d. Odors. The following odors have been associated with microbial spoilage:
sour, putrid, musty.
e. Texture. Textural abnormalities may include coagulation, liquefaction, and/or
f. Indicators of Spoilage in a Closed Container of Canned Foods. Spoilage
occurring in a closed container of canned foods is indicated by one or more of the
Obvious gas production.
Swelling of the lid of the container.
A change in the texture/consistency of the product.
A change in the pH of the product.
(5) An increase in the number of microorganisms seen in the microscopic
examination of the food.
a. Spoilage in Low-Acid Foods. The micrological groups associated with
spoilage in low-acid foods (pH above 4.6) are as follows.
(1) Insufficient processing. Insufficient processing is indicated chiefly by the
survival of bacterial spores, particularly those of the Clostridium species and those of
the Bacillus species, which subsequently spoil the product. Generally, anaerobic
mesophilic spoilage is associated with putrid odors.
(2) Storage at 110F or above. Low-acid foods may be spoiled during
storage above 43C (109F) by a variety of extremely heat-resistant, sporeforming,
thermophilic microorganisms. These bacteria are not pathogenic. In low-acid foods, the
most common forms of thermophilic spoilage and the causative microorganisms are
categorized as follows.
(a) Flat sour spoilage is indicated when the container is not swollen,
and when the pH of the product is significantly lowered. The causative microorganisms
are sporeformers, such as Bacillus stearothermophilus, a facultative anaerobe.
(b) Thermophilic anaerobe (TA) spoilage is indicated by swelling and,
commonly, by the bursting of the container. The condition is caused by obligately
thermophilic, sporeforming anaerobes such as Clostridium thermosaccharolyticum.
This organism produces large quantities of hydrogen and carbon dioxide. The product
usually has a "cheesy" odor.