The levels of total polyphenols and o-diphenols were determined in virgin oils and in chloroform/methanol-extracted oils. The solventextracted oils were richer in polyphenols than the virgin oils. High polyphenol content was associated with a high resistance to oxidation of the oils. A linear relationship was found between polyphenol content and the oxidative stability of the virgin oils during storage at 60 C. After removal of the polyphenols, the oxidative stability of the oils decreased considerably and seemed to depend on polyunsaturated fatty acid concentration.

Polyphenols in olive oils

Available data on phytosterols from the world's literature have been compiled and summarized. There still exists a paucity of data on the quantities of plant sterols in many foods. More extensive data are available on the relative sterol composition. Our compilation shows that plant oils are excellent sources of phytosterols. Nuts and seeds contain moderate levels, and fruits and vegetables generally contain the lowest concentrations of plant sterols. Analyses of the minor sterols, namely, the delta5- and delta7-phytosterols, have become available only recently.

Sterol content of foods of plant origin

Chromatographic analysis of plant sterols in foods and vegetable oils

Tables showing representative values for the vitamin E content of human foods have been developed from all the available reliable information. These tables cover animal products, plant products, fats and oils, baked products, infant foods, and mixed dishes. The effects on vitamin E content are discussed for heating and storage of dairy products, grains, vegetables, and plant oils; for the refining of plant oils; and for the processing and baking of grain products. Causes of variation in vitamin E levels are presented and the distribution of the different forms of vitamin E in foods is shown. The biologic activities of these forms are used to calculate approximate vitamin activity values of representative foods.

Vitamin E content of foods.

Refined, bleached, and deodorized soybean oil and vanaspati (partially hydrogenated vegetable oil blend consisting of peanut, cottonseed, nigerseed, palm, rapeseed, mustard, rice bran, soybean, sunflower, corn, safflower, sesame oil, etc., in varying proportions) were used for deep-fat frying potato chips at 170, 180, and 190°C. Refractive index, specific gravity, color, viscosity, saponification value, and free fatty acids of soybean oil increased with frying temperature, whereas the iodine value decreased. The same trend was observed in vanaspati, but less markedly than in soybean oil, indicating a lesser degree of deterioration. Iodine values of soybean oil and vanaspati decreased from their initial values of 129.8 and 74.7 to 96.2 and 59.6, respectively, after 70 h of frying. Polyunsaturated fatty acids decreased in direct proportion to frying time and temperature. Losses were highest in soybean oil with a 79% decrease in trienoic acids and a 60% decrease in dienoic acids. Levels of nonurea adduct-forming esters were proportional to the losses of unsaturated fatty acids. Butylated hydroxyanisole and tertiary butylhydroquinone did not affect deterioration of soybean oil at frying temperatures.

Changes in the characteristics and composition of oils during deep-fat frying

The unsaponifiable fractions of soybean, cottonseed, coconut, olive, and avocado oils have been studied in detail. The oils differed in the contents of total unsaponifiables, squalene, tocopherols, and sterols and also in the composition of the tocopherol and sterol fractions. The presence of absence of individual unsaponifiable components may help in establishing the identity of each of the investigated oils and in detecting of admixture by another oil.

Studies of unsaponifiables in several vegetable oils

The behaviour was studied in cottonseed oil which had been exposed to frying under controlled conditions in a system in which only the oil, water and/or the antioxidant BHT were present. In the oils, changes which had been caused by heating were evaluated through determination of acid, hydroxyl, TBA and iodine values, extinctions at 232 nm and 460 nm, fatty acid composition, viscosity, amounts of “polymers” and non-urea-adduct-forming fatty acid methyl esters. All the changes were less pronounced when the frying was carried out in presence of either nitrogen or water. The latter protected the oil only if it was present in amounts sufficient to generate such a volume of vapours which could effectively act as an inert gas-blanket. BHT had no delaying effect on the deterioration of the oil during frying. When the oil was heated in the presence of air, the antioxidant's destruction was lessened by the presence of water in the system, but a large portion of BHT was lost through steam distillation.

Effect of water and bht on stability of cottonseed oil during frying

The effects were studied of the processes of degumming, neutralisation, bleaching and deodorisation on the content and composition of the various fractions of unsaponifiables in soya bean oil. The effect of each of the various technological steps on the decrement of the investigated unsaponifiables in the processed oils was different. When compared with the crude oil, the refined soya bean oil contained less tocopherols (by 31 to 47%), sterols (by 25 to 32%) and squalene (by 15 to 37%). No significant differences were observed in the compositions of the sterol and tocopherol fractions of the crude and refined soya bean oils.

Quantitative changes in some unsaponifiable components of soya bean oil due to refining

A study was conducted on the efficiency of several adsorbents (Tonsil L80, Tonsil ACC, Fuller’s earth, Celite, Kaoline, silicic acid, and Florosil) in removing phospholipids and color bodies from phosphoric acid degummed soybean oil. Best results under the condi-tions of the experiments were obtained with Tonsil L80 at a 2% concentration and 100 C (reduction in phosphorus content from 17.3 to 3.1 μ/g oil, and in photometric color from 21.6 to 2.4). Removal of phospholipids from the oil by Tonsil L80 and Tonsil ACC follows the Freundlich equation. A colorimetric method for determination of microamounts of phos-pholipids and a spot test for their quantitative evalua-tion were also developed.

A. Letan

Papers

Studies of unsaponifiables in several vegetable oils

Effect of water and bht on stability of cottonseed oil during frying

Quantitative changes in some unsaponifiable components of soya bean oil due to refining

Pretreatment of soybean oil for physical refining: Evaluation of efficiency of various adsorbents in removing phospholipids and pigments

Characterization of lipids from seeds of the rosacea family