Shelf-Life of Meat Loaves Packaged in Vacuum or Nitrogen Gas I. Effect of Storage Temperature, Light and Time on the Microflora Change

Abstract

The effects of storage temperature, light and time on the microflora of vacuum- or nitrogen-packed meat loaves were examined at intervals during 49 d at −4, 0, 3 and 7°C under dark and lighted displays. Storage of cooked cured meat loaves at −4°C for 49 d produced little increase in lactobacilli numbers (from log10 5.2 to 6.3) but resulted in significant (P<0.05) increases in psychrotrophs (log10 3.9 to 5.9) and anaerobes (log10 5.1 to 6.3 under vacuum). Storage time and temperature above 0°C resulted in a significant (P<0.05) increase in lactobacilli, psychrotroph and anaerobe numbers, regardless of packaging atmospheres, but the times at which counts reached approx. 108/g were deferred, i.e., day 7 at 7°C, day 21 at 3°C and day 28 at 0°C. Apart from a few exceptions in the numbers of psychrotrohs and lactobacilli, there were no significant differences in the numbers of microflora between vacuum- and nitrogen-packed meat loaves. At day 0, the dominant flora in both types of packaged samples was composed of Pseudomonas (32 to 34%), Brochothrix (24 to 38%), Micrococcus (9 to 22%) and Lactobacillus spp. (7 to 20%). By day 49, Lactobacillus spp. became a predominant part (62 to 76%) of the psychrotrophs. Few significant differences in the composition of psychrotrophs were found among different treatments. With an initial level of 102 coliforms per gram, there was no significant (P>0.05) change in coliforms counts between treatments but the numbers of yeasts and molds were lower in nitrogen-packed samples at 3 and 7°C as compared with similarly treated vacuum-packed samples.