. There were no clear differences among CA treatments in the quality attributes of total soluble solids, acidity, firmness or color. Treatment with 1% O₂ nd 4% CO₂, however, resulted in slightly firmer fruit, with higher acidity than the untreated checks.     

Weight loss and mortality of three life stages of Tribolium castaneum (Herbst) when exposed to four modified atmospheres

Larvae, pupae, and adults of Tribolium castaneum (Herbst) were exposed to atmospheres containing high nitrogen (N₂) or carbon dioxide (CO₂) concentrations at about 50% r.h. and 27°C for periods up to 72 hr. Overall, 99% N₂ caused greater mortality in adults than did 58% CO₂ while 58% CO₂ was more effective against pupae. The difference in mortality to larvae exposed to the two atmospheres was not significant, though 99% N₂ produced greater mortalities by 48 hr. Also, the differences in mortality for larvae and pupae exposed to atmospheres of 58% CO₂ and 97% CO₂ were not significant though 97% CO₂ caused a significantly greater mortality in adults than did 58% CO₂. Both mortality and weight loss of all life stages tested were small when the insects were exposed to an atmosphere of 97% N₂, but weight loss was generally small and mortality was large for those insects exposed to 97% CO₂.When overall weight loss was compared for those insects exposed to 58% CO₂ and 99% N₂, larval weight loss was greater for those exposed to the CO₂ atmosphere; pupal weight loss was not significantly different between the two atmospheres; adult weight loss was greater for those exposed to the N₂ atmosphere.     

Respiration of Rhyzopertha dominica (F.) at reduced oxygen concentrations

Developmental stages of Rhyzopertha dominica were exposed to atmospheres containing 1%, 2%, 3%, 5%, 10% or 15% oxygen (O₂) in nitrogen at 30°C and 70% r.h. Respiration rates were determined with a gas chromatograph. The O₂ intake and carbon dioxide (CO₂) output by insects were expressed in μl/insect h or μl/mg h. Respiration of eggs, young and old larvae, pupae, and adults at normal atmospheric air were at rates of 0.0029, 0.41, 2.52, 0.82, and 2.86 μl CO₂/insect h, respectively. Respiration rates of the same stages in terms of insect weight were 0.14, 4.83, 1.98, 0.64 and, 2.58 μl CO₂/mg h, respectively. At reduced O₂ levels respiration rates of eggs, larvae and pupae were proportional to the O₂ levels. Adult respiration rates were high at 3% and 5% O₂ levels almost reaching that of normal atmospheric air, and were 2.56 and 2.85 μl CO₂/insect h, respectively. In adults, respiration quotient values for the same O₂ levels were higher than at normal atmospheric O₂ and were 1.5 and 1.02, respectively.Respiration of adults in normal air between 20°C and 35°C increased with temperature and gas values varied between 0.89 and 6.82 μl CO₂/insect h, respectively, or 0.93 and 5.63 μl O₂/insect h, respectively.     

Comparative susceptibility of Corcyra cephalonica (Lepidoptera: Pyralidae) eggs to carbon dioxide and nitrogen at different temperatures

The aim of this study was to evaluate the susceptibility of the egg stage of the rice moth Corcyra cephalonica to modified atmospheres (MAs) enriched with CO₂ or N₂ at 25, 30 and 35 °C combined with various exposure times. The tested modified atmospheres containing CO₂ were 20% CO₂, 16% O₂ and 64% N₂; 40% CO₂, 12% O₂ and 48% N_2; 60% CO₂, 8% O₂ and 32% N₂ and 80% CO₂, 4% O₂ and 16% N₂. The tested modified atmospheres containing N₂ were 97% N₂ and 3% O₂ and 98% N₂ and 2% O₂. The results showed that the hatchability responding to modified atmospheres enriched with either CO₂ or N₂ decreased significantly with an increase in exposure time, gas content (%) and temperature. All tested combinations provided complete (100%) egg control in less than 4 days. Based on 100% mortality, shorter exposures were obtained with 80% CO₂ than with N₂ at most tested temperatures. The modified atmospheres enriched with 98% N₂ were more effective than 97% N₂ against C. cephalonica eggs, especially at 35 °C. It is recommended to use high levels of CO₂ in air (80%) and N₂ (98%) in controlling 0–24-h-eggs of C. cephalonica within 24–36 h for CO₂ and 18–72 h for N₂.     

Changes in Sensory Quality of Sterile Cantaloupe Dice Stored in Controlled Atmospheres

Diced cantaloupe flesh that was microbiologically sterile was prepared to study the physiological deterioration of fruit when stored under a range of controlled atmospheres at 4.5°C. Sterile fruit pieces were prepared by boiling whole melons for 3 min, then dicing aseptically. Storage atmospheres were in continuous flow and contained from 0 to 26% CO₂ and 3.5 to 17% O₂. Sensory assessments were carried out by a highly trained panel at 14 day intervals. Acceptable product up to 28 days was obtained for three treatments: 6% CO₂ and 6% O₂, 9.5% CO₂ and 3.5% O₂, and 15% CO₂ and 6% O₂. Overall treatment with 0, 19.5 or 26% CO₂ (irrespective of O₂ concentration) caused significant deterioration in sensory characteristics.     

Respiration by unprocessed pine logs creates a severe hypoxic and hypercapnic atmosphere in enclosed spaces

Wood products, particularly whole, unprocessed logs, are a significant risk pathway for forest insect pests. Freshly harvested logs continue to respire, creating a high carbon dioxide (CO₂), and low oxygen (O₂) atmosphere in enclosed spaces. Such modified atmospheres may reduce the effectiveness of insect control treatments applied during the transit of logs, making it important to accurately quantify how the atmosphere is modified. We used gas chromatography to measure the amount of CO₂ and O₂ respired by radiata pine (Pinus radiata D.Don) logs under three temperatures (10, 15 and 20 °C) in airtight containers for 14 days to simulate real world conditions in a ship’s hold. We repeated the experiment across all seasons (i.e. spring, summer, autumn and winter). The atmosphere in the containers became severely hypoxic/hypercapnic (low O₂/high CO₂) by day five, and our study confirmed that temperature, time and season were significant factors influencing log respiration. Our results suggest that the atmosphere in a ship’s hold during the export of unprocessed wood products changes rapidly to hypoxic/hypercapnic conditions that are then maintained for weeks. This highlights a potential challenge for the effectiveness of insect control treatments during transit of logs, particularly treatments that require respiratory uptake of a toxin by insects.     

Quality and biochemical changes of longan (Dimocarpus longan Lour cv. Daw) fruit under different controlled atmosphere conditions

Sulphur dioxide has been used to control pericarp browning in longan fruit. However, due to health and regulatory concerns, alternative treatments should be tested. The objective of this study was to find the tolerance levels of longan fruit to low O₂ (2%, 5%, 10% and 15%) and elevated CO₂ (5%, 10%, 15% and 20%) at 2 °C. According to the tolerance study, controlled atmospheres (CA) of 5% O₂ + 5% CO₂, 5% O₂ + 10% CO₂ and 5% O₂ + 15% CO₂ were compared with normal air (control) at 2 °C. Pericarp browning and decay incidence of longan were significantly (P ≤ 0.05) higher in control than all the CA treatments. CA storage reduced polyphenol oxidase (PPO) activity, maintained L* value and slowed down a decrease in total phenolic contents (TPC). Pericarp browning was highly correlated with PPO, L* and TPC.     

Insecticidal and residual effect of three pyrethroids against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on stored wheat

Laboratory tests were conducted to assess the use of the pyrethroids, deltamethrin, beta-cyfluthrin and alpha-cypermethrin at the rates of 0.125 and 0.25 ppm, as grain protectants in stored wheat against the rice weevil, Sitophilus oryzae (L.). For this purpose, clean untreated wheat was sprayed with these insecticides and stored for 6 months. During this period, four bioassays were carried out, in order to evaluate the residual efficacy of each pyrethroid. In each bioassay, treated wheat was infested with S. oryzae adults, and dead insects were counted after 1, 2 and 7 d of exposure. In addition, S. oryzae progeny production was estimated on each bioassay, until the production of the F₄ generation. The results indicated that deltamethrin and beta-cyfluthrin, both at 0.25 ppm, were significantly more efficient than the other treatments. Efficacy was notably higher after 7 d of exposure, than after 1 and 2 d. At the same exposure level, 1, 2 and 3.5 months after treatment, at 0.25 ppm, mortality for deltamethrin was approximately 89%, 92% and 86%, respectively, while the corresponding percentages for beta-cyfluthrin were 97%, 83% and 62%, and for alpha-cypermethrin 50%, 49% and 33%. However, at the rate of 0.125 ppm, mortality was ?58% in all cases. In all treatments appearance of F₁-F₄ generations was observed, with the exception of both deltamethrin and beta-cyfluthrin at 0.25 ppm, where only a few F₁ adults were noted, without the production of subsequent generations.     

Controlled‐atmosphere storage of tomato fruit: low oxygen or elevated carbon dioxide levels alter galactosidase activity and inhibit exogenous ethylene action

The effects of 3% O₂ and 20% CO₂, both alone and together with 100 µg g⁻¹ C₂H₄, on ethylene production, chlorophyll degradation, carotenoid biosynthesis and α‐ and β‐galactosidase activity in breaker tomato (Lycopersicon esculentum Mill) fruit were investigated. The low O₂ and high CO₂ atmospheres prevented the rise in ethylene production, total carotenoid and lycopene biosynthesis and α‐ and β‐galactosidase activity and slowed down chlorophyll degradation and loss of firmness (P < 0.05). These suppressive effects were not reversed, or only in part – in the case of chlorophyll breakdown – by addition of 100 µg g⁻¹ C₂H₄ to said controlled atmospheres. After transfer from the various atmospheres to air, flesh firmness decreased and ethylene production, total carotenoids, lycopene and β‐galactosidase II activity increased but these parameters were, in all cases, still significantly different from those of fruit held in air. Keeping tomatoes in controlled atmospheres, even in the presence of ethylene, had marked residual effects. Results suggest an antagonism between elevated CO₂/low O₂ and exogenous ethylene which could determine most of the ripening parameter behaviour under controlled‐atmosphere storage, though a direct regulatory mechanism by O₂ and/or CO₂ should not be discarded. © 1999 Society of Chemical Industry     

Scrubbing carbon dioxide prevents overestimation of insect mortality in long-duration static phosphine toxicity assays

Exposing insects to toxicants such as phosphine (PH₃) in sealed chambers is a common procedure in fumigant efficacy testing. During long exposures, carbon dioxide (CO₂) produced by metabolic processes of fed insects may accumulate in the vessel. As CO₂ enhances the toxicity of several fumigants, concomitant exposure of fumigant and CO₂ may lead to erroneous measurements of insect mortality and thus fumigant toxicity. In this study, the effect of a CO₂ scrubber such as soda lime (a solid formulation of wet hydroxides of calcium, sodium and potassium) or periodic flushing of the headspace, on insect mortality in static PH₃ toxicity assays was compared with an “unscrubbed” (no intervention) treatment. Soda lime was highly effective in removing CO₂ from the headspace of sealed chambers, without measurable loss of PH₃. Mortality of Sitophilus oryzae (L.) adults treated with phosphine in chambers scrubbed with soda lime or flushed (opened) daily was considerably lower than in unscrubbed chambers. Twenty grams of soda lime per litre of exposure chamber is recommended to obtain accurate static fumigant mortality results.     

Tolerance of Sitophilus zeamais (Coleoptera: Curculionidae) to heated controlled atmosphere treatments

Combination heat and controlled atmosphere (CA) postharvest phytosanitary treatments are environmentally friendly alternatives to chemical fumigants. A controlled atmosphere/heating block system (CA-HBS) was used to rapidly assess tolerances of adult maize weevil, Sitophilus zeamais, both under regular air (RA) and CA (1% O₂ and 15% CO₂) conditions. In the RA treatment, thermal death kinetics for S. zeamais adults were determined at temperatures between 46 °C and 52 °C at a heating rate of 5 °C/min. The results showed that thermal death curves of S. zeamais adults followed a 0th-order kinetic reaction model. The required holding times for achieving 100% mortality were 165, 40, 14, and 4 min at 46, 48, 50 and 52 °C, respectively. The activation energy for killing S. zeamais adults was 526.7 kJ/mol. The effects of CA at various temperature-time combinations and heating rates on insect mortality were evaluated. The mortality of S. zeamais adults was higher under CA treatment than in the heat treatment alone. The slowest heating rate (0.1 °C/min) achieved the highest insect mortality in CA treatments but lowest mortality in RA treatments. The information obtained from the CA-HBS can be used to develop combination heat and CA treatments against S. zeamais.     

Effect of controlled atmosphere storage on aflatoxin production in high moisture peanuts (groundnuts)

Shelled peanuts (groundnuts) remoistened to 16.7% were stored for 4 weeks at about 27°C in air (0.03% CO₂, 21% O₂, 78% N₂) and in three modified atmospheres: (1) 13.6% CO₂, 0.3% CO, 0·6% O₂, 84.7% N₂; (2) 12.2% CO₂, 3.1% CO, 0.3% O₂, 83.5% N₂; and (3) 13.6% CO₂, 0.1% CO, 1.5% O₂, 83.9% N₂. Aflatoxins, per cent free fatty acids, and per cent kernel infection by the Aspergillus flavus group were determined weekly. Peanuts in air and in the atmosphere containing 1.5% O₂ accumulated high levels of aflatoxin in 1 and 2 weeks, respectively. In the other two controlled atmospheres aflatoxin B₁ did not exceed 21 μg/kg and the per cent of free fatty acids increased only slightly. None of the treatments eliminated infection by the A. flavus group. After 4 weeks peanuts in all treatments had visible fungal growth on surfaces.     

Residual effect of CO2 on hake (Merluccius merluccius L.) stored in modified and controlled atmospheres

 The residual effect of CO₂ on whole gutted hake kept with three different CO₂/O₂/N₂ gas mixtures: 60/15/25, 80/20/0 and 40/40/20, and two different kinds of atmospheres (controlled and modified) during 12 days followed by conventional storage in ice for up to 30 days was examined by physical, chemical and sensory analyses. Shelf life was longer in lots kept in atmospheres than in control lots and was further prolonged by controlled than by modified atmospheres. The lots kept in the atmosphere with the highest concentrations (80%) of CO₂ exhibited the lowest trimethylamine nitrogen and total volatile basic nitrogen values. However, these were also the lots that scored worst in sensory analysis. The lots that scored best in sensory analysis were those which were kept in the gas mixtures with 60% and 40% of CO₂. Oxidative rancidity was not a problem in the samples stored in the atmosphere with 40% O₂; Thiobarbituric acid levels were lower than 2 mg/100 g in all lots throughout storage, and the assessors detected no rancidity. The residual effect of CO₂ on whole gutted hake was more effective in controlled atmosphere lots. Received: 15 June 2000 / Revised version: 17 August 2000     

The toxicity effects of atmospheres with high content of carbon dioxide with addition of sulphur dioxide on two stored-product pest species: Sitophilus oryzae and Tribolium confusum

Modified atmospheres (MAs) are safe and environmentally friendly alternatives to control pests in stored products. However, to accommodate the requirements of the food industry, the control of insects by a MA can be a too lengthy process. This paper describes the potential of sulphur dioxide as an additive to reduce the long lethal exposure of modified atmospheres (MA) enriched with carbon dioxide for major stored product pests. Specifically, we evaluated whether the addition of SO₂ (0–30,000 ppm) to a high-CO₂ content of 70%–95% MA could enhance its insecticidal effect for the control of Sitophilus oryzae and Tribolium confusum. The addition of 15,000 ppm and 30,000 ppm of SO₂ to 95% CO₂ enhanced control up to 100% in comparison to CO₂ alone for S. oryzae and T. confusum adults when treated for one day in all of the substrates tested. However, the effectiveness of adding SO₂ at reduced contents was lower and depended on the substrate and pest species considered. The addition of SO₂ also increased the mortality of all of the developmental stages of S. oryzae. The increase in mortality with the addition of SO₂ was also observed when included with 70% CO₂. Therefore, the addition of SO₂ can be considered a feasible means of shortening the length of treatment necessary to achieve the control of these two pests using a high-CO₂ MA.