2.9. Effect of ListShield™ on frozen food entrees
Frozen entree samples, in this case fully-cooked, prepackaged
meals served in-flight on airplanes, were received from the
manufacturer in Maine. Frozen entrees containing mixture of beef,
potatoes, broccoli, and tomato sauce were allowed to thaw for
24 he48 h at 2e6 C. The entrees were contaminated at a rate of
5 103 CFU/g, mixed thoroughly, and allowed to colonize for
30 min at 4e6 C. Three entrees were treated with 2 mL of PBS and
three were treated with 2 mL of ListShield™ at a rate of
1 107 PFU/g of meal. The entrees were placed at 4 e6 C for an
additional 30 min and then placed in the freezer for 24 ± 2 h. The
samples were defrosted for 24 ± 2 h at 4e6 C and thoroughly
mixed. Three 25 g samples were transferred into a sterile sampling
bags from each of the six entrees and 10 mL of sterile peptone water
was added to each bag and stomached for approximately 30 s. The
number of viable L. monocytogenes in each sample was determined
by plating 0.1 mL aliquots onto individual MOX agar plates and
colonies were counted following an incubation period of 24 ± 2 h at
30 ± 2 C.