The total degumming process

A novel degumming process is described that is applicable to both undegummed and water-degummed oils. Such totally degummed oils have residual iron contents below 0.2 ppm Fe and residual phosphorus contents that average below 5 ppm P. Therefore, they can be physically refined to yield a stable refined oil while using the same level of bleaching earth commonly used for alkali refined oils prior to deodorization. They can also be alkali refined with reduced oil loss to yield a soapstock that only requires slight acidification for fatty acid recovery, and thus avoids the strongly polluting soap splitting process. The total degumming process involes dispersing a non-toxic acid such as phosphoric acid or citric acid into the oil, allowing a contact time, and then mixing a base such as caustic soda or sodium silicate into the acid-in-oil emulsion. This keeps the degree of neutralization low enough to avoid forming soaps, because that would lead to increased oil loss. Subsequently, the oil is passed to a centrifugal separator where most of the gums are removed from the oil stream to yield a gum phase with minimal oil content. The oil stream is then passed to a second centrifugal separator to remove all remaining gums to yield a dilute gum phase which is recycled. Washing and drying or in-line alkali refining complete the process. After the adoption of the total degumming process, in comparison with the classical alkali refining process, an overall yield improvement of approximately 0.5% has been realized. It did not matter whether the totally degummed oil was subsequently alkali refined, bleached and deodorized, or bleached and physically refined.     

Integrated pollution control in seed oil refining

In edible oil refining, the various processes in current use lead to different by-products and/or waste products and they may also cause some form of pollution. The processes are reviewed in this paper and current or possible means of disposal of these by-products/waste products are discussed to highlight the areas requiring most attention. These areas turn out to be gum disposal when the degumming operation is carried out at a stand-alone refinery, and soapstock effluent resulting from the alkali refining process. Other waste products and pollution sources are found to be unimportant or manageable. Accordingly, a major step forward in pollution abatement in seed oil refining can be achieved by making two changes. The first one entails carrying out the degumming operation at the oil mill rather than at the refinery. This should be done in such a way that the degummed oil is amenable to physical refining. The acid refining process is recommended for this degumming step and consequently, acid refined oil with appropriate quality guarantees will then become the article of trade. The second one involves a switch from alkali refining crude or waterdegummed oil to the physical refining of acid refined oil. For this latter step, a counter-current process is recommended because of its low stripping steam requirement. Dry condensation of the distillate will further alleviate pollution problems associated with deodorization and physical refining. Finally, some processes, that may contribute to pollution control but that still require development, are mentioned.     

Effects of Degumming and Bleaching on 3-MCPD Esters Formation During Physical Refining

Crude palm oil (CPO) was physically refined in a 200-kg batch pilot refining plant. A study of the possible role of degumming and bleaching steps in the refining process for a possible critical role in the formation of 3-chloropropane-1,2-diol (3-MCPD) esters was evaluated. For the degumming step, different percentages of phosphoric acid (0.02–0.1%) as well as water degumming (2.0%) were carried out. Six different types of bleaching clays, mainly natural and acid activated clays were used for bleaching process at a fixed dose of 1.0%. Deodorization of the bleached oils was performed at 260 °C for 90 min. Analyses showed that 3-MCPD esters were not detected in the CPO. Phosphoric acid degumming (0.1%) in combination with acid activated clays produced the highest levels (3.89 ppm) of 3-MCPD esters in the refined (RBD) oil. The esters were at the lowest levels (0.25 ppm) when the oil was water degummed and bleached with natural bleaching clays. However, the refined oil qualities were slightly compromised. Good correlation of 0.9759 and 0.9351 was obtained when concentration of the esters was plotted against acidity of the bleaching earths for the respective acid and water degumming processes. The findings revealed the contribution of acidic conditions on the higher formation of 3-MCPD esters. In order to lower the esters formation, it is important to reduce acid dosage based on the crude oil qualities or to find alternatives to acid degumming process. Neutralization of the acidity prior to deodorization was effective in reducing the formation of 3-MCPD esters.     

Auxiliary Degumming and Pressurized High Temperature Water Washing to Mitigate the Formation of Monochloropropanediols in Palm Oil

This study reports the benefits of auxiliary degumming (Aux.D) and pressurized high temperature (165 °C) water washing (PHTW) to mitigate the formation of monochloropropanediols (MCPD) during labscale physical refining of palm oil. Water-based degumming in combination with bleaching and deodorization are performed as the selected physical refining process. The mitigation concepts Aux.D and PHTW are integrated into the refining protocol and the ultimately observed MCPD levels in the fully refined oils are determined. Aux.D is performed by extracting the hydratable gum from pressed sunflower oil and using it as a degumming agent to further purify palm oil that has been previously subjected to centrifugation and water degumming. This approach enables the mitigation of 3-MCPD from the water washed reference 2.4–0.9 mg kg⁻¹ in ampoules. Even stronger mitigation is obtained when Aux.D is combined with bleaching and executed twice allowing a mitigation from the reference 1.9–0.6 mg kg⁻¹, in ampoules. PHTW is shown to decrease the 3-MCPD content of the refined oil from the reference 2.4–1 mg kg⁻¹, in ampoules and when combined with bleaching and executed twice showing a decrease from the reference 1.9–0.9 mg kg⁻¹. Practical applications: The benefits of these mitigation concepts are confirmed both in sealed ampoule tests and in deodorizer experiments at the lab scale. A combined application of Aux.D or PHTW with physical refining may represent new insights that can help to potentially further mitigate the formation of MCPD in physically refined palm oil beyond the limits achievable with current refining practices.     

The Total Degumming Process – Theory and Industrial Application in Refining and Hydrogenation

The degumming of vegetable oils prior to physical refining is a crucial preliminary step. The degumming process is not only largely responsible for the quality of the final product, but it also determines the amount of bleaching earth to be used, which has a substantial effect on the yield improvement which can be attained by this route. Investigations show clearly that iron, as a pro-oxidant, strongly influences the stability of refined oils, and that oil, degummed before bleaching and physical refining, may contain a maximum of 0.2 ppm Fe, if it is to yield a stable product. The Total Degumming Process has been developed on the basis of these findings, to make it possible to degum oil to a residual Fe-level below 0.2 ppm and a residual phosphorus content below 10 ppm. The principles and industrial application of the process have been considered. The results of industrial production using different raw materials of various qualities have been used to make a comparison between the conventional refining process (neutralization – bleaching – deodorization) and the Total Degumming Process in combination with physical refining. The combination of the Total Degumming Process and a simplified caustic refining process, and the use of Totally Degummed Oil for hydrogenation have also been considered.     

Membrane degumming of crude rice bran oil: Pilot plant study

The procedure for the classical chemical refining of vegetable oils consists of degumming, alkali neutralization, bleaching, and deodorization. Conventional refining of rice bran oil using alkali gives oil of acceptable quality, but the refining losses are very high. A critical work has been carried out to study the application of membrane technology in the pretreatment of crude rice bran oil. Oils intended for physical refining should have a low phosphorus content, and this is not readily achievable by the conventional acid/water degumming process. The application of membrane technology for the pretreatment of rice bran oil has been investigated. The process has already been successfully applied to other vegetable oils. Ceramic membranes, which are important from the commercial point of view, were examined for this purpose. The results showed that the membrane‐filtered oils met the requirements of physical refining, with a substantial reduction in color. It was observed that most of the waxy material was also rejected. Experiments were carried out to establish the relationship between permeate flux and rejection with membrane pore size, trans‐membrane pressure and micellar solute concentration.     

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.     

Detection of DNA during the refining of soybean oil

The isolation of DNA from foodstuffs is the first step in the detection of genetically modified organisms. Refining processes, however, have an irrevocable influence on the quality and quantity of DNA and make detection in refined oil impossible. In order to determine the most significant step in removing DNA from crude soybean oil, two refining processes were considered: chemical refining and physical refining. Although conducted on a lab scale, quality parameters showed that the refining processes were good simulations of the industrial refining. From samples drawn at various refining stages, DNA was extracted with a protocol originally developed for the extraction of DNA from lecithin. The polymerase chain reaction results prove that the protocol was sufficiently useful for extracting DNA from soybean oil. The amplified DNA revealed that degumming is the most important step in removing DNA from crude soybean oil. After degumming, DNA was concentrated in the water fraction; no DNA could be amplified in the oil fractions. During physical degumming, degradation of DNA was observed.     

Origin of problems encountered in rice bran oil processing

Rice bran oil, not being a seed‐derived oil, has a composition qualitatively different from common vegetable oils and the conventional vegetable oil processing technologies are not adaptable without incurring huge losses. The oil's unusual high content of waxes, free fatty acids, unsaponifiable constituents, phospholipids, glycolipids and its dark color, all cause difficulties in the refining process. An attempt was made in this investigation to look into factors that are responsible for such difficulties and to develop suitable methodologies for physical refining of rice bran oil. Special attention was given to dewaxing, degumming and deacidification steps. The high content of glycolipids (∼6%) present in the oil was found to be a central problem and their removal appeared crucial for successful processing of the oil. We have also isolated and identified, for the first time, phosphorus‐containing glycolipids that are unique to this oil. These compounds prevent a successful degumming of the oil and their high surface activity leads to unusually high refining losses during alkali refining. A number of simple processes has been evolved, including 1) a simultaneous dewaxing and degumming process, 2) an unusual enzymatic process to degum the oil, 3) processes for the removal of the glycolipids including the phosphoglycolipids and 4) a process for the isolation of the glycolipids which may have potential applications in the food, cosmetic and pharmaceutical industries. The processing protocol suggested here becomes the first and only one to produce an oil with less than 5 ppm of phosphorus from crude rice bran oil, rendering it thus suitable for physical refining. We believe that the present results are very significant and should contribute to a better utilization of this valuable oil.     

High‐temperature pre‐conditioning of rapeseed: A polyphenol‐enriched oil and the effect of refining

In this work, a pretreatment process for rapeseeds, which involves the use of high‐temperature steam, is presented. This method, besides accomplishing the beneficial effects of the conventional industrial thermal treatment, leads to an enrichment of some important minor compounds (polyphenols and phosphatides) in the resulting oil. Rapeseeds were pretreated at different operative conditions. Then, the seeds were pressed and the press‐cake was solvent extracted. The obtained oils were then refined by both chemical and physical refining techniques, and the influence of each refining step on the content of minor compounds was evaluated. The results show that the amounts of polyphenols and phospholipids present in the oil coming from pretreated seeds increase and that their concentrations depend on the conditioning time. The polyphenols present in the oil correspond mostly to 2,6‐dimethoxy‐4‐vinylphenol (vinylsyringol). The content of polyphenols was only slightly reduced during degumming. Neutralization resulted in a complete removal of these minor compounds. For the physical refining process, the type and amount of bleaching clay used had a significant influence on the content of polyphenols. After deodorization, oil samples with a considerable amount of polyphenols were obtained. These samples show a higher oxidative stability than chemically refined oils.     

Chemical degumming of canola oils

Crude oil produced from 2 varieties of canola (low thioglucoside rapeseed), i.e., Candle and Tower, were chemically degummed using 54 reagents. Phosphorus, iron, calcum and free fatty acid levels, and Lovibond colors were measured. Inorganic and organic acids or their anhydrides gave the best results in terms of phosphorus removal. Phosphoric, nitric and citric acids, and maleic anhydride were used in laboratory refining tests to determine the effects of chemical degumming on the refining process and on refined oil quality. Citric acid and maleic anhydride gave residual phosphorus levels of less than 50 mg/kg, and after refining, resulted in the best quality oil in terms of color, flavor and stability. The chemical degumming agents behaved similarly for expressed, solvent-extracted and blended oils of both varieties tested. One anomalous result was observed: Candle oil was not efficiently degummed by hydrocholoric acid, whereas the Tower oil gave excellent results. The experiments suggest that chemical degumming can significantly improve the quality of crude canola oil, and will lead to improved final products at lower cost to the refiner.     

Experience of Prerefining of Vegetable Oils with Acids

Prerefining of vegetable oils with acids serves general purposes. One is to remove impurities like phosphatides etc. from the crude oils to such a degree that the oil can then be physically refined. Another purpose is to facilitate subsequent alkali refining and to reduce pollution in effluent from alkali refining. After a review of some earlier work results from tests in laboratory scale on soya oil, rapeseed oil and linseed oil will be presented and discussed. Finally, an industrial procedure for acid refining, called “special degumming” will be described.     

Fatty Acid,Phytosterol, and Polyamine Conjugate Profiles of Edible Oils Extracted from Corn Germ,Corn Fiber,and Corn Kernels

This study compared the profiles of fatty acids, phytosterols, and polyamine conjugates in conventional commercial corn oil extracted from corn germ and in two “new-generation” corn oils: hexane-extracted corn fiber oil and ethanol-extracted corn kernel oil. The fatty acid compositions of all three corn oils were very similar and were unaffected by degumming, refining, bleaching, and deodorization. The levels of total phytosterols in crude corn fiber oil were about tenfold higher than those in commercial corn oil, and their levels in crude corn kernel oil were more than twofold higher than in conventional corn oil. When corn kernel oil was subjected to conventional degumming, refining, bleaching, and deodorization, about half of the phytosterols was removed, whereas when corn fiber oil was subjected to a gentle form of degumming, refining, bleaching, and deodorization, only about 10% of the phytosterols was removed. Finally, when the levels of polyamine conjugates (diferuloylputrescine and p-coumaroyl feruloylputrescine) were examined in these corn oils, they were only detected in the ethanol-extracted crude corn kernel oil, confirming earlier reports that they were not extracted by hexane, and providing new information that they could be removed from ethanol-extracted corn kernel oil by conventional degumming, refining, bleaching, and deodorizing.     

Robust and Reliable Quantification of Phospholipids in Edible Oils Using 31P NMR Spectroscopy

Upon storage, crude plant oils will form a solid sediment called gum, which consists mainly of phospholipids (PL). PL are removed during the production of edible oils by a process called degumming. A higher yield is recognized as a major advantage of enzymatic degumming over traditional processes. Robust and accurate PL quantification methods are needed to develop and monitor enzymatic degumming processes. Several techniques, such as atomic emission spectroscopy, liquid chromatography, and thin-layer chromatography, have been applied for the quantification of PL in edible oils. In the past decade, ³¹P NMR spectroscopy has been shown to have advantages over these techniques because of the possibility of the simultaneous, fast, and accurate quantification of different PL directly in the oil. This article demonstrates the application of ³¹P NMR spectroscopy as a method for the quantification of all relevant PL and phosphorous-containing degradation products in crude and refined oils. In addition, the validation results show that this method is robust because the limit of detection is as low as 5 μmol/100 g oil. Variations of less than 5% were obtained for all P-containing compounds present in the oils at concentrations above 100 μmol/100 g oil.     

Wax composition of sunflower seed oils

Waxes are natural components of sunflower oils, consisting mainly of esters of FA with fatty alcohols, that are partially removed in the winterization process during oil refining. The wax composition of sunflower seed as well as the influence of processing on the oil wax concentration was studied using capillary GLC. Sunflower oils obtained by solvent extraction from whole seed, dehulled seed, and seed hulls were analyzed and compared with commercial crude and refined oils. The main components of crude sunflower oil waxes were esters having carbon atom numbers between 36 and 48, with a high concentration in the C₄₀−C₄₂ fraction. Extracted oils showed higher concentrations of waxes than those obtained by pressing, especially in the higher M.W. fraction, but the wax content was not affected significantly by water degumming. The hull contribution to the sunflower oil wax content was higher than 40 wt%, resulting in 75 wt % in the crystallized fraction. The oil wax content could be reduced appreciably by hexane washing or partial dehulling of the seed. Waxes in dewaxed and refined sunflower oils were mainly constituted by esters containing fewer than 42 carbon atoms, indicating that these were mostly soluble and remained in the oil after processing.     

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.     

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.     

Natural refining of extruded-expelled soybean oils having various fatty acid compositions

Simple, low-capital-investment oil refining techniques, which may also meet the needs of natural or organic food industries, were explored to process extruded-expelled (E-E) soybean oils with various fatty acid compositions. Most settled E-E oils are naturally low in phosphatides (<100 ppm phosphorus) and were easily water degummed to low phosphorus levels (<55 ppm). Free fatty acids were reduced to 0.04% by adsorption with 3% Magnesol^®. Magnesol reduced residual phosphorus contents to negligible levels. This material also adsorbed primary and secondary oil oxidation products. Our adsorption refining procedure was much milder than conventional refining, as indicated by little formation of primary and secondary lipid oxidation products and less loss of tocopherol. The remaining challenge to effective natural refining is the removal of off-flavor components. Our adsorption treatment reduced the natural flavor of soybean oil but flavor was still present, probably too strong for many consumers. Polyunsaturated oils oxidized more easily than did the other types of oils; therefore, precautions should be taken when refining such oils. High-oleic soybean oil, on the other hand, had excellent oxidative stability and better flavor characteristics after degumming and adsorption with Magnesol compared with other oils.     

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.     

Changes in the Composition of Tocopherols and Fatty Acids in Postdeodorisation Condensates during Refining of Various Oils

For refining of different plant oils the same industrial installations are used and the last stage is the process of deodorisation. The waste product obtained during the deodorisation process is the postdeodorisation condensate (oil scum). Oil scum contains several valuable components, such as polyunsaturated free fatty acids and tocopherols. Qualitative and quantitative composition of tocochromanols and free fatty acids depend on the kind of the refined oil. Postdeodorisation condensates from the refining of rape, sunflower and soybean oils were investigated. Prevailing acid in all postdeodorisation condensates was the oleic acid the quantity of which ranged from 50% to 58.7%. Second was the linoleic acid, which was found in quantity amounting to 20% during the refining of rape and soybean oils, but in the condensate coming from sunflower oil its content was by 10% greater. The results obtained during quantitative determination of tocochromanols correlated with their quantity in oils, but we observed greater distillation of γ-T and α-T than of δ-T. The reason for this is smaller quantity of δ-T in the oil which is undergoing the process of deodorisation.