Comparison of homogenizing, shaking, and blending on the recovery of microorganisms and endotoxins from fresh and frozen ground beef as assessed by plate counts and the Limulus amoebocyte lysate test

Abstract

Of 3 methods studied, brisk shaking of samples in dilution blanks by hand and homogenization by a stomacher were compared relative to their capacity to recover both endotoxins and viable bacteria; blending with a Waring blender was compared with these 2 methods only on the recovery of viable cells. Aerobic plate counts were essentially the same by the 3 methods for fresh meats, with the stomacher producing slightly higher aerobic plate counts and significantly higher gram-negative counts determined by violet red bile agar. The stomacher produced significantly higher aerobic plate counts and violet red bile agar results on frozen meats than did shaking. Endotoxins were determined by the Limulus amoebocyte lysate test; results by shaking and stomacher on 15 single samples of frozen meat were identical. Of Limulus amoebocyte lysate-negative beef which was spiked with known endotoxin, a higher percentage of recovery was obtained with the stomacher. Although both aerobic plate counts and violet red bile agar counts were found by shaking and stomacher to decrease significantly in frozen meats, endotoxin content was not significantly affected. The stomacher was the better method overall, especially when meats are to be examined for their content of viable gram-negative bacteria, endotoxins, or both.