Effects of processing on the quality and stability of three unconventional Sudanese oils

In a refining experiment, on a laboratory scale, crude oils from Sclerocarya birrea (SCO), sorghum bugs (SBO), water‐extracted melon bugs (MBO H₂O) and solvent‐extracted melon bugs (MBO SOL) were processed by alkali refining. Quality changes were characterized by the determination of free fatty acids (FFA), peroxide value, tocopherols, sterols, phosphatides and stability against oxidation (Rancimat test). In addition, the fatty acid composition was determined. It is clear that the contents of phosphatides, peroxides, tocopherols, sterols as well as oxidative stability were reduced during processing, while FFA were nearly totally removed. The content of phosphorus was reduced in SCO, SBO, MBO H₂O and MBO SOL by 26, 19, 12, and 78%, respectively, while complete oil processing removed 95, 99, 96 and 99% of the FFA in crude oils, respectively. The level of total tocopherols decreased during processing by 38.7, 83.8, 100, and 33.3%, respectively. The color decreased through the processing steps up to bleaching; then, in the deodorization step, it darkened sharply in all samples. No change in the fatty acid composition was observed. The order of oxidation stability was crude > degummed > deodorized > neutralized > bleached, in SCO; and crude > degummed > neutralized > bleached = deodorized, in MBO H₂O; and crude > degummed > deodorized > neutralized > bleached in MBO SOL; while in SBO, the order of oxidative stability was deodorized > crude > degummed > neutralized = bleached. Total sterols decreased by 42–92% in the processed oils, compared with crude oils.     

Effects of processing steps on the contents of minor compounds and oxidation of soybean oil

The processes of degumming, alkali refining, bleaching and deodorization removed 99.8% phospholipids, 90.7% iron, 100% chlorophyll, 97.3% free fatty acids and 31.8% tocopherols from crude soybean oil. The correlation coefficient between the removals of phosphorus and iron in soybean oil during processing was r = 0.99. The relative ratios of α-, β -, γ- and δ-tocopherols in crude oil, degummed oil, refined oil, bleached oil and deodorized soybean oil were almost constant, γ- and δ -tocopherols represented more than 94% of tocopherols in soybean oil. The order of oxidation stability of oil is crude > deodorized > degummed > refined > bleached oil.     

Thermal degradation of FA and catfish and menhaden oils at different refining steps

The thermal degradation (weight loss) of individual FA and of catfish and menhaden oils collected from different refining steps was investigated by thermogravimetric analysis. The heat resistance of FA was partially dependent on chain length and degree of unsaturation. The weight loss of catfish and menhaden oils increased with increased heating temperatures, regardless of the oil refining process. All oil samples (except crude catfish oil) were decomposed after the heating temperature reached 550°C. Based on the thermogravimetric curves, the following thermal stability sequence at different refining steps for both catfish and menhaden oils was proposed: crude > degummed > neutralized > bleached > deodorized oils.     

Determination of Melting Points,Specific Heat Capacity and Enthalpy of Catfish Visceral Oil During the Purification Process

Changes in melting points, enthalpy, and specific heat capacity of catfish visceral oil at each step of the purification process were studied. Melting points of −46.2 to 21.2 °C for crude oil, −45.9 to 11.5 °C for degummed oil, −44.3 to 11.4 °C for neutralized oil, −47.1 to 9.9 °C for bleached oil and −52.3 to 8.0 °C for deodorized oil were observed. Enthalpy (kJ/kg) was 74.1 for crude oil, 74.7 for degummed oil, 75.1 for neutralized oil, 79.3 for bleached oil, and 84.3 for deodorized oil. The specific heat capacities at 20 °C for crude, degummed, neutralized, bleached, and deodorized oils were 1.69, 1.96, 1.97, 1.91, and 1.83 kJ/kg °C, respectively.     

Quality of oil from damaged soybeans

Various processing steps were explored in an at-tempt to improve the quality of oil from field- and storage-damaged soybeans. A crude soybean oil (5.7% free fatty acid) commercially extracted from damaged soybeans was degummed in the laboratory with different reagents: water, phosphoric acid, and acetic anhydride. Two alkali strengths, each at 0.1 and 0.5% excess, were used to refine each degummed oil. After vacuum bleaching (0.5% activated earth) and deodorization (210 C, 3 hr), these oils were un-acceptable as salad oils. A flavor score of 6.0 or higher characterizes a satisfactory oil. Scores of water and phosphoric acid degummed oils ranged from 4.5 to 5.1, while acetic anhydride degummed oils aver-aged 5.6. Flavor evaluations of (phosphoric acid de-gummed) single- and double-refined oils (210 C deodorization) showed that the latter were signifi-cantly better. Flavor scores increased from 5.0 to about 6.0. To study the effects of deodorization tem-perature, the crude commercial oil was alkali-refined, water-washed and bleached with 0.5% activated earth, but the degumming step was omitted. Flavor evalua-tion of oil deodorized at 210, 230, and 260 C showed that each temperature increment raised flavor scores significantly. Further evaluations of specially proc-essed oils (water, phosphoric acid, and acetic anhy-dride degummed oils given single and double refinings and deodorized at 260 C) showed that deodorization temperature is the most important factor affecting the initial quality of oil from damaged beans. Flavor evaluations showed that hydrogenation and hydro-genation-winterization treatments produced oils of high initial quality, but with poorer keeping proper-ties than oils from normal beans. No evidence was found implicating nonhydratable phosphatides in the oil flavor problem. Iron had a deleterious effect in oils not treated with citric acid during deodorization. Presented at AOCS Meeting, Philadelphia, September 1974.     

A Highly Stable Soybean Oil-Rich Miscella Obtained by Ethanolic Extraction as a Promising Biodiesel Feedstock

Soybean oil is industrially obtained upon hexane extraction. In biodiesel production, soybean oil is submitted to phospholipid removal in order to improve its quality before transesterification. An extraction process was employed to produce ethanolic oil-rich miscella, which can be directly transesterified to produce biodiesel without prior refining. We assessed the oxidative stability of the miscella and three other soybean oils, namely degummed, alkali-refined, and refined–bleached–deodorized (RBD) oil. In vitro antioxidant assays as well as the identification and quantification of tocopherols and isoflavones were also performed. Although hexane-extracted oils showed higher tocopherol contents than miscella, this latter sample and its direct biodiesel demonstrated superior stability in accelerated tests. Miscella also outperformed hexane-extracted oils in all in vitro assays. This behavior can be explained by the presence of phenolic compounds with higher affinity to ethanol than hexane, which was confirmed by the identification of isoflavones glycitein, genistein, and acetyldaidzin, found only in miscella. This study showed that the ethanolic extraction of soybean oil generated a highly stable lipid feedstock for biodiesel manufacture.     

Quality Changes and Tocopherols and γ-Orizanol Concentrations in Rice Bran Oil During the Refining Process

The quality changes and the concentrations of tocopherols and γ-oryzanol, during successive steps of rice bran oil refining (RBO), were studied. For this purpose, samples of crude, degummed, neutralized, bleached, dewaxed and deodorized RBO were taken from an industrial plant and analyzed. The moisture, pH, acidity, peroxide value and unsaponifiable matter, were determined. The fatty acid composition was evaluated by GC, and the concentrations of tocopherols and γ-oryzanol were determined using HPLC with fluorescence and UV–Vis detection, respectively. To identify γ-oryzanol components, fractions of the HPLC eluant were collected and analyzed using mass spectrometry. Oil refining reduced the peroxide value and acidity to 1 and 3% of the values obtained in crude RBO, respectively. The fatty acid composition were not significantly altered during refining. The concentrations of the tocopherols in RBO followed the order α > (β + γ) > δ. The total concentration of tocopherols was 26 mg/100 g, and remained practically unaltered during refining. Up to nine components were distinguished in γ-oryzanol. After collecting the elution fractions, up to six components were identified by electrospray mass spectrometry. Refining reduced the total concentration of γ-oryzanol to 2% of its initial value.     

Effect of processing on the oxidative stability of low erucic acid turnip rapeseed (Brassica rapa) oil

The effect of various processing conditions on the composition and the oxidative stability of mechanically pressed (90–95°C) rapeseed oil was investigated. The five different rapeseed oils included crude (nondegummed), superdegummed, steam stripped (at 140°C for 4h, nondegummed), physically refined (degummed, bleached and deodorized at 240°C), and cold pressed (40°C) oils. Oils were autoxidized in the dark at 60°C and under light at 25°C. Oxidation was followed by measuring changes in the peroxide values (PV) and the consumption of tocopherol and carotenoid was measured. In the dark the oils reached PVs of 10 meq/kg in the order: cold pressed > superdegummed > steam stripped ≅ crude > refined. However, under light conditions the order changed as follows: cold pressed > crude ≅ steam stripped > superdegummed > refined. Processing had no effect on fatty acid composition nor α-tocopherol content of the oils. Superdegumming and steam stripping decreased the carotenoid content of the oils while cold pressing and refining reduced also chlorophyll, γ-tocopherol and phosphorus content of the oils.     

Zu den Veränderungen von Rapsöl und Leinöl während der Verarbeitung

Changes of rapeseed and linseed oil during processing During processing of crude oil in a large oil mill, three samples each of rapeseed and linseed were investigated at each processing stage, i.e. press oil, solvent-extracted oil, mixed oil, and degummed/caustic refined oil. In the case of rapeseed also bleached and desodorized oils (230°C; 3.0 mbar for 2 h) were investigated. Rapeseed and linseed oil showing the typical major fatty acids contained less than 1% trans-isomeric fatty acids (trans fatty acids = TFA). Linseed oil had a similar TFA-concentration as rapeseed oil, and the concentrations did not change during the processing stages up to degummed/caustic refined oil, and were also unchanged in the bleached rapeseed oil. Desodorization of rapeseed oil, however, trebled the TFA concentration to 0.58%. The detected tocopherol patterns were typical of rapeseed and linseed oils. There was no difference between mixed oil and degummed/caustic refined oil in the total concentration of tocopherols. Neither had bleaching any effect. Rapeseed oil desodorization diminished total tocopherol concentration by 12% from 740 mg/kg to 650 mg/kg. Due to degumming/caustic refining the phosphorus concentration of both oils decreased to less than a tenth compared to mixed oil. Other elements determined in degummed/caustic refined rapeseed oil were not detectable (manganese < 0.02 mg/kg, iron < 0.4 mg/kg, copper < 0.02 mg/kg, lead < 10 μg/kg) or only as traces zink 0.1 mg/kg, cadmium 2 μg/kg). In linseed oil, which initially showed a higher trace compounds concentration, a significant decrease was found by degumming/caustic refining. Iron could not be detected. There were traces of zinc, manganese, copper, lead, and cadmium. There was no difference between the acid values of rapeseed and linseed crude oil. Acid value decreased drastically already during the degumming/caustic refining stage. The crude linseed oils had a higher peroxide value, anisidine value and diene value than the corresponding crude rapeseed oils. With peroxide values of ≤ 0.1 mEq O₂/kg found in almost all investigated rapeseed oils, no effect of refining could be detected. The anisidine value showed an increase after bleaching. Desodorization trebled the diene value.     

Rice bran oil. V. The stability and processing characteristics of some rice bran oils

1. The extraction, processing, characteristics, and stability properties of nine batches of hexane-extracted rice bran oil were investigated. The oils were refined, bleached, and deodorized and their color and stability determined. Samples of the bleached oils were hydrogenated to approximately shortening consistency, deodorized, and the stability of the hydrogenated products determined.
2. Pilot plant extractions of five batches of rice bran yielded crude oils equivalent to 91% of the hexane-soluble portions of the bran.
3. The nine crude oils whose content of free fatty acids ranged from 2.0 to 6.3% were refined by the cup method with losses ranging from 12.0 to 23.5% although the neutral oil content of six crude rice bran oils ranged from 89.9 to 92.6%.
4. The Lovibond color of the nine refined oils ranged from 35 yellow and 4.5 red to 70 yellow and 9.5 red, and the color of the bleached oils ranged from 15 yellow and 1.5 red to 35 yellow and 3.2 red.
5. Steam-refining, employed in conjunction with alkali-refining, proved effective as a means of reducing the losses in refining rice bran oil.
6. The nine batches of refined, bleached, and deodorized rice bran oils had iodine values ranging from 101.3 to 105.7 and stabilities averaging 24 hours.
7. Nine bleached oils hydrogenated to approximate shortening consistency had iodine values averaging approximately 66 and stabilities averaging 370 hours.
8. Refined, bleached, and deodorized rice bran oil is bland but has some tendency toward flavor reversion.
9. The most outstanding characteristics of rice bran oil is its exceptional stability after hydrogenation.

     

Supercritical CO2 degumming and physical refining of soybean oil

A hexane-extracted crude soybean oil was degummed in a reactor by counter-currently contacting the oil with supercritical CO₂ at 55 MPa at 70°C. The phosphorus content of the crude oil was reduced from 620 ppm to less than 5 ppm. Degummed feedstocks were fed (without further processing,i.e., bleaching) directly to a batch physical refining step consisting of simultaneous deacidification/deodorization (1 h @ 260°C and 1–3 mm Hg) with and without 100 ppm citric acid. Flavor and oxidative stability of the oils was evaluated on freshly deodorized oils both after accelerated storage at 60°C and after exposure to fluorescent light at 7500 lux. Supercritical CO₂-processed oils were compared with a commercially refined/bleached soybean oil that was deodorized under the same conditions. Flavor evaluations made on noncitrated oils showed that uncomplexed iron lowered initial flavor scores of both the unaged commercial control and the CO₂-processed oils. Oils treated with .01% (100 ppm) citric acid had an initial flavor score about 1 unit higher and were more stable in accelerated storage tests than their uncitrated counterparts. Supercritical CO₂-processed oil had equivalent flavor scores, both initially and after 60°C aging and light exposure as compared to the control soybean oil. Results showed that bleaching with absorbent clays may be eliminated by the supercritical CO₂ counter-current processing step because considerable heat bleaching was observed during deacidification/deodorization. Colors of salad oils produced under above conditions typically ran 3Y 0.7R.     

Effect of processing on the composition and oxidative stability of coconut oil

The effect of various processing procedures on the composition and oxidative stability of coconut oil has been studied. The crude oil is relatively stable but major reductions in oxidative stability occur during the bleaching of oil degummed with phosphoric acid; during alkali refining; during the deodorization of oil degummed with citric acid and bleached; and during the deodorization of oil processed with a combined phosphoric acid degumming and bleaching operation. The reasons for the loss of oxidative stability during processing are discussed with reference to changes in the composition of the oil. Residual traces of citric acid or phosphoric acid play an important role in stabilizing processed oils. The tocopherol content is also important, although no additional stabilization of the oil occurs on adding levels of tocopherol above those present naturally in the crude oil. A combined phosphoric acid degumming and bleaching process leads to smaller losses of tocopherols than sequential treatments.     

Composition and sensory qualities of minimum-refined soybean oils

Commodity (normal) and high-oleic soybean oils extracted by extrusion-expelling (E-E) were minimally processed using water degumming and adsorptive deacidification to produce edible oil. Degummed and deacidified oils were deodorized at 150°C for 1 h by purging with N₂, CO₂, or steam. They were also conventionally deodorized for quality comparisons. Generally, the oxidative stability of the properly gas-purged commodity oils was better than that of the conventionally deodorized oils. Total tocopherols, FFA contents, and colors of the deodorized oils were not significantly different among the treatments. Sensory analysis of the oils showed that the toasty/nutty flavors of the gas-purged oils, especially for the degummed oils, were more intense than those of the conventionally deodorized oils. The beany flavors of gas-purged oils were not significantly different from those of conventionally deodorized oils, although the flavor intensities tended to be slightly higher in gas-purged oils. The overall flavor intensities of the gas-purged oils were similar to those of conventionally deodorized oils. Therefore, E-E soybean oil has the potential to be minimally refined to produce edible oil with good compositional and sensory qualities.     

Studies on antioxidant treatments of crude vegetable oils

Treatments of crude safflowerseed, soybean, sunflowerseed and cottonseed oils with the antioxidant compounds butylated hydroxyanisole (BHA), propyl gallate (PG) and tertiary butylhydroquinone (TBHQ) have been investigated. PG and TBHQ were effective in inhibiting oxidative degradation of the crude oils subjected to long term storage as determined by measurement of peroxide formation in the oils during storage and by determination of AOM and oven (145 F) stabilities of the oils before and after storage. Of particular interest were the oxidative stability characteristics of these oils after they had been stored for relatively long periods in crude form (with and without the antioxidants) and then alkali refined, bleached and deodorized. The data from stability tests on these refined oils indicate that vegetable oils protected with potent antioxidants, such as PG or TBHQ, during storage in the crude form might yield refined, bleached and deodorized oils with somewhat higher initial oxidative stability and with better response to further antioxidant treatment.     

Flavor and oxidative stability of oil processed from null lipoxygenase-1 soybeans

The role played by lipoxygenase in the flavor quality of soybean oil was investigated by comparing the oil processed from special soybeans lacking lipoxygenase-1 (Forrest x P.I. 408251) with the oil from normal (Century) beans. Quality assessment was based on sensory evaluations and on capillary gas chromatographic (GC) analyses of volatiles of the extracted crude, partially processed, and refined, bleached and deodorized oils. In direct comparisons of oil products from the two types of beans, no significant differences were found in either flavor quality or in flavor stability based on total volatiles, and in analyses for 2,4-decadienal. Although thermal tempering did not significantly affect the initial flavor scores of crude and degummed oils from Century and low L-1 soybeans, the initial scores of refined and bleached oils from Century soybeans were significantly improved by this treatment. Similarly, thermal tempering was just as important in producing good quality flour from the special beans lacking lipoxygenase-1 as the flour from normal beans. Therefore, factors other than lipoxygenase-1 appear to affect the food quality of soybean oils and meals.     

Laboratory continuous deodorizer for vegetable oils

A laboratory-scale continuous deodorizer, based on a modified Snyder distillation column, was constructed and tested for the deodorization of alkali-refined and bleached vegetable oils. Soybean oil extracted with supercritical carbon dioxide and without further processing also was deodorized to a finished edible oil. Results of taste panel evaluations of the finished oils show that the quality of oils deodorized over a temperature range of 194–260 C is equivalent to commercial salad oils. Oil flow rates are 1 to 2 ml/min, and contact time is about 5 min; a vacuum of 0.5 to 1.0 mm Hg is maintained with countercurrent steam flow of 1 to 5% of the oil weight. Small samples of oil (250–1000 ml) are readily accommodated in this equipment, and the deodorization conditions more nearly simulate commercial practice than do traditional small-scale batch deodorizers. Presented at the AOCS meeting in Philadelphia, PA in May 1985.     

Deacidification of high-acid rice bran oil by reesterification with monoglyceride

Autocatalytic esterification of free fatty acids (FFA) in rice bran oil (RBO) containing high FFA (9.5 to 35.0% w/w) was examined at a high temperature (210°C) and under low pressure (10 mm Hg). The study was conducted to determine the effectiveness of monoglyceride in esterifying the FFA of RBO. The study showed that monoglycerides can reduce the FFA level of degummed, dewaxed, and bleached RBO to an acceptable level (0.5±0.10 to 3.5±0.19% w/w) depending on the FFA content of the crude oil. This allows RBO to be alkali refined, bleached, and deodorized or simply deodorized after monoglyceride treatment to obtain a good quality oil. The color of the refined oil is dependent upon the color of the crude oil used.     

Degumming and bleaching ofLesquerella fendleri seed oil

A lesquerella species (Lesquerella fendleri) being investigated as a domestic source of seed oil containing hydroxy fatty acids shows good agronomic properties and is being tested in semi-commercial production.Lesquerella fendleri seeds contain 25% oil, of which 55% is lesquerolic acid (14-hydroxy-cis-11-eicosenoic). Oils produced in pilot-plant quantities by screw press, prepress-solvent extraction and extrusion-solvent extraction processes have been refined in the laboratory by filtering, degumming and bleaching. Two American Oil Chemists’ Society (AOCS) standard bleaching earths and two commercial earths were compared for effectiveness in bleaching these dark, yellow-red, crude lesquerella oils. Free fatty acids (1.3%), iodine value (111), peroxide value (<4 meq/kg), unsaponifiables (1.7%) and hydroxyl value (100) were not significantly affected by degumming and bleaching, but phosphorus levels of 8–85 ppm in the crude oils were reduced to 0.5–1.1 ppm in the degummed and bleached oils. Crude oils had Gardner colors of 14, which were reduced to Gardner 9–11 in the degummed and bleached oil, depending on bleach type and quantity used. AOCS colors in the range of 21–25R 68–71Y were obtained. By including charcoal in the bleaching step, a considerably lighter oil could be obtained (Gardner 7).     

Sulfur content of rapessed oils

Sulfur contents in rapeseed oils were determined by reduction with Raney nickel, acidification, and titration of released H₂S with mercuric acetate. The sulfur contents decreased with successive steps of industrial processing, i.e., crude oil, 17–31 ppm S; degummed, 16 ppm; alkali refined, 4–9 ppm; bleached, 3–5 ppm; and deodorized, <1 ppm. Laboratory-extracted oil from sound seed contained no detectable sulfur, regardless of the glucosinolate content of the seed. Heating of the seed or addition of water to the seed prior to extraction increased the sulfur in the oil-less, however, for low-glucosinolate seed than for high-glucosinolate seed. Laboratory-extracted oils from green, frost-damaged, and bin-heated seed contained appreciable amounts of sulfur. Contribution No. 403, Department of Plant Science, University of Manitoba.     

Flavor and oxidative stability of northern-grown sunflower seed oil

Flavor and oxidative stabilities of a northern-grown sunflower seed oil were investigated. Taste panel and oxidative evaluations were made on alkali-refined, deodorized, unbleached samples treated with commercial antioxidant mixtures, phenolic antioxidants, metal scavengers and added trace metals. Similar evaluations were conducted on a sample of the same oil after bleaching. Commercial antioxidant mixtures containing both phenolic antioxidants and a metal scavenger improve the flavor and oxidative stabilities of refined unbleached oil. Although phenolic antioxidants alone improve oxidative stability as measured by the active oxygen method test, flavor stability did not improve significantly for antioxidant-treated refined, unbleached samples after accelerated storage. Conversely, alkali-refined and bleached sunflower oil responded to treatment with certain phenolic antioxidants. Although iron and copper are deleterious to oil stability at concentrations of 0.1 ppm, such metal-inactivating agents as citric acid are effective in improving flavor stability. N. Market. Nutr. Res. Div., ARS, USDA.