Listeria monocytogenes F5069, ATCC 19111, Scott A, and two L. monocytogenes strains isolated from egg were evaluated for growth and thermal resistance in liquid whole egg. Each strain grew in liquid whole egg at temperatures between 4 and 30°C, except Scott A which did not grow at 4 or 10°C. Generation times ranged from 24 h for F5069 to 51 h for ATCC 19111 at 4°C and from 7.8 h for one of the egg isolates to 31 h for ATCC 19111 at 10°C. Maximum populations for each strain increased with increasing growth temperature and were between 105 and 3 × 108 CFU/g. Decimal reduction times (D-values) of each L. monocytogenes strain in raw liquid whole egg were similar to D-values reported in milk. The heat resistance of all strains was similar. For L. monocytogenes F5069, D-values ranged from 22.6 min at 51°C to 0.20 min at 66°C. The zD-value for F5069 was 7.2°C. Minimal pasteurization parameters (60°C, 3.5 min) for liquid whole egg would result in 99 to 99.9% inactivation (populations reduced 2 to 3 log cycles) of the L. monocytogenes strains tested.
Commercially broken raw liquid whole egg (LWE) was obtained from 11 processing establishments across the United States on 3 or 4 occasions over an eight-month period. The samples were evaluated for the presence of Listeria species by the FDA, USDA, and cold enrichment procedures. Forty-five Listeria isolates were obtained from 15 of 42 (36%) egg samples. Both the USDA and FDA methods were useful for isolation of Listeria species, resulting in 12 and 8 positive samples, respectively. Six samples were positive by both procedures. Listeria was isolated from one sample by cold enrichment. The most frequently isolated species was L. innocua, which was found in all (15) of the listeriae-positive samples. L. monocytogenes was the only other species isolated and was obtained from 5% (2) of the egg samples. The USDA and FDA procedures each yielded one L. monocytogenes-positive sample. The two L. monocytogenes-positive samples contained estimated populations of 1 and 8 CFU L. monocytogenes/ml and were obtained from the same plant during the spring and early summer sampling times. Twelve (80%) of the 15 Listeria-positive samples were solids-adjusted LWE. Thus, Listeria species, including the psychrotrophic pathogen L. monocytogenes, are present in commercially broken raw LWE.
The ascospores of Saccharomyces cerevisiae were over lOO-fold more resistant than vegetative cells of the same strain. The Da of spores in apple juice was 6.1 min and the z value was 3.8"C; in a Chenin blanc wine the D,s was 0.57 min and the .z value was 6.7"C. The presence of sugar in the heating medium increased spore resistance while alcohol reduced it; varying pH over the range 3.0 to 7.0 had little effect.
Site visits to 15 apple juice or cider facilities were conducted in New York State. Washed apples, pulp, press juice, final product, and other samples, when appropriate, were sampled aseptically. Samples were plated on acidified potato dextrose agar, before and after heating at 70°C for 1 -2 hr. For unheated samples, molds predominated in fruit, yeasts and molds in pulp, and yeasts in press and final juice samples. Average counts were 2.8 x 104, 7.3 x 104, 1.7 x 105, and 1.4 x 105/g, respectively. Heat resistant yeasts, molds, and bacteria were isolated frequently, generally at a level of less than 1 per log.
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