Meat Fats of Better gives a characteristic pungent odor is responsible for most of the economic losses of fats and fatty foods. Oxidative rancidity in lard is par- Quality ticularly serious. Moreover, most proc- essing that is undertaken to improve Waldo C. Ault, other properties (such as odor and Roy W. Riemenschneider^ color) tends to reduce the stability of Steward G. Morris fats. It has been difficult, therefore, to apply the various processing techniques to lard. The edible meat fats^ lard and tal- Before satisfactory progress could low, are almost completely digestible. be made in understanding oxidative They are high-energy foods and con- rancidity and in producing fats of tain substances necessary for good nu- satisfactory stability, methods for pre- trition. They also are of great economic dicting stability and evaluating anti- importance. Our lard production alone oxidants were necessary. Reasonably amounts to 2/2 billion pounds a year— effective methods for accomplishing approximately equal to the combined those ends are available, but because production of soybean and cottonseed of the many factors involved none of oils. them gives perfectly clear-cut results. It seems strange, therefore, that The methods most widely used are they have received so little attention. the active-oxygen method, frequently Probably that is because they are by- referred to as the Swift stability test; products of the meat-packing industry, oxygen-absorption measurements; in- or because we regard the rapid expan- cuioation tests; and baking tests. sion in the production of soybean oil as The active-oxygen method involves more exciting. Be that as it may, the bubbling purified air or oxygen factors that affect the quality and ac- through the melted fat under stand- ceptance of these fats deserve careful ardized conditions, usually at 210^ F. consideration. The time in hours requiied to develop The properties open to improvement rancid odor or a peroxide content indi- are keeping quality, or stability, physi- cative of rancidity is noted. To an ex- cal characteristics—such as plastic perienced technologist, this tim.e is of range, consistency, and the creaming value as a basis for comparison in pre- power—odor, flavor, color, and smoke dicting the life of a fat or in estimating point (temperature at which a fat or the worth of an antioxidant that may oil begins to smoke). have been added to the fat under test. Stability is the main one. Without By use of suitable equipment, the better keeping quality, the application time a sample of fat requires to reach a of other techniques would have little level of oxygen uptake preestablished value, because the best shortening is as the rancid point may be determined unfit for use if it has a strong odor or under standardized and comparable flavor—if it is rancid. The chief causes conditions. In this instance also, the are atmospheric oxidation, absorption time is of value in predicting the of odors, and the action of enzymes storage life of a fat or in estimating the and micro-organisms. Rancidity that is m.erit of an antioxidant. Workers at the caused by atmospheric oxidation and Eastern Regional Research Laboratory 90:2722°--51 44 671 672 19 5 0-1051 YEARBOOK OF AGRICULTURE reported that results obtained by the bility of the meat fats by feeding an method usually lead to the same con- antioxidant substance to an animal clusions as those of the acti\'e-oxygen before slaughter. The investigators miethod, but because of manipulation reported that of a wdde variety fed, difficulties it is not so generally used. tocopherol was the only antioxidant Keeping quality may also be de- deposited in the adipose tissue to a termined by merely incubating samples significant extent. of fat in open beakers or jars in an In attempting to produce a meat fat oven at a temperature usually of 145° of good stability, it is therefore im- F., although occasionally higher tem- portant to conduct the ]:>rocessing op- peratures are used. A comparison of erations in such a manner as to min- the time required for rancidity to de- imize destruction of any antioxidant velop in each sample is a measure of substances present. That means the their stability. The rancid point may be avoidance of unnecessary exposure of detected by sense of smell or by chem- the fat to fight, air, or high tempera- ical determination of peroxide content. tures. The fat must not be held at high When an effective antioxidant is temperatures while exposed to air for added to a fat, the keeping time of the long periods. It is also important to fat before developnrient of rancidity keep metal contamination as low^ as may be increased fivefold to tenfold. possible. Some metals, in the form of The test methods we have described their salts or oxides, are know^n to have provide an approximate measure of a pro-oxiclant efí'ect; that is, they re- the increase in stability of the fat. duce the stability of fats markedly. However, only a few of the antioxi- That is particularly true of iron and dants that are capable of protecting copper. In fact, copper is such a pow^ cr- the bulk fat wall continue to stabilize ful pro-oxidant that its addition to the the fat after it has been used in baked extent of a few tenths of one part per products. In other w^ords, most anti- million makes lard rancid in about 20 oxidants do not have ^'carry over" into minutes at temperatures of boiling baked goods. Consequently, standard- water. ized baking tests have become neces- Copper or copper-bearing alloys, sary in evaluating antioxidants for therefore, should not come into con- edible fats. In such baking tests, the fat tact with the fat during the handling (with or without added antioxidant) is and rendering processes. It is hardly baked in a pastry or cracker recipe and possible to eliminate au iron from the the stability of the products is noted. equipment, but elimination of rust, The methods for determining the especially following shut-down periods, stability of fats can also be used in helps. Increased stability can be ob- studies aimed at minimizing destruc- tained by equipping the processing and tion of the natural antioxidants in fats rendering departments with aluminum, during processing. stainless-steel, and glass- or plastic- The meat fats have a much lower lined tanks, pipes, and pumps. content of the more elTective natural A process for removing contaminat- antioxidants than do most vegetable ing metals from fats has been de- fats. The naturally occurring antioxi- scribed. The fat is treated with tannic dants include lecithin, or cephalinlikc acid and subsequently filtered. The substances, and tocopherols. Many in- filtration apparently removes the vestigators believe that tocopherols, the metals and the excess tannic acid. efi'ectivc antioxidant of most vegetable If metal contamination is not too oils, are also present in traces in lard great, the metal may be deactivated if they are not destroyed by processing. % adding a compound that unites with Rather extensive experiments at the the metallic ion. Such bound metal has University of Minnesota ofTer little no pro-oxidant properties. Citric acid, hope for increasing the oxidative sta- esters of phosphoric acid, ascorbic acid. iVIEAT FATS OF BETTER QUALITY and esters of ascorbic acid and isoas- less expensive than most of the anti- corbic acids arc examples of edible oxidants. Therefore, their use usually compounds that are metal deactivators results in important economics. Con- in fats. sequently, most of the lard on the mar- The use of such precautions during ket today that has improved stability processing will result in the production contains syncrgistic antioxidant mix- of meat fats with increased stability. tures. The low content of natural aiitioxidant An ideal antioxidant for use in foods substances, however, probably pre- should have the following qualifi- cludes the preparation of meat fats that cations : have stabilities such as are usually Effective stabilizing action under found in the hydrogenated vegetable- conditions of use. oil shortenings unless some substance No harmful physiological effect, that will delay oxidative degradation even in quantities considerably greater is added. Besides the natural anti- than those likely to be used and even oxidants, synthetic compounds that when ingested over long periods of will do this are known. Such substances time. generally contain or consist of com- At least sufficient solubility in fats pounds having quinol, phenol, amino, to facilitate its use; greater solubility or Sulfide groupings. is usually advantageous. The mechanism by which antioxi- Freedom from objectionable odor, dants perform their function is still not color, or flavor even after storage. clear, but an eíTective antioxidant is Stability to whatever processing is always capable of being oxidized in the necessary after it is incorporated in the medium and under the conditions fat. found in the oxidizing substrate. Usu- Protective action which carries over ally the antioxidant will be nearly gone into baked goods. before peroxides develop in appreci- Economy in use and availability in able amounts and before rancidity can amounts needed. be observed. Despite this list of requirements, sev- A large number of compounds bring eral substances have been declared ac- about a marked enhancement of the ceptable as antioxidants for use in lard stability when they are added to fats in federally inspected plants subject to that contain phenolic antioxidants. provisions governing the concentration They are ineíTective, however, in sub- and statements on the label. The sub- strates devoid of natural or added stances include gum guaiac, tocopherol phenolic antioxidants. The compounds concentrates that contain at least 30 are generally referred to as antioxidant percent tocopherol, nordihydroguaia- synergists, or simply synergists.