b. Cause of Sour Odors and Flavors. Sour odors and flavors are produced by
the growth of bacteria in a microaerophilic environment. The bacteria involved are
relatively thermal-tolerant lactic acid bacteria, usually lactobacilli.
(1) The bacteria ferment the sugars in the food, which are used as a food
source. As the bacteria grow in the food item, they produce as a by-product of their
metabolic activities various organic acids, such as formic, acetic, and butyric.
(2) These organic acids are deposited in the food items, where they cause a
lowering of the pH of the product. As the pH is lowered, the product develops a sour
odor because of the shift toward the acid side of the pH scale.
c. A Result of Underprocessing. Cured meats sometimes develop sour odors
and flavor several days after processing. This is invariably the result of
underprocessing, followed by growth of the surviving microorganisms. The
microorganisms involved are relatively thermal-tolerant lactic acid bacteria, usually
lactobacilli. These bacteria ferment the sugars in the cured meats with a consequent
lowering of the pH of the product. This type of spoilage is more common in the larger
sausages, as well as in hams, and can be controlled by the same procedures
recommended for the prevention of green cores in sausages.
d. Summary. Sour odor may be summarized by the following diagram.
+ High Temperature
1-16. PUTRID ODOR
Putrid odors are found most commonly in large cuts of meats. The putrid odor is
very offensive. Many describe the odor as being foul or tainted. You, the veterinary
food inspection specialist, should be aware that a foul odor is characteristic and
desirable in certain products, such as Limburger cheese.
a. Abnormal Characteristics. In addition to the putrid odor, abnormal
characteristics of affected items include a putrid flavor and changes in the texture and
color of the product. A darkening effect on the product will be seen in the development
of the putrid-odor condition. A softening of the texture, resulting in a mushy product,
accompanies the formation of putrid odor.