The efficacy of water, chlorinated water (100 ppm), peracetic acid solution (0.05%), and commercial citric acid-based produce wash (0.25%) to reduce the population of Listeria monocytogenes on precut lettuce was tested. Samples were inoculated with a mixture of equal amounts of five L. monocytogenes strains at a level of 4.7 log CFU/g, and analyzed on the day of washing and after 3 and 6 days of storage at 6 degrees C. Sanitizer reduced the number of L. monocytogenes at maximum 1.7 log CFU/g and number of L. monocytogenes reached the inoculation level during 6 days of storage. Thus, disinfectants do not eliminate L. monocytogenes on precut lettuce and cannot be solely relied on in producing precut lettuce safely. The inoculated L. monocytogenes strains were recovered at different rates after 6 days of storage; one of these strains was not recovered at all. Thus, strain-specific differences exist in the ability of L. monocytogenes to survive the washing treatments of the lettuce.
Imazalil and ethylenediamine-tetraacetic acid (EDTA) were incorporated into low-density polyethylene (LDPE) aimed at producing antimicrobial packaging films for foodstuffs. Moulded plates (thickness 2mm) containing 5% of EDTA inhibited Bacillus subtilis, whereas 0.05–0.25% of imazalil had strong activity against Aspergillus niger. Further tests for antimicrobial activity, migration and oxygen and water vapor barrier properties were carried out using biaxially stretched LDPE films containing different combinations of both substances. The addition of imazalil and EDTA increased the oxygen transmission rates and water vapor permeabilities, although the effects with imazalil films were not as significant. Transparency of the EDTA containing films decreased rapidly as a function of added EDTA, whereas imazalil films were optically faultless. Total migration into 3% acetic acid and 10% ethanol was below 4 mg/dm2. Although imazalil retained its activity against A. niger on a high level (inhibition zones >30 mm), the activity of EDTA was gone. None of the samples inhibited Escherichia coli.
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