A Review on Frying: Procedure, Fat, Deterioration Progress and Health Hazards

Abstract

For decades, frying has been a popular technique for the preparation of foods, both on domestic and industrial scales. The effects of edible oil type and frying operation conditions on the shelf‐life of fried products, the deterioration progress and the health hazards of fried foods have been studied by various researchers. To achieve a clear conception of the present situation, a collection of the results obtained from previous studies about product deterioration and safety issues due to the frying process, along with related tables, are of prime importance. According to the studies, it can be concluded that a vacuum, oil replenishment, frying temperature, and time of process are the most important parameters affecting the quality of oils and fried products; hence, by controlling them, it is possible to prevent the formation of toxic compounds and loss of nutritional components to a considerable extent during frying operation. Furthermore, according to recent studies indicating significant formation of toxic compounds before the chemical indices of the oil reach the disposal point, more studies are needed to determine whether they are formed at levels that compromise safety and affect consumers’ sensory perception before the established discard points.

Perspectives on the use of seed oils in the South African diet

“…mainly lauric, myristic, palmitic and stearic acids; monounsaturated fatty acids (MUFAs), mainly oleic acid; and/or of polyunsaturated fatty acids (PUFAs) from the omega-6 (n-6) (linoleic or arachidonic acid) and omega-3 (n-3) family [α-linolenic acid, eicosapentaenoic acid (EPA), docosapentaenoic (DPA) and docosahexaenoic acid (DHA)], as well as of the transfatty acids present. 3 The impact of dietary fat and oil on health and disease is now also better understood as certain fatty acids are essential nutrients involved in important physiological processes, including brain development and functioning. They can also reduce the risk of the development of nutrition-related non-communicable diseases.…”

“…23 Therefore, canola is not genetically modified, and neither is the canola, olive or sunflower plants used for oil production in South Africa, as discussed by Opperman et al 1 The natural trans-fat content of seed oils is almost negligible. 1,3,24 However, during the refining of oils, and depending on the applied deodorisation conditions, trans-fatty acids can be formed, but generally, the total trans-fat content remains below 1%, 25 as also confirmed for several brands of South African olive, sunflower and canola oils by Opperman et al 1 The trans-fat content of oil may also increase when used for an excessive time at high frying temperatures, 26 but the formation of trans-fat during frying is highly dependent on the type of oil used, temperature, total frying time, and how often the oil is replaced or replenished. 3,27 Nonetheless, the use of partially hydrogenated oils used mainly by the food industry is still recognised as the main source of trans-fat in the human diet.…”

“…The good news is that partially hydrogenated oils is currently being replaced by other means of improving fat characteristics of industrially produced food, such as the blending of different oils. 3 Furthermore, most countries, including South Africa, have now enacted legislation to greatly reduce and soon forbid the presence of trans-fat, and thus the use of partially hydrogenated oils, in commercially prepared foods, owing to their detrimental health effects. [28][29][30] Opperman et al 1 made a valuable contribution by measuring oxidation products and the fatty acid composition of newly purchased South African canola, olive and sunflower oils.…”

“…42 The thermal stability of frying oils, which increases with the degree of saturation and antioxidant content, is another important criterion in the selection of a frying medium. 3 Increasingly, fast food industries use palm oil, which has a high degree of saturation (50% SFA, 42% oleic and 12% linoleic acid) and has been proven to be extremely stable while frying food. 3,43 Thus, it is not possible to expect oils used in frying to be able to adhere to the joint FAO/WHO recommended ratios of SFA, MUFA and PUFA, 6 and at the same time provide better oxidative stability during frying.…”

“…3 Increasingly, fast food industries use palm oil, which has a high degree of saturation (50% SFA, 42% oleic and 12% linoleic acid) and has been proven to be extremely stable while frying food. 3,43 Thus, it is not possible to expect oils used in frying to be able to adhere to the joint FAO/WHO recommended ratios of SFA, MUFA and PUFA, 6 and at the same time provide better oxidative stability during frying. 3 Furthermore, frequent fried food consumption was associated with risk of incident type 2 diabetes mellitus in two large cohort studies and are therefore not one of the best ways to prepare food.…”