EFFECT OF CONTROLLED ATMOSPHERE PACKAGING ON PSYCHROTROPHIC GROWTH AND SUCCESSION ON STEAK SURFACES.

Abstract

Top loin steaks were used to determine the influence of packaging procedure on the microbial growth and succession on the top and bottom surfaces of steaks during a 12 day storage period. The following packaging treatments were used: (1) Gas permeable Resinite film overwrap as a control; (2) gas flush with 1% CO, 40% O₂, 59% N₂ for 2 minutes followed by film overwrap; (3) loose packaging in gas impermeable barrier bags with 100 to 150 cc ambient air; (4) 15% CO₂, 40% O₂, 45% N₂ gas atmosphere; (5) 60% CO₂, 40% O₂ gas atmosphere; and (6) 10% CO₂, 5% O₂, 85% N₂ gas atmosphere. Total psychrotrophic counts obtained from the top and bottom surfaces did not differ significantly for most sampling periods. Similar growth patterns were observed on both steak surfaces, increasing (P <.05) primarily between Day 3 and Day 9 of post-treatment storage. The steaks packaged within the gas atmospheres had lower (P<.05) total growth than the control steaks. Comparing atmospheres, the steaks packaged in relatively low CO₂ and O₂ levels (10% and 5%, respectively) had lower (P<.05) microbial growth than steaks packaged in 15 to 60% CO₂ and 40% O₂ when initial contamination was low. Pseudomonas dominated the microflora on the steak surfaces in all packaging treatments during early storage. Other aerobic organisms which survived gas atmosphere treatments include Coryneforms, Micrococcus, and Microbacterium, although they did not show large increases in growth. Coryneforms were also competitive on the bottom surface of the control steaks despite domination by the pseudomonad organisms. Loose packaging in impermeable barrier bags allowed the growth of Serratia liquifaciens after 6 days of storage. This bacterium also tended to dominate the flora within the gas atmosphere packages, although other facultative organisms (Enterobacter aerogenes and Yersenia enterocolitica) were also identified. When initial contamination was low, the gas atmospheres provided an effective means of prolonging the shelf-life of fresh beef steaks.