Abstract Soybeans are one of the most important crops in terms of volume and applications of the products obtained from them. Grown for oil and protein production, soybeans are feedstock for food, feed, fuel, and biobased products. Today, soybean oil can be found in most food products, as a result of its availability and positive nutritional and functional properties. The extensive scientific research and development conducted by both industry and academia on soybean oil is a main contributor to its important positioning among oils. This article provides a comprehensive review of this work, including information on the composition of soybeans, soybean oil, and other soybean lipids, especially as affected by environment, variety, and genetic modification; the physical properties of soybean oil, grading of soybeans, oil extraction, and the effect of various extraction techniques on oil quality and the various soy protein ingredients; basic refining and processing of soybean oil and soybean refinery co‐products; the major uses of soybean oil; trading rules for soybean oil; and the oxidative quality of soybean oil along with its health aspects.

The amounts of soybeans and total vegetable oil crops have been rising for a number of years. World production of soybeans in 2003 was estimated to be 184.49 million MT out of 317.89 million MT total for vegetable oil crops, making soybeans the world’s largest oilseed crop, rivaled only by palm oil (1). The 2003 crop of soybeans was expected to yield 29.85 million MT of soybean oil out of a total of 91.79 million MT of vegetable oil worldwide. The U.S. production of soybean oil was estimated at 8.59 million MT for 2002, of which 7.86 million MT was consumed domestically. During 2002–2003, Brazil produced 4.90 million MT and Argentina 4.12 million MT of soybean oil (2). The U.S. price of crude soybean oil has varied from $0.24/kg to $0.62/kg over the past 5 years with the lower prices being more recent (1). Soybeans owe their dominance of the oilseed market to the value of their protein, which is much greater than that of other oilseeds. Of the oilseed meals produced in 2003, 129.58 million MT out of a total of 185.69 milllion MT was soybean meal (1). Of the money made on extracting soybeans, the meal accounted for between 51% and 76% of the total in the last 10 years. Soybean oil of typical composition performs well as a salad oil, but it is usually hydrogenated for use as a margarine stock or frying oil. Soybean oil’s stability to oxidation also is limited by its content

The objective of this work was to study the frying stability of soybean oil (SBO) with reduced linoleate (18∶2) and linolenate (18∶3) and elevated oleate (18∶1) contents. High-oleate SBO [HO SBO, 79% oleic acid (OA)] and a control (conventional SBO, 21.5% OA) were tested as is, as well as blended in different ratios to make three blended oils containing 36.9, 50.7, and 64.7% OA, abbreviated as 37%OA, 51%OA, and 65%OA, respectively. In addition, a low-linolenate (LL) SBO containing 1.4% 18∶3 and 25.3% 18∶1 was tested. Bread cubes (8.19 cm3) were fried in each of 18 oils (6 treatments×3 replicates). We hypothesized that stability indicators would be indirectly related to the total 18∶2 plus 18∶3 percentages and/or the calculated oxidizability. In general, the results were fairly predictable based on total 18∶2 and 18∶3 concentrations. The overall frying stability of the six oil treatments, from the best to the poorest, was: 79%OA, 65%OA, 51%OA, LL≥37%OA, and the control, with respective total compositions for 18∶2 plus 18∶3 of 10.3, 23.6, 36.3, 59.6, 48.9, and 62.8%. The greatly reduced concentration of 18∶3 in the LL SBO made it more stable than the 37%OA, even though the combined composition of 18∶2 and 18∶3 of LL was greater than that of the 37%OA. Blending conventional SBO with HO SBO had a profound effect on the oxidative stability index and color of the blended oils, but the values were not linearly predictable by the percentage of control in the blended oil. Other stability indices, including calculated oxidizability, calculated iodine value, conjugated dienoic acid value, and viscosity, changed in linear response to an increased proportion of the control in the blends.

The percentages of oleate (18∶1), linoleate (18∶2), and linolenate (18∶3) in blended soybean oils (SBO) were evaluated for their impact on flavor stability and quality in fried foods. Six SBO treatments, including a control (conventional SBO, 21.5% 18∶1) and a high-18∶1 SBO (HO, 79% 18∶1), were tested. In addition, these two oils were mixed in different ratios to make three blended oils containing 36.9, 50.7, and 64.7% 18∶1, abbreviated as 37%OA, 51%OA, and 65%OA, respectively. Also, a low-18∶3 (LL) SBO containing 1.4% 18∶3 and 25.3% 18∶1 was tested. Bread cubes (8.19 cm3) were fried in each of 18 oils (6 treatments ×3 replicates). The fresh and stored bread cubes fried in 79%OA were second to the cubes fried in LL in overall flavor quality, were the weakest in intensity of stale, grassy, fishy, cardboard, and burnt flavors by sensory evaluation, and contained the least amounts of hexanal, hexanal, t-2-heptenal, t,t-2,4-nonadienal, and t,t-2,4-decadienal in volatile analysis. Other treatments were intermediate in these sensory and instrumental evaluations, as related to their 18∶1, 18∶2, and 18∶3 concentrations. In general, the results suggested that the overall flavor stability and eating quality of foods fried in the six oil treatments from the best to the poorest would be: LL≥79%OA, 65%OA, 51%OA, 37%OA, and control.

Soybean oil (SBO) is an oxidatively unstable oil, largely because of the high concentration of linoleic acid (18:2) and linolenic acid (18:3). The unsaturated fatty acids, oleic acid (18:1), 18:2, and 18:3 in SBO oxidize in a ratio of 1:10.3:21.6. To improve oxidative and flavor stability, the SBO may be hydrogenated to reduce the concentration of PUFA (and increase the saturated FA); however, trans fatty acids (t FA) are formed and saturated fatty acids are increased during this process. There are health concerns over the consumption of a diet high in trans FAs and high in the ratio of saturated fatty acids to PUFA. Lowering the 18:3 content to a level similar to that obtained by partial hydrogenation, but without trans formation and increasing saturation has been objectives of plant breeders. A diet high in monounsaturated has been shown to help reduce health risks. Elevating 18:1 in seed oils has become more and more common.;The objectives of this study were to (1) study the effects of two low levels of 18:3 concentration (~1.0% and 2.2%) on the oxidative and flavor stabilities of SBO and (2) determine the optimum percentage of oleic acid (OA) in six SBOs (including high-oleic SBO (79%OA), conventional SBO (control), three blended oils containing 36.9%, 50.7%, and 64.7%OA, abbreviated as 37%OA, 51%OA, and 65%OA, respectively, and a low-linolenic (LL, contained 1.4% linolenic acid) SBO, to obtain maximum frying stability while retaining good flavor potential.;In general, results of the storage study suggested that the SBO containing 1.0% 18:3 had generally significant better oxidative and flavor stability during storage at 21 and 32°C than did SBO contained 2.2% 18:3. Results of the frying study suggested that the order of oxidative stability of the six oil treatments was: 79%OA > 65%OA > 51%OA > LL ≥ 37%OA > Control, and that the order of flavor stability and eating quality of foods fried in them was: LL ≥ 79%OA > 65%OA > 51%OA > 37%OA > Control.;These findings should help soybean breeders more precisely decide compositional targets to produce SBO that have desirable properties.

The effects of linolenic acid (18∶3) concentration, combined with IBHQ addition, temperature, and storage time, on the flavor stability of soybean oils (SBO) were evaluated. A descriptive panel was trained to evaluate the overall oil quality and the intensity of individual flavors of SBO during 12 mon of storage under fluorescent light at both 21 and 32°C. Chernoff faces were used to achieve a simplified and integrated interpretation of the multivariate sensory data and to facilitate the interpretation of the vast amount of the data. In early storage, SBO with low 18∶3 (2.2% 18∶3, LLSBO) showed better flavor stability than did SBO with ultra-low 18∶3 (1.0% 18∶3, ULSBO). This trend disappeared during storage. During 10- to 12-mon storage, a painty flavor became predominant in all oils, which may have made it difficult for panelists to detect differences in treatment effect on flavor characteristics of SBO. During early storage, oils with TBHQ addition had poorer overall oil quality and stronger beany, painty, and fishy flavors than did oils without TBHQ addition. This trend disappeared as storage time progressed to 10 mon. Oils storedat 32°C had poorer overall oil quality and stronger painty, fishy, and beany flavors than did oils stored at 21°C starting from 2-mon storage.

The effects of linolenic acid (18∶3) concentration, combined with TBHQ addition, temperature, and storage time, on the oxidative and flavor stabilities of soybean oils (SBO) were evaluated. During storage under fluorescent light at both 21 and 32°C, the SBO with ultra-low-18∶3 concentration (1.0%, ULSBO) generally had greater oxidative stability than did SBO with low-18∶3 concentration (2.2%, LLSBO). The ULSBO had about half the p-anisidine value of LLSBO throughout storage. Although the ULSBO initially had significantly greater PV and poorer (lower) sensory scores for overall flavor quality than did LLSBO, significant differences disappeared with storage. The ULSBO had a lower content of polar compounds and greater oil stability indices than did LLSBO when TBHQ was present. All oils were more oxidatively stable with TBHQ addition, but the TBHQ addition did not result in improved flavor stability early in storage. In all tests, oils stored at 32°C were less stable than oils stored at 21°C. The TBHQ had a better antioxidant capacity when the 18∶3 concentration was lower. The retardation effect of TBHQ on lipid oxidation and the improved stability of ULSBO over LLSBO were more easily detected when the storage temperature was higher.