LIPIDES 85 



come, all unsaturated fats absorb large quantities of oxygen with 

 considerable rapidity and develop, with equal rapidity, a characteristic 

 rancid odor and flavor. The length of time involved before a fat or 

 oil begins to absorb large quantities of oxygen is known as the induc- 

 tion period. The induction period of a fat is of vital importance 

 in so far as predicting its keeping quality is concerned. Fats with 

 short induction periods cannot be stored for any length of time and 

 consequently cannot be used in products where long storage is neces- 

 sary. 



The length of the induction period of a fat or oil seems to depend 

 largely on the presence of small concentrations of substances other 

 than the fat itself. These substances may be divided into two main 

 classes: (1) compounds which inhibit oxidation of the fat, and (2) 

 compounds which accelerate decomposition. The first group (those 

 which inhibit oxidation) includes compounds which are readih 

 oxidized and which absorb large quantities of oxygen. A compound 

 which prevents oxidation of a fat or oil and, in so doing, lengthens 

 the induction period is called an antioxidant. Such a substance will 

 continue to inhibit the oxidation of the material it is protecting until 

 the antioxidant itself is completely oxidized. Although the chemical 

 nature of many of the naturally occurring antioxidants is unknown, 

 it has been definitely established that ascorbic acid and a-tocopherol 

 (vitamins C and E) have effective antioxygenic properties. Many 

 synthetic compounds have been shown to possess antioxygenic proper- 

 ties, but some of them cannot be used in food products because of 

 their toxicity. 



Opposing the action of the antioxidants in fats and oils is another 

 group of compoimds which accelerates the oxidation of the parent 

 compound. Such substances are known as pro-oxidants; copper lactate 

 is an example. Among the most noted pro-oxidants arc the copper, 

 iron, and nickel salts of organic acids. It is generally believed that 

 the majority of pro-oxidants are formed during the processing and 

 refining of a fat. Regardless of their origin, pro-oxidants are important 

 factors when considciing the keeping {jualitics of a fat. 



Fat Analysis 



It was mentioned in a previous })aragraph that fats arc mixtures 

 of glycerides; even the simplest fats are complex mixtures of individual 

 glyceride molecules. For example, if there are three different acids 

 attached to the glycerol molecule, three different geometric isomers 

 can occur, according to the position of attachment of these acids on 

 the glycerol molecule. If there are four different acids in the mix- 



