Effects of thermally oxidized triglycerides on the oxidative stability of soybean oil

Soybean oil purified by silicic acid column chromatography did not contain peroxides, free fatty acids, phospholipids or oxidized polar compounds. The purified soybean oil was thermally oxidized at 180°C for 96 hr in the presence of air. The thermally oxidized compounds (31.3%) were separated from the purified soybean oil by gradient elution silicic acid chromatography. Thermally oxidized compounds contained hydroxyl groups, carbonyl groups andtrans double bonds according to the infrared spectrum. Thermally oxidized compounds were added to soybean oil and purified soybean oil at 0, 0.5, 1.0, 1.5 and 2.0% to study the effects of these compounds on the oxidative stability of oil. The oxidative stabilities of oils were determined by gas chromatographic analysis of volatile compound formation and molecular oxygen disappearance in the headspace of oil bottles. The thermally oxidized compounds showed prooxidant effects on the oxidative stabilities of both refined, bleached and deodorized soybean oil and purified soybean oil. Duncan’s Multiple Range Test showed that thermally oxidized compounds had a significant effect on the volatile compound formatiion and oxygen disappearance in the headspace of oil at α=0.05.     

Hydrogenation of oxidized soybean oil

Anderson Clayton Foods, Richardson, TX 75080 Portions of refined and bleached soybean oil were stored at various temperatures for various lengths of time, then hydrogenated to 70 iodine value (IV) to find the effect of peroxides on the rate of hydrogenation and on characteristics of hydrogenated product. Samples were treated up to 3 wk at up to 65°C and provided samples with peroxide values (PV) of up to 358. All samples were analyzed, hydrogenated, and reanalyzed. Peroxides affected the fatty acid composition as determined by gas chromatography, the calculated iodine value based on fatty acid composition, and rate of hydrogenation. Peroxides also affected the selectivity of hydrogenation and slope of the solids curve in hydrogenated products.     

The contribution of saturated acyl groups to the volatiles of oxidized soybean oil

U-¹⁴C-Stearic acid was interesterified into soybean oil and the resulting oil was oxidized to high peroxide values at 25 C and at 125 C. Volatile oxidation products were isolated and found to have a count that was not significantly above background. Journal paper no. 6715 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project 1856.     

Effects of processing on quality of soybean oil

The fate of major and minor components of soybean oil is examined at each stage of processing. Relationships are then drawn upon the effect on the quality of finished oil. General topics covered are (a) triglycerides and polyunsaturated fatty acids, (b) free fatty acids, (c) mono- and diglycerides, (d) phospholipids, (e) minor constituents, such as tocopherols, color bodies, and metal ions, (f) rearrangement and decomposition products, (g) foreign or toxic compounds not native to soya and (h) other additives, such as refining aids.     

Effects of soybean pretreatments on crude oil quality

The effects of soybean pretreatments, including infrared (IR) radiation, oven toasting, microwave heating and live steam treatment on crude oil quality were investigated. Free fatty acid, oxidation value, carbonyl value and tocopherol content were used to monitor crude soybean oil quality. All soybean pretreatments were effective in improving the quality of oils from 15 and 18% moisture beans. Based on the analyses, recommended treatments are 3–4 min for IR at 220V–250W; 1 min for microwave heating at 650 W–2450 mHz; 1–1.5 min for steam heating; and 100–120°C, 30 min for oven toasting. Heat treatment of high-moisture soybeans before extraction yielded crude oil with a lower content of phosphatidic acid as compared to that of the untreated beans.     

Quantitation of flavor volatiles in oxidized soybean oil by dynamic headspace analysis

A dynamic headspace procedure was developed for isolating the volatiles from oxidized soybean oil and trapping them on an adsorbent under conditions that gave minimal decomposition of hydroperoxides (50°C for 30 min at a helium flow of 75 mL/min). The volatiles were desorbed from the adsorbent and separated by gas chromatography (GC) on a methyl silicone capillary column. Equations were derived from theoretical considerations that allowed the actual concentration of each flavor component in the oxidized oil to be calculated from the area of the GC peaks. The reliability of the method and calculations was demonstrated by recovery experiments. The concentration of 2-heptanone in a mineral oil emulsion, equivalent in flavor intensity to each component, was calculated and summed to estimate the overall flavor intensity of the samples. The overall estimations were compared with the concentrations of 2-heptanone observed to be equivalent in flavor intensity to the oxidized oil samples when these were tasted in emulsion. The concentrations of individual components calculated from the headspace volatiles data were all present at concentrations below their flavor thresholds, and the simple sum of the intensities of their flavors generally accounted for less than half of the flavor intensities of the oil samples. The differences in the headspace and sensory analyses might be attributed to the flavor of the unoxidized oil, synergistic interactions, and/or the presence of unmeasured flavors components.     

Effects of expander process on the phospholipids in soybean oil

Crude oils were extracted from soybean flakes and collets by conventional and expander processes, respectively. The phospholipids were removed by degumming, and the lecithins were produced by using commercial procedures. The effects of the expander process on the degumming efficiencies were evaluated. The differences in the phosphatide compositions of the oils and the lecithins produced from expander and conventional processes were compared by high-performance liquid chromatography. The phosphorus content indicated that expander-processed oil contained more phosphorus (985 ppm) than the conventional oil (840 ppm). However, the phospholipids in the expander-processed oil were more hydratable than those in the conventional oil. After degumming, the phosphorus content in the expander-processed and conventional oil were reduced by 93.2 and 78.6%, respectively. The expander-processed lecithin contained 74.3% acetone-insoluble matter (AI), and the conventional lecithin contained 65.8%. More phosphatidylcholine was found in the expander-processed lecithin (39.78%, based on AI) than in the conventionally processed lecithin (34.19%). The phosphatidylinositol contents of the expander-processed lecithin and the conventional lecithin are almost the same (19.95 and 19.97%). The phosphatidylethanolamine in the expander-processed lecithin (12.36%) was lower than that in the conventional lecithin (18.07%).     

Effects of hydrogenation and additives on cooking oil performance of soybean oil

Soybean oil was continuously hydrogenated in a slurry system to investigate the effects of linolenate content and additives on cooking oil performance. Room odor evaluations carried out on oils heated to 190 C after frying bread cubes showed that the oils hydrogenated with Cu catalyst to 2.4% linolenate (Cu-2.4) and with Ni catalyst to 4.6 linolenate (Ni-4.6) had a significantly lower odor intensity score than the unhydrogenated soybean oil (SBO). Other hydrogenated oils (Cu-0.5 and Ni-2.7) were not significantly better than SBO. Oil hydrogenated with Ni (Ni-0.4) scored poorly because of its strong “hydrogenated-paraffin” odor. The performance of all partially hydrogenated oils (2.4, 2.7 and 4.6% linolenate) was improved by adding methyl silicone (MS), but the most hydrogenated oils (0.5 and 0.4% linolenate) were not improved. Although with tertiary butyl hydroquinone (TBHQ) no improvement was obtained, with the combination of TBHQ + MS all odor scores were lower, indicating a synergistic effect. Evaluations of bread cubes after intermittent heating and frying showed that the breads fried in most hydrogenated oils (Ni-0.4, Cu-2.4 and Ni-2.7) were rated significantly better in flavor quality than breads fried in SBO. The bread cubes fried in MS-treated oils had significantly higher flavor quality scores than breads fried in SBO or SBO containing TBHQ. Dimer analyses by gel permeation chromatography and color development after heat treatments also did not correlate with sensory analyses.     

The impact of furanoid fatty acids and 3-methylnonane-2,4-dione on the flavor of oxidized soybean oil

Oils from soybeans with high or low contents of furanoid fatty acids were evaluated during storage for flavor intensity of soybean oil (SBO) off-flavor, but no significant differences were found. In addition, the compound 3-methylnonane-2,4-dione (MND), a breakdown product of furanoid fatty acids suggested by other researchers to contribute to reversion flavor of SBO, was evaluated for its contribution to off-flavor. The compound was synthesized in the laboratory and purified by gas chromatography (GC) on a Silar 10 C column. GC analysis of the purified MND on a nonpolar SPB-1 column showed two well-separated main peaks that have been suggested to represent keto and enol forms. Between these two peaks, a bridge of poorly resolved compounds may have represented various possible enol forms or an equilibration among these forms during the GC separation. MND had an intense straw-like and frulty odor when evaluated at the outlet of a gas chromatograph. Sensory evaluation of MND in a mineral oil/water emulsion system showed that its flavor intensity increased almost imperceptibly with increased concentration (from 0.09 to 2.56 ppm). An explanation for this unusual flavor response may be that, when molecularly dispersed in air, MND has an intense odor, but when placed in a mineral oil or soybean oil emulsion, MND may exist in a form with relatively low flavor intensity, or it may be bound by the media. The concentrations of MND in SBO at various peroxide values were measured at 0 to 0.804 ppb, which were far less than concentrations tested in mineral oil/water emulsions during sensory evaluation and below published odor threshold values for MND in oil. Therefore, these results do not support the theory that furanoid fatty acids or MND contribute strongly to the reversion flavor of SBO. This is Journal Paper J.17472 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 3396.     

Effects of minor compounds on hydrogenation rate of soybean oil

The poisoning effects of minor compounds in soybean oil on the activity of nickel-based catalysts during hydrogenation was investigated. Several soybean oils prepared by different processes were used as the starting oils for hydrogenation. Soybean oil prepared by combining neutralization with degumming and then followed by bleaching leads to a slower hydrogenation rate than an oil prepared by sequential degumming, neutralization and bleaching with activated clay. The selection of bleaching earth used in the bleaching process affected the hydrogenation rate. Soybean oil bleached with neutral clay showed a slower hydrogenation rate. Higher amounts of phosphorus compounds, oxidation products, β-carotene and iron in these oils accounted for the slower hydrogenation rate. Storage of refined and bleached soybean oil greatly affected the hydrogenation rate. An increase in the oxidation products of RB soybean oil during storage was the major reason for the decrease in the hydrogenation rate.     

Effects of β-carotene on light stability of soybean oil

β-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.     

Effects of quenching mechanisms of carotenoids on the photosensitized oxidation of soybean oil

The effects of 0, 1.0 × 10”⁻⁵, 2.5 × 10⁻⁵, and 5.0 × 10⁻⁵ M β-apo-8'-carotenal, β-carotene, and canthaxanthin on the photooxidation of soybean oil in methylene chloride containing 3.3 × 10⁻⁹ M chlorophyll b were studied by measuring peroxide values and conjugated diene content. β-Apo-8'-carotenal, β-carotene, and canthaxanthin contain 10,11, and 13 conjugated double bonds, respectively. The peroxide values and conjugated diene contents of oils containing the carotenoids were significantly lower (P<0.05) than those of control oil containing no carotenoid. As the number of conjugated double bonds of the carotenoids increased, the peroxide values of soybean oils decreased significantly (P<0.05). The quenching mechanisms and kinetics of the carotenoids in the photosensitized oxidation of soybean oil were studied by measuring peroxide values. The steady-state kinetics study showed that carotenoids quenched singlet oxygen to reduce chlorophyll-sensitized photooxidation of soybean oil. The singlet-oxygen quenching rate constants ofβ- apo-8'-carotenal, β-carotene, and canthaxanthin were 3.06 × 10⁹, 4.60 × 10⁹, and 1.12 × 10¹⁰ M⁻¹sec⁻¹, respectively.     

Effects of silicone resins on copolymerization of acrylated epoxidized soybean oil

In this work, effects of the silicone resins on copolymerization of the acrylated epoxidized soybean oil were investigated. Rheological characteristics, curing behaviors, and thermal properties of acrylate epoxy soybean oil prepolymer (AP), silicone prepolymer (SP), and their hybrids (AP/SP) were studied in detail. Spots in a snowflake pattern were observed on the fracture section surface of cured AP/SP hybrid resins by SEM. According to the change of polymer groups revealed by Fourier transform infrared, a possible reaction between AP and SP was proposed. The curing mechanism of AP/SP hybrids was researched, which was suggested to be an autocatalytic curing process. Furthermore, the degree of cure, the activation energy (E_α) and the reaction frequency factor (A) of the curing reaction were estimated. It was found that the cure kinetic of AP/SP hybrid resins could be well-described by a Sesthk-Bergglen model with the numerical optimization based on the Kissinger method and the Malek approach. The experimental results show that the mass retention rates of AP/SP hybrid resins were significantly increased after curing, indicating that the thermal stability of AP was enhanced with the addition of SP.     

Effects of ultrasonication on glycerin separation during transesterification of soybean oil

The aim of this study was to determine the effects of high-intensity ultrasound irradiation and temperature on glycerin separation start time and separation rate during the transesterification of soybean oil. Response surfaces methodology was used to design the experiments. Reaction temperature, ultrasonication level and duration of ultrasonication at three levels were assigned as the control variables. The progressing transesterification reactions were monitored using a low-intensity ultrasound measurement system, which measures the ultrasound time of flight in glycerin as glycerin separates during the reaction. The effects of ultrasonication level, duration of ultrasonication and temperature on glycerin separation start time and separation rate were statistically significant at p < 0.01 level. The effect of the interaction between temperature and duration of ultrasonication on glycerin separation start time was also statistically significant at p < 0.05 level. The process conditions that provided the lowest starting times for glycerin separation were determined to be the reaction temperature of 50 °C, ultrasonication of 5 min and ultrasonication rate of 90%. Low-intensity ultrasound measurement techniques and response surfaces experimental design are useful tools in determining the effects of various variables on the transesterification of vegetable oils.     

Effect of soybean pretreatment on the color quality of soybean oil

Color reversion in soybean oil can be prevented by reducting the enzyme activity of soybeans before cracking and flaking. Soybean oil extracted from steamed, intact soybeans (18% moisture) had lower Rm (max. red) values in RBD oil, higher amounts of γ-tocopherol, plus its isomers, in both crude and RBD oil, and also higher amounts of hydratable phosphatides in crude oil than those in the oils from the same beans without steam treatment. For soybean pretreatments, a toasting process is less effective than the steaming process for the inhibition of color reversion of soybean oil. To prevent the occurrence of color reversion in RBD soybean oil, the amount of γ-tocopherol and γ-TED (5-[tocopheryloxy]-γ-tocopherol) should be above 550 ppm in crude oil.     

Effects of emulsifiers on the oxidative stability of soybean oil TAG in emulsions

The effects of two types of commercial emulsifiers, sucrose FA esters and polyglycerol FA esters, on the oxidation of soybean oil TAG-in-water emulsions were studied. Both emulsifiers influenced the oxidative stability of soybean oil TAG in the emulsion, but they had little effect on the oxidation of TAG in bulk phase. When the TAG were dispersed with sucrose esters having the same FA composition, the oxidative stability increased as their hydrophilic-lipophilic balance (HLB) increased. On the other hand, when the HLB was the same, the oxidative stability increased with increasing acyl chain length of the FA esterified on sucrose ester. However, the effect of the polyglycerol ester could not be explained by the relationship with HLB or the acyl composition. When the stability of TAG in emulsion was compared under the same concentrations of TAG, emulsifier, and oxidation inducer, the TAG dispersed with sucrose esters were oxidatively less stable than with polyglycerol esters. Analysis of the emulsion droplet size suggested that the lower oxidative stability of TAG dispersed with sucrose esters was partly due to their relatively smaller droplet sizes.     

Effects of processing on the oxidative stability of soybean oil produced in Mexico

The stability parameters of 22 samples of soybean oil produced in Mexico were determined. Samples were analyzed for moisture, color, free fatty acids, peroxide value, p-anisidine value, fatty acid profile, metals, flavor, and Rancimat test for oxidative stability. Results obtained were compared with the stability parameters of soybean oil sproduced in the United States and Costa Rica. The fatty acid profile in all samples analyzed corresponded to the expected profile for a 100% soybean oil. Sixty-four percent of the oils had oxidative stabilities similar to those reported for soybean oils from the United States and Costa Rica. This suggests that in spite of the good quality, the soybean oil production process in Mexico needs further improvement. Especially important is maintaining appropriate control during the degumming and bleaching steps. Special consideration should be given to preserving the natural antioxidants present in the oil.     

Effects of cultivar and tempering procedures on crude soybean oil volatiles

The effects of soybean cultivar and tempering procedures on crude soybean oil volatiles were investigated by gas chromatography/mass spectrometry (GC/MS). Varietal differences in volatiles were not obvious. Trends in volatile contents due to tempering were noted primarily when comparing mean peak areas of these compounds in oils stored 16 days at 60°C. Differences in volatiles in response to tempering were not apparent in oils that had not been stored. Equilibration of beans with water resulted in oils with higher volatile contents than those from untempered beans. Steaming lowered volatiles from equilibrated values, and pressure steaming had an even more dramatic lowering effect.     

Effects of supercritical CO2 extraction parameters on soybean oil yield

A series of operational parameters of supercritical fluid extraction of soybean oil (pressure: 300–500 bar, temperature: 40–60 °C, CO₂ mass flow rate: 0.194–0.436 kg/h and characteristic particle size: 0.238–1.059 mm) were investigated in a laboratory scale apparatus. The results show that the extraction yields were significantly affected by applied operational extraction parameters. The increase in pressure, temperature and solvent flow rate improved the extraction yield. The extraction yield increased as the particle size decreased depending on decreasing intra-particle diffusion resistance. To describe the extraction process Sovova's model was used and very good agreement with the experimental results was obtained. Based on the experimental data the internal and external mass transfer coefficients were estimated. To explore the influence of the extractor size on this process, soybean samples were extracted using different extraction basket volumes (0.2 L and 5 L) and related model parameters were examined. The mass transfer coefficient in the fluid phase increased with the increase in extractor size, while the mass transfer coefficient in the solid phase was independent of the extractor size.