臭氧水清洗结合气调包装对鲜切杭白菜保鲜效果的研究

以1.8mg/L臭氧水清洗的鲜切杭白菜为试验材料,研究不同气体组分的气调包装(CK为空气;A为5%O_2+5%CO_2+90%N_2;B为5%O_2+10%CO_2+85%N_2;C为10%O_2+5%CO_2+85%N_2;D为10%O_2+10%CO_2+80%N_2)对鲜切杭白菜保鲜效果的影响。结果表明:B组低氧高二氧化碳的包装能有效地抑制鲜切杭白菜上微生物的生长,保持其较好的感官品质,同时延缓VC、叶绿素及可溶性固形物含量的降低,防止杭白菜过快失水,有效地保证鲜切杭白菜的货架期在15d以上。     

High carbon-di-oxide modified atmospheric packaging on quality of ready-to-eat minimally processed fresh-cut iceberg lettuce

Fresh-cut lettuce is a very well-known salad for today''s routines because it obliges minimal preparation to minimize the loss of health beneficial vitamins, minerals, antioxidants and other phytochemicals. It is a prodigious challenge to serve its consumers fresh. Quality of freshly processed lettuce under high CO₂ modified atmosphere packaging (MAP) has been investigated as a realistic alternative technique for its preservation. Storage under high CO₂ atmospheric treatments exhibited a significant impact in microbial development, electrolyte leakage, volatile metabolites and sensory quality of fresh-cut iceberg lettuce. This storage condition (MAP 1: 5 kPa O₂ and 20 kPa CO₂ balanced by N₂ at 7 °C for 6 days) inhibited the growth of mesophilic bacteria and yeasts; delayed the enzymatic browning (cut-edges and intact surface) of fresh-cut iceberg lettuce and overall visual quality was also in acceptance limit. The development of off-odors was perceived in high CO₂ MAP as a consequence of volatiles (ethanol and acetaldehyde) accumulation which was persisted at an inexcusable level during 6 days of storage periods.     

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.     

Effect of oxygen on aroma volatiles and quality of fresh-cut cantaloupe and honeydew melons

Cantaloupe and honeydew melon cultivars were processed and stored under a high oxygen passive modified atmosphere packaging (MAP) or reduced oxygen controlled atmosphere (CA; 5 kPa O₂ + 10 kPa CO₂ and balance N₂) for 14 days at 5 °C. Atmosphere did not affect softening rate or soluble solids content and had a negligible effect on colour. Volatile compounds known as flavour-important in melons were extracted using stir bar sorptive extraction (SBSE) and quantified via GC–MS. Acetate esters increased more in MAP than in CA. Non-acetate esters increased markedly in both cultivars and storage types. Alcohols were more abundant in honeydew than in cantaloupe. Aldehydes decreased during storage in both cultivars and storage types. Lower O₂ availability under CA conditions likely suppressed some of the esters relevant to the aroma of fresh-cut melon. Results suggest that package O₂ levels are more important in determining aroma than other quality attributes of fresh-cut melon, and high O₂ levels may be required to reveal desirable aroma compounds.     

Maintenance of safety and quality of refrigerated ready-to-cook seasoned ground beef product (meatball) by combining gamma irradiation with modified atmosphere packaging

Abstract: Meatballs were prepared by mixing ground beef and spices and inoculated with E. coli O157:H7, L. monocytogenes, and S. enteritidis before packaged in modified atmosphere (3% O₂+ 50% CO₂+ 47% N₂) or aerobic conditions. The packaged samples were irradiated at 0.75, 1.5, and 3 kGy doses and stored at 4 °C for 21 d. Survival of the pathogens, total plate count, lipid oxidation, color change, and sensory quality were analyzed during storage. Irradiation at 3 kGy inactivated all the inoculated (approximately 10⁶ CFU/g) S. enteritidis and L. monocytogenes cells in the samples. The inoculated (approximately 10⁶ CFU/g) E. coli O157:H7 cells were totally inactivated by 1.5 kGy irradiation. D¹⁰‐values for E. coli O157:H7, S. enteritidis, and L. monocytogenes were 0.24, 0.43, and 0.41 kGy in MAP and 0.22, 0.39, and 0.39 kGy in aerobic packages, respectively. Irradiation at 1.5 and 3 kGy resulted in 0.13 and 0.36 mg MDA/kg increase in 2‐thiobarbituric acid‐reactive substances (TBARS) reaching 1.02 and 1.49 MDA/kg, respectively, on day 1. Irradiation also caused significant loss of color and sensory quality in aerobic packages. However, MAP effectively inhibited the irradiation‐induced quality degradations during 21‐d storage. Thus, combining irradiation (3 kGy) and MAP (3% O₂+ 50% CO₂+ 47% N₂) controlled the safety risk due to the potential pathogens and maintained qualities of meatballs during 21‐d refrigerated storage. Practical Application: Combined use of gamma irradiation and modified atmosphere packaging (MAP) can maintain quality and safety of seasoned ground beef (meatball). Seasoned ground beef can be irradiated at 3 kGy and packaged in MAP with 3% O₂+ 50% CO₂+ 47% N₂ gas mixture in a high barrier packaging materials. These treatments can significantly decrease risk due to potential pathogens including E. coli O157:H7, L. monocytogenes, and S. enteritidis in the product. The MAP would reduce the undesirable effects of irradiation on quality, and extend the shelf life of the product for up to 21 d at 3 °C.     

Quality of fresh-cut tomato as affected by type of cut,packaging, temperature and storage time

Long-life Calibra tomatoes (Lycopersicum esculentum Mill.) were minimally fresh processed in slices or wedges and packaged in polypropylene (PP) trays. Passive and active (3 kPa O₂+0 kPa CO₂ and 3 kPa O₂+4 kPa CO₂) modified atmosphere packages (MAP) were used at 0 and 5 °C. After 14 days, the gas composition within passive MAP packages was 11–13 kPa O₂+5.5–6 kPa CO₂ and 8–9.5 kPa O₂+10.5–11.5 kPa CO₂ at 0 and 5 °C, respectively. The gas composition reached in active MAP at both temperatures for both types of cuts was around 7–10.5 kPa O₂ and 7–9 kPa CO₂. The highest C₂H₄ level (15 L L^–1) was found in passive MAP at 5 °C, while in active MAP at both temperatures about 6 L L^–1 C₂H₄ accumulated. After 7 days of storage at 0 °C, the tomato pieces showed better aroma, appearance and overall quality than those stored at 5 °C. No difference between MAP treatments was found, although both led to a better appearance and overall quality than controls in air. After 14 days at 0 °C, only MAP treatments kept a good flavour, overall quality and texture, with no differences between them. After 14 days at 5 °C in all treatments, the flavour fell below a fair condition and the slices showed a slight senescence. MAP significantly reduced total plate counts (TPC) of slices at 5 °C, although only active MAP reduced TPC in wedges after 14 days at 5 °C. A visibly better appearance and overall quality was found in slices than in wedges. The main factors influencing the quality of tomato pieces were the storage duration and temperature. To keep the quality of fresh-cut tomatoes, one should consider three factors for selection: a suitable low chilling sensitive tomato cultivar, an adherent placenta and optimal maturity stage at harvest.     

Antimicrobial and Antioxidative Strategies to Reduce Pathogens and Extend the Shelf Life of Fresh Red Meats

Abstract: The shelf life of packaged fresh red meats is most frequently determined by the activity of microorganisms, which results in the development of off‐odors, gas, and slime, but it is also influenced by biochemical factors such as lipid radical chain and pigment oxidation causing undesirable flavors and surface discoloration. The predominant bacteria associated with spoilage of refrigerated meats are Pseudomonas, Acinetobacter/Moraxella (Psychrobacter), Shewanella putrefaciens, lactic acid bacteria, Enterobacteriaceae, and Brochothrix thermosphacta. The spoilage potential of these organisms and factors influencing their impact on meat quality are discussed. High O₂‐modified atmosphere (80% O₂+ 20% CO₂) packaging (MAP) is commonly used for meat retail display but vacuum packaging remains the major MAP method used for meat distribution. Two‐step master packaging (outer anoxic‐20% CO₂+ 80% N₂/inner gas‐permeable film) is used for centralized MAP distribution, but CO use (0.4%) in low O₂ packaging systems is limited by consumer uncertainty that CO may mask spoilage. Active packaging where the film contributes more than a gas/physical barrier is an important technology and has been studied widely. Its application in combination with MAP is very promising but impediments remain to its widespread industrial use. The influence of processing technologies including modified atmospheres on lipid oxidation and discoloration of meats are analyzed. Because both organic acids and antioxidants have been evaluated for their effects on microorganism growth, in concert with the prevention of lipid oxidation, work in this area is examined.     

Innovative active modified atmosphere packaging improves overall quality of fresh-cut red chard baby leaves

The antimicrobial effects and quality changes of O₂, He, N₂ or N₂O-enriched active modified atmosphere packaging -MAP- (100 kPa initial gas partial pressure) compared to a chlorinated −100 mg L⁻¹ NaClO- passive MAP (control) in fresh-cut Red Chard baby leaves up to 8 days at 5 °C were studied. High O₂ MAP (>85 kPa O₂) inhibited natural microflora growth during 7 days at 5 °C. Regarding control treatment, no differences for He and N₂O-enriched MAPs on microbial growth were found although control samples were previously disinfected. Initial total phenolics content (613 mg ChAE kg⁻¹ fw) increased up to 61-93% after 6 days at 5 °C under O₂, He, and N₂-enriched MAPs. Vitamin C content decreased up to 67% after shelf life in control samples while lower decreases were monitored in samples stored under non-conventional MAPs. He-enriched MAP preserved the total chlorophylls content throughout shelf life. After 8 days at 5 °C the overall sensory quality of all treatments showed a moderate decrease while still being scored at the limit of usability. In conclusion, He and O₂-enriched MAPs are useful tools in the preservation of fresh-cut Red Chard quality.     

Effect of ripeness on the shelf-life of fresh-cut melon preserved by modified atmosphere packaging

Fresh-cut ‘Piel de Sapo’ melon was processed at different ripeness stages and stored under modified atmosphere packaging for 35 days at 5 °C. Raw material firmness and soluble solids content ranged from 6.5 to 3.9 N and 11.1 to 14.3 °Brix, respectively. The effects of a 2.5 kPa O₂+7 kPa CO₂ packaging atmosphere and a dip of 1% ascorbic acid and 0.5% calcium chloride on physiology, microbiological stability as well as color and firmness were evaluated. An intermediate stage of ripeness at processing was the most suitable to extend the shelf-life of fresh-cut ‘Piel de Sapo’ melon. Green-mature fresh-cut melon reduced CO₂ accumulation and ethanol production. In addition, a treatment with ascorbic acid and calcium chloride in combination with modified atmosphere packaging, contributed to a greater extension of the shelf-life of fresh-cut melon than that reported for fruits stored under non-modified atmosphere, slowing down the growth of microbial populations, maintaining the original color and reducing softness. Thus, the shelf-life of green-mature fresh-cut ‘Piel de Sapo’ melon dipped in an ascorbic acid and calcium chloride solution and packaged under modified atmosphere was about 10 days.     

Preservation of precut white cheese by modified atmosphere packaging

Effects of modified atmosphere packaging (MAP) on storage stability and quality of precut fresh and aged white cheese were investigated. Fresh or aged white cheese was cut into small cubes and packaged in five different atmospheres [0% O₂ + 0% CO₂ + 100% N₂ (MAP1), 10% O₂ + 0% CO₂ + 90% N₂ (MAP2), 0% O₂ + 75% CO₂ + 25% N₂ (MAP3), 10% O₂ + 75% CO₂ + 15% N₂ (MAP4) and aerobic (air)]. Control samples were packaged in brine and vacuum for fresh and aged white cheese, respectively. Changes in gas composition, total plate count, lactococci, lactobacilli, yeast and mould counts, proteolysis, lipolysis, pH, colour, texture and sensory properties were investigated during refrigerated storage. The best packaging treatment for the fresh cheese was MAP3, as it inhibited mould growth and protected the hardness. MAP2 can be recommended for the packaging of the aged cheese, as it decreased lipolysis.     

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.     

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.     

The impact of packaging system and temperature abuse on the shelf life characteristics of ground beef

New ground beef packaging systems have warranted investigation of their spoilage and quality characteristics. Furthermore, analysis of ground beef spoilage in modified atmosphere packaging (MAP) and stored at abusive temperature is lacking. This research aimed to determine the effect of packaging systems and temperature abuse on the sensory and shelf-life characteristics of ground beef. Ground beef patties were packaged using polyvinyl chloride overwrap (OW), HI-OX MAP (80% O₂, 20% CO₂), LO-OX MAP (30% CO₂, 70% N₂), CO-MAP (0.4% CO, 30% CO₂, 69.6% N₂), or vacuum (VAC) prior to color, odor, biochemical, and microbial analyses over display. CO-MAP exhibited more desirable color and consumer acceptability throughout display. Lean discoloration and odor scores were lower for anaerobic packaging than aerobic packaging. Microbial results mirrored sensory preferences for anaerobic packaging. These results indicate anaerobic packaging extends shelf-life properties and desirable sensory attributes throughout display and temperature abuse.     

Effects of initial low oxygen and perforated film package on quality of fresh‐cut cabbages

The effects of perforated film packages (PFP) with different oxygen partial pressures (5, 8 and 10 kPa) and a barrier package (BP) at 21 kPa of O₂ on the quality of fresh‐cut cabbages were studied at 5 and 20 °C. The microbial growth, appearance, flavor, ascorbic acid content and polyphenol oxidase activity were determined during storage. The results indicated that fresh‐cut cabbages had better color retention and quality in PFP. Oxidation of ascorbic acid (AA) and browning of fresh‐cut cabbage were inhibited effectively using a PFP and an initial oxygen partial pressure equal to 5 kPa. Analysis of microbial growth also showed that the total count on fresh‐cut cabbage was relative lower in PFP with an initial low O₂ content. Loss of total ascorbic acid was much lower in PFP than that in BP by suppressing AA oxidation. The results of sensory evaluation showed that flavor and appearance were maintained effectively at 5 °C and significant differences in flavor were found between PFP and BP both at 5 and 20 °C, while significant differences in appearance were found between PFP and BP only at 20 °C. Copyright © 2007 Society of Chemical Industry     

METHOD FOR MEASURING CO2 ABSORPTION IN CO2 and N2 PACKAGED FRESH MEAT1

Headspace gas composition of meat stored in modified atmosphere packaging (MAP) undergoes dynamic changes as a result of packaging film permeability, postmortem metabolic activity, CO₂ absorption in water and lipid, and bacteria growth and respiration. A combined analytical and experimental method was developed to investigate CO₂ absorption by packaged fresh meat in a gas-impermeable environment and during isothermal storage. the ideal gas law was used as a theoretical basis and a gas-impermeable and constant-volume chamber was constructed to evaluate the theoretical derivation. Changes in headspace pressure caused by dynamic interactions between beef and MAP atmospheres were monitored to predict concentration changes of CO₂ within the chamber. the proposed methodology for measuring CO₂ concentration changes was confirmed by gas analysis and proved valid for prediction of headspace CO₂ concentration changes in MAP gas-impermeable systems within the range of initial gas composition 20% to 100% CO₂ balanced with N₂, at temperatures ranging from 3 to 13C, and an initial headspace pressure of 155 kPa.     

Effects of novel modified atmosphere packaging on lipid quality and stability of sardine (Sardina pilchardus) fillets

Modified atmosphere packaging (MAP) is an efficient method to increase shelf-life of fishery products by inhibiting bacterial growth and oxidative reactions. Beside the traditional gases used for MAP, novel gases such as argon (Ar) and nitrous oxide (N₂O) were approved for food use in the European Union. The present research investigates the effect of MAP with unconventional gas mixtures, that previously positively affected microbial shelf-life, on colour, lipid oxidation and sensorial characteristics of sardine fillets during storage. Four atmosphere conditions were tested: Air (20.8% O₂/79.2% N₂), N₂ (30% CO₂/70% N₂), N₂O (30% CO₂/70% N₂O) and Ar (30% CO₂/70% Ar). Samples were stored for 12 days at 3 °C. Results showed that the removal of oxygen significantly inhibited the oxidation process; however, most of the investigated parameters related to fat oxidation did not show any improvement, except for a slight decrease in lipid hydrolysis and improvement in sensory properties in the packaging containing Ar.     

Combined effects of irradiation and modified atmosphere packaging on minimally processed Chinese cabbage (Brassica rapa L.)

Cut Chinese cabbage with air, CO₂ or CO₂/N₂ packaging was irradiated at doses up to 2 kGy and the microbiological and physicochemical qualities were investigated during a refrigerated storage for 3 weeks. Irradiation significantly reduced the microorganisms, and additionally, the modified atmosphere packaging (MAP) enhanced the reduction of the total aerobic and coliform bacteria during storage. Irradiation effectively inhibited the changes of the titratable acidity and pH, while a significant effect was not shown in the texture by irradiation. Antiradical and antioxidant activity, and the phenolic contents were slightly increased by irradiation at 0.5 kGy, while the phenolic contents were reduced by irradiation over 1 kGy. Our results suggest that irradiation at 1 kGy or above can be used to enhance the microbial safety of cut Chinese cabbage without a significant loss in the quality attributes.     

Modified atmosphere packaging of filleted rainbow trout

Shelf‐lives of filleted rainbow trout (Oncorhynchus mykiss) packaged in over‐wrap, vacuum and gas mixture conditions and stored at 1 ± 1 °C were compared by measurement of pH, total volatile bases (TVB), hypoxanthine content, lipid oxidation (TBARS value), superficial counts of aerobic psychrotrophic flora and sensory analysis (colour, odour and flavour). The gas mixtures evaluated were 10% O₂ + 50% CO₂ + 40% N₂, 10% O₂ + 50% CO₂ + 40% Ar, 20% O₂ + 50% CO₂ + 30% N₂, 20% O₂ + 50% CO₂ + 30% Ar, 30% O₂ + 50% CO₂ + 20% N₂ and 30% O₂ + 50% CO₂ + 20% Ar. Sensory quality deterioration was delayed and bacterial growth as well as increases in pH, TVB and hypoxanthine levels were reduced by modified atmosphere packaging (MAP). Lipid oxidation was higher in gas packages with 20 and 30% O₂ than in those with 10% O₂. Vacuum‐packed fillets presented the lowest TBARS values. In summary, MAP gave rise to a significant extension of shelf‐life when compared with vacuum and over‐wrap packaging. No significant differences were found between the packages containing either N₂ or Ar. The best evaluated atmosphere consisted of 10% O₂ + 50%CO₂ + 40% N₂/Ar. © 2002 Society of Chemical Industry     

Effects of chitosan-based coating and modified atmosphere packaging (MAP) on browning and shelf life of fresh-cut lotus root (Nelumbo nucifera Gaerth)

The present study investigated the effect of chitosan coating containing antibrowning agents and modified atmosphere packaging (MAP) on the browning and shelf life of fresh-cut lotus root stored at 4 °C for 10 days. The atmosphere in the packages was evaluated for O₂ and CO₂ concentrations. The browning on the surface of lotus root slices was prevented by chitosan-based coating and MAP treatment. L* values of coated + MAP and control samples were 68.8 and 48.9 after 8 days storage, respectively. For a^? and b^? values, samples of coated + MAP treatment had the slowest increasing trends among all the treatments. At the end of storage, the coated + MAP samples exhibited the lowest polyphenol oxidase (PPO) activity and malondialdehyde (MDA) content. Its highest overall visual quality (OVQ) scores (> 7) demonstrated that chitosan-based coating + MAP treatment could provide a better inhibitory effect on the browning and extend the shelf life of fresh-cut lotus root.Industrial relevance: Fresh-cut vegetables have drawn the attention of industry as a novel lightly processed product. Both edible coating and MAP treatment cause changes in atmosphere composition and respiration rate of lotus root slices. This combined treatment could be used to control the browning and improve the storage life of this fresh-cut vegetable. This information could be useful for the development of novel application to edible coating and MAP design for lightly processed lotus root.     

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