Rancidity, oxidative

One disadvantage of fats contained within foodstuffs is the deterioration of the fat through oxidative rancidity. Many consumers find the aroma and flavor of deteriorated fats in foods repulsive, while others are fond of country ham and butter which owe thek aroma and flavor to fat rancidity and other breakdown products. The use of antioxidants (qv) makes such products commercially viable. 

Another type of chemical change is initiated by light, which may trigger autolytic, that is, free radical (Type I) or singlet oxygen (Type II) reactions. These changes are routinely classified as oxidation. Rancidity in cosmetics, especially those containing unsaturated Hpids, is commonly prevented by use of antioxidants (qv). 

Stability refers to a measure of the extent to which a fat resists the development of oxidative rancidity, and thus it is a measure of the induction period. Stability is usually expressed as the time that elapses under specified conditions before rancidity can be detected. 

RAMANATHAN L and DAS N p (1993) Natural products inhibit oxidative rancidity in salted cooked ground fish, J Food Sci, 58, (2), 318-20. 

Lipids are hydrolyzed by moisture and heat into free fatty acids, though hydrolytic enzymes may be deactivated by extrusion. Also, unsaturated fatty acids may imdergo oxidative rancidity (Camire et al., 1990). 

Fats deteriorate in two ways. One is normally a chemical process the other is normally enzymatic. They are oxidative rancidity and lipolytic rancidity. In the former, oxygen (normally in the form of a free radical) adds across double bonds. As this is a zero activation energy process it is... 

This specification is for butter oil, which is butter with the water removed. The free fatty acid limit is to detect lipolytic rancidity while peroxide value specification is to limit oxidative rancidity. The copper limit arises because copper catalyses the oxidation of fats. The absence of neutralising substances is to prevent a high titration for free fatty acids being covered up by the addition of alkali. 

The second way in which fats deteriorate is oxidative lipolysis. This is an entirely different process in which oxygen free radicals add across double bonds. Oxidative rancidity can be prevented or reduced by several different routes. One way is to ensure that no double bonds are present. Another is to use anti-oxidants that act as free radical traps. Exposure to oxygen and ultraviolet light should be avoided. Reducing the temperature has no effect since free radical processes have a zero activation energy. 

Oxidative rancidity is not necessarily a problem unless a polyunsaturated fat such as sunflower oil has been used. Where such a fat is used oxidative rancidity can occur and, as autoxidation occurs where the reaction becomes self-catalysing as oxygen free radicals react, some very unpleasant tastes can appear very quickly. In general, the effect of oxidation on biscuits at the end of their shelf life is that a cardboard taste starts to appear. 

The addition of soy proteins to beef tended to inhibit rancidity development (35,30,36). Figure 1 graphically demonstrates the inhibitory effect of soy on oxidative rancidity. The addition of soy protein to emulsions had no effect on rancidity (TBA values) (l l). 

SOD is more heat stable in milk than in purified preparations in milk it is stable at 71°C for 30 min but loses activity rapidly at even slightly higher temperatures. Slight variations in pasteurization temperature are therefore critical to the survival of SOD in heated milk products and may contribute to variations in the stability of milk to oxidative rancidity. 

Fresh plant and animal tissue when dried to a water activily much below 0.97 show irreversible disruption of metabolic processes Products susceptible lo oxidation and oxidative rancidity can be treated with antioxidants and vacuum or inert gas packed to minimize exposure to oxygen. Low temperature storage can further reduce the tale of chemical deterioration. 

Shahidi, F. and Wanasundara, U. 1998. Methods of measuring oxidative rancidity in fats and oils. In Food Lipids. Chemistry, Nutrition, and Biotechnology (C.C. Akoh and D.B. Min, eds.) pp. 377-396. Marcel Dekker, New York. 

One of the factors responsible for the quality deterioration of foods is lipid oxidation. All foods containing fat are susceptible to oxidative rancidity, which can render the food unacceptable to the senses and also reduce nutritional quality. 

Tarladgis, B.G., Pearson, A.M., and Dugan, L.R. Jr. 1964. Chemistry of the 2-thiobarbituric acid test for determination of oxidative rancidity in foods. II.-Formation of the TBA-malonaldehyde complex without acid-heat treatment. J. Sci. Food Agric. 15 602-607. 

Yamauchi, K., Nagai, Y., and Ohashi, T. 1982. Quantitative relationship between alpha-tocopherol and polyunsaturated fatty acids and its connection to development of oxidative rancidity in chicken skeletal muscle. Agric. Biol. Chem. 46 2719-2724. 

The first report on antioxidative effect of MRP was made by Franzke and Iwainsky (3). Shortly afterward Griffith and Johnson (4) reported that the addition of glucose to cookie dough resulted in a better stability against oxidative rancidity during storage of the cookies. Research on antioxidative MRP was then mainly performed by groups in Japan. A symposium on Maillard Reactions in Food held in Uddevalla, Sweden, 1979 included also the aspect of antioxidative properties. The contributions on this subject contained also brief reviews (5, 6, 7). Most of the work has been done on model systems. Some applications in food systems have, however, also been reported (8 - 11). 

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