Types of Bacteria and Shelf-Life of Evacuated Carbon Dioxide-Injected and Ice-Packed Broilers

Abstract

Broiler carcasses were packed in low-permeability film bags that were evacuated, injected with C0 2 , then held at 2 C. Broilers were examined microbiologically and for off-odor to determine the shelf-life and types of bacteria. Vacuum level did not significantly affect bacterial counts. Broilers stored in 65"7o C0 2 had a 1-day longer shelf-life than those held in 20o/o C0 2 and about a 5-day longer shelf-life than ice-packed broilers. Spoiled carcasses from either 20 or 65% C0 2 packages had an acid-sour off-odor, and more than 90% of the bacteria present were Lactobacillus. Ice-packed broilers had the typical putrid off-odor at spoilage, and more than 95% of the bacteria were non-pigmented Pseudomonas. Kraft (19) listed 24 genera of bacteria as isolates from poultry and Cox (9) found one additional genus. Only a few genera, however, affect the acceptability and shelf-life of poultry meat. Most observers found many different types of bacteria at the time of slaughter, but on carcasses that were held aerobically at 0-5 C the Pseudomonas or Achromobacter groups predominated at the time of spoilage (1,3,5,15,22.23). Coyne (12), Haines (16), Ogilvy and Ayres (22) and Scott (28) found that the two principal spoilage organisms Pseudomonas and Achromobacter were inhibited by C0 2 • Average generation time for Pseudomonas apparently was reduced as a logarithmic function of C0 2 level (22). Haines (16) and King and Nagel (17) found that C0 2 levels of 20 to 70% doubled the generation time for Pseudomonas if other environmental factors were constant. Thomson (32) found that psychrotrophs were inhibited by 10 and 20o/oC0 2 • The predominant spoilage microorganisms on beef stored in air were Pseudomonas and Achromobacter (2,18,26). Gardner et al. (13) found that 96% of the microflora on spoiled stored pork were Pseudomonas or Achromobacter. Clark and Lentz (8) found that in vacuum-packaged beef held at 5 C, the Pseudomonas and the Moraxella-Acinetobacter group were inhibited by 15% C0 2 • Shank and Lundquist (29) showed that the spoilage of vacuum-packaged cured meats involved lactic acid bacteria almost exclusively. Patterson and Gibbs (23) found that lactobacilli were the predominant spoilage bacteria on beefthat was vacuum packaged and held at 0-2 C. Pierson et al. (24) found that 95% of the bacteria on anaerobically packaged beef were lacto-bacilli. Lactobacillus and other lactic acid bacteria whose growth is not significantly inhibited by C0 2 have a direct bacteriostatic effect on many gram-negative bacteria (14) and on three strains of Pseudomonas and one strain of Salmonella typhimurium (25). In this study we aimed to determine the effect of C0 2 and vacuum on types of bacteria on broilers in commercially feasible, bulk shipping packs of low permeability film, and to determine the effect of this microf1ora on shelf-life and olfactory quality of broilers. MATERIALS AND METHODS A "Conofresh 4000" packaging system (Continentia! Forest Industries-Corrugated, Greenwich, CT) 4 was used to package 560 broiler carcasses in a simulated commercial evacuated, C0 2-flushed bulk pack. Chilled broilers were taken from the drip line at a commercial processing plant and placed four to a plastic film bag (7 cc/100 in 2 , permeability); then bags were placed into a wax coated corrugated box for insertion into the packaging chamber. The chamber was evacuated to 10, 17 or 24 inches of Hg. Carbon dioxide was injected into a film bag to either 20 or 65%, and the bag was sealed. Percentage of C0 2 in each bag was not measured directly, but was based on extrapolation from the known pressure applied by the C0 2 injection mechanism; the pressure required to produce each C0 2 content with this packaging equipment had been determined previously. The packs were held at 2 C and sampled for microorganisms and for off-odor after S, 9, 12, 15 and 18 days of storage. Controls consisted of broilers that were packed in ice and held in wax-coated corrugated boxes and stored at 2 C. Controls were also sampled microbiologically and for off-odor after 5, 9, 12, 15 and 18 days of storage. All treatments were duplicated.