The effect of carbon dioxide gas alone or in combinations on the mortality of Tribolium castaneum (Herbst) and T. confusum du Val (Coleoptera, Tenebrionidae)

Adults of Tribolium castaneum (Herbst) and T. confusum du Val exposed to various mixtures of N₂ or He and O₂ were killed when the O₂ concentration reached to 1·7% or below, whereas the adults exposed to CO₂ : O₂ mixtures were killed mostly due to the deleterious effects of CO₂ itself. At 26·7°C and 38 ± 6%r.h., 95 per cent mortality of T. confusum adults was obtained by an exposure of 271 hr to 45% CO₂ : 55% air mixture; 58 hr to 62% CO₂ : 38% air mixture; and 47·5 hr to 80% CO₂ : 20% air mixture, while for T. castaneum adults 95 per cent mortality required 192, 60, and 44 hr respectively. Data obtained by exposing mature and immature stages of both species to 100% CO₂ suggest that adults were the most susceptible, followed by larvae, eggs and pupae. Generally speaking, inactive stages (egg and pupal) were more tolerant to CO₂ than active stages (larval and adult). Increasing the temperature from 15·6° to 26·7°C resulted in increased insect mortalities; the degree of response varying in different stages. Increasing r.h. decreased the susceptibility of adult insects to 100% CO₂.

Under airtight conditions 200 adult T. castaneum with 8 g of food medium sealed in 1·2 1. glass flasks depleted the O₂ supply from 20·9% to a critical 1·7% level in 7 days, and adults of T. confusum depleted to the 1·6% level in 5 days of airtightness, and both species produced about 20% of carbon dioxide gas.     

Influence of packaging method and length of chilled storage on microflora, tenderness and colour stability of venison loins

Sections of venison loins (LD) weighing approximately 300 g from 12 red deer (Cervus elaphus) were packaged using four packaging methods: (a) vacuum packaging, (b) CO₂ flushed using a nylon containment film (CO₂-Nylon), (c) CO₂ flushed using an ultra-high barrier containment film (CO₂-UHB), and (d) CO₂ flushed using an aluminium foil laminate containment film (CO₂-Foil) and stored for 1, 6, 12 and 18 weeks at 0°C. Meat pH values were lower in all CO₂ flushed meat packages (P<0·05) than in vacuum packaged meat. Lactic acid bacteria and total anaerobic counts increased over storage time in all packages regardless of treatment up to values of log₁₀ 7·8 and 7·6 g⁻¹, respectively. Tenderness tended to increase as meat was stored for up to 18 weeks. Colour scores taken during simulated retail display indicated that colour deteriorated more rapidly when meat was stored for 12 and 18 weeks than for 1 and 6 weeks. Vacuum packaging and gas flushing (CO₂-Foil) resulted in higher initial colour scores than venison packaged in the CO₂-Nylon or CO₂-UHB materials. Venison stored for 18 weeks also exhibited a higher proportion of packages containing off odours, lower flavour desirability and flavour intensity scores as well as higher off flavour scores than meat stored for shorter times. The implications of these effects are discussed. Although there were few significant differences in microbial growth and sensory characteristics due to packaging method or containment film, vacuum packaging appeared to be the most economic and produced meat of better colour stability.     

Pressing and supercritical carbon dioxide extraction of walnut oil

The objective of this study was to evaluate the oil extraction process from walnut seeds by pressing followed by extraction with supercritical CO₂. In pressing experiments, a factorial arrangement was conducted in order to study the combined effects of seed moisture content (2.5%, 4.5% and 7.5%) and pressing temperature (25, 50 and 70 °C) on oil recovery and quality parameters. For all conditions tested, the oil quality compared well with that of cold-pressed walnut oil. Oil recovery increased significantly as moisture content raised. Highest oil recovery (89.3%) was obtained at 7.5% moisture content and 50 °C temperature. The cake resulting from pressing at these conditions was extracted with CO₂ in a high pressure pilot plant with single stage separation and solvent recycle. The effects of two different pressures (200 and 400 bar) and temperatures (50 and 70 °C) with regard to oil yield and quality, and time required for extraction were analyzed. At each condition, the extraction rate changed with the mass of solvent and extraction time. At first, the mass of oil extracted was determined by the oil solubility in CO₂ and a linear relationship was observed, where the slope results in the solubility of oil in CO₂ at the experiment conditions. After that, the extraction rate was governed by solubility and diffusion, and continuously decreased with time. The colour changed along the extraction from a whitish clear product to a yellow one. Tocopherol and carotenoid contents were significantly higher than those obtained by pressing. Extraction conditions did not affect significantly the fatty acid composition.     

The storage life of chilled pork packaged under carbon dioxide

Pork cuts of longissimus dorsi muscle with overlaying fat and skin were packed under vacuum in film of low oxygen transmission rate, or under CO₂ in gas impermeable aluminium foil laminate. Cuts were stored at +3 or −1·5°C. Vacuum packaged cuts were grossly spoiled by Brochothrix thermosphacta after 2 weeks' storage at 3°C and after 5 weeks at −1·5°C. Cuts packaged under CO₂ were grossly spoiled by B. thermosphacta after 5·5 weeks' storage at 3°C. Growth of B. thermosphacta was suppressed when CO₂ packaged cuts were stored at −1·5°C. At that temperature, slow growth of enterobacteria was detected after a lag of about 18 weeks. The enterobacteria caused gross spoilage of an increasing proportion of cuts between 18 and 26 weeks. Muscle tissue with pale, soft, exudative (PSE) characteristics tended to lose colour after long storage periods, apparently because of loss of myogglobin with exudate. Until spoilage, the eating qualities of pork appeared little affected by prolonged storage.     

A novel use of modified atmospheres: Storage insect population control

The research described here aimed to establish the feasibility of using modified atmospheres (MA) to protect commodities throughout their storage life by using oxygen (O₂) levels that disrupt the life cycles of the target beetle species. Rather than achieving complete mortality of all stages, the aim was to identify more easily obtainable MAs that would kill the most susceptible stage and prevent population growth. Simulated burner gas and nitrogen (N₂) atmospheres with O₂ contents between 3% and 6%, were tested, along with a N₂-based MA with elevated carbon dioxide (CO₂) (10–20%).

Laboratory tests were carried out on five species of stored-product beetles, Cryptolestes ferrugineus, Oryzaephilus surinamensis, Sitophilus granarius, S. oryzae and Tribolium castaneum. After exposure to the MAs for 28 d an assessment was made of the mortality of adults, the number of adults from progeny produced under the MAs and, for the simulated burner gas, the number of adults from progeny produced in a 28-d period after exposure to the MA. The tests were carried out at 20 and 25 °C with 75% and 85% r.h. at each temperature.

The O₂ content preventing population growth varied with species and temperature. For simulated burner gas or N₂ it was about 4% for O. surinamensis, S. granarius and S. oryzae, and about 3% for C. ferrugineus and T. castaneum at 25 °C. At 20 °C it was about 3% for all species tested. When CO₂ was increased to 10% or 20%, reducing O₂ to 5% was sufficient to eliminate emergence of S. granarius at 20°C, but a few individuals emerged at 25 °C. For C. ferrugineus there was a 95% reduction with 5% O₂ plus 20% CO₂ at 20 °C, but not at 25 °C.     

The effects of residual oxygen concentration and temperature on the degradation of the colour of beef packaged under oxygen-depleted atmospheres

Samples of beef longissimus dorsi (LD), approximately 5 × 5 × 1 cm, were packaged in pairs under 10 litre volumes of N₂ or CO₂ containing O₂ at concentrations between 100 and 1000 ppm. The packaged samples were stored at temperatures of 5, 1, 0 or −1·5°C, for times between 4 and 48 h. Samples of beef psoas major (PM) were packaged under N₂ or CO₂ containing O₂ at between 100 and 600 ppm, and stored at −1·5°C for 24 or 48 h. After storage, each sample was assessed for colour deterioration and discoloration, and for the fraction of metmyoglobin in the surface pigment.

The results obtained with N₂ and CO₂ atmospheres were similar. The colours of all LD samples had deteriorated after 4 h storage at 5 or 1°C, although the degree of deterioration increased with increasing O₂ concentration. All LD samples stored for 12 h at 5 or 1°C were extensively discoloured, with metmyoglobin fractions generally exceeding 60%, but those stored at −1·5°C for 48 h or less, under O₂ concentrations ≤ 400 ppm had undergraded colours. The colours of some LD samples stored at −1·5°C under about 600 ppm of O₂ were also undergraded, but the colours of samples stored under 800 or 1000 ppm had deteriorated by 24 h. The colours of LD samples stored at 0°C under > 200 ppm had deteriorated after 24 h storage, and the colours of samples stored under 100 ppm O₂ had deteriorated after 48 h storage. All PM samples were wholly discoloured after storage at −1·5°C. Evidently, the colour of beef muscle of high colour stability is resistant to degradation by atmospheres containing < 600 ppm of O₂ when the meat is stored at sub-zero temperatures, but not when the storage temperature is at or above 0°C. Beef muscle of low colour stability, such as the PM, will discolour at all low concentrations of O₂ irrespective of the storage temperature.     

Centralised bulk pre-packaging of fresh pork retail cuts in various gas atmospheres

A centralised bulk pre-packaging technique (laboratory method), utilising various gas mixtures (c. 100% CO₂; c. 75% CO₂:25% N₂; c. 80% O₂: 20% CO₂ and c. 25% CO₂:50% N₂:25% O₂), was evaluated in terms of quality attributes such as microbiology, colour, odour and consumer acceptability. According to the bacterial counts recorded, all four packaging treatments were successful in prolonging the storage life (21 days c. 0°C) of centralised bulk pre-packaged pork retail cuts, while still ensuring a subsequent shelf life of at least 3 days (c. 0°C). The gas mixture comprising c. 25% CO₂:50% N₂:25% O₂ was the most successful treatment in terms of acceptability and colour scores.     

The effect of moisture level on high-moisture maize (Zea mays L.) under hermetic storage conditions—in vitro studies

Under humid and warm conditions harvested grains are susceptible to molding and rapid deterioration. Therefore, they should be dried to safe moisture levels that inhibit the activity of microorganisms. Drying to these moisture levels is not economical for farmers in developing countries. Preservation of grains at intermediate moisture levels under hermetic storage conditions could be feasible and economical in warm and moist climates.

The purpose of the current study was to examine the effect of various moisture contents (m.c.) on the quality of maize grains in self-regulated modified atmospheres during hermetic storage.

Maize at 14, 16, 18, 20 and 22% m.c. was initially conditioned for 28 days in tightly wrapped plastic bags and then stored in sealed containers at 30 °C for up to 75 days. Carbon dioxide produced within the containers replaced the oxygen. As the m.c. increased the time for O₂ depletion shortened, from 600 h at 14% m.c. to 12 h at 22%. The maize at 20 and 22% m.c. exhibited the highest dry matter (DM) losses, the lowest germination rates and the highest yeast and bacteria counts. The major fermentation product in the hermetically sealed maize was ethanol (0–5 g kg⁻¹ DM), along with lower concentrations of acetic acid (0–1 g kg⁻¹ DM).

The results obtained from the in vitro experiments indicate that maize at the tested moisture levels can be stored satisfactorily under sealed conditions in which self-regulated atmospheres provide protection against microflora damage. Further large-scale trials will be needed to evaluate the economic feasibility of storing high-moisture maize.     

The effect of wholesale vacuum and 100% CO2 storage on the subsequent microbiological, colour and acceptability attributes of PVC-overwrapped pork loin chops

The shelf life of chops cut from pork loins, after either vacuum or 100% CO₂ storage (0, 7 or 14 days), was determined. The PVC-overwrapped chops were assessed, following a shelf life study of 0, 2, 5 or 7 days at 0 or 5°C, regarding quality attributes such as microbiological contamination levels, colour and acceptability. The study indicated that according to the psychrotrophic counts, the PVC-overwrapped retail chops, from the vacuum as well as the 100% CO₂ stored pork loins (0, 7 or 14 days), still attained a conventional shelf life of 3 days.

Lactic acid bacteria and pseudomonads largely represented the psychrotrophic counts. No clear pattern could be detected regarding the colour scores except that the samples displayed at 0°C tended to retain colour longer. These samples were also judged to be more acceptable, although the determination of acceptability was subjective.     

Effect of carbon monoxide in modified atmosphere packaging, storage time and endpoint cooking temperature on the internal color of enhanced pork

The objective of this research was to evaluate the effects of gas atmosphere, refrigerated storage time, and endpoint temperature on internal cooked color of injection-enhanced pork chops. Enhanced chops were packaged in 0.36% CO/20.34% CO₂ (CO-MAP), 80% O₂/20% CO₂ (HO-MAP), or PVC-overwrapped (PVC-OW; controls), stored at 4 °C for 0, 12, 19 or 26 days, displayed for 2 days then cooked to six endpoint temperatures (54, 60, 63, 71, 77, and 82 °C). L^*, a^*, and b^* values, hue angle and chroma were determined on the internal cut surface of cooked chops. Chops packaged in CO-MAP had the highest a^* values; a^* value began increasing on day 14. The lowest hue angles occurred in chops cooked to lower endpoint temperatures. Chops in CO-MAP had lower hue angles and higher chroma than those in HO-MAP and PVC-OW. Above 71 °C, hue angle and chroma increased. Overall, CO-MAP packaged chops stored for longer time periods then cooked to lower endpoint temperatures appeared reddest. HO-MAP packaged chops were less red, did not change over time, and appeared more well done at lower endpoint temperatures than those in other gas atmospheres. CO-MAP packaged chops retained redness even after cooking at 82 °C.     

Chilled storage life of hot-boned, pre-rigor, salted minced beef

Pre-rigor beef mince with 2% added salt was stored under CO₂ at −1.5 °C (A). The same mince with 100 ppm sodium nitrite was stored under CO₂ at 5 °C (B) and −1.5 °C (C), and under vacuum at −1.5 °C (D). Microbiological and sensory analyses were carried out for up to 21 weeks. Indicative storage life was taken as the time for microbial numbers to reach 10⁷ colony forming units per g. Mince stored under regimes B or D attained these numbers by 6 and 14 weeks, respectively; mince stored under regimes A and C had not attained these numbers by the end of the storage trial. Mince stored at 5 °C developed storage flavours of sufficient intensity to be detectable by consumers by 9 weeks storage. In general, the other minces did not develop unacceptable levels of storage or off flavours. Over 90% of the added sodium nitrite had disappeared after 10 weeks of storage, partly through conversion to sodium nitrate. Mince pH was not affected by the storage conditions and remained at about 6.0. The water holding capacity of the pre-rigor mince deteriorated during prolonged storage.     

Combined effect of modified atmosphere bulk packaging, dietary vitamin E supplementation and microbiological contamination on colour stability of Musculus gluteus medius

Five Simmentaler type calves were fed diets supplemented with 500 mg vitamin E per day and five fed control diets. Rump steaks from each carcass were PVC-overwrapped and bulk packaged in 100% CO, or 20% CO₂:80% O₂. Bulk packs were stored up to 42 days at 4°C and steaks displayed up to 7 days at 4°C. Bacterial counts of rump steaks from either packaging treatment were not significantly influenced during bulk storage or retail display by supplementation with dietary vitamin E. Both packaging treatments delayed bacterial growth during bulk storage. Aerobic plate counts of rump steaks stored in 100% CO₂ were lower than those of rump steaks stored in 20% CO₂: 80%: O₂. This study showed that rump steaks supplemented with dietary vitamin E can be bulk packaged in 20% CO₂: 80% O₂ or 100% CO₂ and stored for up to 42 days with shelf life of 4–7 days.     

The display life of retail-packaged beef steaks after their storage in master packs under various atmospheres

Beef strip loins were divided into four portions. One portion of each loin was vacuum-packaged and then stored at −1·5°C. The other portions were each divided into three steaks, which were retail-packaged. The retail packs were master-packaged under atmospheres of N₂, CO₂, or O₂ + CO₂ (2 : 1, v/v) and then stored at 2°C. Product was assessed after storage times of up to 60 days. At each assessment, a vacuum pack and a master pack of each type, each containing product from the same loin, were withdrawn from storage. The vacuum-packaged product was cut into three steaks, which were retail-packaged. The newly prepared retail packs and those from the master packs were displayed in a retail cabinet, at air temperatures that averaged between 3 and 5·7°C, and were assessed twice daily until the product was judged to be unacceptable. When first assessed, steaks cut from vacuum-packaged product were generally considered desirable, with little metmyoglobin in the surface pigment, although the edges of same steaks were discoloured. Steaks stored under N₂ or CO₂ for 4 days or less were only slightly desirable at best, with metmyoglobin forming relatively large fractions of the surface pigment. However, after storage under N₂ or CO₂ for 6 days or more, metmyoglobin fractions were low, and the steaks bloomed to a desirable red colour. Steaks stored under O₂ + CO₂ had lower metmyoglobin fractions, and were desirable after storage for up to 8 days. However, the fractions of metmyoglobin increased, and steaks were judged to be less desirable after longer storage times. Steaks stored under O₂ + CO₂ for 20 days were unacceptable. After storage, the numbers of bacteria on steaks from vacuum packs and N₂, CO₂, and O₂ + CO₂ atmospheres were, respectively, <10⁴, <10⁶, <10⁵, and <10⁴ CFU/cm². The flora from steaks stored under CO₂ were composed wholly of lactic acid bacteria. Other flora were dominated by lactic acid bacteria, but contained fractions of enterobacteria and/or Brochothrix thermosphacta.

The appearance of product from vacuum packs generally was unacceptable after 72 h of display. The display life of steaks stored under N₂ or CO₂ was shorter than that of the product from vacuum packs when product was stored for 2 days or less, or 46 days or more. After other storage times, the product from vacuum packs or master packs with N₂ or CO₂ atmospheres had a similar display life. The display life of product stored under O₂ + CO₂ was similar to that of product from vacuum packs or CO₂ or O₂ + CO₂ was similar to that of product from vacuum packs after storage times of 8 days or less but was shorter after storage times of 12 or 16 days. The flora on displayed product from vacuum packs or CO₂ or O₂ + CO₂. atmospheres did not attain the maximum number of 10⁷ CFU/cm². and the product did not develop off-odours of microbial origin. However, numbers of 10⁷ CFU/cm² were approached or attained during display of product stored under N₂ for 28 days or longer, and some of that product developed moderate off-odours. It then appears that, under temperature regimes that are common in commercial practice, retail-packaged strip-loin steaks with a display life of 2 days or longer can be obtained from master packs after storage periods of up to about 2, 4, or 7 weeks, respectively, with master-pack atmospheres of O₂ + COPin2 (2 : 1, v/v), N₂, or CO₂.     

The turnover of the gut contents (traced with inulin-carboxyl-C), tritiated water and Na in three stored product insects

On food labelled with inulin-carboxyl-¹⁴C, adults of four species of insects accumulated an amount of ¹⁴C comparable to that in a weight of food solids equal to their loss of body solids during the first days of fasting. All of this ¹⁴C was subject to clearance from the body and could be accounted for in the cage debris. The time dependence for clearance of the ¹⁴C while held on unlabelled food was, in several tests, comparable to that for its accumulation from the labelled food; and the time dependence for its clearance while fasting was similar to that of the body solids loss. In contrast to the ¹⁴C of inulin, ²²Na was concentrated in the body; its clearance was that of a first-order process from a single compartment, but the clearance was slower on food to which NaCl had not been added and very slow while fasting. The rate of solids ingestion was calculated as the product of the weight of body solids lost while fasting and the fractional rate of ¹⁴C turnover while feeding. The following data from tests at 20°C in 85% r.h. are representative. A Sitophilus granarius adult of 4.1 mg fresh weight ingested 170 μg of tapioca solids each day, of which the weight of carbon is only slightly more than the 55 μg of carbon lost each day as CO₂: its 1.6 mg of body water had a turnover of 12%/day to which food moisture contributed 17%, metabolic water production (identified with the molar rate of CO₂ production) contributed at most 39%, and diffusion contributed atlleast 44%. An Oryzaephilus surinamensis adult of 550 μg fresh weight feeding on oatflakes ingested 47 μg of solids per day while 9.5 μg was lost as carbon with CO₂: its 260 μg of body water had a turnover of 34%/day to which ingested moisture contributed 10%, metabolic production 15% and diffusion 75%. The booklouse Liposcelis bostrychophilus of 40 μg fresh weight ingested 1.25 μg of yeast solids each day while the carbon loss with CO₂ was only 0.18 μg/day and eggs were produced. Its 30 μg of body water had a turnover of 40%/day to which ingested moisture contributed 4%, metabolic production 5%, diffusion approximately 40% and physiological absorption of vapor nearly 50%. A few data were also reported for Sitophilus oryzae.     

Equilibrium sorption isotherms and thermodynamic properties of starch and gluten

A modification of the GAB isotherm (Guggenheim–Anderson–De Boer) is proposed in order to correlate the sorption data for water activities higher than 0.9. The proposed isotherm retains the desirable properties of the GAB isotherm, i.e. good fitting in the range of a_w between 0.05 and 0.80, and also provides a noticeable improvement in the fitting quality for high values of a_w, by introducing a new term with an additional constant. Sorption data for native potato starch and gluten at different temperatures (2°C, 20°C, 40°C and 67°C) were well correlated for the whole a_w range. For starch at 67°C, the values of the constants of the proposed equation do not follow the same tendency obtained for lower temperatures, suggesting that the structure of the material could be changed due to the high temperature. The proposed isotherm can be of interest in the area of drying given that there are few isotherms that accurately represent sorption data at different temperatures in the zone of high a_w. Also, it can be useful to predict other thermodynamic functions. In addition, a new procedure is proposed to determine the isosteric heat by using a second order polynomial for representing the variation of moisture as a function of temperature at a fixed water activity.     

The mortality of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae) at moderate temperatures

A method using conductive heating is described for quickly obtaining and maintaining moderate temperatures in grain while minimising grain moisture loss. A model is developed to analyse insect mortality at a range of conditions on log-time logit and log-time probit scales. Values of LT 50, LT 99, and LT 99.9 are presented for adult and immature stages of Sitophilus oryzae in wheat from 42 to 48°C at 12% m.c. and for immature stages of Rhyzopertha dominica in wheat from 45 to 53°C at 9, 12 and 14% m.c. Data show that the heat tolerance of all life cycle stages for both species are different, with a degree of progressive change relative to each other as temperature changes. For R. dominica, the thermal tolerance of life cycle stages also changes relatively with changes in grain moisture content. In general, all stages survive longer at a given temperature as grain moisture increases and the effect of moisture on survival increases as temperature decreases. Values for LT 99.9 for the most heat tolerant stage of R. dominica at 9% m.c. range from 78.22 to 2.49 h between 45 and 53°C. At 12% m.c. they range from 96.81 to 3.36 h, and at 14% m.c. from 114 to 4.14 h. In general, at 12% m.c. the heat tolerance of S. oryzae is about 5°C less than R. dominica with LT 99.9 ranging from 37.36 to 3.71 h between 42 and 48°C. At this level of mortality, immature stage three is generally the most heat tolerant stage of R. dominica, whereas it is stage two for S. oryzae. The results are discussed in relation to practical applications of heat disinfestation and in terms of a general model of mortality. The results are also considered in the context of other available information on the heat treatment of both species.     

Effect of gas barrier characteristics of films on aflatoxin production by Aspergillus flavus in peanuts packaged under modified atmosphere packaging (MAP) conditions

The effects of the gas barrier characteristics of three films (ASI, ASII and ASIII) and storage temperature on the growth of, and aflatoxin production by, Aspergillus flavus in peanuts packaged in air and under a modified gas atmosphere of CO₂:N₂ (65:35) were investigated. Mold growth was barely visible in air packaged peanuts using high-medium barrier films (ASI and ASII) and stored at 20°C with more extensive growth occurring in air packaged peanuts stored at 25 and 30°C. Extensive mycelial growth and sporulation occurred in all air packaged peanuts in a low barrier film (ASIII), especially at 30°C. Gas packaging inhibited mold growth in peanuts packaged in a high gas barrier film at 20°C. However, mold growth occurred in gas packaged peanuts packaged in film ASII at higher storage temperatures while extensive mycelial growth was observed in all peanuts packaged in film ASIII irrespective of storage temperature. Levels of aflatoxin greater than the regulatory limit of 20 ng/g were detected in all air packaged peanuts with the highest level of aflatoxin (76 ng/g) being detected in peanuts packaged in a high gas barrier film ASI. Aflatoxin production was inhibited in gas packaged peanuts using a high barrier film. However, higher levels of aflatoxin were detected in all gas packaged peanuts in medium-low gas barrier films (ASII and ASIII), particularly at higher storage temperatures. This study has shown that MAP using a CO₂:N₂ (65:35) gas mixture was effective in controlling aflatoxin production by A. flavus in peanuts to levels less than the regulatory limit of 20 ng/g. However, the antimycotic effect of low O₂-high CO₂ atmospheres is dependent on the gas barrier characteristics of the packaging films, especially at higher storage temperatures.     

Beef shelf life in low O(2) and high CO(2) atmospheres containing different low CO concentrations

The use of atmospheres with low concentrations of CO (0.1 to 1%), in combination with O₂ (24%), high CO₂ (50%) and N₂ (25 to 25.9%), for preserving chilled beef steaks was investigated. The atmosphere used as reference contained 70% O₂+20% CO₂+10% N₂. Bacterial counts showed that all atmospheres containing CO greatly reduced total aerobic population numbers, including Brochothrix thermosphacta. Lactic acid bacteria, however, were not affected. CO concentrations of 0.5–0.75% were able to extend shelf life by 5–10 days at 1±1°C, as demonstrated by delayed metmyoglobin formation (less than 40% of total myoglobin after 29 days of storage), stabilisation of red colour (no change of CIE a* and hue angle after 23 days), maintenance of fresh meat odour (no variation of sensory score after 24 days) and significant (P<0.01) slowing of oxidative reactions (TBARS).     

Sorption isotherms of salted minced pork and of lean surface of dry-cured hams at the end of the resting period using KCl as substitute for NaCl

The effect of KCl on sorption isotherms was determined on salted minced meat (with 0%, 30% and 100% molar substitution of NaCl by KCl) at 5 °C and 25 °C and meat from a 3 mm thick slice from the surface of dry-cured hams (with 0% and 35% molar substitution of NaCl by KCl) held at 70–75%, 75–80% and 80–85% air relative humidity during the resting period.

The sorption isotherms were determined gravimetrically by exposing the meat samples to several atmospheres of known relative humidity controlled by different saturated salts according to the COST90 method. The sorption equipment consisted of a chamber containing 11 containers, covering the water activity (a_w) range from 0.112 to 0.946 at 25 °C. The hermetically closed sorption containers filled with KCl and minced meat samples were irradiated at 3 kGrey (gamma irradiation ⁶⁰Co). The water content at equilibrium was higher in minced meat with NaCl than in minced meat with KCl (100% molar substitution of NaCl by KCl) at 5 °C within the range of 0.4313 and 0.7565 a_w. However, when substitution was 30% in minced meat and 35% in hams the isotherms were similar to isotherm without substitution.     

Induced tolerance of Sitophilus oryzae adults to carbon dioxide

Sitophilus oryzae adults were exposed to 40% carbon dioxide (CO₂) in air for seven successive generations and to 75% CO₂ in air for ten successive generations at 26°C and 100% relative humidity (r.h.). The tolerance factor (LT₉₅ selected generation/LT₉₅ non-selected generation) at the 7th generation of insects exposed to 40% CO₂ was 2.15 and at the 10th generation exposed to 75% CO₂, was 3.34. Reduction of the r.h. to 60% in the 75% CO₂ atmosphere caused shortening of exposure times required to obtain the same mortality values, but the tolerance factors remained stable. Removal of selection pressure for five generations of the 40% CO₂ and four generations of the 75% CO₂ selected strains caused significant reduction in tolerance. Augmentation of oxygen concentration to 21% in atmospheres containing 40 and 75% CO₂ did not markedly alter the tolerance factors from those obtained with atmospheres containing the same CO₂ concentrations in air.