Gas-forming microorganisms were isolated from gas-swollen ground beef chubs obtained from a commercial source and were phenotypically identified as Hafnia alvei. In in situ experiments, the isolated H. alvei strains produced gas in inoculated irradiation-sterilized ground beef chubs. A five-strain cocktail of H. alvei isolates was inoculated on beef trim. The inoculated beef trim samples were treated with either a water wash (W) at 65 psi for five passes (a pass refers to the application of successive multiple antimicrobial treatments to inoculated beef trim on a moving processing conveyor belt at a speed of 1 cm/s under heat ducts or oscillating spray nozzles), W plus a 2% (vol/vol) lactic acid wash (L) at room temperature at 30 psi for three passes (W/L), or a combination treatment (COMB) consisting of W plus 82°C water for three passes plus 510°C hot air for six passes plus L, or were not treated (control). After treatment, the beef trim was ground and vacuum packaged. The numbers of H. alvei were reduced with water alone and with the aforementioned antimicrobial intervention treatments. For the untreated and inoculated control samples, the numbers of H. alvei increased from 7.03 to 8.40 log CFU/g after 7 days of incubation at 4°C. However, the numbers of H. alvei treated by successive antimicrobial interventions (COMB) were initially reduced to 5.25 log CFU/g and increased to just 6.9 log CFU/g after 7 days of incubation at 4°C. Gas was produced in untreated control samples after 3 days at 15°C (15 of 15 inoculated chubs). However, in meat treated with W, W/L, and COMB, gas was produced after 4 to 5, 7 to 8, and 9 to 10 days of storage at 15°C, respectively. These results demonstrate the effectiveness of multiple antimicrobial interventions in reducing H. alvei numbers on beef trim and subsequently delaying gas formation in the resulting ground beef chubs.
†Names are necessary to report factually on available data; however, the U.S. Department of Agriculture neither guarantees nor warrants the standard of the product, and the use of the name by the U.S. Department of Agriculture implies no approval of the product to the exclusion of others that may also be suitable.
‡Present address: Department of Food Science and Human Nutrition, Washington State University, Pullman, Washington.