Genetically modified low-linolenic acid soybean oil (LL-SBO) was compared to partially hydrogenated soybean oil (PH-SBO). Samples were heated on a Teflon pan at ~180°C until a selected end point of ≥20% polymer content was reached. High-performance size-exclusion chromatography analysis indicated the PH-SBO contained >20% polymer after 20 min of heating, whereas the LL-SBO sample contained >20% polymer after 10 min. Supercritical fluid chromatography analysis indicated degradation rates of 0.161 ± 0.011 min −1 for LL-SBO and 0.086 ± 0.004 min −1 for PH-SBO. The volatile compounds were identified and quantitated with static headspace-GC-MS. 1-Heptene (239.9 ppm) and hexanal (1486.1 ppm) were present at the greatest concentration among the volatile compounds in LL-SBO. The volatile compounds present in the greatest concentrations in heated PH-SBO were hexanal (376.9 ppm) and pentane (82.1 ppm). After 10 min of heating, the LL-SBO oil FFA value (2.66%), p-anisidine value (386.5 abs/g oil), Food Oil Sensor reading (18.75), and color intensity (Y = 4.0, R = 1.0) were significantly greater than those of PH-SBO after 14 min of heating (4.28%, 298.5 abs/g oil, 16.08, Y = 1.0, R = 0.1, respectively). There was a significant difference in the degradation rates between LL-SBO and PH-SBO (P < 0.05). The PH-SBO was more stable than the LL-SBO.Genetic improvements in vegetable oils will continue to play an important role in the development of new frying oils. In 1997, an estimated 23 million acres of genetically modified oilseeds were planted in North America (1). The topic of genetically improved oils has become an area of intense research because most consumers prefer to avoid the saturated and trans FA found in hydrogenated oils. In one set of genetically engineered oils, the FA components have been altered to provide high-stability oil without hydrogenation (2). The frying performance of genetically modified oils has been investigated to determine the effect of changing the FA composition on oil stability and odor intensity. A deep-fat frying study of soybean and canola oils, modified by hydrogenation and/or mutation breeding, indicated a reduction in odor intensity for low-linolenic acid oil (3).Billek (4) investigated the effect of different frying methods on polar-material formation. Ten minutes of pan-frying was comparable to approximately 20 h of deep-fat frying, because these are the heating times required to reach approximately the same percentage of polar materials.Many investigators have published work on deep-fat frying, but very few have studied oil deterioration during pan-frying (5), even though pan-and grill-frying are convenient and common cooking methods used in households and restaurants for preparation of meat, eggs, and vegetables (6). Stir-frying, a form of pan-frying, is a common practice in Chinese cooking. In a study of volatile compounds found during stir-frying, oil was heated at ~200°C in a Chinese wok for 3 min with constant stirring (7). In another study, a thin film of trilinolein was applied t...
The changes occurring in two oil samples [EPG-00 soyate (transesterified soybean oil) and soy oil esterified propoxylated glycerol (EPG-08 soyate, a model, fat substitute compound)] were compared after heating at approximately 190 degrees C for 12 h/day. The EPG-00 soyate sample required 48 h of heating to attain a polymer content >20%, while the EPG-08 soyate required only 36 h. After 48 h of heating the EPG-00 soyate sample, the free fatty acid value (FFA) increased from 0.19 to 0.79, the acid value (AV) increased from 0.10 to 1.59, and the p-anisidine value (p-AV) increased from 1.6 to 195.4. In comparison, after only 36 h of heating, the EPG-08 soyate sample had FFA, AV, and p-AV increases from 0.19 to 0.71, from 0.26 to 1.36, and from 1.1 to 191.7, respectively. The triacylglycerol substrate degradation rate for EPG-00 soyate was k = 0.0126 +/- 0.0003 h(-)(1), while the rate for EPG-08 soyate was k = 0.0166 +/- 0.0017 h(-)(1). The results suggest that the EPG-00 soyate or transesterified soybean oil is slightly more stable than EPG-08 soyate.
Vegetable oils have been deacidified using supercritical carbon dioxide and membrane processing. However, the pressures required are substantially greater than those used in industry. Therefore, the feasibility of using subcritical carbon dioxide (at much lower pressures) and membrane processing to separate free fatty acids (FFA) from triacylglycerols (TAGs) was examined. First, FFA/TAG solubility tests were completed (10-25°C and 68-136 atm). The oil samples were separated using a FilmTec NF90 or a FilmTec BW30 membrane in a deadend type cell. Within the range examined, the greatest solubility for oleic acid was at 25°C and 136 atm. For soybean oil TAGs, the greatest solubility was at 20°C and 136 atm. However, for the separation of the two components, 20°C and 68 atm was best among the condition combinations examined. The solubility of oleic acid ranged from 0.294 to 0.455 mg/mL in subcritical carbon dioxide, while the solubility of triacylglycerols ranged from 0.066 to 0.139 mg/mL. The FilmTec BW30 membrane provided significantly better separation of FFAs from TAGs than did the NF90 membrane. Both membranes were selective for oleic acid, although the BW30 had greater selectivity for oleic acid (b oleic acid = 2.12, b TAGs = 0.24) than the NF90 membrane (b oleic acid = 1.26, b TAGs = 0.81).
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