Hydrolytic rancidity

Rancidity causes various off-flavor, off-odor, texture, and nutrient damage in muscle food. Accelerated rancidity is a greater problem in fish with a high oil content (herring, salmon, tuna), though in some oily fish (mackerel) their strong flavor can mask taste changes. There are three types of rancidity: Hydrolytic Rancidity, Oxidative Rancidity, Microbial Rancidity.

Hydrolytic rancidity also called hydrolysis or enzymatic oxidation, is a term that describes off flavors and aromas caused by release of short chain fatty acids from acylglycerols. It is the result of the hydrolysis of fats with the liberation of one or more volatile fatty acids.

Hydrolytic rancidity is commonly caused by lipase enzymes of bacterial origin. The process sometimes requires a catalyst, resulting in the production of glycerol and free fatty acids. Most foods contain triglycerides and water, this pathway is common for the development off-odors.

Increase in fatty acid results from the enzymatic hydrolysis of esterified lipids. Free fatty acids content has been used to establish the grade of deterioration.
Hydrolytic rancidity