Stable and healthful frying oil for the 21st century

Food Technology.12 Stable and healthful frying oil for the 21st century This article is by S. P. Kochhat, technical director for Good-Fry international NY, Research and Deuelotnnent Centre, 48 Chi/tern Crescent, Earley, Reading RG6 IAN, Eng/mId (phone: 44-118-9261611; fax: 44-118-9626079; e-mail: goodfry@rocketlnoif.com). Healthful eating is part of the creed of our modem lifestyle. These days, a considerable number of mainstream consumers are becoming aware of health benefits of specific food ingredients. Frying oils also are changing owing to consumer demand for healthful snack products and convenience foods. Most likely, the majority of consumers all over the world wiil continue to eat fried foods in the 21st century. It would be helpful if the snack industry and the fast-food sectors could offer food products that are as nutritious as possible. Traditionally, less-stable liquid oils have been hydrogenated to enhance their oxidative stability for deep-fat frying use. However, considerable amounts of trans and positional isomer fatty acids are formed during hydrogenation, which have been described as 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 flavor stability of frying oils and fats is by adding natural annexidarive components and their precursors present in the plant kingdom. The oil or fat used for frying becomes pan of the food being fried. The nutritional quality of the frying oil is therefore of great importance with regard to the qualiry of fried foods, such as potato chips, potato crisps, and fried pellet products. Frying oil quality influences oil absorption and the types of byproducts and residues absorbed by fried food. The development of new, stable, and healthful frying oil for the manufacture of healthier snack products and convenience foods in the new century has been considered. Chemistry of deep-fat frying Deep-fat frying is a complicated thermal-chemical process that produces fried foods with desirable color, appearance, flavor, and texture. During the frying process, oil is continuously or repeatedly subjected to temperatures of 170-200"C in the presence of air and moisture. Under these conditions, several changes occur in food, namely, starch gelatinization, protein denaturation, water vaporization, and textural changes. In addition, many chemical reactions rake place in oil during frying operations at elevated temperature, which may be grouped into oxidation, polymerization, and hydrolysis. Details on the chemistry of deep-fat frying are generally known. The detrimental effects of various minor components, such as free Farry acids, trace metals and partial glycerides, which may occur in the frying oil or may migrate from the food product into the oil, have been reported. Typical frying oils and fats During the past 20 years, the once traditional use of groundnut (peanut) oil for frying purposes has become rare or special. These days, in (he United Kingdom and other European countries, alternative vegetable oils, namely refined rapeseed oil, lightly hydrogenated rapeseed oil, palm oil/rapeseed oil or soybean oil blends, and palm olein or "super" oleins are used. Owing to regional choice and for special product applications, animal fats (beef tallow or lard) also are employed as a cooking medium. In exceptional cases, sunflower seed oil and/or partly hydrogenated sunflower seed oil is used as a frying medium. Generally, palm oil or slightly hydrogenated palm oil is used for producing pre-fried french fries. frozen chips, and other convenience foods. Increasingly, palm olein, because of its good performance due to natural high oxidative stability, is becoming rhe Volume 11 June 2000 Inform

'" Table I Characteristics of selected frying oils and fats Palm Palm Palm "super" RSO" HRSOb oil olein olein Tallow Fatty acid [wt %) C14:0 1.1 1.1 1.4 3.2 C16:0 4.5 4.5 44.0 3'.8 33.7 24.3 C18:0 1.5 5.5 4.5 4.4 3.6 18.6 C18:1 5'.0 72.0 39.2 42.5 47.0 42.6 C18,2 21.0 14.0 10.1 Il.2 13.8 2.6 C18,3 J 1.0 1.0 0.4 0.6 0.4 0.7 Others 3.0 3.0 0.7 0.4 0.1 8.oJ Iodine value 116.0 53 58 65 47 Slip point (0e) 13 38 22 4 43-45 IPC (hours) at 120 C 3-4 8-' 15-16 12-14 12-14 2-6 a Refined and deodorized rapeseed oil; bpanly hydrogenated rapeseed oil, which contained 22% trans fatty acids; c induction period, which indicates oxidative stability of the oil; dc16: 1,3.7%; C17:0, 1.5; C17: 1,0.8%. oil of choice for the major snack food manufacturers in many European Union counrries. The more unsarurnred oil products or special long-life oils containing blends of hydrogenated oils usually are used by caterers and the Fast-food service industry. lmpormur chnracrcrisrics of industrial frying oils are high oxidative stability, high smoke point, low foaming, low melting point, bland flavor, and nutritionally desirable attributes. Table I gives characteristics of some selected frying oils and fats that are used by the catering industry, fast-food sector, and snack rnnnufacrurers. Generally, in North America, the frying industry and fast-food restaurants employ frying fats and shortenings based on cottonseed oil, hydrogenated soybean oil, and/or rapeseed oil. Several new frying oils having good stability are emerging on the horizon (Table 2), such as Nu-Sun, a mid-oleic sunflower oil, and high-oleic sunflower seed oil. Criteria of healthful frying oil The concept of a healthful frying oil has been questioned and debated to a considerable length. Since the lipid composition of the fried food is thought to be an important factor at the time of frying, appropriate criteria for the fatty acid composition of such an oil are considered to be: rich in monounsaturated, C18:1 (>75%), low in saturated (CI6:0, C14:0, C12:0) and polyunsaturated fatty acids (<15%), very low in linolenic acid, C18:3 «1.5%), and practically zero content of trans fatty acids Moreover, it is commonly accepted among nutritionists that when the requirement of essential fatty acids (EFAs), n-3 and n-e fatty acids, is met in the body, dietary lipids rich in monounsaturated fatty acids, such as CIS: I, are beneficial to the oxidative stability of the low-density lipoprotein (LOL) component of serum lipids. Several animal studies have shown the superiority of an oleic-rich oil, such as high-oleic sunflower seed oil (HOSO), over normal sunflower seed oil in generating LOL cholesterol that is less prone to oxidation. These days, it is generally accepted that oxidized LOL-cholesterol initiates the early stage of atherosclerosis. The higher oxidative stability of LOL-cholcsrerol has been reported in human subjects ingesting HOSO compared with those consuming normal sunflower seed oil diets. Table 3 gives general guidelines about the effects of fatty acids on total cholesterol level and lipoproteins. Healthful oils also should be rich in natural antioxidants, in tocopherols, Volume I I June 201Xl Inform

, Food Technology Table 2 Typical fatty acid composition of new frying oils and of normal sunflower seed oil and olive oil Sunflower seed oils Olive oil Parameter Nonnal No-Sun" HOSOb (virgin) Fatty acid CI6:D 7.0 8.8 4.3 9.2 C18,0 4.5 2.3 4.2 3.3 CIS: 1 IS.7 64.5 81.3 73.9 CIS:2 67.0 22.1 8.2 10.0 C18:3 0.8 0.4 <0.1 0.8 Others 2.0 1.9 2.0 2.8 Iodine value 134 95 83 83 IJ>C (hours) at 110 C 4.5 12 19 10 a Nu-Sun is mid-oleic acid sunflower seed oil, now grown commercially in the United States; b high-oleic sunflower seed oil; c induction period, which indicates oxidative stability of the oil. and preferably m j-rocopherol. Additional requirements of healthful oils are rhar the fried product should be very [ow in trails polyenes, in cyclic fatty acids, and in phytosterol oxides. Since the toxicity of cyclic furry acids formed from linolenic acid, C 18:3, seems greater than that from linoleic acid, CI8:2, it appears beneficial to have as little as possible linolenic acid in a frying oil. It should be mentioned here that French regulations do not permit a Table 3 Effect of fatty acids on cholesterol and lipoproteins Fatty acid Cholesterol level LOLa Saturated Increase Increase Trans Increase Increase Polyunsaturated Decrease Decrease slightly Monounsaturated Decrease Decrease Increase Decrease Decrease No effect a Low-density lipoprotein cholesterol ("bad" cholesterol); b high-density lipoprotein cholesterol ("good" cholesterol). Source: Yodice, R., Fat Sci. Tee/mol. 92:121-126 (l990). Volume I I June 2000 Inform

'15 HO 6.s. A venasterol to) Citrostadienol A 7 - Avenasterol Figure I:Structurel of sterols contilining ethylldene group frying far or oil containing more [han 1% linolenic ferry add to be used for deep-fat frying in the catering industry. The formation of cyclic fatty acids has, however, been noticed to be negligible during continuous industrial frying. Development of stable and healthful frying oils The concept of a stable frying oil came into existence when Alf Silkeberg artended a course on frying at the University of California-Davis, on May 17, 1990. He left with one thought in mind: To produce a stable frying oil that would be low in saturates and would not require hydrogenoricn. With the aid of scientists from Germany. India, Sudan, Sweden, and the United States, a stable and healthful frying oil was ereared and is being marketed under the brand name Good-Fry Oil. The main component of this oil is high-oleic sunflower seed oil. Its oxidative and flavor stability are funher enhanced by the addition of a small portion of refined sesame seed oil (550) and rice bran oil (RBO). Table 4 provides typical characteristics of Good-Fry Oil and Good-Fry Sunclive Oil. The latter contains a small portion of virgin olive oil. Both RBO and sesame oil contain large amounts of.o.5-ave.nasterol and related erhylidene group-containing sterols, which are in a N = Sterol ring b H the region of 295~J55 mg/ioo g in RBO and 84-265 mg/100 g in 550, respectively. Unlike most other sterols,.6.5-avenasrerol (and related sterols, namely,.6.7 -avenasterol and cirroscadienot] (Figure 1) acts as an antioxidant at elevated/frying temperatures. This antioxidant activity has been ascribed to the formarion of an allylic free radical at C29 followed by isomerization to a relatively stable tertiary free radical at C24 (Figure 2A). It should be emphasized that these ethylidene group-containing sterols show little or no antioxidant activity at room temperature, 100 C, or 120 C. That is, if one attempts to measure oxidative stability of the oil conmining such sterols by traditional methods, for example, Rancimar or 051, the results of their anrioxidative efficacy will be practically zero/negligible. This is probably due to formation of a lesshindered peroxy radical, which is ineffective at interrupting free-radical chain reactions (Figure 2b). The formation of this peroxy radical from a stable hin- Figure l:hechanisms for andoxldant..ctivity of sterols containing ethylidene group in the side ch;ain, (h) fonn..tlon of stable tertiary free r.adial <It C14 and (lb) fonn..tion of lenstable p4!rox)' r.adlcal Volume II lune 2000 Inform

Food Technology Table'" Typical characteristics Parameter Appearance Flavor Iodine value Peroxide value Free fatty acids Fatty acid (% weight) C16,0 C18,0 C18:1 C18:2 C18,3 Others Trans Farry acids Vitamin E Other anrioxidarive components' of Good-Fry frying oils Good-Fry oil Clear, transparent Bland, no foreign odor 84-90, typical 86 1.0 meq 02/kg 0.05% as oleic acid 4.5 3.7 78.6 10.7 0.1 2.4 <0.5 40 mgfloo g 100 mg/loo g Good-Fry sunolive oj]b Clear, transparent Mild olive oil Typical 86 1.5 meq 02/kg 0.15% as oleic acid 5.0 3.6 78.3 10.7 0.2 2.2 <0.5 38 mg/ioo g 100 mg/ioo g Q Contains a small portion of refined sesame oil and rice bran oil, produced according ro patent (Silkeberg and Kochhar; 1998); b in addition to (Q), also contains 10% virgin olive oil;' including cryzancl, sesame lignans, 65_ and a7-avenasterol, and desmeehylsrerols. dered radical derived from a5-avenasrerol is favored at high partial pressures of oxygen. During frying of food, an oxygen deficiency caused by steam volatilization in the frying oil favors rhe formation of a stable tertiary radical at C24 (Figure 2A). Another beneficial effect of ethylidenc group-containing sterols is that they retard the loss of tocopherols in heated oils and thus enhance the frying life of the oil and subsequently prolong shelf-life of fried snacks. A range of other potent components such as sesamolin (antioxidant precursor), sesaminol and its isomers, sesamol and its dimer present in sesame seed oil, and oryzanol (a group of ferulic acid esters of sterols) present in RBO have been shown to possess strong srabilizinglbeneficial effects during frying cper- anons. Figure 3 presents the mechanisms for the liberation of sesamol and sesaminol isomers from sesamolin during the frying operation. The protective role of sterol ferulares (oryzanol) can be explained by the formation of five resonance-stabilized Structures (Figure 4) that are very effective at interrupting the auroxidnrion chain reactions. Moreover, sesame oil contains 40--60 mgltoo g of tocopherols, mainly 'ttocopherol, while RBO contains 70-140 mg/ioo g tocopherols, 50-80% of which are j-roccpberol and )'- roconienol. It is interesting to note that sesamol and sesarninol compounds show synergistic effects with j-roccpherol and retard the degradation of a-tocopherol at frying temperature. These potent antioxidative compo- nents and precursors are largely retained by means of the special refining procedure, patented for the production of the Good-Fry Constituents (GFC), which are a blend of refined sesame seed oil and RBO. To sum up, this stable edible oil was initially creared for two purposes: (a) to be as healthful as virgin olive oil, and (b) when used for industrial frying, to be as stable or more stable than partially hydrogenated liquid oils andlor palm oil. However, this stable oil can be used for other food applications. This oil has been approved for labeling as a "dietetic" oil by the Federal Institute for the Health Protection of the Consumers in Berlin, Germany. The edible oil is now commercially available in Europe. The sun-olive oil, with a mild olive oil fla- Volume I I June 2000 Inform

vor, is sold in retail stores in Sweden and also is available to retailers in orher countries. Also, this type of stable frying oil, with irs Mediterranean image of healthful diet is being adopted by several European Union snack manufacturers for producing healthful snacks of excellent taste and quality. Moreover, for consumers concerned with low-fat diers, these oils can also be used to manufacture many convenient foods for healthful eating in the new cenrury. Bibliography New Developments of industrial Prying, edited by S.P. Kochhar, PJ Barnes & Associates, Bridgwater, United Kingdom, 1997. Blumenthal, M.M., A New Look at the Chemistry and Physics of Deep-Fat Frying, Food Technol. 45:68-71 (1991). Kochhar, S.P., Safety and Reliability during Frying Operations-Effects of Detrimental Components and Fryer Design Features, in Fryi"g of Food, edited by D. Bcskcu and I. Elmadfa, Technomic Publishing Co. lnc., Lancaster, Pennsylvania, 1999, pp 253-269. (A) Sesamolin (8) ~ ~::.~j" + o~ ~ _. Sesamol ~"" Samin,.~.~ 2 ~.. I.~~aminOI ~6 E.. I -apr-sesammc ~ /, - pi-sesammo Sesamol;~'C0 I ~,. -~'~'.~ Diasesamlnol Figure l:hechanisms fol"the liberation of segmol ~samolin during frying operation coost (A) and sesaminol isomer's(8) from COOSt Silkeberg, A., and S.P. Kochhar, Refining of Edible Oil Retaining Maximum Antioxidative Potency, European Patent Application No. 98102528.1-2109, 13.02.98 and other worldwide patent applications pending, 1998. Willer. W.c., and A. Ascheno, TrailS Fatty Acids: Are rhe Effects Only Marginal? Am. l- Public Health 84:722-724 (1994).0 o ccse Figu", -4: Resonanc. stabill:r.edstructures of sterol ferulate Volume II June 2000 Inform