Oxidative rancidity: a reaction of the triglycerides with oxygen; Hydrolytic rancidity : a reaction causing the fatty acids to be released from the glycerol backbone. Lipolysis, the enzymic hydrolysis of milk lipids to free fatty acids and partial glycerides, is a constant concern to the dairy industry because of the detrimental . Rancidity is the development of unpleasant smells in fats and oils, Hydrolytic rancidity Oxidative rancidity (auto-oxidation)Caused by the.

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Rancidity is the complete or incomplete oxidation or hydrolysis of fats and oils when exposed to air, light, or moisture or by bacterial action, resulting in unpleasant taste and odor. Specifically, it is the hydrolysis or autoxidation of fats into short-chain aldehydes and ketoneswhich are objectionable in taste and odor. In certain cases, however, the flavors can be desirable as in aged cheeses.

Rancidification can also detract from the nutritional value of food, as some vitamins are sensitive to oxidation. Three pathways for rancidification are recognized: Hydrolytic rancidity refers to the odor that develops when triglycerides are hydrolyzed and free fatty acids are released.

This reaction of lipid with water may require a catalystleading to the formation of free fatty acids and glycerol. In particular, short-chain fatty acidssuch as butyric acidare malodorous. Oxidative rancidity is associated with the degradation by oxygen in the air.

The double bonds of an unsaturated fatty acid can be cleaved by free-radical reactions involving molecular oxygen.

This reaction causes the release of malodorous and highly volatile aldehydes and ketones. Because of the nature of free-radical reactions, the reaction is catalyzed by sunlight. For example, even though meat is held under refrigeration or in a frozen state, the poly-unsaturated fat will continue to oxidize and slowly become rancid. The fat oxidation process, potentially resulting in rancidity, begins immediately after the animal is slaughtered and the muscle, intra-muscular, inter-muscular and surface fat becomes exposed to oxygen of the air.


This chemical process continues during frozen storage, though more rsncidity at lower temperature. Oxidative rancidity can be prevented by light-proof packaging, oxygen-free atmosphere air-tight containers and by the addition ranncidity antioxidants.

Microbial rancidity refers to a process in which microorganisms, randidity as bacteria or moldsuse their enzymes such as lipases to break down fat. Consuming rancid food products is unlikely to cause immediate illness or harm, although rancidification can reduce the nutritional value of food by degradation of nutrients.

Antioxidants are often used as preservatives in fat-containing foods to delay the onset or slow the development of rancidity due to oxidation.

Natural antioxidants include ascorbic acid vitamin C and tocopherols vitamin E. The natural antioxidants tend to be short-lived, [8] so synthetic antioxidants are used when a longer shelf-life is preferred.

The hydrolyfic of water-soluble antioxidants is limited in preventing direct oxidation within fats, but is valuable in intercepting free radicals rancidlty travel through the aqueous parts of foods.

A combination of water-soluble and fat-soluble antioxidants is ideal, usually in the ratio of fat to water. In addition, rancidification can be decreased by storing fats and oils in a cool, dark place with little exposure to oxygen or free radicals, since heat and light accelerate the rate of reaction of fats with oxygen. Antimicrobial agents can also delay or prevent rancidification by inhibiting the growth of bacteria or other micro-organisms that affect the process.

Oxygen scavenging technology can be used to remove oxygen from food packaging and therefore prevent oxidative rancidification. Oxidative stability is a measure of oil or fat resistance to oxidation.

Principles of Biochemistry (2+1)

Because the process takes place through a chain reactionthe oxidation reaction has a period when it is relatively slow, before it suddenly speeds up. The time for this to happen is called the “induction time”, and it is repeatable under identical conditions temperature, air flow, etc.


There are a number of ways to measure the progress of the oxidation reaction. One of the most popular methods currently in use is the Rancimat method. The volatile oxidation products largely formic acid [9] are carried by the air current into the measuring vessel, where they are absorbed dissolve in the measuring fluid distilled water.

By continuous measurement of the conductivity of this solution, oxidation curves can be generated. The cusp point of the oxidation curve the point where a rapid rise in the conductivity starts gives the induction time of the rancidification reaction, [10] and can be taken as an indication of the oxidative stability of the sample.

The Rancimat method, the rancidihy stability instrument OSI and the oxidograph were all developed as automatic versions of the ranciddity complicated AOM active oxygen methodwhich is based on measuring peroxide values, [10] for determining the induction time of fats and oils. Over time, the Rancimat method has become established, and it has been accepted into a number of national and international standards, for example AOCS Cd 12b and ISO From Wikipedia, the free encyclopedia.

Naturwissenschaftliche Grundlagen der Lebensmittelzubereitung.

Ullmann’s Encyclopedia of Industrial Chemistry. Retrieved from ” https: Food preservation Food science.

FPT Oxidative and hydrolytic rancidity

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