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A new method has been developed to estimate the stabilising activity of synthetic and natural food additives at frying. Non‐refined and refined vegetable fats and oils were heated at a temperature of 170°C after adding water‐conditioned silica gel for two hours. The degraded products were measured to assess the oil stability at frying temperature. The determination of polymeric triglycerides by size exclusion high‐pressure liquid chromatography (HPLC) was carried out for the estimation of the oxidative heat stability of vegetable fats and oils. Tocopherols, various tocopherol esters and phytosterol fractions, phenolic compounds, like quercetin, oryzanol, ferulic acid, squalene, butyl hydroxytoluol (BHT), butyl hydroxyanisol (BHA), and other compounds, like ascorbic acid 6‐palmitate and gallates, are added to refined sunflower and rapeseed oil and their efficacy determined. Both linoleic and oleic rich oils gave comparable results for the activity of the various compounds. α‐tocopherol, tocopherol esters, and BHA have low effects at frying temperature. Ascorbic acid 6‐palmitate and some phytosterol fractions were found to have the greatest antioxidant activity. Corn oil was more stable than soybean oil and rapeseed oil better than olive oil. It was also observed that non‐refined oils proved to have a better stability at elevated temperature than refined oils. The results show that the stability of the vegetable oils at frying temperature is a function of more than just the fatty acid composition. There is evidence which supports a co‐relationship between the unsaponifiable matter content and oxidative stability. It is believed that a radical peroxidation mechanism predominates at lower temperatures. When a large volume of oil is heated in a fryer and the oxygen supply is poor, non‐radical reactions such as elimination (acid catalysed dehydration) or nucleophilic substitution take place.

Summary :The formation of acrylamide during food frying is generally influenced by food type, thermal treatment and equipment. The acrylamide concentration is increased when frying oils containing a higher level of polar materials or silicone or larger amounts of diglycerides. This effect may be caused by moisture escaping from food that has an enhancing effect on the heat transfer. It was noticed that if the moisture in the frying operation was bound by special adsorbents, the acrylamide content could be reduced by more than 50%. The effects of several additives like citric acid on the formation of acrylamide during frying of chips were also investigated. The mechanism of acrylamide formation in fried foods is discussed to explain these findings.

Deep‐fat frying is a complex, thermal chemical process that produces fried foods with desirable colour, appearance, flavour, and texture. Normally, less stable liquid oils are hydrogenated to enhance their oxidative stability for deep‐fat frying purposes. However, considerable amounts of trans and positional isomer fatty acids are formed during hydrogenation, which are nutritionally undesirable. The stability of frying oils is sometimes increased by careful blending of polyunsaturated oils with more saturated oils. The natural way of improving oxidative and flavour stability of frying oils and fats is by adding natural antioxidative components and precursors present in the plant kingdom, such as 'virgin' olive oil, sesame seed oil (SSO) and rice bran oil (RBO). A variety of natural antioxidative components, present in these oils, comprise tocopherols and tocotrienols, special sterols e.g. Δ5‐avenasterol and sterol esters, squalene, sesamolin, sesamol, sesaminol and related compounds, polyphenols, etc. Various antioxidative components present in SSO and RBO are largely retained in Good‐Fry® Constituents (GFC), manufactured according to European patent as well as USA and worldwide patent applications pending (Silkeberg and Kochhar, 2000) Generally, palm olein, palm oil, partly hydrogenated rapeseed oil/soybean oil and/or their blends are mainly used by the frying industry for the production of a variety of snack products and pre‐fried convenience foods. Several new frying oils with good oxidative stability, which do not require hydrogenation, are now commercially available on the European market, for example high‐oleic sunflower seed oil stabilised with GFC. The results showed that the addition of 6% GFC to unhydrogenated rapeseed provided crisps, produced on industrial scale, with stability similar to those fried in palm olein without GFC. Shelf life of crisps fried in soybean oil, iodine value 130, was substantially increased by addition of 5% GFC. The Good‐Fry® Constituents can also be added, with advantages of flavour stability of fried snacks, to oils such as palm oil or palm olein at lower levels of 2%. It is forecasted, to meet an ever‐growing consumer demand of 'healthier' snack products, the usage of natural antioxidative components in stabilising frying oils rich in monounsaturated fatty acids (MUFAs) will grow tremendously.