Influence of the vegetable oil refining process on free and esterified sterols

The influence of the refining process on the distribution of free and esterified phytosterols in corn, palm, and soybean oil was studied. Water degumming did not affect the phytosterol content or its composition. A slight increase in the content of free sterols was observed during acid degumming and bleaching due to acid-catalyzed hydrolysis of steryl esters. A significant reduction in the content of total sterols during neutralization was observed, which was attributed to a reduction in the free sterol fraction. Free sterols probably form micelles with soaps and are transferred into the soapstock. The steryl ester content remained constant during all neutralization experiments, indicating that hydrolysis of steryl esters did not take place during neutralization. During deodorization, free sterols are distilled from the oil, resulting in a gradual reduction in the total sterol content as a function of the deodorization temperature (220–260°C). A considerable increase in the steryl ester fraction was found during physical refining, probably owing to a heat-promoted esterification reaction between free sterols and FA.     

食用植物油中溶剂残留量的顶空气相色谱标准加入法测定研究

对食用植物油中的溶剂残留测定方法进行了改进。用样品作基体配制标准溶液,采用顶空进样气相色谱测定,标准加入法定量。方法线性范围在ofμg／g-200μg/g,检测低限1．0μg/g,在1-μg／g-200μg／g浓度范围内,标准添加回收率为87．8％-107．4％．相对标准偏差6．06％-11．8％。本方法采用标准加入法进行定量,样品和标准的基体一致,避免了基体的影响,该法简便、快速,适合食用植物油中的溶剂残留的分析。     

Development of steryl ester analysis for the detection of admixtures of vegetable oils

The steryl ester content and composition of 28 samples from 10 vegetable oil types have been determined by isolation of the steryl esters by high-performance liquid chromatography and analysis by gas chromatography. The oils can be classified into oils with a high content (>4000 mg/kg) of steryl esters (corn and rapeseed); oils with a medium content (1400–2400 mg/kg) of steryl esters (sunflower oil and high-oleic sunflower oil); and oils with a low content (<1200 mg/kg) of steryl esters (safflower, soybean, cottonseed, groundnut, olive, and palm oils). The composition of the steryl ester fraction varies to a greater extent for different oil types than for different varieties of the same oilseed. The developed method is promising for authentication of some oils, and is particularly suitable for detecting admixtures of low levels of corn or rapeseed oils.     

Viscosities of vegetable oils and fatty acids

Data for viscosity as a function of temperature from 24 to 110°C (75 to 230°F) have been measured for a number of vegetable oils (crambe, rapeseed, corn, soybean, milk-weed, coconut, lesquerella) and eight fatty acids in the range from C₉ to C₂₂. The viscosity measurements were performed according to ASTM test methods D 445 and D 446. Several correlations were fitted to the experimental data. Correlation constants for the best fit are presented. The range of temperature in which the correlations are valid is from 24°C (75°F), or the melting point of the substance, to 110°C (230°F). The correlation constants are valuable for designing or evaluating such chemical process equipment as heat exchangers, reactors, distillation columns, mixing vessels and process piping.     

Minor constituents of vegetable oils during industrial processing

We report the effects of individual steps of industrial refining, carried out in Brazil, on the alteration of selected minor constituents of oils, such as corn, soybean, and rapeseed oils. Total sterols, determined by capillary gas chromatography (GC), decreased by 18–36% in the fully refined oils, compared with the crude oils. The total steradienes, dehydration products of sterols, were determinedvia a simple clean-up on a short silica gel column, followed by high-performance liquid chromatography (HPLC) with ultraviolet detection. The level of steradienes, normally not present in crude oils, increased after each refining step, especially after deodorization. Thus, the content of steradienes increased after deodorization by about 15- to 20-fold in corn and soybean oils, and by about 2-fold in rapeseed oil. The total steryl esters were also determinedvia clean-up on a short silica gel column, followed by HPLC with evaporative light scattering mass detection. A minor decrease in the level of steryl esters was observed after complete refining. The individual tocopherols and tocotrienols were determined by HPLC with a fluorescence detector. The level of total tocopherols and tocotrienols decreased by about 2-fold after complete refining of corn oil and by about 1.5-fold in soybean and rapeseed oils. In all three cases, maximum reduction of tocopherols was observed after the deodorization step. The level of polymeric glycerides, determinedvia clean-up on a short silica gel column followed by size-exclusion HPLC, increased to some extent (0.4–1%) during refining. The level oftrans fatty acids, determined by capillary GC, also increased to a substantial extent (1–4%) after refining. Part of doctoral thesis of Roseli Ap. Ferrari to be submitted to Faculdade de Engenharia de Alimentos, Universidade de Campinas, Campinas, Brazil.     

The determination of tocopherols in vegetable oils by square-wave voltammetry

Square-wave voltammetry (SWV) has been applied to the determination of tocopherol concentrations in eight vegetable oils: canola, corn, olive, peanut, safflower, sesame, soybean, and sunflower. This technique has a lower limit of detection and somewhat better resolution than differential-pulse voltammetry (DPV) and is significantly faster than both DPV and high-performance liquid chromatography (HPLC), the technique most often used for tocopherol determinations. The tocopherols are oxidized at a stationary glassy carbon electrode as its potential is scanned from 0.40 to 1.00 Vvs Ag/AgCl at a rate of 20 mV/s. The currents that arise from these oxidations are directly proportional to the tocopherols’ concentrations. A standard addition method is used to determine the tocopherol contents of the oils listed. Under the conditions employed, the limit of detection is 10 mg/L tocopherol in oil.     

Densities of vegetable oils and fatty acids

Complete data for density as a function of temperature have been measured for a number of vegetable oils (crambe, rapeseed, corn, soybean, milkweed, coconut, lesquerella), as well as eight fatty acids in the range C₉ to C₂₂ at temperatures from above their melting points to 110°C (230°F). The specific gravity and density measurements were performed according to American Society for Testing and Materials (ASTM) standard test methods D 368, D 891 and D 1298 for hydrometers and a modified ASTM D 369 and D 891 for pycnometers. Correlation constants, based on the experimental data, are presented for calculating the density of fatty acids and vegetable oils in the range of temperature from 24°C (75°F) or the melting point of the substance, to 110°C (230°F). The constants are valuable for designing or evaluating such chemical process equipment as heat exchangers, reactors, process piping and storage tanks. Estimated density of fatty acids by a modified Rackett equation is also presented.     

Acidity of oryzanol and its contribution to free fatty acids value in vegetable oils

Model oil systems containing physically refined rice bran oil to which oryzanol was added were examined to determine the effects of oryzanol concentration on FFA values. When oryzanol was added to the model oils at a 0.5% level and FFA was determined, increases in FFA value were 0.28% as determined with phenolphthalein, 0.58% with thymolphthalein, and 0.07% with alkali blue 6B. Oils containing added oryzanol at 0.5–1.5% showed a proportionate increase in FFA values with an average increase of 0.413% per gram of oryzanol. A direct titration of purified oryzanol showed an acidity of 42.5% expressed as FFA. In spectroscopic studies, the phenolic group in the ferulic acid moiety of oryzanol was titrated by sodium hydroxide. Based on these data, indicator correction factors for oryzanol's acidity and a formula for calculating real FFA content of vegetable oils containing oryzanol were developed.     

Chemical modification of vegetable oils for lubricant applications

Owing to the unfavorable impact on the environment of mineral oil-based lubricants, there has been a steady increase in the demand for biodegradable, environment-friendly lubricants. However, development of a biodegradable base fluid that could replace or partially substitute conventional mineral oil is a big challenge. Vegetable oils are recognized as rapidly biodegradable and are thus promising candidates as base fluids in environment-friendly lubricants. Vegetble oils have excellent lubricity, but poor oxidation and low-temeprature stability. This paper presents a series of structural modifications of vegetable oils using anhydrides of different chain lengths. The reaction was monitored and products were confirmed by NMR, FTIR, gel permeation chromatography, and thermogravimetric analysis (TGA). Experimental conditions were optimized for research quantity and for laboratory scale-up (up to 4 lb=1.8 kg). The thermo-oxidation stability of these new lubricant base fluids was tested using pressure differential scanning calorimetry and TGA. The chemically modified base fluids exhibit superior oxidation stability in comparison with unmodified vegetable oils. These base fluids in combination with suitable additives exhibit equivalent oxidation stability compared with mineral oil-based formulations.     

Predicting oxidative stability of vegetable oils using neural network system and endogenous oil components

The usefulness of Artificial Neural Network Systems (ANNW) to predict the stability of vegetable oil based on chemical composition was evaluated. The training set, comprised of a composition of major and minor components of vegetable oil as inputs and as outputs, induction period and values of slopes for initiation and propagation, was measured by oxygen consumption. The best predictability was achieved for oils stored at 35°C with light exposure, when the major fatty acids, chlorophylls, tocopherols, tocotrienols, and metals were used as predictors. For oils stored at 65°C without light, a good predictability was obtained when composition of the major fatty acids and the amounts of tocopherols and tocotrienols were used. These results suggest that vegetable oil stability can be successfully predicted by ANNW when partial oil composition is known.     

Formation of headspace volatiles by thermal decomposition of oxidized fish oilsvs. oxidized vegetable oils

To understand the reasons for differences in oxidative stability among edible oils, the temperature dependence was investigated for the development of volatile lipid oxidation products in fish oils and in vegetable oils. A rapid headspace capillary gas chromatographic method was developed to determine volatile oxidation products of omega-6 (n-6) polyunsaturated fats (pentane and hexanal) and omega-3 (n-3) polyunsaturated fats (propanal) at different decomposition temperatures. Headspace gas chromatographic analyses of partially oxidized menhaden, bonita and sardine oils could be performed at 40°C, whereas soybean, canola, safflower, high-oleic sunflower and high-oleic safflower oils required temperatures greater than 100°C. Volatile formation by thermal decomposition of oxidized oils had lower apparent activation energies in fish oils than in vegetable oils, and significantly higher apparent activation energies in high-oleic oils than in polyunsaturated oils. The activation energy data on headspace volatiles provided another dimension toward a better understanding of the thermal stability of flavor precursors in unsaturated fish and vegetable oils. Presented at the ISF/AOCS joint meeting, Toronto, Canada, May 10–14, 1992.     

High-resolution gas-chromatographic determination of diacylglycerols in common vegetable oils

The gas-chromatographic determination of partial glycerides of sunflower (both high- and low-oleic acid varieties), peanut and extra virgin olive oil was studied with a polar capillary column characterized by its high thermal stability. This column allows for the determination of single diacylglycerols separated as a function of the position occupied by the individual fatty acids on the glycerin backbone as well as by the degree of unsaturation of the fatty acids.     

Processing vegetable oils using nonporous denser polymeric composite membranes

Membrane processing offers several advantages over conventional processes for edible oil refining. In recent years, processing solvent-extracted, screw-pressed, and used frying oils using nonporous denser polymeric composite membranes without pretreatment and addition of chemicals has been extensively investigated. In the present review, results obtained with real and model systems have been summarized and a comprehensive explanation is provided on the mechanism of rejection and differential permeation of oil constituents. Phospholipid-TG and pigment-TG systems are construed as conventional solute-solvent systems, and tocopherol-TG and FFA-TG systems are treated as liquid mixtures exhibiting differential permeability. Dense membrane theory appears more applicable than the reverse osmosis theory in qualitatively explaining the differential permeability of liquid constituents of the oil. Membrane processing of oils appears to have the potential to be a one-step process, especially for screw-pressed oils, in producing a premium-quality product. However, the development of suitable membranes that enable higher fluxes is necessary for industrial adoption of this technology.     

Polymerization of vegetable oils and their uses in printing inks

Ink vehicles were prepared by the polymerization of vegetable oils. By controlling the polymerization conditions, the desired viscosity, color and molecular weight could be achieved for a variety of vegetable oils with a broad range of iodine values and fatty acid compositions. The effect of temperature and catalyst on polymerization rates were evaluated, and polymerization rate constants were calculated. Of the oils tested, the polymerization rate constant of safflower oil was the highest, followed by soybean, sunflower, cottonseed and canola oils in decreasing order. Use of a catalyst shortened the heating time by about 25–50% or lowered the polymerization temperature requirement by 25–30°C.     

Lithographic and letterpress ink vehicles from vegetable oils

Our objectives for this study were to produce vegetable oil-based printing ink vehicles that did not require any petroleum components, which meet or exceed industry standards for rub-off resistance, viscosity and tackiness for a variety of printing applications. These objectives were satisfactorily met. Vehicles were completely compatible with carbon black, making them suitable for black ink formulations. In addition, the resulting vehicles had exceptionally light colors, and permitted formulations of colored inks that had substantially reduced pigment levels compared to industry standards.     

Continuous hydrogenation of vegetable oils in reactors equipped with static mixers

Continuous hydrogenation of industrially refined soybean oil with Harshaw Ni catalyst was achieved in a slurry column equipped with Sulzer SMV motionless mixers. The influence of the operating parameters (temperature, pressure, catalyst concentration and gas velocity) was investigated. The presumption that, in this equipment, the liquid-solid mass transfer limits the rate of the process is in good agreement with the experimental data.     

The analysis of sterol degradation products to detect vegetable fats in chocolate

A method for the detection of hydrocarbon sterol degradation products (sterenes) has been adapted for the analysis of noncocoa butter vegetable fats in chocolate. The method involves solvent extraction of the fat separation of the sterene fraction, and analysis of individual sterenes with mass spectrometric detection. The sterene composition of refined noncocoa vegetable fats was determined in samples of cocoa butter, and retail chocolates. The presence of known sterenes was confirmed for all of the refined vegetable fats and for a single sample of cocoa butter, the processing history of which was not known. Detection of vegetable fat added to chocolate at the 5% level was demonstrated. Sterenes were detected only in chocolates labeled as containing vegetable fats. This technique has potential use as a screening method for the detection, but not quantification, of refined vegetable fat in chocolate.     

Studies of thermal polymerization of vegetable oils with a differential scanning calorimeter

Vegetable oils are often thermally polymerized to provide a vehicle for printing inks and paints. The formations of isomerization, and the intra- and intermolecular bonds involved in the thermal process are crucial in designing a product with the appropriate characteristics. It was found, with a differential scanning calorimeter, that the thermal polymerization of various vegetable oils could be activated at lower temperatures under a dry-air purge and/or in the presence of metallic catalysts. The Diels-Alder reaction and the formation of intermolecular bonds in alkali-refined soybean oil under a dry-air purge could be activated at 99 and 161°C in the presence of metallic catalysts, compared with 231 and over 300°C in the absence of metallic catalysts, respectively. The energies needed to activate the Diels-Alder reaction and to form intermolecular bonds were calculated, and is in good agreement with available data. The hardness test of baked vegetable-oil systems was also implemented to qualitatively determine the degree of cross-linking.     

The use of vegetable oils to recover compounds from aqueous solutions

Corn oil, canola oil, olive oil, sunflower oil, peanut oil and soyabean oil were tested as extractants for the recovery of organic compounds from aqueous solution. Short chain aliphatic alcohols and acids were poorly recovered (K_d < 1.0) while most esters, aldehydes and aromatic compounds tested were satisfactorily recovered (K_d > 2.0) from aqueous solution by vegetable oils. K_d is defined as the ratio of the concentration of the dissolved substance in the extractant to that in the aqueous phase. The exception was caffeine which was poorly extracted from water. The type of oil used appeared to have limited effect on K_d. Increasing the reaction temperature resulted in increased K_d for most readily extractable compounds. Acidulated fatty acid was also tested as an extractant. Although it generally resulted in a greater K_d than the oils or hexane control, acidulated fatty acid was less desirable as an extractant because it tended to create an emulsion with the aqueous phase under the test conditions.     

Oil fractionation as a preliminary step in the characterization of vegetable oils by high-resolution 13C NMR spectroscopy

One hundred nine oil samples were separated chromatographically to obtain oil fractions with a decreased TAG content but with enhanced levels of the minor components that define oil genuineness and quality. The oils, which included virgin olive oils from different cultivars and regions of Europe and north Africa and refined olive, “lampante” olive, refined olive pomace, hazelnut, rapeseed, high-oleic sunflower, corn, grapeseed, soybean, and sunflower oils, were fractionated on a silica gel column with hexane/diethyl ether as the mobile phase eluent. The method was highly reproducible, and the fraction obtained contained about 15% unmodified TAG and 85% polar compounds, which included polymeric TAG, oxidized TAG, DAG, MAG, and FFA, in addition to other minor polar components of the oils. The presence of these compounds, in an enriched fraction, should provide information about the thermal, oxidative, and hydrolytic alterations of the oils, as well as many compounds of interest in determining oil genuineness. The results indicate that these fractions can provide more information than the original oils for NMR or other spectroscopic studies used in the determination of oil quality.