Untitled

Abstract

SUMMARY Frying temperatures and minor constituents of oils and fatsTwo important classes of minor constituents of oils and fats are tocopherols and sterols. Both these classes are biologically active and they also affect the stability and performance of an oil at elevated temperatures. Tocopherols are phenolic antioxidants that react with free radicals and their concentration is reduced signifantly when the oil is heated. a-TocopheroI is lost faster during deep-fat frying than the beta, gamma and delta homologues. In the presence of stronger antioxidants, natural or synthetic, losses of a-tocopherol can be eliminated. Unchanged phytosterols naturally present in vegetable oils are believed to be beneficial for the health. Depending on the chemical structure, phytosterols may act as prooxidants or antioxidants. Sterols with an ethylidene group in the side chain have been found effective in retarding polymerisation at temperatures similar to those of deep-fat frying. Under unfavourable conditions (high temperature, presence of air) oxidation products are formed from sterols and a marked increase in the oxidation rate of the fat is observed. Oxidation products of the main phytosterols, p-sitosterol and stigmasterol, are: hydrocarbons (3,5-diene and 3,5,22-triene), mono-, di-and triunsaturated ketosteroids (4-en-3-one, 3,5-dien-7-one, 3,5,22-trien-7-one), 5,6-epoxy derivatives, 3,7-diols and pregnane derivatives. Other minor constituents which may affect the rate of degradation of unsaturated triacylglycerols at high temperatures are squalene, pigments and phospholipids. Squalene and phospholipids have both been reported to retard the degradation of unsaturated fatty acids under simulated frying conditions. High chlorophyll levels were found to increase the rate of tocopherol decomposition and formation of polymers in rape seed oil heated at 180°C.

Sterol, Triterpen Dialcohol and Fatty Acid Profile of Less- and Well-Known Istrian Monovarietal Olive Oil

“…This sterol has an ethylidene functional group in the side chain of its molecular structure, which retards polymerisation and oxidation of triglycerides during frying at high temperatures. This is especially important knowing that other antioxidants, such as tocopherols and polyphenols, are heat sensitive, while other sterols without the mentioned structural feature exhibit adverse or no effects (Gordon & Magos, 1983;Gordon & Magos, 1984;Boskou, 1998). Furthermore, Istarska bjelica oils were differentiated with statistical significance from other varieties by the highest level of 24-methylene-cholesterol and campestanol as well as the lowest level of Δ-7-avenasterol.…”

Επιδραση Δισακορεστων Φυτοστερολων Στη Σταθεροτητα Θερμαινομενων Ελαιων Και Χαρακτηρισμος Των Προιοντων Οξειδωσης Της Στιγμαστερολης

“…Σ2^ζ_2ΙΠ_5ΐ9 § §2^ΐΰΐ9_ § §9!ί9! :νώμενων_ελαίων Η προσβολή των μη γλυκεριδικών συστατικών των λιπαρών υλών από το ατμοσφαιρικό οξυγόνο στη διάρκεια της θέρμανσης έχει συνήθως ως απο τέλεσμα την ελάττωση της συγκέντρωσης τους (32)(33)(34)(35)(36) λόγω σχηματισμού προϊόντων οξείδωσης (37)(38)(39)(40). Η ελάττωση αυτή διαπιστώθηκε και έμμεσα με την παρατήρηση ότι η προσθήκη των ασαπωνοποίητων συστατικών ορι σμένων ελαίων σε διάφορες λιπαρές ύλες παρείχε προστασία έναντι αντι δράσεων οξειδωτικού πολυμερισμού κατά τη θέρμανση (41,42).…”