Oklahoma Cooperative Extension Service FAPC-231 Why Peanut Oil is Good for Frying Food January 2020 Nurhan Turgut Dunford Oklahoma Cooperative Extension Fact Sheets Oil/Oilseed Specialist, Oklahoma State University are also available on our website at: facts.okstate.edu Peanuts (Arachis hypogea), also known as Similar to the other vegetable oils, peanut oil groundnuts, are the edible seeds of a legume. The mainly constitutes of triacylglycerides (Table 1). name of the domesticated peanut species comes Although phospholipids (polar lipids) have some from two Greek words: Arachis meaning a weed health benefits, they are usually removed during and hypogaea, an underground chamber referring refining because they precipitate out of the oil dur- to a weed growing below soil surface. Although a ing storage and handling and adversely affect the peanut is technically considered a pea and belongs functionality of the oil due to their surface active to the fabaceae of bean/legume family, it is gener- properties. Crude oil may contain up to 1% polar ally included amongst the oilseeds because of its lipids, while refined oil would have less than 30 high oil content. ppm phospholipids. Tocopherols are recognized There are thousands of peanut cultivars but the as natural antioxidants. Crude peanut oil contains most popular ones are Spanish, Runner, Virginia relatively high amounts of tocopherols, 175-1300 and Valencia. Cultivar selection for particular ap- mg/kg. There are a number of clinical studies in- plication is important because of the differences in dicating that phytosterols may lower cholesterol flavor, oil content, size and shape of each peanut levels in blood. Phytosterol content of crude peanut type. For example, the cultivar Virginia is preferred oil is quite high, 901-2854 mg/kg. Unfortunately, for in-shell peanut marketing and in-shell gourmet tocopherols and phytosterols are lost during con- snacks; Spanish peanuts are favored for making ventional edible oil refining, and they end up in candy, salted nuts and peanut butter; Runner by-products. Quality of edible oils is assessed by cultivars are mostly used to make peanut butter; measuring its free fatty acid (FFA) content. Lower and Valencias are selected for their large size, at- FFA content in crude oil lowers refining losses and tractive bright-red skin and very sweet taste. They increases oil stability. FFA of crude peanut oil less also are good for fresh use as well as boiled or than 1%, which is within the acceptable range by roasted peanuts. industry. Good quality refined peanut oil would Peanuts are rich in protein, oil and fibers. De- contain about 0.01% FFA. pending on the variety, climate, maturity and agro- Peanut oil fatty acid composition may vary de- nomic practices used, peanuts may contain 40 to pending on the maturity, genotype and growth lo- 50% oil. The oil extraction process is very similar to cation. Typical fatty acid distribution for regular and the techniques used for other oilseeds (See OSU high oleic peanut oil is shown in Table 2. Fatty acid Fact Sheets FAPC-158 Oil and Oilseed Processing composition of oil is the main criteria for choosing I and FAPC-159 Oil and Oilseed Processing II). In an oil for a given application. Regular peanut oil summary, shelled peanuts are cleaned, dehulled, has higher saturated fatty acid content than many cracked, and heat and moisture conditioned prior other commodity oils such as canola and soybean to extraction. Peanuts are usually flaked before oil. That is one of the reasons peanut oil is good for solvent extraction. For large scale processors, oil high temperature applications such as frying. Al- extraction using hexane is the preferred method though unsaturated fatty acids are better for health, due to its high oil yield. Mechanical pressing pro- highly unsaturated oils are less stable and prone duces lower oil yield. to oxidation. The rates of oxidation of unsaturated Division of Agricultural Sciences and Natural Resources • Oklahoma State University fatty acids increase with increasing unsaturation. the amount of primary oxidation products (OSU For example, if it is assumed oxidation rate of a Fact Sheet FAPC-197 Edible Oil Quality). Good saturated fatty acid is 1, relative oxidation rates of quality oils would have very low peroxide value. unsaturated fatty acids with the same number of The smoke point is the temperature at which oil carbon atoms but 1, 2 and 3 unsaturated bonds produces a continuous stream of smoke during on the molecule would increase 10, 100 and 200 heating. This parameter is very important for evalu- times, respectively. Hence, high concentration ating suitability of an oil for frying applications. In of monounsaturated fatty acids, such as oleic general, regulations specify 200 degrees Celsius acid (one unsaturated bond on the molecule), is as the minimum for frying oils. Smoke point of preferred in oils to be used for food applications, peanut oil is about 230 degrees Celsius, which specifically for applications requiring cooking and is higher than the required 200 degrees Celsius. longtime high temperature exposure such as frying. Peanut allergies are due to specific proteins. Fatty acid composition of many oilseeds have In general, refined oils do not contain detectable been modified to meet requirements of various amount of proteins. However, depending on the applications, i.e. cooking/frying oil, industrial ap- degree of processing and handling, minor amount plications, dietary supplements, etc. New cultivars of proteins might end up in oil. of peanuts with modified fatty acid composition also have been released. Oleic acid concentra- Properties that Make Peanut Oil a Good Frying Oil tion in traditional or regular peanut oils range from 1. High smoke point is one of the main rea- approximately 41 to 67%, whereas in high-oleic sons peanut oil is preferred as frying oil. peanut oils, this fatty acid content is close to 80% High temperature frying allows food to (Table 1). A primary functional benefit of high-oleic cook quickly resulting in a crispy coating oils is an extended shelf life. Oleic acid enrichment with very little oil absorption. in peanuts has been achieved through classical 2. Although crude peanut oil has a nutty breeding techniques. The research carried out aroma, refined oil is odorless. Hence, it at the Oklahoma State University Robert M. Kerr does not interfere with the flavor of the Food and Agricultural Products Center on high oleic formulated foods. peanut varieties developed for the southern U.S. 3. Off-flavor and odor development is quite states including Oklahoma indicated conventional low during frying with peanut oil. genetic selection for high-oleic concentration did 4. Due to its relatively higher saturated fatty not cause any significant unintentional change in acid content, peanut oil is more stable than peanut nutritional composition. many other regular vegetable oils, such Physical properties of peanut oil determine as regular soybean oil. Hence, peanut oil its functionality in food formulations. For example, stands better to extended high heat expo- peanut oil solidifies from -1 to 3 degrees Celsuis, sure, minimizing the formation of harmful hence, it is not good as a salad oil (Table 3). The oxidation products. iodine value (IV) is a measure of unsaturation level of oil. IV of regular peanut oil is within the range re- ported for other vegetable oils. Density and viscos- ity are fundamental physical parameters that are important for various process engineering design Table 1. Constituents of peanut oil. calculations common in the edible oil industry. Vis- Constituent Regular Crude Oil cosity is the relative thickness or resistance of the Triacylglyceride (%) 95 – 97 oil to flow. Both density and viscosity of the refined peanut oil fall within the range reported for those Monoacylglycerides (%) 0.03 – 0.09 of other vegetable oils. High-oleic peanut oils are Diacylglycerides (%) 1.3 – 2.0 reported to have both lower densities and higher Polar Lipids (%) 0.1 - 1.0 viscosities than those for regular peanut oils. The Free fatty acids (%) 0.2 – 0.6 viscosity differences were most apparent at cooler Unsaponifiables (%) 0 – 1.0 temperatures. Main components of unsaponifiable fraction of oils are tocopherols and phytosterols. Tocopherols (mg/kg) 175 - 1300 Peroxide value is a measure of the oil quality and Phytosterols (mg/kg) 901 - 2854 FAPC-231-2 Table 2. Fatty acid composition of peanut oil. Fatty Acid Regular High-oleic Capric (10:0) - - Lauric (12:0) 0 - 0.1 - Myristic (14:0) 0 - 0.1 - Palmitic (16:0) 8.3 -14.0 7.0 Palmitoleic (16:1) 0 – 0.2 - Stearic (18:0) 1.9 – 4.4 3.0 Arachidic (20:0) 1.1 – 1.7 1.0 Behenic (22:0) 2.1 – 4.4 4.0 Lignoceric (24:0) 1.1 - 2.2 2.0 Oleic (18:1) 36.4 - 67.1 76.0 Gadoleic (20:1) 0.7 – 1.7 2.0 Erucic (22:1) 0 - 0.3 - Linoleic (18:2n-6) 14.0 – 43.0 4.0 Alpha Linolenic (18:3n3) 0 – 0.1 - Nervonic (24:1) 0 – 0.3 - Total Saturated 14.6 – 26.9 17.0 Total MUFA 37.1 – 69.3 78.0 Total PUFA 14.0 – 43.1 4.0 Table 2. Physical properties of peanut oil. Parameter Range Relative density 0.914 - 0.917 (g/cm3, 20oC/water at 20oC) Refractive index (40oC) 1.460 - 1.465 Smoke point (oC) 226 Melting point (oC) -1 - 3 Specific heat (J/g at 20oC) 1.910 - 1.916 Saponification number 187 - 196 Iodine value 83 - 107 Color (Lovibond) Yellow 16-25; Red 2.0 Peroxide value (meq/kg) 1.0 Viscosity (at 21oC, mPas) 71 FAPC-231-3 The Oklahoma Cooperative Extension Service WE ARE OKLAHOMA The Cooperative Extension Service is the largest, for people of all ages.