Reducing Oil Losses in Alkali Refining

Neutralization is an important step in the chemical refining of edible oils. Free fatty acids (FFA) are generally removed in neutralization as sodium soaps but neutral oil is also entrapped in the emulsion and removed with the soap during centrifugation. Thus, alkali neutralization causes a major loss of neutral oil in the chemical refining of edible oils. The effects of demulsifiers (NaCl, KCl, Na₂SO₄ and tannic acid) on reducing alkali refining losses of refined palm, soybean, and sunflower oils (used as model oils) incorporated with FFA from rice bran oil were investigated. Adding small amounts of demulsifiers to the alkali neutralization step significantly reduced neutral oil loss of these model oils. All demulsifiers except for tannic acid had similar effects on refining losses in all oil model systems. The optimum demulsifier content was 1.0 % (w/w of oil).     

Physical refining of edible oils

Physical refining of edible oils offers several advantages over alkali refining. The method described for physical refining of rapeseed oil involves several novel factors, including the availability of cold-pressed rapeseed oil low in phosphatide content and deacidification/deodorization in a film molecular evaporator. Parameters are presented from a pilot plant unit with an output of 500 metric tons per year. Further applications of the technology are proposed, including the processing of oils to pharmaceutical-grade products.     

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.     

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.     

Effects of plant‐scale alkali refining and physical refining on the quality of rapeseed oil

The physical refining of soybean oil was introduced as an energy saving and environmentally friendly procedure alternative to the traditional alkali refining, and the process was successfully applied to other vegetable oils. We had compared the two procedures in industrial refining under conditions, which enable a clear comparison. In nine plant‐scale experiments, crude rapeseed oil, taken from the same tank of crude oil, was processed on the same day both by alkali refining and by physical refining. Quality changes (free fatty acids, peroxide value, conjugated fatty acids, polar lipids, minor constituents) were determined, and also their stability against oxidation (Rancimat and Schaal Oven Test), and the fatty acid composition. In refined oils, the sensory acceptabilities and the sensory profiles were assayed. Finally deodorized oils, produced by the two methods, did not appreciably differ in their sensory characteristics and chemical composition, excepting slightly higher concentration of isomeric polyunsaturated fatty acids in physically refined oils. During storage for one year in commercial packagings at 15 °C, oxidative and sensory changes were negligible.     

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.     

Perspectives on processing methods,equipment and procedures

World population growth and increasing per capita consumption will place significant demands on the food oils industry in the coming years to maimize efficiency of raw material use and to optimize processing operations. Other demands on the processor of food oils center on resolving issues that are already impacting on the industry, i.e., energy conservation, pollution abatement, and diminishing reserve of petroleum-based resources. Research now in progress in the laboratory may form the basis for the industry response to these challenges. Innovative methods of raw material preparation will be needed to obtain a higher quality oil. Alternative solvent processing could use alcohol or aqueous extraction or supercritical fluids. Each of the processing techniques used to produce a finished edible oil from crude oils, from degumming through alkali refining and bleaching to deodorization, is subject to change, and the form of these changes can be perceived from the directions of current research. Formulation of solid fats from liquid oils may see a shift from metal-catalyzed reactions to the use of immobilized enzymes. Implementation of many of the process changes will depend on equipment development and application of advanced engineering concepts to assure their assimilation into the food oil industry. By projecting the successful integration of the chemical, process design and engineering sciences, a realistic picture of the year 2000 can be formulated.     

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.     

Effects of Crude Rice Bran Oil Components on Alkali-Refining Loss

The effects of minor components in crude rice bran oil (RBO) including free fatty acids (FFA), rice bran wax (RBW), γ-oryzanol, and long-chain fatty alcohols (LCFA), on alkali refining losses were determined. Refined palm oil (PO), soybean oil (SBO) and sunflower oil (SFO) were used as oil models to which minor component present in RBO were added. Refining losses of all model oils were linearly related to the amount of FFA incorporated. At 6.8% FFA, the refining losses of all the model oils were between 13.16 and 13.42%. When <1.0% of LCFA, RBW and γ-oryzanol were added to the model oils (with 6.8% FFA), the refining losses were approximately the same, however, with higher amounts of LCFA greatly increased refining losses. At 3% LCFA, the refining losses of all the model oils were as high as 69.43–78.75%, whereas the losses of oils containing 3% RBW and γ-oryzanol were 33.46–45.01% and 17.82–20.45%, respectively.     

Physical refining

By reviewing current commercial physical refining processes a prospectus is suggested for the future objectives in this field of edible oil processing. The paper reviews widely used physical refining processes for the relatively high free fatty acid (FFA) laurics and palm oil and a commercial operation for physical refining of maize and sunflower oils. In addition, the relatively new departure of physical refining of soybean oil is discussed using data from recent development work. This system is used to demonstrate present trends in the development sector of the industry. Reference to similar work on pretreatment of rapeseed oil is included. The discussion is used to suggest guidelines for design of a flexible physical refining system for application to major oils processed by European refiners. There is still no physical refining process that can handle successfully on a commercial scale all qualities of soybean oil. We must envisage a system of physical refining that is able to deal with the most difficult soybean oil and thus assume it will handle all the less difficult oils.     

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.     

Removal of copper from hydrogenated soybean oil

Hydrogenation with a copper-chromite catalyst at 170 C, 30 psi, increased the copper content of a refined, bleached soybean oil from 0.02 to as much as 3.8 ppm. Removing residual copper from soybean oil is essential to the successful use of copper catalysts for selective hydrogenation. Various methods were examined to remove this copper, including alkali refining, bleaching, acid washing, citric acid treatment and cation-exchange resin treatment. Properly conducted, each of the methods except alkali refining gives 95% or higher removal of copper introduced during hydrogenation. Ion exchange appears to be the most economical, but addition of about 0.01% citric acid during deodorization may be needed to inactivate traces of unremoved copper. Soybean oil hydrogenated with a copper-chromite catalyst, bleached or treated with an ion-exchange resin and deodorized with 0.01% citric acid added had low AOM peroxide values and acceptable flavor scores after eight days at 60 C which indicate that removal of residual copper from the oil should be adequate for the production of stable oils low in linolenic acid content. Presented at AOCS Meeting, Chicago, October 1967.     

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.     

The effect of processing conditions upon the nutritional quality of vegetable oils

On the basis of the chemical, physical, and biological criteria used, all of which have been shown to be sensitive indicators of heat damage to oils, it must be concluded that the overall nutritional quality of an oil is not adversely affected by alkali refining, adsorptive decolorizing, or deodorization; that higher temperatures of deodorization (238C) produce oils nutritionally equivalent to those deodorized at lower temperatures (160C); and that the normal processes used in manufacturing edible oils improve the resistance of these oils to heat damage. Presented at the 6th Congress of the International Society for Fat Research, London, 1962.     

Degumming,dewaxing and refining

Degumming, dewaxing and refining are aimed at removing certain fat-soluble impurities. The different operations can be done separately or in various combinations depending on, e.g., the type of feedstock and the desired refining result. State-of-the-art of water degumming and chemical (alkali) refining are discussed with special emphasis on quality and yield of products and byproducts. Dewaxing, which is of special interest for some oils such as sunflower oil, maize oil and ricebran oil, can be performed either by a filtration process or by centrifugal separation in connection with water degumming or alkali refining.     

Trace metal contents,chemical properties and oxidative stability of capelin and herring oils produced in norwegian plants

The iron and copper contents of 14 crude capelin oils, two herring oils and one blend produced in oil meal plants in northern Norway were determined by atomic absorption spectroscopy (AAS). Their oxidative stability, peroxide (PV), benzidine (BV) and iodine values (IV), free fatty acids (FFA) and tocopherol contents were also evaluated. The oxidative stability was found to be more dependent on the tocopherol content and BV of the crude oils than on their content of trace metals. Changes in iron, copper and nickel contents were determined by AAS after refining and hydrogenation of marine oils in two Norwegian hydrogenation plants. The content of trace metals in the oils and hydrogenated products decreased as a result of alkali refining and bleaching to the lower limits of detectability by the method used, and amounted to 0.01 (oils), 0.02 and <0.3 ppm for iron, copper and nickel respectively.     

Physical refining of edible oil

Physical refining of edible oils has received renewed interest since the early 1970s when the process was reintroduced on a large scale to refine palm oil in Malaysia. Subsequent laboratory and field tests have also shown that physical refining can be used as a substitute for caustic or chemical refining, not only for high free fatty acid (FFA) oils such as palm, but also on low FFA oils such as soybean oil. In either case, the physical refining system results in lower oil loss than chemical refining and also eliminates pollution problems associated with soapstock acidulation. In physical refining, however, the oil pretreatment and efficiency of the distillation are two very important factors that must be considered to guarantee continuous production of high quality products. This paper reviews the physical refining system as it is today and how it can be used on two different edible oils. An actual case study showing the effects of the pretreatment in a commercial operation is also presented. Presented at the 73rd AOCS annual meeting, Toronto, 1982.     

Trace metal content of a herring oil at various stages of pilot-plant refining and partial hydrogenation

Samples of a typical Atlantic herring oil at various stages of pilot-plant processing were analyzed for cadmium, selenium, arsenic, mercury, copper, lead, and zinc. The FAO/WHO Codex Alimentarius requirements for low levels of specific metals in edible oils were always difficult to meet completely in either a washed and bleached oil or in two lots of oil processed from one crude oil by the additional steps of partial hydrogenation and deodorization. The mercury content of the crude oil was relatively low and was not greatly affected by processing. The selenium level of 47 ppb in the crude oil was significantly lowered by hydrogenation and deodorization. Arsenic was removed by alkali refining. The lead content was reduced by only 40% upon refining, probably because lead was present as an organometallic material. The concentration of the other heavy elements was generally lowered during processing.     

Determination of free fatty acids and diacylglycerols in native vegetable oils

The analysis of free fatty acids (FFA) and diacylglycerols (DG) by GLC may be used to detect the deacidification of oils. Free fatty acids are removed from the oil during neutralization or physical refining, while the corresponding DG remain in the oil. This will change the ratio of FFA to DG. For analysis, oils with tricaprin as internal standard are silylated and injected on-column onto a short high-temperature capillary column. Extracted oils showed higher amounts of FFA and DG than pressed oils from the same batch of seeds. There are only minor changes in the ratio of FFA to DG according to the yield of pressing or due to washing the oil.     

Iodine values of acidulated coconut oil soapstock

Summary Analyses and comparisons of a number of representative samples have shown that acidulated coconut oil soapstock may have an iodine value as much as 100% greater than that of the corresponding refined oil without any contamination being involved. Exactly what the spread between any given soapstock and oil will be apparently depends on the free fatty acid content of the original crude oil and the relative efficiency of the refining process. It was found that, for coconut soapstocks produced by standard laboratory refining tests, the relation between free fatty acid content and iodine value spread can be represented by the formula I.V. Spread=9.5–759 FFA. The efficiency of the refining process affects results insofar as it reduces the entrainment of neutral oil. Removing all of the neutral oil from four laboratory-produced soapstocks prior to acidulation raised the iodine value approximately two units in all cases. The practical significance of these results is obvious. A refiner processing high grade crude coconut oil of 9.5, iodine value by a highly efficient refining procedure cannot be expected to produce an acidulated soapstock of less than about 18.0 in iodine value. With higher free fatty acid crude oil and less efficient refining procedures lower iodine values are possible, but since soapstock is of minor economic value compared to refined oil, the trend will always be toward better grade crude oils and more efficient refining processes.