Thermal Food Processing

Thermal Processing of Poultry Products 225
substantially less heat resistant than a clinical isolate of S. Typhimurium when
heated in liquid yolk. Because the study was conducted at only one water bath
temperature (55°C, without correction for come-up times), neither D nor z D values
were reported. In the second study, Schuman et al. 105 sought to kinetically characterize
the heat resistance of A. hydrophila in raw liquid whole egg using an
immersed sealed capillary tube procedure. Decimal reduction times of four individual
strains of A. hydrophila at 48, 51, 54, 57, and 60°C were found to range
from 3.62 to 9.43 min (at 48°C) to 0.026 to 0.040 min (at 60°C). Both egg
processing plant isolates were more heat resistant than the ATCC strains. The z D
values were 5.02 to 5.59°C, similar to those for other non-spore-forming bacteria.
Although this study indicated that A. hydrophila is substantially less heat resistant
than Salmonella liquid whole egg, it is important for egg processors to take
measures to prevent postpasteurization contamination of liquid egg products by
Aeromonas spp. and other psychrotrophic pathogens, including L. monocytogenes.
At the time of this review, no other reports on the thermal resistance of Aeromonas
spp. in other liquid egg products or in shell eggs cooked under simulated food
service conditions were available in the published scientific literature.
Although several investigators have attempted to kinetically characterize the
thermal inactivation of A. hydrophila in model buffer systems and in skim
milk, 137,138 each study yielded nonlinear (tailing) survivor curves, which complicated
analysis of the thermal destruction data. The previous studies yielded
diphasic (tailing) inactivation curves, in which surviving populations of 10 2 to
10 5 CFU/ml of solution were detected long after the initial linear phase of
inactivation. For purposes of calculating D values, these authors 138 disregarded
the tailing portions of the survivor curves, while noting the potential significance
of microbial subpopulations of apparently greater heat resistance than the rest of
the inoculum. Using a buffered peptone system, Stecchini et al. 139 reported that
the inactivation of A. hydrophila in 9-ml capped test tubes was a nonlinear process,
best described mathematically by a complex hyperbolic function.
7.4 CONCLUSIONS
Application of heat continues to be the most efficient method for preserving food.
Current issues facing producers of poultry products and food processors in general
include the persistence of L. monocytogenes in RTE products, antibiotic-resistant
bacteria, and handling of animal coproducts. The USDA has issued regulations to
address the Listeria problem in RTE meats, as described in this chapter. The use
of antibiotics in animal production is also being addressed by both poultry companies
and governing bodies worldwide by reducing or eliminating their use. Between
40 and 50% of a carcass is not destined for human consumption and thus must be
handled and recycled if possible. Poultry meat from this nonedible portion is often
used as an animal feed component. Concern over the bacterial levels in these
products reentering the food cycle through the feed has been debated. The survival
of Salmonella in poultry meat and bone meal has been shown to be well below
levels found in foods for human consumption. The high temperatures and times