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1.2.11 Microbiological study before storage.




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This article is from the Food Preserving FAQ, by Eric Decker ericnospam@getcomputing.com with numerous contributions by others.

1.2.11 Microbiological study before storage.

Microbial quality of samples before baking. Uninoculated and inoculated
samples with APC of 4.08 and 4.24 log10 CFU/g, respectively, were not
significantly different (P>0.05). Before baking, black colonies were
not detected in uninoculated samples. However, black colonies were
detected in inoculated samples, which had C. sporogenes PA 3679 at
level of 3.23 log10 CFU/g, immediately after inoculation. Microbial
quality of samples after baking and before storage. After baking,
uninoculated and inoculated samples had APC at non-detectable levels.
Similarly, after storage at room temperature and at 35 C for 90 days,
counts were still non-detectable by our methods (data not shown). These
results indicated that vegetative cells of non-sporeforming
microorganisms were either irreversibly injured or totally destroyed
by the baking treatments applied. Levels of C. sporogenes PA 3679 in
bread samples after baking. In uninoculated samples, black colonies
were not detected before baking. Following all baking treatments, no
black colonies were detected in any of the uninoculated samples either
(Table 3), suggesting no activation of endogenous spores of clostridia
prior to storage.

In inoculated products, counts of C. sporo genes PA 3679 were significantly
reduced (p>O.OS) for all baking treatments with the exception of 191 C for
45 min (Table 3). Reductions from the initial load of 3.23 log10 CFU/g
generally ranged from 1.24 to 1.52 log, with the 177 C, 50 min treatment
unexpectedly resulting in the lowest count (<1 log10CFUfg). The reductions
in levels of C. sporo genes PA 3679 were not significantly different
(P>0.05) among the baking treatments of 177 C for 30 and 40 min, of 191 C
for 50 and 55 min and of 204 C for 40, 45 and 50 min. These data seem to
support the heating profile study at the center of breads, which showed
no significant difference (P>0.05) among the ultimate internal temperatures
after baking treatments. Inconsistencies in survival rate of spores for
different baking treatments (higher counts after 50 min of baking at 204
C than at 177 C) could be partly due to errors in enumeration, because of
the nonhomogeneous nature of the product or to faster setting of the dough
at higher baking temperatures, providing better protection to the spores
from heat effects in the surrounding environment.

Although these treatments reduced the level of inoculated spores of C.
sporo genes PA 3679, they did not completely destroy them in the baked
products. Whether or not endogenous spores in the products were totally
destroyed by the temperature-time combinations used in this study was
not certain. Storage studies should elucidate the existence of surviving
spores. Only uninoculated and inoculated products baked at the low
temperature (177 C) were further investigated during the storage
study, because these products were more desirable from a consumer
acceptance standpoint.

 

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