Deodorization and deacidification of edible oils with dense carbon dioxide

Near-critical carbon dioxide shows potential for extraction of free fatty acids, off-odors or flavors from edible fats and oils. Deacidification and deodorization of a simulated, roasted peanut oil with dense CO₂ was performed at various temperatures, pressures and extraction factors in a pilot-scale, packed extraction column with an i.d. of 2.86 cm and a height of 162 cm. Pyrazine and its derivatives are major components of roasted peanut aroma. At constant temperature and pressure, the distribution coefficient (m) for pyrazine derivatives was inversely related to the degree of substitution of methyl groups (molecular weight) and boiling point, that is, the solubility was directly related to the compounds volatility. CO₂ fluid-phase density alone could not explain the equilibrium solubility behavior of either fatty acids or pyrazines. At constant fluid-phase density, m for pyrazine derivatives decreased with increasing pressure and temperature, while that for fatty acids increased. At 20 MPa pressure, increasing the temperature from 47 to 57°C increased m for pyrazines, but decreased m for fatty acids, indicating that the system was within the retrograde region for fatty acids. Free fatty acid solubility was inversely related to chainlength and, in the supercritical region, directly related to the degree of unsaturation. Deodorization is mass-transfer-controlled, and deacidification is thermodynamically constrained. The efficient deodorization and deacidification of an actual crude oil pressed from roasted peanuts was accomplished by extraction with CO₂ at 47°C and 20 MPa. Extraction with carbon dioxide may be particularly useful for deacidifying expensive specialty fats with high initial acidity, or where the quality and purity of the extracted components are of importance.     

TLC as a tool for quantitative isolation of conjugated trienoic FA

Conjugated trienoic FA—α-eleostearic, β-eleostearic, and punicic acids—were preferentially isolated in pure form from the total methyl esters of the respective oils by simple silica gel TLC using hexane/diethyl ether as the mobile phase (94∶6). The subsequent saponification of the separated methyl ester fractions upon cooling at −20°C yielded individual acids in crystalline form. Melting points, conventional UV spectroscopy, and GLC confirmed the identity of the conjugated trienoic FA. The method finds potential application in benchscale reaction optimization using pure FA and in the preparation of standard reference materials of these acids, as these oils are widely used in the coatings industry.     

Further studies on artificial geometrical isomers of α-linolenic acid in edible linolenic acid-containing oils

Fifteen samples of commercial edible soybean and rapeseed oils (and mixtures of these) from Belgium, Great Britain and Germany have been analyzed for theirtrans-polyunsaturated fatty acid content. Only one sample out of the 13 refined samples, and the two cold-pressed samples, contained trace amounts oftrans isomers. Others contained between 1 and 3.3% of their total fatty acids as geometrical isomers of linoleic and linolenic acids. The degree of isomerization (DI) of linolenic acid varied between 10.5 and 26.9%. Combining results obtained in this study together with corresponding data for French oils (totalling 21 samples) indicates that the relative percentages of individual linolenic acid geometrical isomers depend on linolenic acid DI. Relationships linking these parameters could be approximated by straight lines, at least for DIs lying between 9 and 30%. Extrapolation to DI=0 suggests that the relative probabilities of isomerization of double bonds in positions 9, 12, and 15 are 41.7, 6.1 and 52.1%, respectively, at the very beginning of the isomerization reaction. At that time, the probability of a simultaneous isomerization of double bonds in positions 9 and 15 is close to zero. Thet,c,t isomer is apparently formedvia thec,c,t and thet,c,c isomers, the former being somewhat more prone to a second geometrical isomerization than the latter. The relative proportion of thec,t,c isomer is practically independent from the DI, at least between 9 and 30%, which would suggest that this isomer is an “end-product” of thecis-trans isomerization reaction.     

Physical refining of coconut oil: Effect of crude oil quality and deodorization conditions on neutral oil loss

In the present study, neutral oil loss (distillative and mechanical carry-over) during physical refining of coconut oil was quantified. Neutral oil loss seems to depend on both the crude oil quality and the process conditions during deodorization. The distillation of volatile glyceridic components (monoand diglycerides), originally present in the crude oil, was confirmed as the major cause for the neutral oil loss. The amount of these volatile components in crude coconut oils cannot be derived as such from the initial free fatty acid content. A lower deodorization pressure with less sparge steam resulted in a larger neutral oil loss than a higher pressure with more steam. A “deodorizability” test on a laboratory scale under standardized conditions (temperature=230°C, pressure=3 mbar, time=60 min, sparge steam=1%), to evaluate crude oil quality and to obtain a more accurate prediction of the expected neutral oil loss and free fatty acid content in the fatty acid distillate, is described.     

Offset printing inks based on rapeseed and sunflower oil. Part I: Synthesis and characterization of rapeseed oil-and sunflower oil-modified alkyd resins

Two sets of alkyd resins of variable oil lengths with the required properties for offset printing ink formulations, modified by sunflower and rapeseed oil, were synthetized according to the “monoglyceride” process. The influence of the acyl composition of the modifying vegetable oil and of the oil content on alkyds’ properties was determined by detailed chemical and rheological characterization. Molecular structure, size, and molecule size distribution appeared to be linked to these two factors. A comparative study with two usual linseed oil-modified alkyds led to determination of the more appropriate alkyds for applications in offset varnishes.     

Deacidification of sulfur olive oil. I. Single-stage liquid-liquid extraction of miscella with ethyl alcohol

In this study, a systematic and detailed investigation on liquid-liquid extraction of sulfur olive oil miscella in hexane with aqueous ethanol solutions was performed. Optimal extraction conditions for recovery of free fatty acids (FFA) with a minor loss of neutral oil were determined in bench-scale single-stage extractions. It was concluded that, to ensure deacidification with a low triglycerides loss, it is appropriate to extract the miscella with 30% or more dilute ethanol solutions. It was also noted that under these circumstances the free fatty acid percentage extracted is not affected by increases in contents of FFA and partial glycerides of sulfur olive oil, and the solvent must be saturated with hexane before extraction. Changing the oil:hexane ratio in miscella from 1:2 to 2:1 by weight did not have any significant effect on extraction results.     

Deacidification of sulfur olive oil. II. Multi-stage liquid-liquid extraction of miscella with ethyl alcohol

In this study, laboratory-scale multi-stage cross- and counter-current extractions of sulfur olive oil miscella with 70 and 80% ethanol saturated with hexane were investigated. For cross-current extraction, the extraction factor for free fatty acids was constant in each extraction stage. Therefore, the extraction factors determined in single-stage extractions were used to calculate the extracted free fatty acid percentages for cross-current and counter-current multi-stage extractions and results were in close agreement with the experimental data. It was possible to determine the amount of solvent and the number of stages required for counter-current extraction to remove the desired amount of free fatty acids from a given sulfur olive oil with 70 or 80% ethanol. Comparison of the results for these two solvents showed that 80% ethanol was more suitable.     

Mineral acid-catalyzed condensation of meadowfoam fatty acids into estolides

Meadowfoam fatty acids (83% monoenoic fatty acid), reacted with 0.01–0.1 mole equivalents of perchloric acid, gave 33–71% yield of estolide, an oligomeric 2° ester, resulting from self condensation. Equimolar amounts of perchloric acid to fatty acid failed to produce estolide but converted the fatty acids to a mixture of lactones, mainly γ-eicosanolactone. Temperature plays a critical role; higher temperatures (75–100°C), at the same acid concentration, provide lactones while lower temperatures (20–65°C) yield estolides. Lower acid levels (<0.1 mole equivalents) gave the best yields (≈70%) at 65°C. The estolide and monomer were characterized by nuclear magnetic resonance, infrared high-pressure liquid chromatography, gas chromatography, gas chromatography/mass spectrometry. The estolide is a mixture of oligomers with an average distribution near 1.65 ester units. The ester linkages are located mainly at the original double bond positions but have some positional isomerization to adjacent sites in accord with carbocation migration along the alkyl chain. The residual double bond of the estolide was extensively isomerized fromcis totrans and positionally along the chain. The distilled monomer is similar in structure to the unsaturated portion of the estolide with geometrical and positional double bond isomerization. In addition, a significant amount of cyclization of the fatty acids to lactone (≈30%) had occurred.     

气相色谱法测定食品油脂中的十八碳反式脂肪酸

反式脂肪酸是在油脂的加氢反应或高温精炼过程中伴随产生的一类不饱和脂肪酸,过多的食用这些成分可能会对人体健康产生危害。食品油脂中以十八碳反式脂肪酸最为常见。采用气相色谱法对食品中十八碳反式脂肪酸的检测进行了实验摸索,获得了一套准确度高、精确度好的方法,可应用于日常监督检测。     

A comparative study of two heating procedures in the physical refining of edible oils

Two mixtures of refined sunflower seed oil, one with oleic acid and the other with olive oil distillates from a laboratory plant, were physically refined using nitrogen as stripping gas in a discontinuous deodorization pilot-plant scale installation (30-L capacity). Two heating procedures were tested: one using independent electrical heating for the oil and the gas distillates so as to maintain the same temperature in both, and another in which only the oil was heated and controlled, resulting in a difference in temperatures in the oil and the gas distillates. Two different oil temperature values and three nitrogen flow rates were also assayed. The statistical technique of blocking with paired comparisons was used to analyze the results. These results showed that maintaining the same temperature in the oil and gas distillates had a positive effect on free fatty acid distillation rate and vaporization efficiency. Oil temperature and nitrogen flow rate also influenced some of the aforementioned responses.     

Effect of Selected Polyhydric Alcohols on Refining Oil Loss in the Neutralization Step

Alkaline neutralization is a classical method for removal of free fatty acids (FFA) in crude oil. It is generally accompanied by neutral oil loss. Thus, reduction of refining losses associated with alkaline neutralization is very desirable. Refined, bleached and deodorized (RBD) palm oils with different FFA contents were used as oil models in this study. FFA in the oil models were neutralized with sodium hydroxide in polyhydric alcohols as neutralization media. Glycerol, propylene glycol and ethylene glycol in water were effective neutralization media. FFA in the oil models were totally removed in one step of neutralization, while percentages of refining losses were different. The losses were increased in the order of water > propylene glycol > ethylene glycol > glycerol used as neutralization media. Also, a higher concentration of polyhydric alcohol in the neutralizing media significantly reduced the percentage of refining loss (p < 0.05). Glycerol (90% in water) was the most effective neutralization media (p < 0.05). When neutralization was carried out on crude palm oil (containing 7.53% FFA), refining loss was reduced from 36.1% (in water) to 20.0% (in 90% glycerol in water).     

Sepiolite: An effective bleaching adsorbent for the physical refining of degummed rapeseed oil

The efficiency of Turkish sepiolite in bleaching degummed rapeseed oil has been investigated. Experimental results indicate that the bleaching efficiency is more dependent on the ratio of sepiolite to oil than on operating parameters such as contact time and temperature. An increase in the sepiolite dosage reduces the color bodies of the rapeseed oil. Its effect on oxidation state, however, is complex and related to both primary and secondary oxidation products. The removal of impurities such as chlorophyll a, β-carotene, and phosphorus increases with increasing sepiolite dosage and reaches a maxumum at 1.5% sepiolite addition and 100°C bleaching temperature. Chlorophyll a, β-carotene, and phosphorus adsorptions can be described by a mechanism involving surface are and porosity of acid-activated sepiolite as key variables. The sorption is also independent of the polarity of the adsorbate molecules. Direct comparison of activated sepiolite with the commercial bleaching earth Tonsil 210 FF shows that in some respects sepiolite offers significant advantages.