b. Hydrolytic Rancidity. Hydrolytic rancidity is the second type of rancidity. It
results from the splitting of fatty acids from their glycerol esters.
(1) Release of free fatty acids. This lipolysis requires the presence of water.
It may be mediated by heat, acidity, alkalinity, or lipolytic enzymes. These lipolytic
enzymes may be native to the food or introduced by microorganisms. From dairy fats,
the hydrolytic release of butyric, caproic, and caprylic acids produces odors which are
usually described as goaty. Hydrolysis of coconut and other lauric-acid-containing fats
releases principally capric and lauric acids, which produce a soapy taste. When warm,
the odor resembles hot buttered popcorn. It is the free fatty acids that produce the
odors resulting from hydrolytic rancidity.
(2) Control. Prevention of hydrolytic rancidity requires the use of fully
refined oils, careful processing to ensure the inactivation of lipolytic enzymes, and
packaging and storage to prevent the introduction of fat-splitting microorganisms.
(3) Special problem areas. Lipolytic rancidity continues to be a problem,
especially in confections containing coconut fats or contaminated spices.
c. Ketonic Rancidity. The final type of rancidity is ketonic rancidity. It results
from the growth of microorganisms among whose metabolic products are odorous
methyl ketones. In coconut oils, mold growth, requiring moisture and a nitrogenous
nutrient, produces ketones, presumably by beta-oxidation. The resultant odor is said to
resemble Roquefort cheese. Hydrolysis also occurs, releasing free fatty acids which
impart a soapy taste.
1-15. SOUR ODOR
Sour odors may be detected in several different types of food. In some foods, a
sour odor may be normal and desirable, as in sour cream, buttermilk, and other
products. However, in many products, a sour odor is undesirable. This condition may
be described as an uncontrolled reaction which results in the formation of an abnormal
sour odor and flavor. Any food with a high moisture content is susceptible to the
development of a sour odor and flavor. Examples of products where a sour odor and
flavor is undesirable are large cuts of meats, sausages, dairy products, and many types
of canned products.
a. As Indicator of an Unwholesome Product. The abnormal characteristics
exhibited by a product that has undergone sour-odor development include the formation
of sour odor and sour flavor. The odor of the product is not normally affected until the
sour odor condition has progressed to an unwholesome phase. Texture may not be
affected until latter stages of the deterioration of the product.