The influence of storage and display conditions on the color stability of display-ready pork loin roasts

A total of 216 pork loin samples were utilized to examine the color stability of master-packed, display-ready pork cuts stored in three different atmospheres (100% CO(2), 100% N(2) and 70% O(2) and 30% CO(2)) at three storage temperatures (-1.5, 2, and 5 °C) for four day intervals up to 28 days, and then subsequently displayed aerobically for up to 30 hr. The composite results clearly indicated color stability was progressively lost during both chilled storage and subsequent aerobic display. However, retention of color stability was maximized by storage at -1.5 °C. In addition, storage in 100% CO(2) tended to maximize retention of color stability, despite the fact samples stored in 70% O(2) and 30% CO(2) were brighter and redder following storage and prior to subsequent aerobic display.     

Static, Controlled (CO2) Atmosphere Packaging of Retail Ready Pork

Wrapped boneless pork loin roasts and slices were stored at 4°in bulk under constant CO₂ concentrations of 50% and 100% for 1 and 2 wks. Samples stored under 50% CO₂ for 2 wks could subsequently be displayed (aerobic) for 3 days without becoming unacceptable or for 6 days if previously held under 100% CO₂ for 14 days. Aerobic shelf-life at 4°of the latter samples equalled that of fresh pork chops under simulated retail display. Physicochemical characteristics during storage did not limit acceptability. Reusable master packs have application for distribution of retail ready cuts under controlled atmosphere packaging.     

THE EFFECTS OF FROZEN STORAGE ON THE RETAIL ACCEPTABILITY OF PORK LOIN CHOPS AND SHOULDER ROASTS

Uncured shoulder roasts and loin chops were utilized to evaluate the effects of frozen storage for different intervals (0, 56, 84, 112, 140, 168 and 196 days) in different protective storage wraps (oxygen–permeable retail wrap, polyethylene bags, aluminum foil, and freezer paper) upon factors contributing to their retail acceptability after thawing and 24 h of subsequent display. The composite results of this study indicate that uncured pork cuts can be successfully frozen and stored for at least 196 days at ?30° C in still air, in the dark, in any of the protective storage wraps evaluated, and be thawed for 24 h at 2° C prior to being retailed and generally be as acceptable as their fresh counterparts during 24 h of retail display.     

Effects of distribution packaging method and storage time on the physical properties and retail display characteristics of pork

The sensory characteristics of pork chops from bone-in loins and Boston butts (n = 65 each) were affected little by primal loin and the butt packaging method (paper wrap, vacuum pack and gas flush) and storage time (7, 10 and 14 days) under industry conditions. However, loin chops fabricated from vacuum-packaged loins after 14 days of storage had less (P < 0·05) discoloration and two-toning than chops fabricated from other loins. All loin chops were placed in retail display and overwrapped with a polyvinyl chloride film after fabrication at each storage time. Vacuum-packed butts stored for 10 and 14 days produced chops with less discoloration and two-toning, and higher overall appearance scores (P < 0·05) compared to chops from paper-wrapped or gas-flushed cuts. Vacuum-packaging resulted in higher quality retail cuts than paper-wrapped or gas-flushed packaging. Thus, it is recommended that the pork industry and retail distribution system utilize vacuum-packaging as the primary method to store and ship fresh pork before retail sale.     

Centralized packaging of retail meat cuts: a review.

Centralized packaging of retail meat cuts is growing more popular because of its economies and potential to maintain quality, enhance safety, and extend the shelf life of fresh meat. Requirements for optimizing shelf life of centrally prepared retail cuts for periods up to 15 weeks are slightly different from those needed to extend the shelf life of fresh, chilled meat. Chilled meat primarily deteriorate at the cut or uncut muscle surface. In long-term storage, primal cuts are placed in an atmosphere saturated with carbon dioxide and containing very low residual oxygen. These cuts are held at -1.5+/-0.5 degrees C. When the meat is removed, it is fabricated into retail or food service cuts. New fresh surfaces are created in the process, revitalizing the meat's appearance. After being prepared for retail display, the meat normally has four more days of shelf life. Depending on the meat species, shelf life is usually limited by development of undesirable organoleptic changes, usually defects in color, which are independent of microbial presence. The microbes consist of a lactic acid bacterial population that maximizes under storage conditions at about 10(8) CFU/cm2 well before shelf life ends. Circumstances are different with centralized distribution of retail-ready fresh meat. The wholesale storage period following initial packaging of the retail cuts is about 20 to 30 days. Prepared products must withstand retail display for up to 2 days without further manipulation of package contents. Retail packages are simply moved from their storage container (usually a unit or overwrap containing a modified atmosphere) to retail display, where desirable meat color develops upon exposure to air. Three gas atmospheres have some potential to satisfy storage needs for centralized distribution of retail-ready packages: 100% CO2, 100% N2, or 70% N2 + 30% CO2. Shelf life is limited by undesirable changes in surfaces exposed at initial packaging, caused by growth of psychrotrophic bacteria. If 100% CO2 is used, these are all lactic acid bacteria (LAB). Therefore, initial bacterial numbers on the meat and storage temperature become critical to success. The most attractive storage option is 100% CO2 used at - 1.5 +/-0.5 degrees C. This review presents the reason for that recommendation, along with basic concepts of meat chemistry, a discussion of modified atmosphere packaging, meat microbiology, and current results with simulated centralized packaging of retail-ready meats.     

The influence of controlled atmosphere and vacuum packaging upon chilled pork keeping quality

A total of 48 pork loin section (1 kg) with normal inherent muscle quality were utilized to evaluate and compare the effects of a vacuum packaging system and a CO(2) controlled atmosphere packaging system on keeping quality of chilled pork stored at -1·5°C. Results indicated based upon appearance CO(2) packaged porl loin had a storage life of greated than 15 weeks and vacuum packaged pork loid had a storage life of slightly over 12 weeks. However, off-flavor development coinciding with lactic acid bacteria reaching maximum numbers presently restricts the actual storage life of pork loin stored at -1·5°C to 9 weeks in both packaging treatments. Therefore, if microbial contamination on the commercial product can be reduced significantly to prevent spoilage organisms, including lactics, from rapidly growing to maximum numbers, storage life of pork loin at -1·5°C can be extended sufficiently to accomodate all domestic and export applications using either vacuum or CO(2) packaging.     

A comparison of modified atmosphere and vacuum skin packing for the storage of red meats

The performances of two commercially available packaging systems for prolonging the shelf-life of fresh meat were compared at 1°C and during simulated retail display. Beef and pork loin steaks in modified atmosphere packs (MAP), containing 75% O2 and 25% CO2, developed an initial bright red (beef) or pink (pork) colour, which gradually changed to brownish-red or -pink after 12 days; similar samples in vacuum skin packs (VSP) remained purple-red throughout the storage period. Off-odours developed more rapidly in MAP (8–12 days), possibly due to more extensive growth of Brochothrix thermosphacta and the effects of aerobic conditions on the metabolites of lactic acid bacteria, which predominated in both types of packs. Evidence of rancidity, using thiobarbituric acid assay, was demonstrated in MAP beef after approximately 8 days, but not in VSP. Drip losses in MAP increased after 6 days' storage, but remained generally low in VSP. Physical texture (shear force values of cooked samples) of beef was unaffected by packaging method, but pork in VSP was significantly more tender ( P < 0.001) than in MAP.     

The display life of retail packaged pork chops after their storage in master packs under atmospheres of N(2), CO(2) or O(2) + CO(2)

Commercial, bone-in pork loins were divided into four portions. One portion of each loin was vacuum packaged, then stored at -1.5 °C. The other portions were each divided into three chops, which were retail packaged. The retail packs were master packaged under atmospheres of N(2), CO(2) or O(2) + CO(2) (2:1, v/v), then stored at 2 °C. The pork was assessed after storage for up to 42 days. At each assessment, a vacuum pack and a master pack of each type, each containing product from the same loin, were withdrawn from storage. The vacuum packaged portion was cut into three chops, which were retail packaged. The chops from all packagings were displayed in a retail cabinet which maintained average air temperatures between 3 and 6 °C. The chops were assessed twice daily until they were judged to be of undesirable appearance. After storage for 1 or 2 days, the chops from all master packs appeared less desirable than the freshly cut chops. After all longer storage times, chops from N(2) and CO(2) atmospheres appeared as desirable as freshly cut chops, as did chops from O(2) + CO(2) that were stored for up to 16 days. However, chops stored under O(2) + CO(2) for 21 days appeared undesirable. Chops stored under N(2) or O(2) + CO(2) developed spoilage odours, after storage for 28 or 21 days, respectively. Bacteria were more numerous on the fat than on the muscle tissue. The numbers of bacteria were 10(7) cfu cm(-2) on the fat surfaces of chops stored under vacuum or N(2) for 42 days. The numbers of bacteria were 10(6) cfu cm(-2) on the fat surfaces of chops stored under CO(2) for 42 days or under O(2) + CO(2) for 21 days. At those times, only lactobacilli were isolated from chops stored under CO(2), but small or large fractions of enterobacteria were present in the flora on chops stored under vacuum or N(2), respectively, while the flora on chops stored under O(2) + CO(2) contained large fractions of Brochothrix thermosphacta and Gram negative, strictly aerobic, spoilage bacteria. After all storage times, chops cut from vacuum packaged portions remained of desirable appearance when displayed for 48 hr or longer. Chops stored under N(2) or CO(2) for between 2 and 35 days, or under O(2) + CO(2) for between 4 and 12 days, retained a desirable appearance during display for the same times as the freshly cut chops. Off-odours were apparent in chops after their display following storage under vacuum or CO(2) for 21 days, or under N(2) or O(2) + CO(2) for 12 days. The numbers of bacteria on the fat surfaces of chops spoiled by off-odours were ≥ 10(5) cfu cm(-2). The flora on chops removed from display were generally enriched for B. thermosphacta, enterobacteria and/or Gram negative aerobes as compared with the flora on the chops when they were removed from the storage packs. Those data indicate that the storage life of master packaged, display ready pork will probably be severely limited by the poor hygienic condition of commercial products, to little more than 1 week for product stored under N(2) or O(2) + CO(2) or < 3 weeks for product stored under CO(2).     

THE EFFECTS OF FROZEN STORAGE AND THAWING ON THE RETAIL ACCEPTABILITY OF HAM STEAKS AND BACON SLICES1

Ham steaks and bacon slices were frozen and stored at ——30° C in still air in 4 protective storage wraps (oxygen–permeable retail wrap, polyethylene bags, aluminum foil, and freezer paper) to determine the influences of frozen storage and subsequent thawing on the retail acceptability of cured pork cuts after 24 h of simulated retail display. The composite results of this study indicate that irrespective of the type of protective wrap utilized, ham steaks and bacon slices could be stored in still air, in the dark, at ?30° C for at least 140 and 112 days, respectively, and generally be as acceptable as their fresh counterparts, after 24 h of simulated display. Therefore, it may be economically beneficial to merchandise cured pork cuts, which have been frozen, stored, and thawed. However, since it is a general practice among consumers to purchase meat at retail outlets, take it home, and freeze and store it for a period of time prior to consumption, further research must be completed evaluating the effects of refreezing on the palatability and ultimate acceptability of cured pork cuts. In addition, since all thawed cuts may not be sold during the first 24 h of display, further research is required to establish the effects of frozen storage and subsequent thawing on factors contributing to the retail caselife of cured pork cuts, before the retailing of frozen and thawed cuts can be recommended as a merchandising method to increase efficiency within the meat industry.     

Physical, Sensory and Microbiological Characteristics of Lamb Retail Cuts Vacuum Packaged in High Oxygen-Barrier Film

Lamb chops and steaks from fresh (F) or vacuum packaged (VP) racks, loins and legs were packaged in polyvinyl chloride (PVC) film or vacuum packaged in high oxygen-barrier (HOB) film. Use of previously vacuum packaged (PVP) cuts did not affect overall appearance of rib or loin chops during subsequent retail display but HOB film-packaged leg steaks from PVP cuts had lower overall appearance scores than did leg steaks from F cuts. Prior VP storage negatively affected flavor desirability and odor at the conclusion of retail display (4 days in PVC or 10 or 15 days in HOB film). Pseudomonas spp. were a dominant part of the microflora of PVC-wrapped chops while L. cellobiosus was a dominant part of the microflora of HOB-wrapped chops.     

Centralized bulk pre-packaging of pork retail cuts

The performance of a commercial bulk pre-packaging system was compared to a laboratory system in terms of quality attributes such as microbiology, colour, odour, and acceptability of PVC-overwrapped pork retail cuts. A similar retail shelf life of 3 days was achieved after either 0, 7, or 14 days bulk storage with both packaging systems. The colour of the samples from both systems was pale to normal during the trial. After 14 days storage the samples from both systems were still acceptable and had a fresh meat odour. The results show that the commercial system (Cryovac GFII, Darex Africa (Pty) Ltd, Kemptonpark RSA) may be applied successfully for 100% CO₂ bulk packaging of PVC-overwrapped pork retail cuts.     

Effects of pork muscle quality on bacterial growth and retail case life

The effects of muscle quality (PSE, normal, DFD) upon the bacteriology and retail case life of pork chops were determined. Pork loin chops were processed from boneless backs after 90 days of frozen storage at -30°C. Variation in bacterial numbers was due to a highly significant (p < 0·001) storage time by muscle quality interaction. During simulated retail display, total psychrotrophs, Pseudomonas spp., Brochothrix thermosphacta and Enterobacteriaceae were lowest on PSE pork and highest on DFD pork in comparison to normal pork. Differences in bacterial densities were due to a longer lag phase in PSE pork and a shorter lag phase in DFD pork than in normal pork. Of the three muscle quality groups, DFD was most susceptible to the development of spoilage odours, while PSE pork was most sensitive to deterioration in appearance.     

The chilled storage life and retail display performance of vacuum and carbon dioxide packed hot deboned beef striploins

Two cooling regimes that complied with the New Zealand meat hygiene requirement that hot deboned meat be chilled to +7 °C or less within 24 hr of leaving the slaughter floor were evaluated for the production of chilled table meats. Electrically stimulated hot deboned bull beef half striploins were either vacuum or carbon dioxide packed before being cooled in accordance with either Regime 1 (cool at +5 °C for 24 hr, transfer to chiller operating at −1.0 ± 0.5 °C) or Regime 2 (cool at +5 °C for 24 hr, hold at 5 °C for 6 days, transfer to chiller operating at −1.0 ± 0.5 °C). Striploins were removed from −1.0 °C storage 8, 28, 42, 56, 70, 84 and 98 days after slaughter and subjected to microbiological, tenderness, sensory and retail display performance evaluations.

Both Regimes 1 and 2 produced meat of acceptable mean tenderness, 8 kgF (MIRINZ Tenderometer) in either vacuum or carbon dioxide packs within 28 and 8 days of slaughter, respectively. However, 70 days after slaughter the first signs of over-ageing became apparent. Steaks from Regimes 1 and 2 maintained acceptable visual appearance during retail display at 5 °C for 48 hr and 24 hr, respectively. After these times, the product was judged by the panel to be unacceptable because of its dull dark lean tissue and grey to green discoloration of the fat. Poor colour stability during retail display was mirrored by deterioration of sensory attributes, particularly aroma which is indicative of incipient spoilage. While carbon dioxide packaging in combination with Regime 1 offered an initial microbiological advantage over vacuum packaging, this advantage was not, however, carried over into retail display.

Poor colour and sensory stability during retail display suggest that chilled table cuts derived from hot deboned bull beef are more suited to the Hotel-Restaurant-Institutional (HRI) trade than supermarket retailing. To serve the HRI, vacuum packed hot deboned bull beef primal cuts processed by Regime 1 appear to be the combination of choice. This combination would enable commercial processors to produce quality table beef with a chilled storage life of up to 70 days.     

Thawing of lamb loin chops in air and CO(2). Effect on colour and drip

Colour retention and drip loss was assessed during retail display for chilled lamb chops displayed fresh or stored in CO(2) for 7 weeks before display, and for chops frozen for various times and thawed in air or CO(2). A sensory panel found fresh lamb chops to have an acceptable display life of 1 day, while chops which had been frozen for 1 day and then thawed lasted 2 days. Holding chops for 7 weeks in a CO(2) atmosphere at - 1·5°C improved display life to 3 days, but frozen chops held for 7 weeks before thawing had deteriorated in colour, and only one group was acceptable on the initial day of display. Initially there were no differences in Hunter L values (brightness) due to treatment, but chilled chops or those frozen for 1 day showed a greater increase in L values by the second day than those frozen for 7 weeks, after which there was no change in brightness. Hunter a values (redness) were higher in chilled chops and those thawed after 1 day's frozen storage than those frozen for 7 weeks before thawing. Hunter b values (yellowness) were greater at all times in chilled chops held for 7 weeks and varied amongst the other treatments. The measured per cent drip from chops frozen for only 1 day was greater on thawing than drip from chops frozen for 7 weeks before thawing. Drip during display, assessed by a sensory panel, increased more in those chops stored either chilled or frozen for 7 weeks before display.     

Effects of Different Chilling Methods on Hot Processed Vacuum Packaged Pork

Longissimus muscle (loin section) was removed from each side of 24 pork carcasses within 20 min postmortem. Each muscle was divided in half (N = 96 sections), vacuum packaged and allotted to one of four treatments: (1) normal chilling, (2) propylene glycol immersion, (3) crust freezing, or (4) high temperature conditioning and four storage intervals (N = 6) or 0, 7, 14 or 28 days. Rapid chilling with propylene glycol increased (P<0.05) purge. Shear force values were increased when loins were rapidly chilled (P<0.05) but few sensory differences were observed. Off-odor scores increased (P<0.05) with increasing storage time. Normal chilling resulted in lighter muscle color scores than rapidly chilled loin sections. Rapid chilling does not have a beneficial effect on palatability or shelf life of hot-processed fresh pork.     

The retail display life of steaks prepared from chill stored vacuum and carbon dioxide-packed sub-primal beef cuts

Chilled striploins and cube rolls from ten Australian steers (grain-fed for 150 days) were trimmed of external fat and cut transversely into portions approximately 10 cm thick, each weighing between 750 and 1000 g. These 'retailer-ready' cuts were each wrapped in drip saver pads and slid inside a plastic sleeve before being individually placed into a clear plastic high oxygen barrier film, metallized film or conventional vacuum bag. Cuts in clear plastic and metallized film packs were packaged in an oxygen-free saturated carbon dioxide atmosphere (CO(2)-CAP), those in vacuum bags were conventionally vacuum-packed. All packs were returned to the chiller for further cooling. After 24 hr, half the clear plastic and metallized CO(2)-CAP packs were carbon dioxide master-packed in groups of eight. Retailer-ready cuts in both clear plastic and metallized film single unit and master-packed CO(2)-CAP packs were air freighted to New Zealand and sea freighted to Japan for assessment. The control vacuum packs were all consigned to New Zealand. Assessments in both countries after 39-89 days storage at between 0 °C and -1.0 °C indicated that fat colour stability limited the retail display life of steaks cut from meat in these retailer-ready packs to approximately 48 hr. In this regard, meat from single unit CO(2)-CAP, master pack CO(2)-CAP and vacuum packs performed similarly. Lean meat colour and sensory attributes remained acceptable for up to 48 hr after displayed product was rejected because of grey-green fat discoloration. The microbiological status of retailer-ready cuts removed from CO(2)-CAP packs after 89 days chilled storage was superior to that of cuts from vacuum packs. Clear plastic and metallized film CO(2)-CAP packs performed comparably.     

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.     

Effect of modified gas atmosphere packaging after dip treatment on myoglobin and lipid oxidation of beef steaks

Fresh beef loin steaks were packaged in atmosphere of: (A) 20% CO(2) + 80% O(2) after dip treatment (dipped in 70% ethanol solution containing 3% l-ascorbic acid and 0·08% dl-α-tocopherol), (B) air after dip treatment, (C) 20% CO(2) + 80% O(2) without dip treatment and (D) air without dip treatment (control). After 3,6,9 and 13 days' storage at 4°C, the samples were evaluated for MetMb formation, TBA number and pH. The beef steaks stored in 20% CO(2) + 80% O(2) with or without dip treatment for 13 days maintained an acceptable meat colour. The TBA numbers of samples stored for 13 days in air and 20% CO(2) + 80% O(2) after dip treatment were significantly lower than those of samples without dip treatment. Beef steaks stored for 13 days in 20% CO(2) + 80% O(2) after dip treatment exhibited no change in pH. Data suggested that dip treatment with ascorbic acid and tocopherol solutions before modified gas atmosphere packaging was very suitable for the storage of retail cuts of beef loin steak.     

Effects of micro-perforated film on the quality and shelf life improvements of pork loins during chilled storage

The effects of micro-perforated film (MPF) packaging method on the quality and shelf life of pork loin during chilled storage were investigated, compared with non-packaging (control) and non-perforated film (PPF) packaging. Loins were removed from five hogs after slaughter and chilling, and each loin was portioned into four parts. These samples (40 sections) were allocated to each of five intervals (0, 1, 4, 7 and 14 days) to minimize variation among treatments and stored for 14 days under 55±10% relative humidity and 0±1?°C. Total aerobic counts of control sample were significantly lower than those from MPF or PPF loins after 14 days of storage. At 14 days, the counts of Pseudomonas and Enterobacteriaceae in the samples from MPF were significantly lower than those from PPF. At 7 days, 'L' value for the control and 'a' value for PPF were significantly lower, and ΔE values for the control were significantly higher than other samples. During storage time, percentage weight loss was the most in the control samples with MPF following and PPF the least. Accordingly, water contents decreased highest in the control samples followed by those from MPF and PPF. TBA values increased with storage time, however no significant differences were observed among treatments. Sensory evaluation analyses showed that MPF samples were generally better evaluated in all parameters over the storage time. Therefore, it has been concluded that MPF could be used as an effective packaging technology since it extends the shelf life of fresh meat by controlling the microbial growth and evaporation at a moderate level.     

The display of retail packs of ground beef after their storage in master packages under various atmospheres

Batches of coarsely ground beef trimmings were each divided into four portions. One portion from each batch was vacuum packaged, then stored at -1·5°C. The other portions were finely ground and distributed in retail packs. The retail packs were master packaged under atmospheres of N(2), CO(2) or O(2) + CO(2) (2:1, v/v), then stored at 2°C. The product was assessed after storage times of up to 32 days. For each assessment, a vacuum pack and a master pack of each type, each containing products from the same batch, were withdrawn from storage. The vacuum packaged product was finely ground and distributed into retail packs. The newly prepared retail packs and those from the master packs were displayed in a retail cabinet in which air temperatures averaged 4 ± 2°C. The appearance of the displayed product from each storage packaging was assessed twice daily until it was judged to be unacceptable. At the beginning and end of the display, the product in each pack was assessed for discoloration and off-odours, the chemical states of the muscle pigment at the exposed surface were estimated, and the surface microflora was characterized. The appearance of the product displayed after storage in a vacuum pack, for times up to 32 days, became unacceptable within 48 h. A product stored in any of the master packs for 1 day appeared unacceptable after 6 h of display. The display life of products stored under N(2) or CO(2) was similar to that of the vacuum packaged products when storage times were between 2 and 24 days but the display life was shorter when the storage times were 28 or 32 days. The display life of products stored under O(2) + CO(2) was similar to that of the vacuum packaged product when storage times were 2, 4 or 6 days, but the appearance of products stored under O(2) + CO(2) for 8 days or longer was unacceptable when master packs were opened. Apart from those latter packs, a product was not discoloured when storage packs were opened. However, all products were discoloured, and the metmyoglobin fractions of the surface pigments had increased, when the product was withdrawn from display. The products in all storage packagings developed flora dominated by lactic acid bacteria. The spoiage flora on products stored in vacuum pack or under O(2) + CO(2) did not attain the maximum numbers of 10(7)/g during either storage or display. Those maximum numbers were attained on products stored under N(2) and CO(2) after 16 and 28 days storage respectively. Some products stored under N(2) for 16 days or longer developed moderate or strong off-odours during display that were ascribable to microbial action. Other products developed only slight, non-microbial off-odours during display. Retail-ready packs or ground beef master-packaged under an oxygen-depleted atmosphere could then have a useful storage life of about 30 days in commercial circumstances.