Evaluation and suitability of biomaterials for modified atmosphere packaging of fresh salmon fillets

An evaluation of the suitability of commercially available biopolymers on the shelf‐life of fresh salmon fillet was done. The comparison included two different types of biomaterials, poly lactic acid (PLA)‐based and starch‐based materials, and two traditional materials, amorphous polyethylene terephthalate/polyethylene (APET/PE) and high‐density polyethylene (HDPE). Fresh salmon fillets were stored at 4°C in modified atmosphere (60% CO₂ and 40% N₂) for 5, 7, 9 and 14 days. The biomaterials have been briefly evaluated with respect to composition and mechanical properties. The effect of different packaging materials on bacterial growth, off‐odour, pH and colour was investigated. The traditional materials (APET/PE and HDPE trays) offered the best protection regarding the bacterial growth. A relatively high level (log 6 CFU/g) of total viable counts was detected after 9 days and 14 days for fillets stored in biomaterials and traditional materials, respectively. The level of lactic acid bacteria and H₂S producing bacteria followed almost the same pattern. Storage in traditional materials resulted in higher intensity of freshness (fresh odour) compared with the samples stored in biomaterials; after 14 days, the salmon stored in starch‐based pouches was regarded as having lower intensity of freshness compared with APET/PE trays and PLA‐based pouches. The opposite result was obtained regarding the colour of the salmon, where the biomaterials resulted in higher intensity of fresh colour compared with the traditional materials although the surface of the salmon at the end of the experiment was dry and unpleasant. Copyright © 2011 John Wiley & Sons, Ltd.     

Preservation of freshness of rainbow trout fillets packaged with carbon dioxide-nitrogen gas mixture (studies on gas-exchange packaging of fresh fish,part 2)

Gas-exchange packaging was applied to preserve freshness of rainbow trout fillets. The fillets were packaged in pouches of coextruded laminate (ethylene vinyl acetate/ polyvinylidene chloride-polyolefin) with a carbon dioxide-nitrogen gas mixture (N₂ : CO₂ = 6 : 4). Other fillets were wrapped with polyvinyl chloride film as a reference group. Changes in sensory score of colour and flavour, K-value and bacterial counts of the fillets were investigated during storage at 5°C. After 2 days the fillets wrapped with polyvinyl chloride film lost their gloss. In addition, an amine-like odour was detected after 3 days. The gas-packaged fillets, however, showed little change in colour, flavour and bacterial counts, and retained their fresh appearance for 3 days.     

Influence of the Preservation Process on the Quality of Carp Fillets

An investigation was carried out on the microbiological quality of carp fillets linked to slaughtering methods, variation in temperature, storage time and packing as well as recording the main bacterial flora (total aerobic bacteria, Enterobacteria and Pseudomonas sp. and lactic acid bacteria). The results of this study showed the following. (i) The working room temperature (5–18°C) and dipping of the fillets in ice water did not have any influence on the microbiological quality of the carp fillets. However, for industrial purposes it would be more adequate to work at low temperature. (ii) The packaging process (air, vacuum or modified atmosphere) had significant effects on the microbiology of the fillets. (iii) Only those fillets under a modified atmosphere offered a shelf-life of 10 days or more (up to 14 days). (iv) MA packaging with 50% CO₂ gave the best results with regard to limiting microbiological growth. (v) Storage of the fillets at a temperature higher than 3°C should be prohibited as well as potential breaks in the cold chain.     

Predicting changes in oxygen concentration in the headspace of nitrogen flushed packages by the ambient oxygen ingress rate method

The ambient oxygen ingress rate (AOIR) method is an alternative/supplementary method to Ox‐Tran for measuring the oxygen transmission rates of packages. The AOIR method facilitates high‐capacity testing of packages under realistic food storage conditions, on the one hand, and on the other hand provides the possibility to predict the oxygen concentration over time in packages flushed with nitrogen at the time of packaging. The predicted oxygen concentration values showed good agreement with experimental values for flexible packages stored over a period of 91 days at 23°C and 38°C. The prediction of the oxygen concentration in­nitrogen‐flushed packages may be a useful tool, e.g. in shelf life studies, in the selection of the optimal food package as regards to oxygen protection and within quality control purposes. Copyright © 2002 John Wiley & Sons, Ltd.     

Recyclable mono materials for packaging of fresh chicken fillets: New design for recycling in circular economy

The focus on sustainability and circular economy is leading to a need for development of new food packaging concepts, including recyclable materials that ideally consist of a single material in a monolayer system. This research was focused on the possibility of replacing complex multilayered material [amorphous polyethylene terephthalate/polyethylene (APET/PE)] with simple recyclable mono material [high-density polyethylene (HDPE)] for packaging of chicken fillets in modified atmosphere packaging (CO₂/N₂: 60%/40%). Bacterial growth measured as total viable count (TVC), lactic acid bacteria and Enterobacteriaceae, Brochothrix thermosphacta and Escherichia coli for chicken fillets packed in HDPE mono materials was compared with chicken fillets packed in APET/PE. TVC increased during the storage period (24 days) with high level of TVC count (7 log₁₀ CFU/g) recorded at Days 19–20 of storage in both HDPE and APET/PE material. No significant differences were recorded in off-odour between chicken stored in APET/PE compared with HDPE in CO₂/N₂ atmosphere during the storage period (samples were regarded as acceptable on the 24th day of storage). The drip loss increased in all samples during storage, and no significant differences between samples stored in different materials were recorded. Significant differences in bacterial growth were recorded between samples with different gas volume to product volume (G/P) ratio (Day 17), implying that higher G/P ratio is resulting in lower TVC count. The lowest G/P ratio caused the highest drip loss, whereas addition of CO₂ emitter reduced the drip loss to some extent. This research is very encouraging as it provides new insight into the use of monolayer materials as well as the importance of design for recycling in circular economy.     

Quality Evaluation of Grated Graviera Cheese Stored at 4 and 12°C using Active and Modified Atmosphere Packaging

The effect of active [oxygen absorber (OA) combined with an ethanol emitter (EE)] and modified atmosphere (100% Nitrogen) packaging in combination with a high barrier experimental polyethylene terephthalate‐silicon oxides//low density polyethelene film on shelf‐life extension of grated Graviera cheese stored at 4 and 12°C was investigated. Microbiological (total viable counts, Pseudomonads, lactic acid bacteria, Enterobacteriaceae and Yeasts/Moulds), physico‐chemical (pH, thiobarbituric acid and colour) and sensory (odour and taste) changes occurring in the product were monitored as a function of treatment and storage time (10 weeks). Sensory shelf‐life was approximately 1, 1.5, 4.5, 6, 9 and at least 10 weeks for control samples (12 and 4°C), for N2 packaged samples (12 and 4°C) and samples packaged with the OA + EE (12 and 4°C), respectively. At the point of sensory rejection, yeasts and moulds increased from 2.00 to 3.60 and 5.55 log CFU/g for control samples stored at 4 and 12°C, respectively. Similarly, for samples stored under nitrogen, yeasts and moulds reached 2.00 and 2.32 log CFU/g at 4 and 12°C, respectively. Yeasts and moulds in samples with the OA + EE remained below 2 log CFU/g throughout the entire storage period, irrespective of storage temperature. pH varied between 5.72 and 6.49 depending on specific treatment. Malondialdehyde absorbance ranged between 0.05 for fresh samples and 0.79 mg/kg at the time of sensory rejection of samples. Light parameters L and b decreased while parameter a increased during storage, reflecting a gradual discolouration of all samples and especially those stored at 12°C.     

Effect of ovenproof plastic films on the quality of spotted rose snapper (lutjanus guttatus) fillets during frozen storage

Spotted rose snapper (Lutjanus guttatus) fillets packed in two polymer films, polyamide 6,6 (PA66) and polyethylene terephthalate (PET), were stored at ?20°C for a period of 120 days. Films were tested for melting temperature (PA66 253–257°C and PET 252–255°C), oxygen transmission rate [PA66 51.8 ± 12.9cm³/(m²·24h·atm) and PET 152.7 ± 0.2cm³/(m²·24h·atm)] and water vapor transmission rate [PA66 17.8 ± 1.7g/(m²·24h) and PET 6.5 ± 0.2g/(m²·24h)]. Sensory analyses (firmness, flavour and appearance) were performed at 0, 30, 60, 90 and 120 days of storage after baking the fillets in the same storage bags. For raw fillets, their water‐holding capacity (WHC), total aerobic counts (TAC), pH, trimethylamine (TMA) and shear‐force resistance were measured at the same periods. Sensory analyses after baking showed no differences between the fillets packaged in the two films. The WHC, TAC, pH and TMA values in both products were kept within accepted limits. The fillets packed in PET showed a significant increase in firmness (shear‐force resistance) during the first 60 days of storage and then a decrease at 90 days due to dehydration through the film seals. Over the same period, the fillets packed in PA66 showed no significant changes in firmness. In this study, it was demonstrated that it is possible to develop a ready‐to‐bake fish fillet product by using ovenproof films for packaging during storage. Copyright © 2006 John Wiley & Sons, Ltd.     

Microbiological,colour and sensory properties of fresh beef steaks in low carbon monoxide concentration

Steaks from gluteus medius m. (GM) and longissimus dorsi m. (LD) were packaged in atmospheres containing two low levels of CO (0.2 and 0.4%) in combination with 21% O₂ or without oxygen. The other components of the modified atmosphere packaging systems were carbon dioxide (30%) and nitrogen (balance). Steaks were evaluated on 0, 7, 14 and 21 days of storage at about 2^oC to investigate the effects of the gas mixtures on the microflora, instrumental (CIE L*a*b*) and visual colour and odour. The preservation of colour and odour of GM and LD steaks packaged under low carbon monoxide was best achieved using anoxic mixtures containing 0.2% CO and 30% CO₂. Steaks packaged without oxygen retained a desirable colour and practically did not present a visible discoloration or perceptive off‐odour along the entire storage time. Colour stabilization with 0.2% CO and 30% CO₂, without O₂, following storage up to 21 days at 2°C did not increase microbial risk of products. The increase in CO from 0.2 to 0.4% had a negative effect on the colour of LD steaks which was regarded as ‘artificial’ by some panellists. The higher stability achieved in this study using 0.2% CO may result from increased stability of the colour from Bos indicus × Bos Taurus cross. Discoloration and off‐odour were evident in the GM and LD steaks packaged aerobically after 14 days of storage when the counts of deteriorant bacteria achieved approximately 6.5 to 9.7 log CFU/g. Highest bacteriostatic effect could be obtained if the volume of injected CO₂ was sufficient to saturate the meat and keep in balance around the product during storage. Copyright © 2010 John Wiley & Sons, Ltd.     

Evaluation of the Effectiveness of a New Antimicrobial Active Packaging for Fresh Atlantic Salmon (Salmo Salar L.) Shelf Life

Nowadays, consumers demand for fresh, high‐quality seafood products continues to climb, especially in affluent, developed nations. At the same time, there is increasing attention regarding improved utilization of seafood for human consumption; Atlantic salmon is the main species in Chile aquaculture, and most of the salmon are exported as fresh fish to USA. It is well documented that low storage temperature inhibit bacterial growth and biochemical degradation, thus facilitating prolonged shelf life. Partly freezing the outer fillet layer from ?0.5°C to ?2.0°C (superchilling) has proven to be more efficient in inhibiting biochemical changes and bacterial spoilage compared with traditional chilling. Nevertheless, antimicrobial active packaging offers the possibility to increase product shelf life through the reduction of the microbiological damage of the product during its transportation, and thus increasing consumer safety and health. The main objective of this study was to compare the effects of an active antimicrobial packaging on microbiological growth, sensory attributes and instrumental quality measurements of raw Atlantic salmon (Salmo salar) fillets. Flexible plastic films containing Thymol as antimicrobial agent were used for salmon packaging. Salmon were stored at 2°C, 4°C and 8°C. Analyses of aerobic mesophilic bacteria and psicrophilic bacteria count were carried out at 1, 3, 8, 11, 15 and 18 days. L*a*b* colour evolution, overall sensorial properties and chemical evolution were studied. Application of active antimicrobial packaging for fillet salmon reduced the microbial count for least 18 days at 2°C. No modification of the sensorial properties was detected by the sensorial panel, indicating that the antimicrobial compound used in the present study, thymol, is compatible with salmon packaging. Copyright © 2011 John Wiley & Sons, Ltd.     

Storage of chicken breast meat in paper coated with different types of hydrophobic agents

Chicken meat is well known for its high nutritional value. Its shelf life is short, due to the pronounced perishability, even under refrigeration. Paper bags are usually used as packaging materials, due to their biodegradability. The main negative aspect concerning paper is its high porosity and low moisture barrier. In this regard, it has to be coated/modified with efficient moisture barrier materials. The storage of chicken breast meat wrapped in four types of paper-based materials currently in use in Romania (RO), Italy (IT), Spain (SP) and Slovenia (SLO) is reported. RO and IT are paper coated with polyethylene (PE) film, SP is waxed paper, and SLO is paper modified with hydrophobized starch. The influence of the coating film on the organoleptical, biochemical and microbiological characteristics of the chicken breast meat stored at 4°C was the aim of the study. The mathematical modelling revealed two aspects: (1) the stability period in which the meat safe for consumption is in the range 1.92–2.18 days in the case of all paper types, and (2) cadaverine, the amine generated by protein degradation, is a less sensitive indicator of the meat alteration than microbial growth. The papers coated with PE (RO and IT samples) and with hydrophobized starch (SLO paper) were packaging materials more efficient that the waxed paper (SP sample). The polyethylene film reduced the conversion of putrescine into spermidine in a higher extent than wax.     

Effect of Different Packaging Methods on Quality and Shelf Life of Fresh Reindeer Meat

The impact of different packaging methods [vacuum, modified atmosphere packaging (MAP) (60% CO₂ and 40% N₂) and MAP + CO₂ emitter] on the quality of fresh reindeer meat (M. semimembranosus) stored at 4°C for 21 days was investigated. Colour and odour of the meat, drip loss, pH, microbial content, antioxidant capacity and cooking loss were measured. The MAP + CO₂ emitter resulted in prolonged microbial shelf life compared with vacuum and MAP without CO₂ emitter as lower level of total viable counts was detected after 13 and 17 days. Samples stored with CO₂ emitter also had lower drip loss. Samples stored in vacuum had significant lower L*‐value, higher a*‐value and lower intensity of freshness (odour and colour) compared with those stored in MAP and MAP with CO₂ emitter. However, MAP with a gas‐to‐product volume ratio of 1 : 1 seems to be too low in quality preserving. Increased partial pressure by adding a CO₂ emitter improved bacterial inhibition compared with vacuum and traditional MAP. Copyright © 2014 John Wiley & Sons, Ltd.     

Oxygen transmission rates of packages at ambient,chill and freezing temperatures measured by the AOIR method

The ambient oxygen ingress rate (AOIR) method is an alternative or supplementary method to Ox‐Tran for measuring the oxygen transmission rate (OTR) of packages. The method has high capacity, requires relatively inexpensive equipment and measures OTR at different temperatures and humidity conditions. The aim of this study was, on the one hand, to study the effect of temperature on the OTR for packages produced from different polymer materials and laminates, and on the other hand to evaluate the suitability of the AOIR method at freezing temperature conditions. The OTR for 10 packages with different polymer compositions was measured at 23°C, 6°C and ?25°C. The AOIR method was shown to be a reliable test method for measuring OTR of packages at all the applied test conditions, also at frozen storage temperature. The OTR for the packages decreased with lower temperatures, especially for the packages with the highest OTR values at 23°C. In order to avoid higher packaging expenses than necessary to obtain the required shelf‐life for different food products, the OTR for alternative packages should be measured at the temperature and humidity conditions of intended use. Copyright © 2004 John Wiley & Sons, Ltd.     

Improving the quality of fresh‐cut pineapples with ascorbic acid/sucrose pretreatment and modified atmosphere packaging

The effects of pretreatment and modified atmosphere packaging (MAP) on the quality of fresh‐cut pineapples stored at 4°C were evaluated for 7 days. The pretreatment was conducted by immersing the pineapple slices in a solution containing 0.25% ascorbic acid and 10% sucrose for 2min. MAP contained 4% oxygen, 10% carbon dioxide and 86% nitrogen. Both the pretreatment and MAP could reduce the respiration rate, ethylene production, textural and colour deteriorations, as well as the overall sensory deterioration in fresh‐cut pineapples. MAP could restrain the growth of microbes, but the pretreatment showed little effect. Fresh‐cut pineapples exhibited wet surface and off‐flavour after storage at 4°C for 3 days, while the pretreatment and MAP maintained the quality for up to 7 days. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of modified atmosphere packaging and superchilled storage on the shelf‐life of farmed ready‐to‐cook spotted wolf‐fish (Anarhichas minor)

Modified atmosphere packaging (MAP) combined with superchilling (?1°C) was evaluated as a mild preservation method for farmed spotted wolf‐fish (Anarhichas minor). Portions were packaged in air and in CO2:N2 (60%:40%) atmosphere with a gas:product ratio of approximately 1, at superchilled (?1.0°C ± 0.2°C) or chilled (+4.0°C ± 0.2°C) temperatures. A reduced bacterial growth (p < 0.001), measured as aerobic plate counts (APC) and psychrotrophic bacteria, was observed in modified atmosphere (MA) packaged wolf‐fish at both ?1°C and +4°C, compared to portions in air. MA‐packaged wolf‐fish had improved odour and flavour scores (p < 0.05), but also a higher drip loss than fish stored in air. A shelf‐life of 15 days was obtained at ?1°C for MA‐packaged fish compared to 8–10 days in air, and at 4°C the shelf‐life was 13 days in MA and 6–8 days in air. Copyright © 2006 John Wiley & Sons, Ltd.     

The interrelation of changes in oxygen content and product quality in modified atmosphere packages of peanuts

The aim of this work was to examine the effect of changes in oxygen content in different types of packages for snacks (multilayer laminated materials, cans) and analyse the changes in the sensorial and physicochemical characteristics of the stored products. Roasted and salted peanuts produced by one of the well‐known companies, packed in modified atmosphere packages (MAP) were the object of this investigation. The interdependence of the changes in oxygen content and product quality was examined in relation to the storage period and type of package used. From the results it can be said that changes in oxygen content in packages of peanuts produce similar effects irrespective of the packaging material used. The correlation observed during storage of peanuts, between changes in oxygen content in different packaging materials and changes of the separate sensorial and physicochemical parameters of the product, especially of the peroxide value, may be a basis for validity forecasting and determination of the optimum composition of gas mixture. This study indicates that evaluation of the quality of packages integrally related to their content should consider both product examination and the package and gas mixture composition, as there may exist an interdependence between quality features of the product and oxygen content in a package. Copyright © 2001 John Wiley & Sons, Ltd.     

Effect of Pretreatment and Modified Atmosphere Packaging on Quality of dry Coleslaw mix

The aim of the study was to determine the effect of soaking in chlorinated water (100 ppm chlorine) or mild thermal treatment in water (55°C; 3 min) and modified atmosphere packaging on the quality and shelf life of dry coleslaw stored for 12 days at 4°C. Samples were packaged in low‐barrier film in modified atmosphere containing: 5/10/85, 20/25/55, 50/30/20, 70/30/0 %O₂/% CO₂/% N₂, and air atmosphere. In‐pack gas levels, sensory quality, microbial counts and cell permeability were determined. In comparison to non‐processed coleslaw, pretreatment of coleslaw, both consisting in soaking in chlorine solution and a mild thermal processing, resulted in a reduction by approx. 1 logarithmic cycle for counts of psychrophilic and lactic acid bacteria as well as mesophilic and psychrophilic yeasts, by 1 and 1.7 logarithmic cycle for coliform bacteria and by 2 up to 3 logarithmic cycles for Pseudomonas bacteria. Modified atmosphere (irrespective of its composition) used in product packaging was found to have no effect on the count of mesophilic bacteria. An elevated content of carbon dioxide in modified atmosphere (10, 25 or 30%) inhibited growth of psychrophilic bacteria and Pseudomonas bacteria up to 6 days of storage. In the case of coliform bacteria growth inhibition during storage was recorded both in the samples packaged in air atmosphere and in the atmosphere of 50/30/20 and 70/30/0 %O₂/% CO₂/% N₂. In samples packaged in the atmosphere of 70% O₂ and 30% CO₂ after 12 days the greatest cell permeability was recorded, which was connected with a deterioration of their microbiological quality. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of light and oxygen transmission characteristics of packaging materials on photo‐oxidative quality changes in semi‐hard Havarti cheeses

Changing transmission characteristics of food packaging materials by colouring the materials may be a suitable way of reducing photo‐oxidative quality changes. This study proved that packaging in black laminates provided the best protection of Havarti cheese, followed by a white laminate. However, transparent packaging materials did not protect the product in the critical wavelength range, i.e. 400–500 nm, and changes in colour and odour were already notable after few hours of exposure to fluorescent light. Additionally, secondary oxidation products, hexanal, 1‐pentanol, and 1‐hexanol, were formed in cheese packaged in transparent or semi‐transparent packaging materials. The expected effects of oxygen transmission were difficult to evaluate, due to high residual oxygen levels in the packages. Copyright © 2002 John Wiley & Sons, Ltd.     

Assessment of oxygen levels in convenience‐style muscle‐based sous vide products through optical means and impact on shelf‐life stability

An optical oxygen analyser was used in two small‐scale industrial trials to non‐destructively assess the quality of packaged convenience foods and packaging process. Beef lasagne packed under 70% vacuum and cooked under standard sous vide conditions was monitored for residual oxygen, using disposable sensors incorporated in each pack and a benchtop optical oxygen analyser. High levels of residual oxygen close to ambient were determined in the majority of packs after packaging, as opposed to anticipated levels of 4–5%. Residual oxygen was monitored over product shelf‐life (4 weeks at +4–10°C) along with measurement of microbial growth and lipid oxidation in food by conventional destructive methods. Oxygen levels in packs went down to almost zero between weeks 2 and 3 indicating deterioration of packaged product. Correlation between oxygen profiles and the rate of microbial growth and lipid oxidation was established. The optical oxygen sensor system was shown to provide valuable information about performance of the packaging process, product storage conditions and food quality in a convenient and cost‐efficient fashion and non‐destructively. Copyright © 2004 John Wiley & Sons, Ltd.     

Comparative effects of de‐aeration and package permeability on ascorbic acid loss in refrigerated orange juice

Several factors including pH, cultivar, extraction method, metal ion content and storage conditions affect the rate of ascorbic acid loss in refrigerated fruit juices. While oxygen permeation rate and product de‐aeration also influence ascorbic acid loss, little comparative data on these two variables exist despite the potential usefulness of such data in optimizing the packaging of juice. De‐aerated and non‐de‐aerated single‐strength orange juices were packaged and stored at 7°C in experimental glass containers constructed with oxygen permeability rates of 0·35, 0·39, 0·43, 0·79, 1·18 and 1·60 ml/day/container at 7°C. The rate of ascorbic acid degradation inversely correlated with permeation rate for both de‐aerated and non‐de‐aerated juices regardless of initial dissolved oxygen content. Degradation was best described by zero‐order and first‐order kinetics for de‐aerated and non‐de‐aerated juices, respectively. Headspace volume had no effect on ascorbic acid loss in both de‐aerated and non‐de‐aerated juices when nitrogen flushed. Juice in high oxygen permeability containers showed a faster decrease in ascorbic acid content, independent of initial dissolved oxygen content. These results indicate that both package barrier properties and de‐aeration are major factors in maintaining ascorbic acid in refrigerated orange juice. Copyright © 1999 John Wiley & Sons, Ltd.     

Combined effects of hot water treatment (HWT) and modified atmosphere packaging (MAP) on quality of tomatoes

Effects of hot water treatment (HWT) and modified atmosphere packaging (MAP) on quality of tomatoes were studied. Prior to packaging with low‐density polyethylene (LDPE) film (0.02 mm in thickness), tomatoes were immersed in hot water (42.5°C) for 30 min. Control tomatoes were not treated and were stored for 2 weeks at 10°C and then for 3 days at 20°C without packaging. Steady states of O₂ and CO₂ concentrations inside the package were about 5 and 8%, respectively, and were reached after 6 and 4 days of storage, respectively. MAP reduced weight loss of tomatoes to about 41% of that of unpackaged fruit during a 2‐week storage period. The use of a combination of HWT and MAP reduced weight loss and decay, inhibited color development and maintained firmness of tomatoes but had no effect on soluble solids content or titratable acidity. HWT slightly reduced mold growth of tomatoes stored in MAP. Packaging of control fruit in MAP resulted in stimulation of mold growth around the stem end of the fruit after about 1 week of storage and also resulted in cracking and decay. HWT could be used as disinfectant for tomatoes prior to storage in MAP in order to reduce microbial growth, cracking and decay that may be caused by excessive water vapor inside the package. Copyright © 2003 John Wiley & Sons, Ltd.