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 run, 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.
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 47'4, 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.
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.
SUMMARY
The primary antioxidant activity of quercetin and some of its derivatives was studied in the 36–70°C range in dry systems, using two fatty‐ester substrates, respectively with linoleate and linolenate, as the main constituent undergoing oxidation. Metal contamination was avoided as far as possible, and any residual traces of metals in the thoroughly purified esters were chelated with citric acid.
Methylation of the 3, or 5, or 3 and 7, or 5 and 7 hydroxyls of the quercetin molecule led to considerable reduction of the antioxidant activity, while reduction due to methylation of the 7 hydroxyl was slight. Methylation of the 3′, or 4′, or 3′ and 4′ hydroxyls, or of any single hydroxyl of the B ring, and of an additional hydroxyl or hydroxyls of the A ring, led to a drastic reduction (to 11% or less); the 3,7,3′,4′ tetramethoxy derivative was found to be completely inactive. Hydrogenation of the 2,3 double bond resulted in an antioxidant (dihydroquercetin) with only about half the activity of qnercetin.
The primary antioxidant activity of quercetin seems to be a function of the molecule as a whole and cannot be regarded as an additive property of active hydroxyls. The effect produced by methylation of a particular hydroxyl may, however, be related to the probability of formation of a stabilized free radical by the hydroxyl in question.
The type of the substituted alkyl radical had little or no effect on the activity of the derivative, but replacement of a hydroxyl with hydrogen failed to produce the same effect as methylation of the same hydroxyl.
No indication was found of pro‐oxidant activity of the meta‐hydroxyl grouping in the A ring.
A procedure was devised for detection of adulteration of almond oil with apricot oil. -Tocopherol was found to be the main component in apricot oil, while it was present in almond oil in a limited amount. The developed method calls for a preliminary separation of the tocopherols from the oils' unsaponifiable matter by thin-layer chromatography. Subsequently, the a-and 7-to-copherols are determined either by gas-liquid chromatography or by colorimetry. It was shown that admixtures of as little as 5% apricot oil can be detected by the proposed procedure. 7-T0copherol, present in apricot oil, was responsible for the color which developed during the Bieber test.
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