Internal Atmosphere Composition Research Articles

Setting a safe target internal atmosphere for starch-based coated fruits and vegetables

Fruit surface coatings reduce gas exchange and modify the internal atmosphere composition. However, to set a safe internal atmosphere target, an optimum starch concentration must be determined for each fruit. To avoid the risk of anaerobiosis, surface coatings must be designed considering specificities in the structure and physiology of the product to be coated, properties of the coating solution, and coating-fruit surface interaction. In this study, it was developed a method for estimating the effective proportion of a starch-based coated surface using digital image processing. The starch-coated areas were stained with iodine solution and quantified using coated/uncoated region color image segmentation. To understand the need for surfactant and the optimal temperature for adding surfactant, 3% cassava starch coatings were prepared with and without Tween 40® as a surfactant. Tween 40® was added into starch matrix coating at 18 and 60 °C. These coatings were applied to bananas, mandarin oranges, and bell peppers. The coatings without and with Tween 40® (added at a warm coating) showed weak adhesion to the fruit peels, especially those with high cutin and wax levels (mandarin and pepper). However, adding Tween 40® to a cooled coating enhanced its adhesion regardless of the structure of the fruit peel surfaces. Thus, these results show for the first time that the temperature for adding the surfactant markedly affects the coated percentage area of fruits. Following this, cassava starch coatings at 1.5, 2.0, 2.5, and 3.0% with Tween 40® added at 18 °C were tested on banana and papaya. The internal levels of O 2 and CO 2 were assessed to target safe, coated fruit internal atmosphere. Increasing the starch coating content increased the fruit's coated area, resulting in a decrease in O 2 and increase in CO 2 internal levels. The internal atmosphere build-up with the highest starch content (3.0%) and Tween 40® for papaya was O 2 (5.8 kPa) and CO 2 (6.6 kPa), which is suitable for postharvest papaya storage. However, for bananas, this level of starch coating resulted in very low O 2 (1.9 kPa) and high CO 2 levels (48.6 kPa). These results demonstrate that the internal atmosphere build-up for coated fruits with similar starch matrix coating contents is fruit-specific. • An approach for estimating fruit's starch-coated area was developed. • Image segmentation of stained starch-coated fruit was used to assess the coated area. • Cooling starch matrix before adding surfactant enhances fruit coated surface area. • Internal atmosphere build-up at similar starch coating content depends on fruit type.

Use of PLA/PBAT stretch-cling film as an ecofriendly alternative for individual wrapping of broccoli heads

Broccoli heads are typically packaged and marketed in petroleum-based heat-shrinkable or stretch-cling films that are not biodegradables. These types of films are not compatible with global strategies to reduce plastics waste. One of these strategies is development of biodegradable packaging materials that can be used as an alternative food package. Therefore, a biodegradable stretch-cling film, based on poly(butylene-adipate-co-terephthalate) and poly(lactide) blend (Nature Fresh®), for its application in broccoli head packaging has been studied. To determine suitability of Nature Fresh® film for broccoli packaging, broccoli heads were wrapped in this film and stored at 2°C for 35 d. Broccolis without packaging and wrapped in linear low density polyethylene (LLDPE) were used as controls. Physicochemical and sensory evaluation were determined during storage to study the effect of films on quality and shelf life of broccoli. On the one hand, broccolis packaged in Nature Fresh® and LLDPE presented similar evolution in internal atmosphere composition, color, hydroxycinnamic acids and carotenoids content and overall appearance. On the other hand, weight loss and decrease in firmness were significantly higher in broccoli wrapped in Nature Fresh® compared to LLDPE, but this had no impact on overall appearance. Nature Fresh® extended postharvest storage of broccoli heads at least 21 d at 2ºC, which is an adequate time to market. In conclusion, Nature Fresh® film was a viable packaging alternative to LLDPE to preserve broccoli quality during postharvest storage, while fulfilling global strategies to reduce plastics waste.

Effect of harvest date on off-flavor development in mandarins following postharvest wax application

Mandarins (Citrus reticulata Blanco) are very prone to off-flavor formation following the postharvest application of wax and it had been previously observed that off-flavor also increases with advanced fruit maturity. To more fully evaluate the maturity effect on off-flavor and to determine potential causal mechanisms for it, ‘Owari’ and ‘China S-9’, two Satsuma varieties, were harvested at three to four dates within the harvest season, waxed and placed into storage for either 2 weeks at 5 °C or 1 week at 5 °C + 1 week 20 °C, the latter treatment being expected to develop off-flavor. The testing was conducted over three seasons with ‘W. Murcott’, a non-Satsuma variety, being included in the third season. In all three seasons analyses were conducted for various parameters related to fruit internal atmosphere composition. At the end of the storage period, in the first two seasons, the fruit were evaluated for flavor using a semi-expert sensory panel. Consistently, in seasons 1 and 2 where flavor was evaluated, both Satsuma varieties did not develop off-flavor or a loss in acceptability in the initial harvest. In subsequent harvests, however, off-flavor became increasingly noticeable and was correlated with the decline in flavor acceptability. There were occasional impacts on other flavor attributes, but the results were inconsistent. Advancing maturity in all three seasons was associated with a decrease in internal oxygen and an increase in internal carbon dioxide, except in the case of ‘W. Murcott’ where there was little or no change in internal oxygen and an increase in carbon dioxide. Enhanced fermentative metabolism was indicated in the later harvests in the form of higher ethanol in the Satsuma varieties. Peel gas permeance measurements performed in season 3 showed no meaningful relationship with the internal gas concentrations measured during the season. Respiration rate, however, strongly increased during the season in the Satsuma varieties and decreased in ‘W. Murcott, both changes being associated with the internal gas composition. It is concluded that maturity influences the propensity for off-flavor development in mandarins, but it does not occur in every instance and is influenced by year, storage and temperature. The potential mechanism modulating the change in the three varieties examined in this study appeared to be changes in the rate of respiration, since when respiration is sufficiently high, oxygen levels decline to a level where fermentation occurs, and off-flavor becomes apparent.

Changes in bacterial loads, gas composition, volatile organic compounds, and glucosinolates of fresh bagged Ready-To-Eat rocket under different shelf life treatment scenarios

Temperature abuse and improper shelf life treatment of Ready-to-Eat wild rocket is a leading cause of product quality losses and consumer rejection. It can cause the deterioration of appearance, the build-up of bacterial numbers, and the production of off-odours. This study subjected commercially produced and processed bags of wild rocket to various temperature and shelf life duration treatments that could hypothetically be experienced by a consumer, purchasing bags from supermarkets that have suffered cold-chain breaches. We take a unique experimental perspective that accounts for potential temperature variation scenarios within supermarkets and the home. Bacterial counts, volatile organic chemical production, glucosinolate concentration, and internal bag atmosphere composition were measured under these temperature scenarios and across growing seasons. Our results showed that the season of purchase significantly affects wild rocket respiration and bacterial loads. Prolonged high temperature abuses increased microbial loads, disulfide abundance, and reduced content of the glucosinolate glucoerucin. Short temperature abuse treatments resulted in no significant changes in bacterial numbers, providing bags were returned to cool-chain conditions. Samples stored under these conditions (<5 °C) saw no significant changes. The effect of growth season also significantly affects wild rocket respiration. Summer-grown produce had high bacterial loads, but winter-grown had a higher respiration rates. These data illustrate the importance of maintaining cold-chain conditions for wild rocket to preserve key glucosinolate compounds and prevent sulfide formation via bacterial propagation and anaerobic respiration.

Effect of temperature on glucosinolate content and shelf life of ready-to-eat broccoli florets packaged in passive modified atmosphere

Ready-to-eat fruit and vegetables comprise a group of increasingly demanded value-added products. Broccoli is a highly perishable vegetable with unique nutritional characteristics. Development of minimally processed broccoli products demands varietal-specific knowledge as to which are the packaging conditions that preserve quality throughout shelf life. ‘Legacy’ cultivar broccoli florets were washed, disinfected, packaged in polypropylene and stored at 4, 8 and 15 °C for 21 d. Weight loss, internal atmosphere composition, respiration rate, color, texture, glucosinolate content, antioxidant capacity (AOC) and sensory attributes were evaluated throughout storage time. Results showed that 4 °C helped preserve sensory quality, texture, total glucosinolate content and AOC for 21 d. Temperature fluctuations reaching 15 °C resulted in loss of total glucosinolate content and unacceptable sensory quality. MAP helped mitigate temperature effects, especially at 8 °C. MAP is therefore an appropriate technology which can be applied to extend the shelf-life of ready-to-eat broccoli florets.

Modified atmosphere packaging (MAP) and coating for improving preservation of whole and sliced Agaricus bisporus.

Freshness of mushrooms (Agaricus bisporus) was related to the internal atmosphere composition during modified atmosphere packaging (MAP) experiments using polyvinyl chloride (PVC) wrap, polyethylene-1 (PE-1) and PE-2 films. The packaged mushrooms were stored at 12°C for 7days and lightness value, browning index, weight loss and maturity index were also measured. The results obtained showed that the whiteness of whole mushrooms varied significantly with the type of coating (chitosan and CaCl2), but not with the type of packaging films. It was evident that the extent of darkening in whole mushroom was greater than in sliced ones after coated. In addition, mushroom in PE-2 package exhibited the lowest weight loss due to the lower permeability of film. And the type of packaging films significantly affected the maturity index of mushroom, where PE-2 packaging most effectively lowered maturity index for both whole and sliced mushrooms. By considering the overall quality, it was obvious that PE-2 packaging combined with coating treatment was the most effective to improve the preservation of mushrooms stored at 12°C up to 7days and satisfy consumer acceptance.

Biobased packaging for improving preservation of fresh common mushrooms (Agaricus bisporus L.)

Freshness of common mushrooms was related to the internal atmosphere composition during modified atmosphere packaging (MAP) experiments at 20 °C and 80% RH with stretchable polyvinylchloride (PVC) film, paper, and the same paper coated with a wheat gluten solution. MAP with the stretchable film led to a detrimental deterioration of mushrooms after only one day of storage: dark brown blotches appeared and almost 30% of mushrooms exhibited open veil. This was due to the formation of condensed water at the inner surface of the material and onto mushrooms combined to a high O2 partial pressure (16 kPa) in the headspace. Wheat gluten (WG) coated paper was the most effective to improve the shelf-life of mushrooms since it allowed the preservation of a fair colour, unbroken veils, and an acceptable texture during 3 days. This beneficial effect was attributed to the combination of a medium CO2 (9.5 kPa) and low O2 (2.5 kPa) partial pressure, without condensation. The main drawback of using WG-coated paper was its high water vapour permeability that led to an important weight loss (3.8 wt.% on day 3). However it did not affect the overall quality of mushrooms within the storage duration. Even with the development of micro-perforated materials that provide the largest range of O2 and CO2 permeability values, several limitations are still encountered for synthetic MAP applications such as–an insufficient perm-selectivity ratio that remains lower than 6 (value of 1 for micro-perforated material): generated atmosphere cannot reach both low O2 and low CO2 partial pressures and then are not adapted to CO2-sensitive fresh produces.–unattractive water condensation at the inner surface of the packaging that might occur due to a low water vapour permeability, favouring the development of microorganisms.–their non biodegradability. an insufficient perm-selectivity ratio that remains lower than 6 (value of 1 for micro-perforated material): generated atmosphere cannot reach both low O2 and low CO2 partial pressures and then are not adapted to CO2-sensitive fresh produces. unattractive water condensation at the inner surface of the packaging that might occur due to a low water vapour permeability, favouring the development of microorganisms. their non biodegradability. Previous studies reported a high selectivity ratio and a high water vapour permeability for biodegradable materials made from crops proteins (wheat gluten, for instance) that appeared well adapted for fresh fruits and vegetables preservation. However, despite low cost and such interesting functional properties, these materials exhibited poor mechanical properties and cannot be used as packaging material. Combination with other materials, such as cellulosic fibres, appeared to one way to get round this major drawback without losing its biodegradability. Indeed paper exhibits an environmental-friendliness potential (recyclability, sustainability, biodegradability, and compostability) and a high versatility in food packaging. By choosing common mushrooms, known to be sensitive to high CO2 content, and a stretchable PVC film, commonly used to over-wrap mushrooms in tray (on European market), we demonstrate that this material was greatly less effective than a new biobased material (wheat gluten film coated onto paper) developed in collaboration with Smurfit Worldwide Research Center. This work confirms the interest in developing functionalised paper based packaging material with agro-based polymers adapted to the storage of fresh fruits and vegetable storage in ambient temperature.

TISSUE PERMEANCE OF PRICKLY PEAR CACTUS STEMS (OPUNTIA SPP.) TO CO2, O2 AND H2O VAPOR AS A FUNCTION OF TEMPERATURE AND RELATIVE HUMIDITY

Characterization of the internal atmosphere composition offers the potential to explain variability in response of horticultural products to modified atmospheres (MA) treatments and to quantify permeance of skin to respiratory gases. Stem skin permeance to O 2 βO2) and CO 2 (βCO2) were determined as a function of temperature (T) and relative humidity (RH). Surface chambers close to equilibrium with the stem's internal atmosphere were used to monitor internal atmosphere composition of prickly pear cactus steam. Physical equilibration of chamber contents over fruit surface was completed approximately in 4 h. However, physiological changes in the composition of internal atmosphere indicate that substantial changes continued to develop for extended periods. βO2 decreased in greater proportion than βCO2 at high RH, as a result an inversely proportional relation between permeance to gases and the RH was determined. βH20 also decreased as RH increased. The Arrhenius model describes the T effect on tissue permeance. The following function describes the effect of T and RH on tissue permeance β x = (P 0· RH P 1 +P 2 ).e (1/T) . Surface chambers adhered over stem surface are adequate to quantify the composition of the atmosphere in direct contact with the stem cells.

QUALITY CHANGES IN FRESH CHIVES (ALLIUM SCHOENOPRASUM L.) DURING REFRIGERATED STORAGE

ABSTRACT This study investigates quality changes in fresh chives stored at 0 and 4C during 21 and 14 days, respectively. The product was packaged in trays and covered with polyvinyl chloride films. Weight loss, surface color, total chlorophyll, carotenoids, reducing sugars and browning potential were evaluated in order to determine shelf life at each temperature. In addition, internal atmosphere composition, total phenolics, radical scavenging activity and ascorbic acid content were measured for samples stored at 0C. Results showed that surface color change and losses of green pigments and reducing sugar content could be delayed for a week by storing fresh chives at 0C. The increase in browning potential was of lower magnitude at 0C than at 4C. High quality levels and marketability of fresh chives could be maintained for 2 weeks at 0C. PRACTICAL APPLICATIONSThe marketing of packaged and refrigerated, value‐added culinary herbs is a choice of increasing interest for vegetables processors. However, data on changes in the chemical composition and antioxidative properties of fresh herbs during storage are scarce. This study provides information on how quality attributes of fresh chives are affected under different conditions of postharvest handling and storage.

Modelling the gas exchange rate in perforation-mediated modified atmosphere packaging: Effect of the external air movement and tube dimensions

Perforation-mediated modified atmosphere packages control the gas exchange rate and thus the internal atmosphere composition by judicious choice of dimensions of small tubes in perforations in an otherwise hermetic container. The aims of this work were (i) to study the effect of external turbulence on the gas exchange rate through small perforations, (ii) to develop a mathematical model to predict the effect of tube dimensions and hydrodynamic conditions on gas exchange coefficients, and (iii) validate the model developed during the storage of shredded carrots. Different hydrodynamic conditions in the controlled temperature room due to the storage temperature settings (5, 10 and 15 °C) and PVC tubes dimensions (diameter from 1.5 to 4.5 mm length from 2.0 to 6.0 mm) were tested. Results showed that, as expected, hydrodynamic conditions (induced turbulence) and tube diameter had a significantly positive effect on the mass transfer values, whereas tube length had a negative effect. The permeability ratio between CO 2 and O 2 was 0.83 ± 0.01 and did not show any pattern with the factors tested. The gas exchange coefficients increased with decreasing temperature, as the establishment of lower temperatures implied a frequent air movement. A mathematical model to estimate changes of gas composition over time as a function of tube dimensions and hydrodynamic conditions was developed and found to have good predictive abilities. The model was validated during the storage of shredded carrots at 5 °C in PM-MAP, showing a good agreement between the experimental and predicted gas exchange of O 2 and CO 2. The results obtained in this work showed that hydrodynamic conditions of the cold storage room affected the gas exchange rate in PM-MAP.

Vida útil de fatias de manga armazenadas em embalagem com atmosfera modificada passiva

Fatias de manga fresca e osmoticamente desidratadas foram acondicionadas em bandejas de poliestireno expandido, recobertas com filme de polietileno de baixa densidade (PEBD) e estocadas à temperatura de 5 °C com o objetivo de verificar o efeito da desidratação osmótica e da embalagem com atmosfera modificada passiva na vida útil das frutas. Amostras de manga fresca, acondicionadas nas condições do ar atmosférico, foram utilizadas como controle. As mangas foram avaliadas periodicamente quanto às suas características físico-químicas e microbiológicas, composição da atmosfera interna das embalagens, perda de peso e aceitação sensorial. O processo de desidratação osmótica e o acondicionamento das frutas com atmosfera modificada influíram positivamente na manutenção das características sensoriais e na qualidade microbiológica das fatias de manga. As fatias de manga fresca acondicionadas nas condições do ar atmosférico (FR AR) e com atmosfera modificada (FR MAP) apresentaram uma vida útil de apenas 8 e 14 dias, respectivamente, sendo limitada principalmente por sua aceitação sensorial e contaminação microbiológica. Já as frutas desidratadas osmoticamente e embaladas com atmosfera modificada (OD MAP) apresentaram uma vida útil de 18 dias com boa aceitação sensorial durante toda a estocagem.

Effect of passive and active modified atmosphere packaging on quality changes of fresh endives

Quality changes of fresh endives were related to packaging condition and development of the internal atmosphere composition. Three packaging conditions were tested at 20 °C: a macroperforated oriented polypropylene (OPP) pouch considered as “unmodified atmosphere packaging” (UAP) and a low density polyethylene (LDPE) pouch with or without an individual oxygen scavenger sachet to create active or passive modified atmosphere packaging (MAP), respectively. With a steady modified atmosphere composed of 3 and 4.5 kPa of O 2 and CO 2, respectively, the effect of passive MAP on colour changes in endives was similar to that of UAP. Benefit of MAP of endives was obtained by using an O 2 scavenger, i.e. active MAP, that did not change O 2 and CO 2 partial pressure during the steady state period, compared to passive MAP, but induced a 50% reduction of the transient period. This reduction led to an important delay in greening and browning of endives.

USE OF CARAMBOLA (AVERRHOA CARAMBOLA L. ´FWANG TUNG´) FRUIT AT TWO STAGES OF MATURITY FOR FRESH-CUT PRODUCTS

Carambola fruit ('Fwang Tung') were picked at two stages of maturity: mature-green (50% yellow) and mature (100% yellow). Fruit were washed with water, dipped in NaOCI solution (200 mg.L -1 for 5 minutes), and stored over night at 10°C. Fruit were sliced manually in to pieces of approximately 1 cm thickness. Slices were rinsed with NaOCI solution at 20 mg.L -1 , drained for 3 minutes, and packaged in polyethylene tereftalate (PET) trays provided with a fit cover (Neoform® N94). Packages were stored at 6.5°C and 85% RH for 9 days, and samples taken every 3 days for physical, chemical and biochemical analysis, respiration, and internal atmosphere composition. Immediately after cutting, slices at both stages of maturity showed a wounding response with a 5-fold increase in respiration rate. Polygalacturonase (PG) and polyphenol oxidase (PPO) activity did not differ between stages of maturity. Despite the less mature stage being less preferred at the sensory evaluation owing to its greenish peel, the best stage of maturity for carambola fresh-cut production was mature-green, due to a higher resistance to cutting, and presenting a better colour and appearance maintenance for up to 9 days.

ACTIVE PACKAGING DEVELOPMENT TO IMPROVE ´STARKING´ SWEET CHERRY POSTHARVEST QUALITY

'Starking' sweet cherry belongs to the Denominacion Especifica Cereza de la Montana, Alicante, Spain and is considered a late season cultivar in this area with several problems for commercialisation mainly due to incidence of decay and a fast loss of sensory quality, both for fruit and green stem. Based on this issue, an active packaging has been developed based on the addition of 1 mL eugenol (essential oil from oregano) to trays and then sealed with polypropylene bags to generate a modified atmosphere (MAP). Also, cherries in MAP (without eugenol) and non-packaged fruits were selected and served as controls. Both bags and non-packaged cherries were stored during 16 days at 2°C and 90% RH. Samples were taken after 2, 6, 9, 13 and 16 days in which the internal atmosphere composition, weight loss, colour, °Brix-titratable acidity ratio, firmness, visual aspect of the stem and microorganism proliferation were evaluated. Steady state atmosphere was reached after 9 days of cold storage with 2-3% of CO 2 and 10-11% of O 2 with no significant differences between treated and control. When fruit quality parameters were determined, those treated with eugenol showed a significant reduction in weight loss compared with control, either under MAP or not. Contrarily, colour parameter L* and fruit firmness remained significantly higher during storage in treated cherries than in controls, under MAP or not. °Brix-titratable acidity ratio increased during storage in control fruits, while no significant changes were observed under MAP storage. When the stem was evaluated, this remained green in cherries stored in MAP, while they became brown in control. Finally, the microbial analysis showed that eugenol treatment reduced yeast, mold and total aerobic mesophylic colonies 2 and 3-log CFU compared with control under MAP or not, respectively. In conclusion, the use of MAP in combination with eugenol is an effective tool on maintaining cherry fruit quality and reducing the occurrence of decay.

Skin Permeance and Internal Gas Composition in `Hass' Avocado (Persea americana Mill.) Fruits

The gas skin permeance and the internal atmosphere composition of `Hass' avocado (Persea americana Mill.) fruits were evaluated during the ripening period by using surface chambers. Plant material was harvested at physiological maturity at Uruapan, Michoacan, Mexico, in November of 2001. Storage was conducted under natural atmosphere at 20°C and 81% RH; the physiological stages were expressed in terms of ethylene internal partial pressures and pulp firmness. The climacteric onset occurred at 18.2 N and the peak was reached at 5.0 N. The interñal partial pressure decreased consistently for O2 while for CO2 increased. This result suggested that the resistance to gas exchange imposed by skin caused that O2 taken up was not enough to supply fruit requirements and also that CO2 was produced faster than the rate at which it was given off to ambient. It was found that skin permeance to O2 and CO2 could vary during ripening period and that avocado skin was more permeable to O2 than to CO2 with a 1.7:1 ratio. Surface chambers were useful to determine internal concentrations and gas skin permeance, but care must be taken to select the best sampling procedure to allow getting accurate values of these parameters.

Characterising ripening behaviour of coated pears in relation to fruit internal atmosphere

Abstract Pear ( Pyrus communis L.) cultivars ‘Bartlett’, ‘Beurre Bosc’, ‘Doyenne du Comice’, and ‘Packham's Triumph’ were treated at harvest or after cold storage with concentrations of 0, 5, 10, 20, 40, and 100% (v/v) of a commercial carnauba-based wax emulsion. Fruit were assessed for ripening and internal atmosphere composition at 0°C/90–95% RH (only for ‘Comice’) and at 20°C/60–70% RH (for all cultivars, after they achieved the chilling requirement to ripen). For all cultivars coated at harvest and ripening at 20°C, respiration rates, softening and colour change followed a Michaelis–Menten model when plotted against internal partial pressure of O 2 p O 2 i , while internal partial pressure of CO 2 ( p CO 2 i ) had virtually no explanatory power for these variables. This supports the notion that modification of p O 2 i rather than p CO 2 i is the principal means by which coating achieves its effects on ripening behaviour of pears during shelf life. Michaelis–Menten constant values ( K m ) for respiration and softening were lower than those for colour change for all cultivars at 20°C. This resulted in colour change being retarded by any level of depression in p O 2 i created by coating, while firmness was substantially reduced only at much lower p O 2 i during shelf life. Plots of p CO 2 i and respiration versus p O 2 i for fruit coated either pre-climacteric (at harvest) or entering the climacteric (after cold storage), indicated that ‘Comice’ and ‘Packham's’ were tolerant to hypoxia whereas, with ‘Bartlett’ and ‘Bosc’, tolerance reduced with advancing ripening, and the latter cultivar was the least tolerant of all four cultivars. During storage at 0°C of ‘Comice’, coatings had a more substantial effect in delaying softening than colour change; firmness retention seemed to be related to increase of p CO 2 i , while the limited suppression of colour change seemed to be related to small reductions of p O 2 i . Therefore, optimisation of surface coatings for pears must account for differences between cultivars and ripening stage at which fruit are coated, as well as the temperature at which the fruit are going to be held.

Physicochemical properties and application of pullulan edible films and coatings in fruit preservation

AbstractThe effects of water, sorbitol and a sucrose fatty acid ester (SE) on the water sorption behaviour and thermal and mechanical properties of pullulan‐based edible films as well as the physiological responses of fruit coated with pullulan have been studied. Incorporation of sorbitol or SE in pullulan films resulted in lower equilibrium moisture contents at low to intermediate water activities (aw), but much higher moisture contents at aw &gt; 0.75; estimates of monolayer values (within 4.1–5.9 gH2O kg−1 solids) were given by application of the Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–DeBoer (GAB) models. A single glass–rubber transition (Tg), attributed to the polysaccharide component, was detected by calorimetry and dynamic mechanical thermal analysis (DMTA) at a sorbitol level of 15–30% DM. With both tests the strong plasticising action of water and polyol was evident in the thermal curves, and the Tg vs moisture content data were successfully fitted to the Gordon–Taylor empirical model. Multifrequency DMTA measurements provided estimates for the apparent activation energy of the glass transition in the range of ˜ 300–488 kJ mol−1. With large‐deformation mechanical testing, large decreases in Young's moduli (tensile and three‐point bend tests) were observed as a result of water‐ and/or polyol‐mediated glass‐to‐rubber transition of the polymeric films. In the moisture content range of 2–8%, increases in flexural modulus (E) and maximum stress (σmax) with small increases in moisture content were found for films made of pullulan or pullulan mixed with 15% DM sorbitol; a strong softening effect was observed when the water content exceeded this range. Addition of sorbitol increased the water vapour transmission rate of the films, whereas addition of SE had the opposite effect. Application of a pullulan/sorbitol/SE coating on strawberries resulted in large changes in internal fruit atmosphere composition which were beneficial for extending the shelf‐life of this fruit; the coated fruit showed much higher levels of CO2, a large reduction in internal O2, better firmness and colour retention and a reduced rate of weight loss. In contrast, similar studies on whole kiwifruits showed increased levels of internal ethylene, which caused acceleration of fruit ripening during storage.© 2001 Society of Chemical Industry

Internal atmosphere composition and skin permeance to gases of pepper fruit

Abstract Characterisation of internal atmosphere composition offers the potential to explain variability in responses of horticultural crops to modified atmosphere treatments and to quantify permeance of fruit skins to the respiratory gases. In this paper, the theoretical basis by which fruit skin permeance can be calculated from other gas exchange variables is presented. Surface chambers close to equilibrium with the fruit’s internal atmosphere were used to monitor internal atmosphere composition of sweet pepper (Capsicum annum, cv. Reflex). Physical equilibration of chamber contents over wounded fruit surface was essentially complete in less than 4 h. However, physiological drift in internal atmosphere composition meant that substantial changes continued to develop over more extensive periods. Removal of cuticle beneath the chamber was shown to be essential for equilibration of chamber contents within physiologically meaningful periods. Samples of atmosphere removed destructively from the fruit cavity consistently contained more O2 but less CO2 than samples similarly removed from the fruit flesh. Levels of CO2 were higher in samples removed directly from the flesh by syringe than in those taken from surface chambers, indicating potential for an effect of the vacuum used to take direct removal samples on sample composition. Permeance of pepper cuticle to CO2 was about ten times greater than that to O2 (∼244 and 24 pmols−1m−2 per Pa, respectively). Removal of cuticle dramatically increased permeance of the fruit surface and hastened equilibration of surface chambers with the fruit’s internal atmosphere. Surface chambers adhered over fruit surface from which the cuticle has been removed would be the most reliable means to assess composition of the atmosphere in immediate contact with the cells of pepper tissue.

Effects of temperature on gas exchange of ‘Braeburn’ apples

Gas exchange attributes of fruits affect their responses to modified atmosphere and surface coating treatments. In this study, variations in respiration rate, internal partial pressures of O2 and CO2, and skin permeance to O2 and CO2 associated with storage at 0, 5, 10, 15, 20, 25, and 30°C were characterised in ‘Braeburn’ apples (Malus domestica Borkh.) There was an 11‐fold difference in respiration rate between fruit kept at 0 and 30°C, although permeance to each of the two respiratory gases differed only by a factor of two. The differing effects of temperature upon these two variables was responsible for the depression of internal O2 and elevation of internal CO2associated with increase in temperature from 0 to 30°C. The magnitude of decline in internal O2 was slightly greater than the increase in internal CO2 over the temperature range in the experiment. For apples that were respiring aerobically, and with a respiratory quotient of unity, this would indicate that the fruit skin had a somewhat higher permeance to CO2 than to O2, Permeance values for the two respiratory gases were strongly related but permeance to CO2 exceeded that to O2 for fruit with a low permeance to O2. This is attributable to the greater ease of diffusion of CO2 through the cuticle, an effect which became more pronounced as transcuticular diffusion was facilitated at high temperatures. Given the importance of internal atmosphere composition in affecting respiration rate and disorder development in apples, the gas exchange characteristics of ‘Braeburn’ appear likely to be influential in the outcome of different storage regimes.

Approaches to optimising surface coatings for fruits

A mathematical model predicted that final water vapour permeance in surface‐coated fruits would depend upon water permeance of the coating but not the proportion of pores blocked on the fruit surface. In contrast, predicted final oxygen (O2) permeance depended upon numbers of pores blocked but not O2 permeance of the coating. Predicted variation in internal atmosphere composition caused by coatings that blocked different proportions of pores on the model fruit surface was consistent with data from two experiments on coated apples (Malus domestica Borkh.). A new equation was developed to characterise the relationship between internal carbon dioxide (CO2) and O2 levels resulting from different coating treatments. Two graphical approaches to assess surface coatings for fresh fruits are presented. In the first, a plot of water vapour permeance against internal O2 was used to identify the most suitable of three surface coatings for reducing water loss in ‘Royal Gala’ apples at 20°C. The second method used a plot of internal CO2 versus internal O2 in coated fruit to identify the crop's internal lower O2 limit (LOLi), which lies just below the optimum internal O2 level for modified atmosphere effects. Coatings containing different concentrations of carboxymethyl cellulose produced internal O2 levels ranging from almost 0 to 16 kPa in ‘Granny Smith’ apples at 20°C. The LOLi of these fruit was estimated using the new equation to be c. 0.8 kPa O2. Large fruit‐to‐fruit variability with some coating treatments indicated that uniformity of response may be as important as average response in selection of coatings. Risks cannot be separated from benefits when using surface coatings to gain modified atmosphere benefits, making their use to achieve modified atmosphere benefits more risk‐laden than for other purposes.