Mass transport analysis in perforation-mediated modified atmosphere packaging of strawberries

A space-and-time dependent mathematical model was developed to predict O₂, CO₂, N₂ and H₂O concentration in perforation-mediated polymeric packages during cold-storage of strawberries. The numerical solution of the corresponding mathematical model was obtained by applying the finite element method (FEM). The problem was solved in a domain corresponding to the headspace of a package augmented by the total void spaces of the contained bulk produce and for realistic boundary conditions. Transport of O₂, CO₂, N₂ and H₂O was modelled based on Maxwell–Stefan equations for gas transport through packaging’s headspace and on Fick’s law for diffusion through the micro-perforated packaging. The model predictions were tested against published experimental data of O₂ and CO₂ concentrations in modified atmosphere packaging storage of strawberries and the agreement is satisfactory. As for reaching the recommended in the literature gases concentrations for strawberry storage, the model predictions revealed that the tested micro-perforated polypropylene packaging combined with the adopted storage conditions are marginally adequate. To this end, the theoretical findings are suggestive of improvements, in terms of material properties, especially with regard to the permeability of the polymeric packaging film.     

Toxicity of carbon dioxide to drugstore beetle Stegobium paniceum and cigarette beetle Lasioderma serricorne

Mortality and sub-lethal effects of carbon dioxide (CO₂) against Stegobium paniceum and Lasioderma serricorne were studied. All life stages of S. paniceum were relatively more susceptible than those of L. serricorne. In both species, the pupal stage was the most tolerant followed by larva, egg and adult. The influence of changing CO₂ concentrations (stepwise increase or stepwise decrease) in comparison with constant CO₂ concentration on the mortality responses of adults of S. paniceum and L. serricorne at fixed Ct products was also examined. Both changing concentrations of CO₂ were more effective than constant concentration and the effect was more pronounced in S. paniceum. CO₂, at LD₅₀ doses, prolonged the developmental period of the survivors in both species. Treatment of adults caused a significant reduction in progeny production indicating an adverse effect on the multiplication potential of the survivors.     

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.     

Effects of controlled atmosphere storage on respiratory metabolism of apple fruit tissue

The effects of CO₂ and O₂ concentrations commonly used in fruit storage upon various respiratory processes in apple fruit tissue have been investigated. In manometric experiments 10% CO₂ inhibited CO₂ release from succinate supplied to peel discs by over 50%; CO₂ release from malate was inhibited at high substrate concentrations, while CO₂ release from pyruvate was not affected. High CO₂ concentrations also inhibited ¹⁴CO₂ release from succinate 1,4-¹⁴C and succinate 2,3-¹⁴C supplied to peel discs. It is concluded that succinate dehydrogenase is the respiratory enzyme most affected by CO₂ concentration. Oxygen uptake was found to be 50% inhibited at ambient concentrations of 0.5% O₂ for cortical tissue and 5% O₂ for peel tissue. It is concluded that cytochrome oxidase is responsible for O₂ uptake in peel and cortical tissue. The apparent low affinity for O₂ in peel respiration may be due to limited O₂ diffusion through the tissue. It is concluded that O₂ uptake by the bulk of the apple is not directly affected by O₂ concentrations employed in fruit storage.     

Changes in enzyme activities in abscission zone and berry drop of ‘Kyoho’ grapes under high O2 or CO2 atmospheric storage

To investigate the effects of high atmospheric O₂ on berry drop in ‘Kyoho’ grapes (Vitis vinifera X V. labrusca), changes in fruit detachment force (FDF), berry abscission and enzyme activities in the abscission zone (AZ) were examined during 60 days of storage in air (control), 40% O₂+30% CO₂ or 80% O₂ at 0 °C and 95% relative humidity. There was a high negative correlation between FDF and berry drop. Cellulase activity increased over time and correlated strongly with berry abscission. Polygalacturonase (PG) activity increased markedly for the first 30 days and then decreased slightly. Pectinesterase (PE) maintained a basal level of activity at low temperatures. Cellulase, PG and PE activities were the lowest in fruits in 80% O₂, followed by 40% O₂+30% CO₂ and air storage. Peroxidase (POD) activity dropped firstly and subsequently rose sharply, which promoted by 80% O₂ and inhibited by 40% O₂+30% CO₂ compared with control. High O₂ suppressed the activities of cellulase, PG and PE, maintained higher FDF, and reduced berry abscission during storage.     

Movement of Cryptolestes ferrugineus (Coleoptera: Cucujidae) in grain columns containing pockets of high moisture content wheat and carbon dioxide gradients

The movement of the adult rusty grain beetle, Cryptolestes ferrugineus (Stephens), in 100 cm long, 10 cm diameter columns, filled with wheat of uniform or non-uniform moisture content (m.c.), was determined for horizontal and vertical placement of columns at 30°C.In horizontal columns filled with wheat of 13.5% uniform m.c., adult C. ferrugineus exhibited a trend of distributing themselves uniformly in the columns after 5 d. In the vertical columns filled with 14.7% uniform m.c. wheat, 44% of the insects moved downward after 7 d showing positive geotaxism. In the horizontal or vertical columns containing pockets of high m.c. wheat, 43-48% of the beetles aggregated in the region of high m.c. after 7 d exhibiting a hygrotactic response. Under CO₂ gradients in the columns filled with uniform m.c. wheat, 65% of C. ferrugineus moved towards higher levels of CO₂ after 1 and 5 d. Also, high levels of CO₂ were more influential in attracting C. ferrugineus (60%) after 1 d in horizontal columns containing high m.c. wheat at one end and high CO₂ levels at the other. In the vertical columns filled with pockets of high m.c. wheat and subjected to CO₂ gradients, movement of C. ferrugineus was more influenced by the combined effects of any two factors out of the three, viz., gravity, higher levels of CO₂ and high m.c. than a single factor.     

Effect of modified atmosphere and vacuum packaging on some quality characteristics and the shelf-life of “morcilla”, a typical cooked blood sausage

The effect of modified atmosphere and vacuum packaging on the shelf-life of “morcilla”, a traditional cooked blood sausage, was investigated. A total of 99 “morcillas” were packaged under vacuum and in modified atmosphere using three different gas mixtures: 15:35:50/O₂:N₂:CO₂ (atmosphere 1), 60:40/N₂:CO₂ (atmosphere 2) and 40:60/N₂:CO₂ (atmosphere 3), and stored during 2, 4, 6 and 8 weeks at 4 °C. Shelf life evaluation was based on pH, water activity (a_w), colour (CIE L*, a*, b*, C* and h*), TBARS formation and microbial counts. The results indicated that, in general, storage time affected (P < 0.05) all parameters whereas no significant differences were observed (P > 0.05) among packaging conditions. Based on the microbial counts, the shelf-life of “morcilla” would be greater than 8 weeks for all packaging conditions. Samples packaged with high CO₂ concentrations (40:60/N₂:CO₂) showed the lowest values of TBARS at the end of storage.     

The influence of headspace and dissolved oxygen level on growth and haemolytic BL enterotoxin production of a psychrotolerant Bacillus weihenstephanensis isolate on potato based ready-to-eat food products

The major objective of this study was to determine the influence of the initial headspace and dissolved O₂ level and vacuum packaging on growth and diarrhoeal enterotoxin production by Bacillus weihenstephanensis on potato based ready-to-eat food products. In general, the lower the initial headspace or dissolved O₂ level the slower the maximum growth rate (μ_max, log₁₀ CFU g⁻¹ d⁻¹), the longer the lag phase duration (λ, d) and the smaller the maximum population density (N_max, log₁₀ CFU g⁻¹) became. The slowest μ_max, the longest λ and the smallest N_max were generally found for growth under vacuum packaging. This implies shorter shelf-lives will occur at higher initial headspace or dissolved O₂ levels as the growth of B. weihenstephanensis to the infective dose of 10⁵ CFU g⁻¹ in such atmospheres takes a shorter time. Significant consumption of dissolved O₂ only occurred when growth shifted from the lag to the exponential phase and growth generally transitioned from the exponential to the stationary phase when the dissolved O₂ levels fell below ca. 75 ppb. Diarrhoeal enterotoxin production (determined via detection of the L2 component of haemolytic BL) was similar for growth under initial headspace O₂ levels of 1-20.9%, and was only reduced when growth took place under vacuum packaging. The reduction in L2 production when growth took place under vacuum was most probably related to the low final cell densities observed under this condition. Both growth and L2 production were inhibited over a 32-day incubation period at 7 °C by 40% CO₂ irrespective of the headspace or dissolved O₂ levels. The results illustrate the importance of residual O₂ and CO₂ on the shelf-stability and safety of modified atmosphere packaged potato based ready-to-eat food products with regards to B. weihenstephanensis.     

The role of peroxidase on the antioxidant potential of fresh-cut ‘Piel de Sapo’ melon packaged under different modified atmospheres

The effects of different initial in-package O₂ and CO₂ concentrations (2.5 kPa O₂ + 7 kPa CO₂, 10 kPa O₂ + 7 kPa CO₂, 21 kPa O₂, 30 kPa O₂ and 70 kPa O₂) on peroxidase activity, vitamin C content, total phenolics and antioxidant capacity of fresh-cut ‘Piel de Sapo’ melon have been investigated for 14 days at 4 °C. The radical scavenging activity of fresh-cut melon strongly increased after 9 days storage related to a synthesis of phenolic compounds, especially under 2.5 kPa O₂ + 7 kPa CO₂ atmospheres. Low O₂ levels best maintained vitamin C and phenolic content during the storage. However, stressful too-low O₂ and high CO₂ levels induced an important increase of peroxidase activity under 2.5 kPa O₂ + 7 kPa CO₂ atmosphere, which was directly related to changes of vitamin C throughout storage. Therefore, 70 kPa O₂ atmospheres are proposed to prevent anaerobic conditions during storage of fresh-cut melon and thus, reduce wounding stress and deteriorative changes related to high peroxidase activity in tissue.     

Microstructure changes of sodium carbonate-soluble pectin of peach by AFM during controlled atmosphere storage

Yellow peaches (Prunus persicu L. Batsch.) were stored under controlled atmospheres (CA) of 2% O₂ + 5% CO₂, 5% O₂ + 10% CO₂, 2% O₂ + 10% CO₂, 5% O₂ + 5% CO₂, and normal atmosphere at 2 °C, to investigate the effects of different concentrations of O₂ and CO₂ on the structure of a single sodium carbonate-soluble pectin (SSP) molecule. The microstructure changes, including aggregates and branches, were studied by atomic force microscopy (AFM) at initially, on the 15th and 45th day. The microstructure of SSP molecules and polymers showed that aggregates separated gradually with the storage time. The degradation took place in the linear backbone as well as in side chains. The degradation of SSP molecules was inhibited by lower O₂ and higher CO₂ concentrations. Almost all of the chains were composed of four basic units with widths of 11.719, 15.625, 19.531 and 17.578 nm, which can be visualized and calculated exactly by AFM. This indicated that parallel linkage or intertwist between the basic units was a fundamental characteristic of SSP molecules.     

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.     

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.     

Physicochemical and Sensory Evaluation of 'Rocha' Pear Following Controlled Atmosphere Storage

ABSTRACT: The effects of several processing factors (storage time, time in the open air at room temperature, and overhead concentrations of O₂ and CO₂) on color, firmness, polyphenol oxidase (PPO) activity, and sensory attributes of pears (cv. Rocha) grown in 2 locations were studied using a multiple linear regression model. Backward elimination (F ≥ 0.005) was used to assess the significant factors. Extended storage time, long‐time exposure at room temperature, and high O₂ concentration played major roles on color changes assessed instrumentally and further confirmed by a sensory panel. Firmness was strongly affected by storage time and by time in the open air at room temperature. Finally, PPO activity was dependent on the growing location.     

Model for Fresh Produce Respiration in Modified Atmospheres Based on Principles of Enzyme Kinetics

A respiration model, based on enzyme kinetics, was proposed for predicting respiration rates of fresh produce as a function of O₂ and CO₂ concentrations. In this model, the dependence of respiration on O₂ was assumed to follow a Michaelis-Menten type equation (r = V_m[O₂]/{K_m+ [O₂]}), and the effect of CO₂ on respiration to follow an uncompetitive inhibition model (r = V_m[O₂]/{Km + (1 + [CO₂]/ Ki) [O₂]}). The model predictions agreed well with published data for a variety of commodities and with experimental data for cut broccoli. Fresh produce respiration rates (O₂ consumption or CO₂ evolution) at various O₂ and CO₂ concentrations, as well as transient and equilibrium gas concentrations within permeable packages, could be accurately predicted with the model equations.     

The effects of thyme (Thymus vulgaris) and rosemary (Rosmarinus officinalis) essential oils on Brochothrix thermosphacta and on the shelf life of beef packaged in high-oxygen modified atmosphere

The objective of the study was to determine the Minimal Inhibitory Concentration (MIC) of thyme (29.4% thymol, 21.6% p-cymene) and rosemary essential oils (27.6% 1,8-cineole, 13.5% limonene, 13.0% β-pinene) against Brochothrix thermosphacta and to establish the feasibility of their use as components of modified atmosphere during beef refrigerated storage. The minimum inhibitory concentration (MIC) of thyme oil against B. thermosphacta is 0.05% and that of rosemary oil 0.5%. The MIC values are independent on strain and temperature of growth, however the bactericidal effects are strain dependent. The addition of any of oil at a concentration equal to 2MIC to the modified atmosphere (80% O₂/20% CO₂) does not significantly influence the microbial quality of meat. At the same time, such a concentration of the essential oils was considerably detrimental to the organoleptic factors.     

Effects of high oxygen concentration on pro- and anti-oxidant enzymes in peach fruits during postharvest periods

Peach fruits (Amygdalus persica cv. Okubao) were stored in air, controlled atmospheres (CA) of 5% O₂ plus 5% CO₂, or CA with high O₂ concentration (70% O₂ plus 0% CO₂ for 15 days, then in CA with 5% O₂ plus 5% CO₂) at 0 °C, to determine the effects of different O₂ and CO₂ atmospheres on the activities of lipoxygenase (LOX), peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), as well as malondialdehyde (MDA) content and membrane integrity during storage periods with or without 3 days of post-storage ripening at 20 °C. SOD, CAT and POD activities of the fruits stored in air markedly decreased during the first 30 days of storage, while LOX activity increased after 15 days. CA (5% O₂ plus 5% CO₂) reduced chilling injury, and delayed the reduction of SOD, CAT and POD activities compared to the control. CA with high O₂ treatment induced SOD and CAT activities and maintained membrane integrity, but no significant effect on alleviating chilling injury was found compared to CA storage. The results indicated that the decrease of SOD and CAT might contribute to the development of chilling injury in peach fruits.     

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.     

DETERMINATION OF GERMINATION PERCENTAGE AND GERMINATION INDEX—COLLABORATIVE TRIAL AND RUGGEDNESS TESTING

A method for the determination of Germination Percentage and Germination Index in malting barley has been tested by the EBC Analysis Committee and approved for inclusion in Analytica-EBC. In the collaborative trial three pairs of barley samples with high, medium and low vigour were analysed by 16 laboratories. The r₉₅ values for the Germination Percentage ranged from 0.5% to 6.3% and the R95 values ranged from 0.5% to 8.7% increasing with lower level of mean germination percentage. The r₉₅ values for the Germination Index ranged from 0.29 to 0.74 and the R95 values ranged from 0.97 to 1.20. The ruggedness testing of the Germination Index shows that the factor temperature has a minor, but significant effect on the result, the factors time for the first count together with the volume of water, have major significant effects. The tested factors have no significant effect on Germination Percentage.     

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.