4-11. OXIDATIVE RANCIDITY
Examine the product for odor/flavor changes which may indicate oxidative
a. Cause. This undesirable flavor results from a reaction between oxygen and
lipids (fats). Milk from some cows develops this defect so quickly and without any
abuse that it is said to oxidize spontaneously. This oxidation may be caused by the
catalytic action of copper ions. Contamination or fortification of milk with iron may also
accelerate this reaction.
b. Terms Used. The oxidation of dairy products leads to flavors termed
cardboard-like, tallowy, or oily.
c. Absence of Change in Color or Texture. No color or textural changes are
evident in the oxidative rancidity of dairy products.
d. Reference. A discussion of oxidative rancidity may be found in paragraph
4-12. HYDROLYTIC RANCIDITY
Examine the product for odor/flavor changes which may indicate hydrolytic
a. Definition. Hydrolytic rancidity is the breakdown of fats by enzymes. This
lipolysis requires the presence of water and may be mediated by heat, acidity, alkalinity,
or any of the lipolytic enzymes 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.
b. Rancid Flavor. The sharp, biting, acrid flavor indicating this condition may
be referred to as a rancid flavor. The flavor may vary depending upon the stage of the
Examine the product for textural changes and darkening of the product which
may indicate dehydration.
a. Definition. Dehydration is a loss of water from a product such as cheese.
Dehydration is usually due to improper storage conditions.
b. Color. Dehydration of a frozen product dries out the surface. Usually the