Rancidity, of fats

Antioxidants retard the oxidative rancidity of fats. Oxidative rancidity comes on suddenly rather than gradually and the problem is caused by the addition of oxygen free-radicals across any double bonds present. For example, with epoxide compounds, rupture of the initial epoxide leads to the production of various aldehydes and ketones - these can be very odiferous. One problem with oxidative rancidity is that it is a zero free energy (AG) process and is therefore not retarded by lowering the temperature. 

Butylated hydroxyanisole is an antioxidant (see Table I) with some antimicrobial properties. It is used in a wide range of cosmetics, foods, and pharmaceuticals. When used in foods, it is used to delay or prevent oxidative rancidity of fats and oils and to prevent loss of activity of oil-soluble vitamins. 

Uses Antioxidant to retard rancidity of fats and oils, in food pkg., topical pharmaceuticals, cosmetics... 

Frankel, E.N. Recent advances in the chemistry of rancidity of fats, in Recent Advances in the Chemistry of Meat, pp. 87-118 (1984) (edited by A.J. Bailey), The Royal Society of Chemistry, London. 

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. 

Butter is used in some, usually more expensive, bakery foods, and is prized for its flavor contribution. Fats are used in some products such as pie cmst, croissants, or puff pastry, up to 60%, based on flour. StabiHty of fats and oils in perishable items such as breads, cakes, or pastries is of no consequence because shelf life is so limited that rancidity does not occur. In cookies and crackers, however, stable fats must be used in the formula since prolonged shelf life could lead to product deterioration with fats that develop rancidity. 

One of the most prominent problems confronting the modem food processor is the prevention of rancidity. Rancidity affects not only the palatability of the food but the nutritive value as well—for example, oxidative spoilage of fats has been shown to be responsible for the partial destruction of the essential fatty acids (6) and of other dietary nutrients such as vitamins A (12) and E (9), and perhaps D (26) and certain members of the B complex (5, 29, SO). When one considers that nearly every food contains some fat and that this fat is subject to oxidative spoilage, the magnitude of the problem of rancidity is at once obvious. 

Of the many tests which have been submitted, the determination of active oxygen or peroxide content seems to give rather good correlation of data. During the oxidation of fat, certain oxygen-containing compounds are formed which are active in the sense that they are capable of liberating iodine from potassium iodide (19). The liberated iodine may be determined quantitatively and it thus becomes a measure of rancidity. 

In spite of inadequacies in laboratory methods, much valuable time is saved through accelerated tests, and much valuable information is obtained. The foods chemist, through the judicious application of these tests, is making rapid progress in the prevention of rancidity, and in improving the quality of fats and fatty foods. 

Davidow (19), of the Food and Drug Administration, has described a colorimetric method applicable to technical chlordan. The method is based on the observation that when technical chlordan is heated with a mixture of diethanolamine and methanolic potassium hydroxide, a purple color is produced. When known amounts of this insecticide were added to cabbage, pears, and fresh and rancid rat fat, recoveries of 74 to 104% of the insecticide were obtained. However, because two crystalline isomers of chlordan isolated from the technical product do not give a colored reaction product with the reagent, further investigation of the method is being made. The red color obtained when technical chlordan is heated with pyridine, alcoholic alkali, and ethylene glycol monoethyl ether, as described by Ard (2), likewise fails with the crystalline isomers of this insecticide. 

The traces of fat in wholemeal flour reduce the shelf life of the flour as they become rancid fairly rapidly. Claims are made that this trace of fat has important dietary properties but the veracity or otherwise of this claim is beyond the scope of this book. 

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. 

As little as 0.1% rancid milk fat proved to be a very effective foam depressant during the condensing of skim milk and whey (Brunner 1950). This effect was attributed to the mono- and diglycerides. 

Storage of fats and oils leads to rancidity, a largely oxidative deterioration that causes development of unpleasant tastes, odors, and toxic compounds.239 Similar chemical changes account for the "drying" of oil-based paints and varnishes. These reactions occur... 

The oxidative degradation represented by the foregoing reactions is referred to as peroxidation. Peroxidation can lead to rapid development of rancidity in fats and oils. However, the presence of a small amount of tocopherol inhibits this decomposition, presumably by trapping the intermediate radicals in the form of the more stable tocopherol radicals (Eq. 15-54), which may dimerize or react with other radicals to terminate the chain. 

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