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-degrees-C The other portions were finely ground and distribut ed in retail packs. The retail packs were master packaged under atmosp heres of N2, CO2 or O2 + CO2 (2:1, v/v), then stored at 2-degrees-C Th e 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For each assessment, a vacuum pack and a master pack of each type, each contain ing products from the same batch, were withdrawn from storage. The vac uum packaged product was finely ground and distributed into retail pac ks. The newly prepared retail packs and those from the master packs we re displayed in a retail cabinet in which air temperatures averaged 4 +/- 2-degrees-C The appearance of the displayed product from each stor age packaging was assessed twice daily until it was judged to be unacc eptable. At the beginning and end of the display, the product in each pack was assessed for discoloration and off-odours, the chemical state s of the muscle pigment al the exposed surface were estimated, and the surface microflora was characterized. The appearance of the product d isplayed after storage in a vacuum pack, for times up to 32 days, beca me unacceptable within 48 h. A product stored in any of the master pac ks for 1 day appeared unacceptable after 6 h of display. The display l ife of products stored under N2 or CO2 was similar to that of the vacu um 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 day s. The display life of products stored under O2 + CO2 was similar to t hat of the vacuum packaged product when storage times were 2, 4 or 6 d ays, but the appearance of products stored under O2 + CO2 for 8 days o r longer was unacceptable when master packs were opened Apart from tho se 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products were discoloured, and the metmyoglobin fractions of the surface pigments had increased, when the product was withdrawn from display.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 develop ed flora dominated by lactic acid bacteria. The spoilage flora on prod ucts stored in vacuum pack or under O2 + CO2 did not attain the maximu m numbers of 10(7)/g during either storage or display. Those maximum n umbers were attained on products stored under N2 and CO2 after 16 and 28 days storage respectively. Some products stored under N2 for 16 day s or longer developed moderate or strong off-odours during display tha t were ascribable to microbial action. Other products developed only s light, 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 circums tances.