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Rancidification is the process of complete or incomplete autoxidation or hydrolysis of and oils when exposed to air, light, moisture, or bacterial action, producing short-chain aldehydes, ketones and free fatty acids. (2024). 9783527306732, Wiley-VCH. ISBN 9783527306732
When these processes occur in food, undesirable odors and flavors can result. In processed meats, these flavors are collectively known as warmed-over flavor. In certain cases, however, the flavors can be desirable (as in ). (2024). 9783527306732, Wiley-VCH. ISBN 9783527306732
Rancidification can also detract from the nutritional value of food, as some are sensitive to oxidation. Similar to rancidification, oxidative degradation also occurs in other hydrocarbons, such as , , and mechanical . (2024). 9783527306732, Wiley-VCH. ISBN 9783527306732
are often used as 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 (vitamin E). Synthetic antioxidants include butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), TBHQ, propyl gallate and ethoxyquin. The natural antioxidants tend to be short-lived, so synthetic antioxidants are used when a longer shelf-life is preferred. The effectiveness of water-soluble antioxidants is limited in preventing direct oxidation within fats, but is valuable in intercepting free radicals that 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 scavenger technology can be used to remove oxygen from food packaging and therefore prevent oxidative rancidification.
The Rancimat method is carried out using an air current at temperatures between 50 and 220 °C. The volatile oxidation products (largely formic acid) 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, and can be taken as an indication of the oxidative stability of the sample.
The Rancimat method, the oxidative stability instrument (OSI) and the oxidograph were all developed as automatic versions of the more complicated AOM (active oxygen method), which is based on measuring peroxide values 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-92 and ISO 6886.
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