The percent solids values of fats and shortenings using nuclear magnetic resonance (NMR) and solid fat index (SFI) have been compared. The samples used were: blends of hard fat and safflower oil, safflower oil hydrogenated to varying degrees, and different types of shortenings. This investigation demonstrated the empirical nature of the SFI technique and shows the nature of the deviations from the solids content determined by the NMR method. The magnitude of the deviation of SFI from the NMR solids content increased with the level of the solids. The SFI values and the NMR solids content were similar at the lower levels (SFI values of 10) but at the upper limit for the SFI method (SFI values of 50) the solids content by the NMR method can be 80% or more, a difference of 30 units. Although the determination of solids content by NMR is reliable, the relationship between SFI values and NMR values for different types of samples is so variable that the calculation of the SFI value from percent solids by NMR, or percent solids from SFI values from prediction equations is not very reliable. Since NMR measures the solids content more accurately than SFI and is applicable over the entire range of solids, 0 to 100%, it will be very useful in fat and oil research and control.

Three analytical methods proposed by various workers for predicting the relative stability of fats and oils to oxidation have been compared on a series of samples. The Eckey Oxygen Absorption, the modification of the A.S.T.M. Oxy-APRIL, 1962 POHLE ET AL.: COMPARISON OF SEVERAL ANALYTICAL TECHNIQUES 227gen Bomb (4), and the Active Oxygen Method (AOM) were applied to eombinatiol~s of animal and vegetable fats and oils, with and without added monoglycerides and antioxidants. The resuits indicate that the Eekey Oxygen Absorption and modified ASTM Oxygen Bomb methods are more precise than the A05{ method, and more in keeping with the experience in the fat and oil field in relation to actual performance stability than the AOM. Experimental relationships of these factors and methods to shelf life storage studies measured organoleptieally will be the subject of a later paper.

A control method is presented for selecting the appropriate processing conditions for alkali refining of crude vegetable oils by the centrifugal process to yield lowest losses with satisfactory color. This technique is sufficiently analogous to actual processing conditions to provide reliable information upon which plant performance can be based.The cup method cannot be used in this manner in that it no longer approximates operating procedures as in the days of kettle refining. The chromatographic neutral oil method, on the other hand, provides an index of the amount of oil available for recovery without regard to the possibility of attaining such levels.For these reasons the centrifugal method fills a void of long standing. Other tangible benefits that accrue from this technique are: selection of sources of oil that can be most profitably refined by establishing the relative value of competitive oils, and a means of evaluating plant efficiency.

The data from several laboratory tests [Active Oxygen Method (AOM), modified ASTM bomb, modified ASTM bomb with catalyst added to the fat, a manometric method and an accelerated oven test] were compared with data from a storage test at 85F evaluated organoleptically at selected intervals. Tests were carried out on lard, hydrogenated vegetable oil and tallow, with and without added monoglyceride, and with and without selected antioxidants. A comparison of the data from the laboratory tests with that from the storage tests indicated: 1) that the different types of fats behave differently, 2) the laboratory tests cannot be used as an index of shelf stability except for a given type of formulation of fat for which the relationship between the laboratory test and the shelf stability is known, 3) the modified ASTM bomb method is the most reliable for estimating shelf life, and 4) the modified ASTM bomb method with catalyst is not as precise as the bomb method, but may be used for control purposes where some accuracy may be sacrificed in the interest of shorter time.

A modification of the A.S.T.M. oxygen bomb method for evaluating the stability of any fat within a period of six hours or less has been developed. It is based upon the addition of selected levels of a copper, catalyst, operating under the conditions previously used without catalyst. The precision of this bomb method has been characterized and the contributions of several factors to the overall variation have been estimated. The research indicates that it will not be possible to express bomb data in terms of AOM values by employing a factor. On the basis of precision obtained by this procedure, it is concluded that it should be readily adaptable to industrial control applications.