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

Oxidative rancidity

Rancidity can occur in many products or ingredients during storage. It affects taste and odor, and can have an impact on nutritive value. The high ambient temperature in the tropics hastens fish spoilage by accelerating the activities of bacteria enzymes and chemical oxidation of fat in fresh.

Spoilage can be non-microbiological, fish lipids contain high proportion of polyunsaturated fatty acids, which are more reactive chemically than the largely saturated fats that occur in mammalian meat. This makes fish far more susceptible to development of oxidative rancidity.

Oxidative rancidity, one of the major causes of quality deterioration in foods, is caused by the oxidative deterioration of lipids by atmospheric oxygen. It is a chemical reaction catalyzed by heat, ultraviolet light, heavy metals and oxygen.

Oxidative rancidity is an oxidation reaction which starts by an unsaturated fatty acid forming a radical. Radicals are highly reactive and will always want to react with something else again. Radicals can be formed spontaneously, for example under influence of light as well as the presence of certain metals.

It is a primary mechanism which deteriorates the quality such as development of off−flavor, rancidity, degradation in texture, changing of color in meat and its products during storage, which renders them and made meat unfit for human consumption. These reactions take meat towards loss of nutritive value and eventually declining consumer confidence in the product.
Oxidative rancidity

Chemical rancidity

Rancidity is associated with characteristic off-flavor and odor of the oil. Rancidity could be as a result of microbial decomposition of fats, oils and other lipids. When these processes occur in food, undesirable odors and flavors can result.

There are two major causes of rancidity. One occurs when oil reacts with oxygen and is called oxidative rancidity.

Fish are the main source of polyunsaturated fatty acids that, unfortunately, are highly susceptible to degradation process, such as oxidation. Oxidative rancidity is a chemical reaction catalyzed by heat, ultraviolet light, heavy metals and oxygen.

Oxidation of fats is caused by a biochemical reaction between fats and oxygen. In this process the long-chain fatty acids are degraded and short-chain compounds are formed. Oxidative rancidity is best controlled by the addition of antioxidants and ‘oxygen scavengers’.

The other cause of rancidity is by a combination of enzymes and moisture. Enzymes such as lipases liberates fatty acids from the triglyceride to form di and/or monoglycerides and free fatty acids and such liberation of free fatty acids is called hydrolysis.

Hydrolysis is also caused by chemical action that is prompted by factors such as heat or presence of water. Rancidity caused by hydrolysis is called hydrolytic rancidity.
Chemical rancidity