Refining cottonseed oil at high rates of shear

Summary Ten crude cottonseed oils obtained from different areas in the South and Southwest were refined with and without the use of high-shear agitation in the step involving the initial mixing of the crude oil and caustic soda solution. In each instance the use of high shear produced a lower color in the refined oil. The improvement with some oils was not marked because they either refined very well by the ordinary method or failed for some unexplained reason to respond readily to high-shear mixing. However a good proportion of the oils which were quite dark after refining by the ordinary method refined to a much lighter oil when high shear was used. It was established that in high shear refining the color of the refined oil decreased as the temperature at which high shear was used decreased, the time at high shear increased, and the rate at which shear was applied increased. However an increase in the latter above a certain value had no effect. Also it was found that the color of the refined oil decreased as the amount and strength of the caustic soda solution increased. Absorption spectra of some of the processed oils indicated that high shear was more effective than ordinary mixing in removing from an oil the gossypol-like and carotenoid color bodies. Presented at the 28th fall meeting of The American Oil Chemists’ Society, Minneapolis, Minn., Oct. 11–13, 1954. One of the laboratories of the Southern Utilization Research Branch, Agricultural Research Service, U. S. Department of Agriculture.     

Silica refining of palm oil

The amount of bleaching earth required in the physical refining process of palm oil depends on the activity of the earth, quality of the oil and final color specification of the refined products. The use of silica (Trisyl) in combination with bleaching clay in palm oil refining has been investigated. The optimum conditions required for Trisyl and bleaching clay are 95–105°C for a period of 30–40 min. Improvements in color performance for palm oil products are noted with the addition of small quantities of Trisyl (0.06–0.24%) to the bleaching clay. Addition of 0.12% Trisyl to 0.4% bleaching clay improved the color of the refined oil by as much as 1.7 Red Lovibond units. Lower phosphorus levels (18.4 and 16.9 ppm) were obtained in the refined oils with an addition of 0.12 and 0.24% Trisyl, respectively, as compared to a level of 36.2 ppm of phosphorus when no silica was added to the earth. Better color stability was also obtained with oils treated with Trisyl. An additional advantage was the reduction in filtration time, leading to possible higher throughput in refining.     

Gaseous ammonia as a refining agent for cottonseed oils

In this investigation the application of gaseous ammonia to cottonseed oil refining was explored. The ammonia reacted quantitatively with the free fatty acids in the oil; its solubility in coftonseed oil was determined as a function of pressure. In “degumming” it was more efficient in removing phosphatides than other agents. A reduction in refining loss resulted for oils refined with gaseous ammonia as outlined and compared with the standard AOCS cup loss analysis. However, the oil colors were substantially higher even though the ammonia treated oils were re-refined with caustic solution. Results using cottonseed oil-hexane “miscellas” containing less than 70% oil showed low refining losses, but the colors were estremely high. Above 70% oil content the losses were higher, but the colors were lower. The colors never equalled “standard cup” results. This study was sponsored by the Texas Engineering Experiment Station and the Cotton Research Committee of Texas.     

Determination of the extent of oxidation of fats

Summary The amount of secondary oxidation products in refined and unrefined fats has been determined by reaction with benzidine acetate in iso-octane absolute alcohol solution, and measurement of the absorption at 350 mμ of the yellow color has been made. An “aldehyde value” has been calculated from this absorption intensity, using cinnamaldehyde as a reference substance. Determination of the aldehyde value and peroxide number of oils before and during refining has given information on the effect of the different refining processes on the state of oxidation of the oils. The effect of hardening on the content of oxidation products of an oil has been investigated. The effect of the amount of oxidation products in the unrefined material on the flavor stability of the refined material and of the margarine made from it has also been studied.     

The effect of bleaching and physical refining on color and minor components of palm oil

An industrially degummed Indonesian palm oil was bleached and steam refined in a pilot plant to study the effect of processing on oil color and on the levels of carotenoids and tocopherols. Five concentrations of one natural and two activated clays mixed with a fixed amount of synthetic silica were used for bleaching. For color measurement, the Lovibond method was compared to the CIE (Commission Internationale de l’Eclairage) L^*,a^*,b^* method. The results showed that the L^*,a^*,b^* method is repeatable and that the values found are highly correlated with the carotenoid content of bleached oil samples. The various clays and synthetic silica mixes removed 20–50% of the carotenoids in the degummed oil, depending on clay concentration and activity. For the two activated clays, pigment adsorption increased with clay amount. Steam refining totally destroyed carotenoids in the claytreated oils by heat bleaching. Total tocopherols in the crude oil amounted to 1000 mg/kg, with γ-tocotrienol as the main tocopherolic component followed by α-tocopherol, α-tocotrienol, and δ-tocotrienol. Tocopherol concentrations increased after the bleaching treatment with the most acid clay, and the increase was proportional to the amount of clay used. Both bleaching and steam refining changed the ratios between the various to copherolic components, especially increasing the relative concentration of α-tocotrienol in the refined oil. An average 80% tocopherol retention was obtained after the treatment with acid clay + synthetic silica and steam refining of palm oil.     

Studies on the pigments of some citrus,prune and cucurbit seed oils when processed with or without cottonseed oil

Pigments of citrus, prune and cucurbit fruit seed oils were studied spectrophotometrically. The citrus fruits used were: orange (O), mandarin (M), bitter orange (BO) and lemon (L). The prunes used were apricot (A), peach (P) and plum (PL); while melon (M), watermelon (WM) and Winter squash (S) were the cucurbits. Absorption spectra and Lovibond color were studied for crude, refined and bleached oils. Cottonseed oil (CSO) was mixed with some of the previous oils in the crude state, then refined and bleached. Absorption spectra of the crude fruit seed oils revealed carotenoid pigments at 400, 425, 455 and 480 nm, chlorophyll at 610 and 670 nm and unknown pigments at 525, 570 and 595 nm. Refining did not remove these pigments, whereas bleaching eliminated them completely. In oil mixtures of CSO+A, CSO+M and CSO+S, interference occurred between gossypol ‘360 nm’ from CSO and the pigments of A, M and S seed oils. Refining the oil mixtures removed gossypol, but its effect on carotenoids, chlorophyll and unknown pigments was limited. Bleaching completely removed all these residual pigments. Lovibond color for all bleached oils was very low (0.2–2 yellow). The refined oils, except those containing Winter squash seed oil, were found to have an acceptable color (0.8–15 yellow). Results of the proposed process reveals the possibility of mixing crude edible oil with crude fruit seed oils, then processing the oil mixture by the conventional methods of refining and bleaching.     

Properties and processing of corn oils obtained by extraction with supercritical carbon dioxide

Crude oils were extracted from wet- and dry-milled corn germs with supercritical carbon dioxide (SC-CO₂) at 50–90 C and 8,000–12,000 psi and were characterized for color, free fatty acids, phosphorus, refining loss, unsaponifiable matter, tocopherol and iron content. They were compared with commercial products. Extraction of wetmilled germ with SC-CO₂ has some advantages over the conventional prepress solvent method commonly used in the industry. For example, SC-CO₂ extraction of wet-milled germ at 50 C and 8,000 psi yields crude oil with a lower refining loss and a lighter color. After laboratory processing, a light-colored, bland salad oil is obtained. Crude, refined, bleached and deodorized oils from SC-CO₂-extracted dry-milled germ appear equivalent to those obtained by expeller pressing. Presented in part at AOCS meeting, Toronto, Ontario, Canada, May 1982.     

Rice brain oil. I. Oil obtained by solvent extraction

1. Freshly milled rice bran has been extracted with commercial hexane and the recovered oil and extracted meal examined for their respective content of wax. The oils were refined and bleached by standards as well as several special methods. The crude, caustic soda refined, and several refined and bleached oils were examined spectrophotometrically.
2. When freshly milled rice bran of good quality is extracted with commercial hexane, an oil of relatively low free fatty acid content is obtained. This oil possesses good color and is as stable as other similar types of crude oils.
3. If the oils is extracted from the brain at a temperature below about 10°C. and the extraction is discontinued at the right time, the extracted oil represents 90–95% of the total lipids in the brain and contains very little wax. This wax, which is readily extracted with hot commercial hexane as well as other types of solvents, amounts to about 3–9% of the total extractable lipids.
4. When subjected to ordinary caustic soda refining methods, good rice brain oils behave much like cottonseed oils of comparable free fatty acid content. Both caustic soda refining in a hydrocarbon solvent and refining with sodium carbonate result in refining losses approximating the absolute or Wesson loss.
5. Some of the refined oils when bleached according to usual practice produce products acceptable for use in the edible trade. However, refined rice bran oil has a definitely greenish cast resulting from the presence of chlorophyll, but this color can be removed by bleaching with a small amount of activated acidic clay.

     

Effect of refining of crude rice bran oil on the retention of oryzanol in the refined oil

The effect of different processing steps of refining on retention or the availability of oryzanol in refined oil and the oryzanol composition of Indian paddy cultivars and commercial products of the rice bran oil (RBO) industry were investigated. Degumming and dewaxing of crude RBO removed only 1.1 and 5.9% of oryzanol while the alkali treatment removed 93.0 to 94.6% of oryzanol from the original crude oil. Irrespective of the strength of alkali (12 to 20° Be studied), retention of oryzanol in the refined RBO was only 5.4–17.2% for crude oil, 5.9–15.0% for degummed oil, and 7.0 to 9.7% for degummed and dewaxed oil. The oryzanol content of oil extracted from the bran of 18 Indian paddy cultivars ranged from 1.63 to 2.72%, which is the first report of its kind in the literature on oryzanol content. The oryzanol content ranged from 1.1 to 1.74% for physically refined RBO while for alkali-refined oil it was 0.19–0.20%. The oil subjected to physical refining (commercial sample) retained the original amount of oryzanol after refining (1.60 and 1.74%), whereas the chemically refined oil showed a considerably lower amount (0.19%). Thus, the oryzanol, which is lost during the chemical refining process, has been carried into the soapstock. The content of oryzanol of the commercial RBO, soapstock, acid oil, and deodorizer distillate were in the range: 1.7–2.1, 6.3–6.9, 3.3–7.4, and 0.79%, respectively. These results showed that the processing steps—viz., degumming (1.1%), dewaxing (5.9%), physical refining (0%), bleaching and deodorization of the oil—did not affect the content of oryzanol appreciably, while 83–95% of it was lost during alkali refining. The oryzanol composition of crude oil and soapstock as determined by high-performance liquid chromatography indicated 24-methylene cycloartanyl ferulate (30–38%) and campesteryl ferulate (24.4–26.9%) as the major ferulates. The results presented here are probably the first systematic report on oryzanol availability in differently processed RBO, soapstocks, acid oils, and for oils of Indian paddy cultivars.     

A laboratory centrifugal refining method for control application

A control method is presented for selecting the appropriate processing conditions for alkali refining of crude vegetable oils by the centrifugal process to yield lowest losses with satisfactory color. This technique is sufficiently analogous to actual processing conditions to provide reliable information upon which plant performance can be based. The cup method cannot be used in this manner in that it no longer approximates operating procedures as in the days of kettle refining. The chromatographic neutral oil method, on the other hand, provides an index of the amount of oil available for recovery without regard to the possibility of attaining such levels. For these reasons the centrifugal method fills a void of long standing. Other tangible benefits that accrue from this technique are: selection of sources of oil that can be most profitably refined by establishing the relative value of competitive oils, and a means of evaluating plant efficiency.     

Production of Rice Bran Oil with Light Color and High Oryzanol Content by Multi-stage Molecular Distillation

Color is regarded as an important quality parameter for rice bran oil (RBO). Nevertheless, numerous grade‐three and grade‐four RBOs with dark color are currently available in the Chinese market. These oils are usually produced by steam refining and exhibit a mahogany color, which is undesired by customers. Here, we describe the development of a new industrially viable refining method based on multi‐stage molecular distillation (MMD), through which decoloration and fractionation of grade‐four RBO were accomplished, and four kinds of products, pigment oil, semi‐refined oil‐I (SRO‐I), semi‐refined oil‐II (SRO‐II), and semi‐refined oil‐III (SRO‐III), were obtained. The pigment oil was hazy and mahogany colored, containing 84.84 % non‐triacylglycerols, mainly pigments, tocopherols, and free fatty acids. SRO‐I was hazy and orange, containing 20,563 mg/kg of oryzanol (accounting for 77–82 % of raw oil) and was 28.68 % of non‐triacylglycerols. In particular, higher content of monounsaturated triacylglycerols, diunsaturated triacylglycerols and non‐triacylglycerols was responsible for the haze. SRO‐II and SRO‐III had a clear yellow appearance and a non‐triacylglycerol content <1.5 %. These semi‐refined oils were mixed directly after MMD and further refined by mild deacidification and winterization to obtain fully refined oil, which met the requirements of commonly used standards. Notably, the final oil exhibited light color and retained nearly 80 % of the oryzanol of raw oil. The yield of final oil reached 80–85 % through the entire refining process.     

Miscella refining

Miscella refining can be practiced as a batch process or, preferably, as a continuous process with oil concentrations through the range of 30–70% by wt of oil. Miscella refining is preferably practiced at the oilseed solvent extraction plant for the economic reason of single solvent recovery system. Three immediate benefits are lower refining loss, lighter colored refined oil, and elimination of water washing. Various types of chemical conditioning, mechanical conditioning, and combinations of both are discussed for miscella refining certain oils. Blends of compatible crude oils can be advantageously miscella refined and, if desired, winterized or hydrogenated to produce oils with unique properties.     

Effect of caustic refining,solvent refining and steam refining on the deacidification and color of rice bran oil

Degummed rice bran oil was deacidified by caustic, solvent and steam refining processes. The steam refining process was optimized through a series of experiments with varying refining times (1–5 hr), temperatures (220–280 C) and amounts of steam (4–20%), at a pressure of 4 mmHg. The most significant factors affecting the degree of deacidification were the refining temperature and amount of steam. The correlation coefficient between quadratic equation obtained and experimental results was 0.96. Acid value and color of steam refined oil were not as good as those of caustic refined oil, but steam refining showed better retention of natural antioxidants than caustic or solvent refining. Steam refining is preferred for deacidification of rice bran oil because of reduced neutral oil loss and elimination of soap production. The important criteria in selecting a deacidification process are known to be the degree of deacidification, neutral oil loss, effect on bleaching and production of soapstock (2,8–10). In comparing caustic refining, solvent refining and steam refining, caustic refining of degummed rice bran oil resulted in satisfactory acid values and color but showed the worst result in neutral oil loss and produced large amounts of soapstock. Solvent refining was not shown to be efficient because of poor deacidification, high losses of neutral oil and darkening of color. Steam refining also was less effective than caustic refining in deacidification and bleaching. However, the degree of deacidification could be improved by development of a process to remove all the free fatty acids (8), and the color problem could be eliminated by including a preliminary bleaching step before steam distillation (10). The application of steam refining to rice bran oil will result in many advantages such as reduced neutral oil loss, no production of soap, and the production of high purity, industrial fatty acids.     

Characterization and processing of cottonseed oil obtained by extraction with supercritical carbon dioxide

Extraction of flaked cottonseed with supercritical carbon dioxide at temperatures of 50–80 C and pressures of 8,000–15,000 psi yields an improved crude cottonseed oil compared to those obtained by conventional solvent or expeller processes. Improvements include lighter initial color, less refining loss and lighter refined bleached colors. Crude cottonseed oils obtained by supercritical fluid extraction require less refining lye and show less tendency to undergo color fixation while in storage. Presented at the AOCS annual meeting, Chicago, May 1983.     

Study on the composition of rice bran oil and its higher free fatty acids value

The compositions of rice bran oils (RBO) and three commercial vegetable oils were investigated. For refined groundnut oil, refined sunflower oil, and refined safflower oil, color values were 1.5–2.0 Lovibond units, unsaponifiable matter contents were 0.15–1.40%, tocopherol contents were 30–60 mg%, and FFA levels were 0.05–0.10%, whereas refined RBO samples showed higher values of 7.6–15.5 Lovibond units for color, 2.5–3.2% for unsaponifiable matter, 48–70 mg% for tocopherols content, and 0.14–0.55% for FFA levels. Of the four oils, only RBO contained oryzanol, ranging from 0.14 to 1.39%. Highoryzanol RBO also showed higher FFA values compared with the other vegetable oils studied. The analyses of FA and glyceride compositions showed higher palmitic, oleic, and linoleic acid contents than reported values in some cases and higher partial glycerides content in RBO than the commonly used vegetable oils. Consequently, the TG level was 79.9–92% in RBO whereas it was >95% in the other oils studied. Thus, refined RBO showed higher FFA values, variable oryzanol contents, and higher partial acylglycerol contents than commercial vegetable oils having lower FFA values and higher TG levels. The higher oryzanol levels in RBO may contribute to the higher FFA values in this oil.     

Phospholipid composition of some plant oils at different stages of refining,measured by the latroscan-Chromarod method

Although the phospholipid composition of crude plant oils has been well studied, not much is known about the effect of the different refining processes on the individual phospholipids. This information is useful to the manufacturer to optimize the refining process. In this study corn, sunflower seed and peanut oils, at different stages of refining, were analyzed with the Iatroscan-chromarod method. The total phosphorus content of the samples was also determined with a classical method. The Iatroscan gave results of acceptable accuracy for the analysis of crude oils with phospholipid-phosphorus values between 145 and 536 ppm. However, for oils at further stages of refining, with phospholipid-phosphorus values between 1 and 10 ppm, less accurate results were obtained. For these oils, the latroscan results had to be supported by conventional thin layer chromatography. Degummed oils contained phosphatidyl-choline (1.1-22 ppm P), phosphatidylethanolamine (1-2 ppm P), phosphatidylinositol (trace-10 ppm P) and phosphatidic acid (trace-5 ppm P). Further refined oils contained no phospholipids with the exception of two samples. Bleached sunflower oil contained about 1 ppm phosphatidylinositol and bleached peanut oil contained ca. 1 ppm phosphatidylethanolamine and 1 ppm phosphatidylcholine. Fully refined edible oils contained no phospholipids.     

The processing and storage characteristics of glandless cottonseed

Two consecutive storage tests of seven and six-months' duration were conducted to determine the relative effects of adverse storage conditions on glandless and glanded cottonseed and the products derived from each. The moisture conditions during storage resulted in extreme quality deterioration in both glandless and glanded seed. The damage sustained by glandless seed was not substantially different from damage occurring to glanded seed. Neither did glandless seed appear to deteriorate at a faster rate. Normal direct solvent extraction processing methods were followed to process seed for products quality evaluations as measured by nitrogen solubility, epsilon amino free lysine, and gossypol content for meals and FFA, cup refining loss, refined color, bleach color and gossypol content for oils. Oil from glandless seed refined and bleached to lower AOCS colors than corresponding glanded seed oils. Refining losses for oils from damaged seed were slightly higher for glandless seed oils. The meal quality from glandless seed was superior in all categories measured. A laboratory of the Cotton Research Committee of Texas operated by the Texas Engineering Experiment Station.     

Thermooxidative stability of vegetable oils refined by steam vacuum distillation and by molecular distillation

Semi‐refined rapeseed and sunflower oils after degumming and bleaching were refined by deodorization and deacidification in two ways, i.e., by steam vacuum distillation in the deodorization column Lurgi and by molecular distillation in the wiped‐film evaporator. The oxidative stability of the oils before and after the physical refining has been evaluated using non‐isothermal differential scanning calorimetry. Treatment of the experimental data was carried out by applying a new method based on a non‐Arrhenian temperature function. The results reveal that refining by molecular distillation leads to lower oxidative stability of the oils than refining by steam vacuum distillation. Practical applications : (i) A method for the refining of edible oils by the molecular distillation in the wiped film of a short‐path evaporator is presented and applied. (ii) Oxidative stability of the oils refined by molecular distillation and steam vacuum distillation is compared. It has been found that refining by molecular distillation leads to lower oxidative stability of the oils than refining by steam vacuum distillation. (iii) Experimental data were treated by applying a new method based on a non‐Arrhenian temperature function. The method enables trustworthy predictions of oil stabilities for the application temperatures.     

Physical refining of edible oils

Crude oils obtained by oilseed processing have to be refined before the consumption in order to remove undesirable accompanying substances. The traditional alkali refining is often replaced by physical refining in which the use of chemicals is reduced. The most widely used method is steam refining. The crude oil quality is very important in order to obtain high quality refined oil. Furthermore, the oil should be efficiently degummed to remove phospholipids as well as heavy metals and bleached to remove pigments. The most important step consists of the application of superheated steam under low pressure and at temperatures higher than 220 °C. Both free fatty acids and objectionable volatiles, formed by cleavage of lipid oxidation products, are removed. A disadvantage is the partial loss of tocopherols. Side reactions, particularly isomerization of polyunsaturated fatty acids, should be minimized. The quality of physically refined oil is close to that of alkali refined oils, but losses of neutral oil are lower and the environment is less polluted. Among other methods of physical refining the application of selective membranes is promising.     

The purification of edible oils and fats

Originally, oils were not refined but with the introduction of solvent extraction, refining became necessary. Crude cottonseed oil was refined by treating the oil with caustic soda and the same process was used for all other oils that needed refining. The subsequent introduction of centrifugal separators converted the original batch process into a continuous process. Degumming was introduced to obtain lecithin but limited to soya bean oil. Physical refining was introduced for high acidity oils like palm oil after the oil had been degummed to low residual phosphorus levels in the dry degumming process, in which the oil is first of all treated with an acid and then with bleaching earth. In Europe, further degumming processes were developed that allowed seed oil to be physically refined and later phospholipase enzymes were introduced to reduce oil retention by the gums and improve oil yield. Given these various oil purification processes, the refiner must decide which process to use for which oil in which circumstances. The paper provides a survey of what to do and when. It also discusses several topics that require further investigation and development.