K. Warner

Frying Stability of Soybean and Canola Oils with Modified Fatty Acid Compositions

Pilot plant-processed samples of soybean and canola (lowerucic acid rapeseed) oil with fatty acid compositions modified by mutation breeding and/or hydrogenation were evaluated for frying stability. Linolenic acid contents were 6.2% for standard soybean oil, 3.7% for low-linolenic soybean oil and 0.4% for the hydrogenated low-linolenic soybean oil. The linolenic acid contents were 10.1% for standard canola oil, 1.7% for canola modified by breeding and 0.8% and 0.6% for oils modified by breeding and hydrogenation. All modified oils had significantly (P<0.05) less room odor intensity after initial heating tests at 190°C than the standard oils, as judged by a sensory panel. Panelists also judged standard oils to have significantly higher intensities for fishy, burnt, rubbery, smoky and acrid odors than the modified oils. Free fatty acids, polar compounds and foam heights during frying were significantly (P<0.05) less in the low-linolenic soy and canola oils than the corresponding unmodified oils after 5 h of frying. The flavor quality of french-fried potatoes was significantly (P<0.05) better for potatoes fried in modified oils than those fried in standard oils. The potatoes fried in standard canola oil were described by the sensory panel as fishy.

Oxidation and quality of soybean oil: a preliminary study of the anisidine test

The anisidine test, a measure of secondary oxidation products in glyceride oils, was applied to a number of soybean salad oils processed from sound and damaged soybeans. A highly significant correlation (−0.68) was found between the anisidine values of salad oils from sound soybeans and their flavor scores. Multiple correlations between flavor scores, anisidine, and peroxide values yielded a correlation of 0.81 and provided a method for predicting the initial flavor scores of sound soybean salad oils. Similar data for oils from damaged beans gave a highly significant, but lower, correlation (−0.65). Comparative studies indicated that sound crude oils usually contain lower levels of oxidation products than damaged crude. Oxidation in both sound and damaged crudes increased roughly in proportion to iron content. Reproducibility of the test and the effects of hydrogenation, accelerated storage, and fluorescent light on anisidine values were studied. Analysis of damaged oils before and after deodorization showed that little, if any, reduction of anisidine value occurred. Deodorization of sound oils, however, lowered anisidine values. In comparison with damaged oils, the anisidine values of sound oils were lower at comparable stages of processing. The poor quality of damaged soybean oil was substantiated by organoleptic evaluations. Flavor scores of oils given special processing treatments increased as anisidine values decreased.

Effects of β-carotene on light stability of soybean oil

Abstractβ-Carotene was added to soybean salad oils to study its effect in inhibiting flavor deterioration due to light exposure. Flavor evaluations indicated that (a) when oils treated with citric acid were exposed to light (7535 lux) for 8 to 16 hr, oils containing 5 to 10 ppm β-carotene showed improved flavor stability compared to oils containing 0 to 1 ppm β-carotene; and (b) when oils were not treated with citric acid, only oils containing 20 ppm β-carotene were more stable to light. Capillary gas chromatographic analysis showed that the addition of 1 to 20 ppm of β-carotene significantly decreased formation of 2-heptenal and 2,4-decadienal in the absence or presence of citric acid. Determination of peroxide values showed the same trends as gas chromatographic analyses of volatiles. In the presence of 15 and 20 ppm β-carotene, some off-flavors, as well as poor ratings for color quality, were reported by panelists. Therefore, flavor deterioration initiated by light can be inhibited effectively in soybean oil, without affecting color quality, by addition of β-carotene at concentrations from 5 to 10 ppm to oils treated with citric acid.

Analysis of tocopherols and phytosterols in vegetable oils by HPLC with evaporative light-scattering detection

Methods were developed for the separation, detection, and quantification of tocopherols and phytosterols by high-performance liquid chromatography with an evaporative light-scattering detector. Four tocopherols— α, β, γ and δ—and four phytosterols—campesterol, β-sitosterol, brassicasterol, and stigmasterol—were analyzed in soybean, sunflower, low-erucic acid rapeseed (LEAR) and corn oils. The use of an evaporative light-scattering detector, in conjunction with modification of methods from the literature to prepare and analyze tocopherols and phytosterols by HPLC, showed consistent results between trials and levels of these minor constituents.

Flavor and oxidative stability of soybean, sunflower and low erucic acid rapeseed oils

Three samples each of soybean, sunflower and low erucic acid rapeseed (LEAR) oils were evaluated for flavor and oxidative stability. The commercially refined and bleached oils were deodorized under identical conditions. No significant differences were noted in initial flavor quality. After storage at 25°C or 60°C in the dark, soybean oils—with or without citric acid—were more stable than either sunflower or LEAR oils. However, in the presence of citric acid, soybean oils were significantly less stable to light exposure than either LEAR or sunflower oils. In contrast, in the absence of citric acid, soybean oils were significantly more light stable than LEAR oils. In either the presence or absence of citric acid, sunflower oil was significantly more stable to light than soybean oil. Analyses by static headspace gas chromatography showed no significant differences in formation of total volatile compounds between soybean and LEAR oils. However, both oils developed significantly less total volatiles than the sunflower oils. Each oil type varied in flavor and oxidative stability depending on the oxidation method (light vs dark storage, absence vs presence of citric acid, 100°C vs 60°C).

Effect of altered fatty acid composition on soybean oil stability

During the last 15 years, hybridization and induced mutation breeding of soybeans have been successful in producing an altered fatty acid composition in the extracted oil. The objective of those investigations was to produce a low-linolenic acid soybena oil. Crude oils extracted from the seeds of three such genotypes were processed in laboratory simulations of commercial procedures to finished deodorized oils. Analysis of the fatty acid composition of the three oils showed the linolenic acid content to be 3.3%, 4.2% and 4.8%. The stability of these finished oils was compared to that of oil from a soybean variety having a linolenic acid content of 7.7% and of a commercial hydrogenated-winterized soybean oil (3.0% linolenic acid). Test and control oils were evaluated by a trained sensory panel initially, after accelerated storage at 60 C and during use at 190 C in room tests. Peroxide values were determined at the time of sensory evaluation. Results indicated there was no significant difference in flavor stability during storage between test and control oils. There was no significant difference, between the oils, in peroxide development during accelerated storage. Compared to control oils, the test oils had improved overall room odor intensity scores and lacked the fishy odors of non-hydrogenated soybean oil and the hydrogenated odors of commercial cooking oil.

Effects of frying oil composition on potato chip stability

Potato chips were fried in six canola (low-erucic acid rape-seed) oils under pilot-plant process settings that represented commercial conditions. Oil samples included an unmodified canola oil and oils with fatty acid compositions modified by mutation breeding or hydrogenation. Chips were fried for a 2-d, 18-h cycle for each oil. Chips and oil were sampled periodically for sensory, gas-chromatographic volatiles and chemical analyses. Unmodified canola oil produced chips with lower flavor stability and oxidative stability than the other oils. The hydrogenated oil imparted a typical hydrogenation flavor to the chips that slightly affected overall quality. the modified canola oil (IMC 129) with the highest oleic acid level (78%) had the lowest content of total polar compounds and the lowest total volatile compounds at most of the storage times; however, the sensory quality of the potato chip was only fair. The potato chip with the best flavor stability was fried in a modified/blended oil (IMC 01-4.5/129) with 68% oleic acid, 20% linoleic acid and 3% linolenic acid.

Low-linolenic acid soybean oil—Alternatives to frying oils

Oil was hexane-extracted from soybeans that had been modified by hybridization breeding for low-linolenic acid (18∶3) content. Extracted crude oils were processed to finished edible oils by laboratory simulations of commercial oil processing procedures. Oils from three germplasm lines N83-375 (5.5% 18∶3), N89-2009 (2.9% 18∶3) and N85-2176 (1.9% 18∶3) were compared to commercial unhydrogenated soybean salad oil with 6.2% 18∶3 and two hydrogenated soybean frying oils, HSBOI (4.1% 18∶3) and HSBOII (<0.2% 18∶3). Low-18∶3 oils produced by hybridization showed significantly lower room odor intensity scores than the commercial soybean salad oil and the commercial frying oils. The N85-2176 oil with an 18∶3 content below 2.0% showed no fishy odor after 10 h at 190°C and lower burnt and acrid odors after 20 h of use when compared to the commercial oils. Flavor quality of potatoes fried with the N85-2176 oil at 190°C after 10 and 20 h was good, and significantly better at both time periods than that of potatoes fried in the unhydrogenated oil or in the hydrogenated oils. Flavor quality scores of potatoes fried in the N89-2009 oil (2.9% 18∶3) after 10 and 20 h was good and equal to that of potatoes fried in the HSBOI oil (4.1% 18∶3). Fishy flavors, perceived with potatoes fried in the low-18∶3 oils, were significantly lower than those reported for potatoes fried in the unhydrogenated control oil, and the potatoes lacked the hydrogenated flavors of potatoes fried in hydrogenated oils. These results indicate that oils with lowered linolenic acid content produced by hybridization breeding of soybeans are potential alternatives to hydrogenated frying oils.

Flavor Score Correlation with Pentanal and Hexanal Contents of Vegetable Oil

Samples of commercially processed soybean, cottonseed, and peanut oils were stored under controlled conditions then evaluated for flavor by a 20-member trained, experienced oil panel and for pentanal and hexanal contents by direct gas chromatography. The oils, which contained citric acid and/or antioxidants, were either aged from 0 to 16 days at 60 C or exposed to fluorescent light for 0 to 16 hr. The simple linear regressions of flavor score with the logarithm of pentanal or hexanal content in aged soybean oil gave correlation coefficients of −0.96 and −0.90, respectively; for cottonseed oil, −0.60 and −0.85; and for peanut oil −0.74 and −0.75. Addition of peroxide values to the linear regressions increased the correlation coefficients. Flavor scores of cottonseed and peanut oil can be predicted from pentanal and hexanal contents, but the technique is slightly more reliable for soybean oil based on the treatments used for these oils.

Comparison of gas chromatographic methods for volatile lipid oxidation compounds in soybean oil

To develop new knowledge on undesirable flavors affecting the quality of foods containing polyunsaturated lipids, we investigated the volatiles in soybean oil oxidized at different conditions by three capillary gas chromatographic methods: (a) direct injection (5 min heating at 180 C); (b) static headspace (20 min heating at 180 C, pressurizing for one min), and (c) dynamic headspace (purging 15 min at 180 C onto a porous polymer trap, desorbing from trap for five min). A fused silica column was used with bonded polymethyl and phenyl siloxane phase. At peroxide values between 2 and 10, the major volatile products found in soybean oil by the three methods were pentane, hexanal, 2-heptenal, 2,4-heptadienal and 2,4-decadienal. The intensities of each volatile compound varied with the analytical methods used.