The display life of retail-packaged beef steaks after their storage in master packs under various atmospheres

Abstract

Beef strip loins were divided into four portions. One portion of each loin was vacuum-packaged and then stored at −1·5°C. The other portions were each divided into three steaks, 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) and then stored at 2°C. Product was assessed after storage times of up to 60 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 At each assessment, a vacuum pack and a master pack of each type, each containing product from the same loin, were withdrawn from storage.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 product was cut into three steaks, which were retail-packaged. The newly prepared retail packs and those from the master packs were displayed in a retail cabinet, at air temperatures that averaged between 3 and 5·7°C, and were assessed twice daily until the product was judged to be unacceptable. When first assessed, steaks cut from vacuum-packaged product were generally considered desirable, with little metmyoglobin in the surface pigment, although the edges of same steaks were discoloured. Steaks stored under N 2 or CO 2 for 4 days or less were only slightly desirable at best, with metmyoglobin forming relatively large fractions of the surface pigment. However, after storage under N 2 or CO 2 for 6 days or more, metmyoglobin fractions were low, and the steaks bloomed to a desirable red colour. Steaks stored under O 2 + CO 2 had lower metmyoglobin fractions, and were desirable after storage for up to 8 days. However, the fractions of metmyoglobin increased, and steaks were judged to be less desirable after longer storage times. Steaks stored under O 2 + CO 2 for 20 days were unacceptable. After storage, the numbers of bacteria on steaks from vacuum packs and N 2, CO 2, and O 2 + CO 2 atmospheres were, respectively, <10 4, <10 6, <10 5, and <10 4 CFU/cm 2. The flora from steaks stored under CO 2 were composed wholly of lactic acid bacteria. Other flora were dominated by lactic acid bacteria, but contained fractions of enterobacteria and/or Brochothrix thermosphacta. The appearance of product from vacuum packs generally was unacceptable after 72 h of display. The display life of steaks stored under N 2 or CO 2 was shorter than that of the product from vacuum packs when product was stored for 2 days or less, or 46 days or more. After other storage times, the product from vacuum packs or master packs with N 2 or CO 2 atmospheres had a similar display life. The display life of product stored under O 2 + CO 2 was similar to that of product from vacuum packs or CO 2 or O 2 + CO 2 was similar to that of product from vacuum packs after storage times of 8 days or less but was shorter after storage times of 12 or 16 days. The flora on displayed product from vacuum packs or CO 2 or O 2 + CO 2. atmospheres did not attain the maximum number of 10 7 CFU/cm 2. and the product did not develop off-odours of microbial origin. However, numbers of 10 7 CFU/cm 2 were approached or attained during display of product stored under N 2 for 28 days or longer, and some of that product developed moderate off-odours. It then appears that, under temperature regimes that are common in commercial practice, retail-packaged strip-loin steaks with a display life of 2 days or longer can be obtained from master packs after storage periods of up to about 2, 4, or 7 weeks, respectively, with master-pack atmospheres of O 2 + CO Pin2 (2 : 1, v/v), N 2, or CO 2.