At the present time, vegetable oils are the source of most of the visible fat in the U.S. diet. They are used as salad and cooking oils, in salad dressing, margarine and shortening. Processing methods include extraction, refining, hydrogenation and interesterification. During storage and use, the products are exposed to oxygen and/or heat, particularly during frying. Processing, storage and use are related to changes in composition, nutritive value and physical characteristics of vegetable oils. Refining removes undesirable minor components present in crude oils. Refined polyunsaturated vegetable oils are the primary dietary source of tocopherols. Hydrogenation modifies physical characteristics and improves sensory and oxidative stability. This process converts some of the polyunsaturated fatty acids to new fatty acid isomers. Although the biochemical effects of these isomers are still being studied, long‐term animal feeding trials and human experience have demonstrated that the partially hydrogenated oils in margarines and shortenings are wholesome foodstuffs. Abusive overheating of fat in air sharply decreases its palatability and nutritive value and may create minor amounts of carcinogenic materials. However, long‐term animal feeding studies with properly used frying fats have revealed little, if any, effect on life span and incidence of pathological conditions.

The protein quality of 34 samples of commercially prepared foods was determined using the Tetrahymena pyriformis W and rat Protein Efficiency Ratio (PER) bioassays. ANRC Reference Casein was used as the reference protein in both assays. The regression equation relating the Tefrahymena Relative Nutritive Value (RNV) and PER was: PER = 0.286 + 0.022 (RNV), r = 0.90 (P < 0.01). This relationship could be used to predict the protein quality of food samples. The use of the Coulter particle counter instead of the direct microscopic counting procedure increased the efficiency of the Tetrahymena assay by reducing counting error and the length of time required. In addition, quantitative information on cell size in relation to quality and quantity of protein in the test sample was obtained. The results of these studies suggest that the Tetrahymena pyriformis W assay may be adapted to provide a rapid, low cost assay for estimation of protein quality of commercially prepared foods.

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