EFFECTS OF SHRINK FILM WRAP ON INTERNAL GAS CONCENTRATIONS, CHILLING INJURY, AND RIPENING OF HONEYDEW MELONS

Honeydew muskmelons (Cucumis melo L.) were individually wrapped with polyvinyl chloride (PVC) shrink film and stored at 2.5° or 7.5 °C for 21 days and examined, then held an additional 2 or 3 days at 20°C and examined again. Nonwrapped melons were the control. The concentration of CO₂ in the cavity of wrapped melons stored 21 days was 5.6% at 2.5°C, 9.1% at 7.5°C, but only 1.1% and 1.5% in the nonwrapped held at 2.5°C or 7.5°C, respectively. Wrapped fruit ripened slower than nonwrapped fruit during storage and subsequent holding at 20°C, after which time 70% of the wrapped melons were rated eating ripe, but 62% of the controls were overripe. Wrapped melons exhibited 30% less chilling injury (CI) symptoms than nonwrapped fruit stored at 2.5°C. The CI symptoms ranged from reddish-brown to dark-brown surface discolorations and sometimes included dry sunken areas of skin. Fresh weight loss was about 1 % in wrapped melons, but 5% in nonwrapped fruit, regardless of storage temperature. Decay incidence was about equal in wrapped and nonwrapped melons after storage at 2.5°C, but was greater for wrapped than nonwrapped melons after storage at 7.5°C. Soluble solids content was about 12.5% in wrapped and nonwrapped melons stored at either temperature.     

PROLONGING THE SHELF-LIFE OF FRESH GREEN CHILE PEPPERS THROUGH MODIFIED ATMOSPHERE PACKAGING AND LOW TEMPERATURE STORAGE

The postharvest quality of green chile fruit was compared after storage in 3 types of packages at 2 temperatures (24C and 8C). Package types were corrugated cardboard boxes, pressed cardboard trays overwrapped with VF-71 polyethylene, or low-density polyethylene (LDPE) bags. Fruit packaged in boxes or overwrapped trays had 24.8% and 10.1% weight loss, respectively, after 1 week of storage at 24C. Fruit packaged in polyethylene bags lost 0.3% weight and remained green. After 1 week at 8C, the weight losses were 3.8%, 1.8% and 0% for the boxed, overwrapped and bagged treatments, respectively. Postharvest quality was maintained up to 4 weeks when fruit were packaged in LDPE bags and stored at 8C. In a second study, steady state O₂ and CO₂ levels were determined inside the LDPE packages as fruit weight and temperature were varied. Storage temperatures were 24C, 16C and 8C. At 8C, steady state O₂ levels ranged from 12.0 kPa to 0.9 kPa, and CO₂ levels ranged from 2.0 kPa to 4.6 kPa as fruit weight was increased from 120 to 480 g. At 24C and 16C, fruit packaged in 480 g units had slower ripening rates than fruit packaged in smaller units; however, fruit stored at 8C remained green the longest, regardless of fruit weight.     

QUALITY OF MINIMALLY PROCESSED LETTUCE AS INFLUENCED BY PACKAGING AND CHEMICAL TREATMENT

Shredded lettuce was packaged in sealed bags of monooriented polypropylene (OPP) film and also in polyethylene (PE) trays overwrapped with a multilayer polyolefin (RD106) or plasticized polyvinyl chloride (PVC) film; and stored at 4C in a refrigerated case during 8 days. Chemical treatment by dipping in a 0.3% ascorbic acid /0.3% citric acid solution did not significantly affect changes in microbial populations or visual sensory attributes. Type of package was not a significant factor for microorganism populations, but was significant (p<0.001) for changes in gas composition and visual sensory attributes. The modified atmosphere within the packages changed from normal air composition to about 1.5% O₂/12% CO₂ for OPP bags and to about 17–18% O₂/1–2% CO₂ for PVC-PE trays and RD106-PE trays after 8 days of storage. The visual sensory quality of the product was retained better in OPP bags than in the other ones.     

Controlling Temperature and Water Loss to Maintain Ascorbic Acid Levels in Strawberries During Postharvest Handling

‘Chandler’, ‘Oso Grande’ and ‘Sweet Charlie’ strawberries were stored for 8 days at 1 or 10°C, or 4 days at 20°C, either unwrapped or wrapped in PVC film to retard were conducted during the 1 water loss. Total ascorbic acid (AA) content was expressed on a dry weight basis to correct for water loss differences between treatments. Loss of AA was low and did not differ between wrapped treatments at 1 and 10°C, but was much greater at 20°C. Wrapping reduced AA loss by 5-fold at 1 and 10°C and by 2-fold at 20°C. The effect was not due to modification of O₂ and CO₂ levels in wrapped treatments, which was minimal. The results indicate that water loss had a greater effect on AA levels than temperature. Combining wrapping with storage at 1 or 10°C reduced AA loss by 7.5-fold compared to unwrapped strawberries stored at 20°C.     

STORAGE QUALITY OF MINIMALLY PROCESSED CABBAGE PACKAGED IN PLASTIC FILMS

The effects of packaging and storage at 3C in a refrigerated case on quality changes of minimally processed cabbage were studied. Shredded cabbage samples were packaged in three forms: bags of monooriented polypropylene film (OPP bags) and polyethylene trays overwrapped with a multilayer polyolefin (RD106-PE tray) or with a plasticized PVC film (PVC-PE tray). All types of package effectively controlled the weight loss. The modified atmosphere in PVC-and RD106- PE trays did not change more than 3% as compared with normal atmosphere levels. However, in OPP bags, O₂ reached 2% and CO₂ increased to approximately 13% after 3 days. The microbiological quality during the storage period for all types of packaging was satisfactory. OPP samples were significantly better (p <0.05) in general appearance, wilting and browning but developed an off-odor. No off-odor was detected in samples packaged in PVC and RD106-PE trays. Shelf life for the three packaging forms was estimated.     

Development of Staphylococcal Toxin and Sensory Deterioration During Storage of Nitrogen and Vacuum Packaged Nitrite-Free Bacon-Like Product

Toxin production by S. aureus was studied in nitrite-free bacon-like product packaged in air permeable film, vacuum packages, and packages flushed with N₂ during storage at 8°C, 12°C or 26°C. Product wrapped in air permeable film deteriorated rapidly at 26°C and was rejected by sensory evaluation prior to staphylococcal enterotoxin detection. Enterotoxin was not detected in vacuum or N₂-flushed packages stored at 26°C. Samples stored at 12°C supported S. aureus growth although enterotoxin was not detected at 12°C or 8°C in any packaging environment. The potential for staphylococcal food poisoning resulting from the production of a nitrite-free bacon-like product was limited under the conditions studied.     

Free-Volume Changes in Flexible, Hermetic Packages Containing Respiring Produce

To investigate free-volume changes in flexible, sealed packages containing respiring fruits and vegetables, a simple method based on the dilution of an injected gas (ethane) in the package was developed. Free-volume decreased steadily at ～3 cm³/day after an initial transient period in low-density polyethylene packages (29-μm-thick film; 600-cm² surface area; initial free volume ～285 cm³) containing 40g of cut broccoli held at 0°C. A general transient model was developed that showed that free-volume changes in flexible packages were a function of differential film O₂, CO₂, and N₂ permeabilities and differential product O₂ uptake and CO₂ production rates. The model predicted that flushing packages with low permeative gases would decrease free-volume depletion rate, whereas flushing with highly permeative gases, such as CO₂, would increase the initial rate considerably.     

Quality and Shelf Life of Individually Shrink-Wrapped Peaches

Fresh redglobe peaches were defuzzed, treated with fungicide and shrink wrapped individually in polyolefin film. The wrapped and unwrapped fruits were stored at 1°C and 10°C, respectively, for periods up to 50 days. Samples of peaches were tested every week to examine the changes in quality as determined by visual observation, weight loss, titratable acidity, % soluble solids, texture and sensory profiles. Weight loss of fruits was reduced tremendously by shrink wrapping. The appearance, flavor and overall eating quality of the wrapped peaches were found to be better than the control fruits. The shelf life of wrapped peaches was 5–6 weeks at both 1°C and 10°C as opposed to 3–4 weeks at 1°C for the control peaches.     

Packaging of Scallops with Sorbate: An Assessment of the Hazard from Clostridium botulinum

Toxin production in shucked scallops by a mixture of 10 strains of Clostridium botulinum (types A, B, E, F) was studied using mouse bioassay. Scallops, with or without 0.1% potassium sorbate, were packaged in air-permeable film or vacuum packaged in impermeable film. Two trials were done in which packages were inoculated with different spore levels and held at 4°, 10° and 27°C. Bacterial counts were made on various selective media. Only type A toxin was observed and this only in evacuated packages held at 27°C. Toxin developed more rapidly in the presence of sorbate. All packages in which toxin was recorded had offensive odors and were visibly spoiled. The potential hazard from botulism is discussed.     

Effect of initial oxygen concentration and film oxygen transmission rate on the quality of fresh‐cut romaine lettuce

Modified atmosphere packaging (MAP) is widely used to maintain the quality of fresh‐cut produce by matching the oxygen transmission rate (OTR) of the packaging film to the respiration rate of the packaged product. The effect of the interaction between film OTR and the initial headspace O₂ on quality of fresh‐cut vegetables has not previously been reported. Romaine lettuce leaves were sliced, washed, dried and packaged with film OTRs of 8.0 and 16.6 pmol s^?1 m^?2 Pa^?1, and with initial headspace O₂ of 0, 1, 2.5, 10 and 21 kPa. Packages were hermetically sealed and stored at 5 °C for up to 14 days. For samples packaged in 16.6 OTR film, increasing the initial headspace O₂ concentration delayed O₂ depletion within the packages, hastened the onset and increased the intensity of discoloration, and inhibited the development of CO₂ injury, acetaldehyde and ethanol accumulation, off‐odors and electrolyte leakage. With 8.0 OTR‐packaged lettuce pieces, ≤1 kPa initial headspace O₂ treatments induced an essentially anaerobic environment within the packages and increased acetaldehyde and ethanol accumulation and off‐odor development. Increasing the initial O₂ concentration above 1 kPa in 8.0 OTR packages transiently increased O₂ concentrations and reduced fermentative volatile production, off‐odors, electrolyte leakage and CO₂ injury. Regardless of initial headspace O₂ concentration, all 16.6 OTR‐packaged samples had severe discoloration after 14 days of storage. Quality was better maintained in 8.0 OTR‐packaged lettuce pieces as the initial headspace O₂ concentration was increased. A 21 kPa initial O₂ treatment of 8.0 OTR‐packaged lettuce maintained good quality throughout storage and had the best overall quality score. Copyright © 2005 Society of Chemical Industry     

Retail Shelf-Life of Pork Dipped in Organic Acid before Modified Atmosphere or Vacuum Packaging

Modified atmosphere packaging (MAP) is increasingly popular for meat, but raw, chilled pork in vacuum or anoxic environments has a purple color. The retail shelf‐life of pork chops dipped in 500 ppm ascorbic acid, 250 ppm citric acid, or no acid dip and stored at 1 °C before simulated retail display in MAP with gas exchange or air‐permeable packaging after vacuum pouch storage was determined. The 80% N₂:20% CO₂ in MAP was exchanged with 80% O₂:20% CO₂, and chops were removed from vacuum packages and overwrapped with permeable film (VP‐PVC) on the 7th day before simulated retail display at 4 °C. Shelf‐life traits were determined at 1, 7, 8, 10, 12, and 14 d postpackaging. The pH values changed with time, but returned to post‐dipped, prepackaged levels at the end of simulated retail storage. Weight loss of chops increased (P < 0.05) in VP‐PVC compared with MAP. The a* values increased (P < 0.05) and L* and b* values decreased during simulated retail display, with higher L*, a*, and b* color values for chops in MAP than VP‐PVC. Log numbers of psychrotrophic microorganisms were higher (P < 0.05) on VP‐PVC samples than for chops in MAP on days 12 and 14. Psychrotrophic counts on ascorbic acid‐treated samples were decreased compared with citric acid or no dipping on pork during simulated retail display. Pork chops in MAP with gas exchange had lighter and redder color, increased weight retention, decreased psychrotrophic counts, and increased lipid oxidation compared with conventional vacuum and overwrap packaging systems.     

Role of Acetaldehyde Production in the Removal of Astringency from Persimmon Fruits under Various Modified Atmospheres

Astringency of persimmons was removed by enclosing the fruits in polyethylene bags under vacuum or by replacing air with N₂ or CO₂. Acetaldehyde produced by the fruit under these conditions accumulated at different rates. The rate of the deastringency process was directly proportional to the level of acetaldehyde accumulation. Thus, the fruit held at 20°C in CO₂ was the first to lose its astringency, but showed internal browning after 1 wk. Fruits under vacuum or N₂, where less volatiles accumulated, maintained their high quality and firmness for 2 wk at 20°C or 3 months at ? 1°C. However, fruit held under vacuum began to show internal browning when acetaldehyde accumulated above a certain level.     

Development of Botulinal Toxin and Sensory Deterioration During Storage of Vacuum and Modified Atmosphere Packaged Fish Fillets

Toxin production by C. botulinum type E was studied in cod, whiting, and flounder filets packaged in air-permeable film, vacuum packages and packages flushed with N₂ or CO₂ during storage at 8°, 12° or 26°C. Cod and whiting filets were flushed with CO₂ and stored continuously at 4°C or cycled between 4° or 8° and 26°C. Cod and whiting fillets were flushed with gas mixtures and stored at 8°C or 26°C. Flounder deteriorated rapidly and was rejected by sensory evaluation prior to toxin detection during vacuum or modified atmosphere storage at 12°C and 8°C but after toxin detection at 26°C. Toxin was present either prior to or simultaneously with sensory rejection of cod and whiting fillets for all vacuum or modified atmosphere treatments and temperature regimens.     

Control of Microbial Spoilage on Fresh Poultry using a Combination Potassium Sorbate/Carbon Dioxide Packaging System

The effects of potassium sorbate combined with vacuum or carbon dioxide modified atmosphere packaging on natural poultry spoilage flora were examined. Fresh chicken thighs were dipped into either 2.5% potassium sorbate solution or distilled water, adjusted to pH 6.0 and packaged on trays in Nylon/Plexar/Surlyn bags. Atmospheres of either air, vacuum or 100% C0₂ were created in the packages which were then stored at 10 ± 1°C for 10 days. Changes in aerobic plate counts, lactic acid bacteria and pseudomonads were monitored. The combination of CO₂ packaging and sorbate treatment provided the most effective inhibitory system against the poultry spoilage organisms, especially Pseudomonas species, without creating a selective environment for the growth of lactic acid bacteria and premature souring of the product. The shelf life of the sorbate/CO₂ samples was extended 3 days over the control/air samples at 10°C.     

Centralized Packaging of Beef Loin Steaks with Different Oxygen-Barrier Films: Physical and Sensory Characteristics

Vacuum packaged beef strip loins (n = 72) were stored (2 ° 1°C) for either 0, 12 or 24 days before fabrication; steaks were packaged and displayed (2°C or 7°C) up to 6 days in oxygen-permeable film or up to 30 days in vacuum packages (medium or high oxygen-barrier film). Steaks displayed at 2°C, rather than 7°C, tended to have higher overall appearance scores especially when steaks were from 12 or 24 day subprimals. Overall palatability of vacuum packaged steaks was unacceptable after 10–15 days of display. Vacuum packaged steaks can be displayed for 10 days if: (1) steaks are from relatively fresh subprimals, (2) steaks are vacuum packaged with high oxygen-barrier film, and (3) steaks are displayed at 2°C. Although visual scores for vacuum packaged steaks were acceptable for 20–30 days, off-odors and off-flavors were limiting factors in determining shelf-life.     

Modified atmosphere packaging as a means to alleviate package expansion of Korean fermented red pepper paste

Summary Korean fermented red pepper paste was packaged under a modified atmosphere (MA) of 30% CO₂/70% N₂ and 100% CO₂. A plain air package was also prepared as a control for comparison. The MA conditions were applied with a high gas barrier film and subsequently with a gas permeable film. Throughout the storage period at 13 °C, package volume, headspace gas composition, microbial flora, surface colour, pH and acidity were measured. An MA of 100% CO₂ suppressed the growth of aerobic bacteria and yeasts, and reduced the CO₂ production from the paste without any adverse effect on product quality, and thus alleviated the volume expansion of flexible packages stored at 13 °C. However, the reduced volume expansion for the package of high‐barrier film was not sufficient in prolonged storage. An MA package of 100% CO₂ using plastic film of appropriate gas permeability could be stored at 13 °C for 150 days without volume expansion or any adverse quality changes, and was also tolerant to temperature abuse conditions at 25 °C.     

Quality of Strawberries Automatically Packed in Different Plastic Films

The quality of strawberries (Fragaria ∞ ananassa Duch. cvs. Oso Grande and Camarosa) non wrapped or packed in cellulose, perforated polypropylene, nonperforated polypropylene (automatically), and polyvinylchloride (manually) during storage at 18°C was compared. Nonperforated polypropylene packages of fruit had the highest CO₂ and the lowest O₂ content, and the most desirable quality parameters. However, this type of package had undesirable appearance due to water condensation. Cellulosic films maintained a well balanced internal atmosphere, but were wrinkled. Perforated polypropylene and polyvinylchloride packages exhibited the best appearance, but fruits packed in perforated polypropylene o films rapidly deteriorated. Unwrapped fruits had the least desirable quality in both varieties.     

Storage of mushrooms in pre-packs: The effect of changes in carbon dioxide and oxygen on quality

Mushrooms (Agaricus bisporus) were picked at the “button” stage (velum differentiated but unbroken) and stored for 3 to 5 days at 2 or 18 °C in styrene punnets (pre-packs) overwrapped with one of a range of plastic films. Concentrations of carbon dioxide and oxygen were measured inside the pre-packs at intervals. When the packs were opened, internal and external browning, loss of weight and diameter of the mushrooms were measured and subjective assessments of quality were made. These parameters were compared with those of mushrooms stored in unwrapped punnets. As a result of the mushroom respiration, the internal atmosphere of the prepack was rapidly modified until, after about 24 h, a rough equilibrium concentration of CO₂ and O₂ was established in the range 4 to 10% CO₂ and 11 to 17% O₂ at 2 °C or 8 to 15% CO₂ and 1 to 2% O₂ at 18 °C; the mean concentration was dependent on the type of film. An equation, applicable to five out of six films that were tested, is proposed to describe the relationship between the equilibrium CO₂ concentrations at 18 °C and the permeability data of the film. At 18 °C, the gas changes inside the pre-packs prevented opening of the pileus and, in combination with prevention of water loss by the film, slowed down deterioration of the mushrooms. However, concentrations of CO₂ much above or below 10 to 12% were associated with increased internal browning. At 2 °C overwrapping generally caused slight external browning of the pileus. The relevance of the results are discussed in relation to the commercial marketing of pre-packed mushrooms.     

Effects of ascorbic acid, rosemary, and Origanox™ in preventing bone marrow discoloration in beef lumbar vertebrae in aerobic and anaerobic packaging systems

Treatments of 1.25% or 2.5% ascorbic acid (AA); 0.1% or 0.2% rosemary; or a combination of 0.15% Origanox™ + 0.3% AA on beef lumbar vertebrae (n = 72) were evaluated for their effectiveness in preventing bone discoloration in retail packages. Vertebrae were held either 6 or 14 d postmortem; cut into 2.54-cm sections; and packaged into either polyvinyl chloride film overwrap (PVC), high-oxygen (80% O₂/20% CO₂) modified-atmosphere packages (MAP), or ultra-low-oxygen (70% N₂/30% CO₂) MAP. Controls and vertebrae treated with 0.1% or 0.2% rosemary discolored significantly, whereas 0.15% Origanox™ + 0.3% AA was effective through d 2 of display in PVC and high-oxygen MAP. In both high- and ultra-low-oxygen MAP, 1.25% AA was as effective as 2.5% AA in preventing bone discoloration. Vertebrae treated with AA or packaged in ultra-low-oxygen MAP had the largest a* values over display time. Bone discoloration was effectively prevented with AA, especially at the 2.5% concentration.     

Changes in antioxidants and taste-related compounds content during cold storage of fresh-cut red sweet peppers

Changes in antioxidants (ascorbic acid, phenolic compounds and carotenoids) and in taste-related compounds (sugars and organic acids) content were monitored in fresh-cut red sweet peppers (Capsicum annuum L., local ecotype “Peperone Cornetto di Pontecorvo”) during 9 days of cold storage. Pepper slices were placed in polystyrene trays, wrapped with a polyvinyl chloride film, and stored at 4 °C or at 8 °C; besides, to evaluate the effect of a prestorage hot water treatment, half of the slices were subjected to a dipping treatment in water at 53 °C for 4 min, before packaging and storage. During storage limited changes in O₂ and CO₂ concentrations were observed within all packages. Storage temperature strongly affected weight loss: at the end of the storage time it was <3 and >10% in fruits stored at 4 and 8 °C, respectively. Sugars (glucose and fructose) content showed a significant increase (+11%) only in fruits stored at 8 °C; this change was due to a concentration effect associated to water loss. A higher increase (+23 and +17% in fruits stored at 8 and 4 °C) was observed in organic acids (citric and malic) content. Minimal processing and storage produced only a quite limited degradation of ascorbic acid. Both hydroxycinnamic acid derivatives and flavonoids accumulated in fruits stored at 8 °C (and not heat treated), whereas at 4 °C phenolics accumulation appeared to be partially inhibited. All the main carotenoids (capsanthin, cucurbitaxanthin A, zeaxanthin, β-carotene and β-cryptoxanthin) markedly accumulated in fruits stored at 8 °C (not heat treated), and showed a general decrease at 4 °C. Hot water treatment did seem to affect organic acids metabolism, though it did not promote ascorbic acid degradation. In addition, it inhibited both phenolics and carotenoid accumulation in fruits stored at 8 °C.