Title of Invention

"A PROCESS FOR THE PRETREATMENT OF IMPROVED RICE BRAN OIL"

Abstract

A process for preparation of improved rice bran oil having characteristic such as herein described which process consists essentially of (a) removal of the glycolipids, more specifically the phosphorus containing glycolipids by treatment of the crude oil with an alcoholic solvent preferably by ethanol and isopropanol containing appropriate quantities of water in a ratio ranging from 1:1 to 1:5 at 25-30°C and separating alcohol-soluble and alcohol insoluble phases after setting for 5 to 20 h (b) treatment of the alcohol-insoluble phase at 25-30C once or twice with hot water (95C) (2-50% w/v), separating the precipitated waxes and gums and (c) subjecting the obtained product to conventional bleaching operation using activated bleaching clays and/or carbon to yield an improved rice bran oil containing 4-6 ppm of residual phosphorous content.

Full Text

Field of Invention The present invention relates to a process for the pretreatment of rice bran oil. More specifically, the present invention relates to a process for the pretreatment of rice bran oil for its fiirther processing by physical refining method. The pretreatment aims at the removal of the glycolipids present in crude rice bran oil. Some components of these glycolipids also contain phosphorus, as shovm by the present authors for the first time (unpublished observation). Owing to the presence of phosphorus containing glycolipids, crude rice bran oil can not be degummed by the known chemical methods to the levels required for physical refining of the oil. This process consists of an alcohol treatment of the crude oil whereby the glycolipids are removed, a simultaneous dewaxing/degumming process which was developed earlier in this laboratory (Kaimal, T.N.B., et al, Indian Patent No. 183639, 2000) and a bleaching step. The alcohols used were either ethyl alcohol or isopropyl alcohol. Background of the invention Rice bran oil is one of the most important vegetable oils. India is the second largest producer of rice (after China) and about 5,00,000 tons of rice bran oil is produced annually in India. Reference may be made with the rice bran oil which is considered to be very good for health as it has a balanced fatty acid composition and a high amount of nutritionally beneficial constituents like y-oryzanol, squalene, tocopherols, tocotrienols etc. (deDecker, E.A.M. and Korver, O., Nutrition Reviews, 54 (11), 1996, S120). In China and Japan rice bran oil is one of the most popular edible oils. However, it is unfortunate that only about 10% of the rice bran oil produced in India goes for direct human consumption. The need of the hour is to find a suitable process for refining of rice bran oil economically. Proper post-harvest technology for oil processing along with proper planning may produce good edible quality rice bran oil. This, in turn, will reduce « the ever-increasing gap between the demand and supply of edible oils in India and will save a considerable amount of foreign exchange. Rice bran oil can contain high amounts of free fatty acid (FFA) and in some cases it reaches 40% or more as the weight of the oil. High FFA entails huge loss of neutral oil occluded in the soap stock produced during conventional alkali neutralization process. For oils containing high FFA, physical refining is the preferred mode of processing. Practical experience with physical refining shows that it leads to desirable results only when a very good quality of starting material is used. For successfiil operation of physical refining efficient pretreatment steps are, therefore, of utmost importance. Critical requirements are very low levels of residual phosphorus and trace metals. For these reasons, the physical refining method is conventionally practiced only for oils and fats such as tallow, palm oil, palm kernel oil, coconut oil etc. which have very low phosphatide contents. There are no efficient pretreatment processes which would make all fats and oils amenable to physical refining irrespective of their initial quality (Forster, A. and Harper, A.J., J. Am. Oil Chem. Soc, 69, 1983, 265). Incomplete removal of undesirable components from the oil in the pretreatment steps can be compensated in some cases by increased bleaching earth usage in the bleaching step (Ohlson, R., J. Am. Oil Chem. Soc, 69, 1992, 195). Lower oil losses attained by steam refining compared to conventional alkali refining do not offset the oil losses due to the increased volumes of bleaching earth needed if proper pretreatments are not done (Balicer, Z., et al, Proceedings of 16th ISF Congress, Ed. J. Hollo, Akade'mini Kiado, Budapest, 1985, .393). The major emphasis, thus, has to be placed on preliminary processing of crude oil prior to steam refining. This should be aimed at removal of any component of the oil that may darken the color or undergo other adverse alterations during the high temperature operation and thus, deteriorate the quality of the oil. It is truly said that technology of physical refining is more about how to remove gums and other impurities in upstream processing, i.e, in degumming and bleaching (Norris, F. A., in Bailey's Industrial Oil and Fat Products, Vol. 3. ed. by T. H. Applewhite, John Wiley & Sons, NY, 1985). The development of physical refining technique, therefore, is more dependent on the development of the pretreatment methods. Degumming is the first step whereby the crude oil is subjected to treatment before the operation of removal of free fatty acid is undertaken. Degumming primarily removes phospholipids and other mucilages from oil and quality of the degummed oil is generally judged by its phosphorus and trace metal contents. If not removed effectively in the initial stages, these impurities may eventually interfere with the subsequent refining steps. Phospholipids present in oils are broadly classified as hydratable and non-hydratable types. While hydratables are removed from oil by a simple water degumming step, non-hydratables need some special treatment. Phosphoric acid and citric acid are commonly used in practice to remove non- hydratable phosphatides. However, as they are not soluble in oil, these acids must be thoroughly mixed to achieve the desired results. Reference may be made to the earlier stages of development of physical refining, the importance of removing phosphatides before bleaching was not fully realized. The « usual practice was to use more bleaching earth; but, even then the finished oil quality was rarely acceptable. The palm oil boom in Malaysia provided the real breakthrough in physical refining in the 1970's. However, the quality assurance for the final products could not be provided during that period (Carlson, K.F., in Bailey's Industrial Oil and Fat Products, Vol 4, fifth edition, ed. by Y.H. Hui, John Wiley & Sons, NY, 1996). More recently, the concern about the effects of various industries on the ecosystem has been increased significantly. Environmental Protection Agencies (EPA) are being set up by different countries and stringent laws are being enforced to guard the environments. The most serious consequences for the edible oil industry was the tightening of the limits of trade effluents and the principal problem was the pollution resulting from the acidulation of soapstocks from chemical refining. With no soapstock production, the physical refining process once again became more attractive. The entire 1980's saw the incorporation of a number of new degumming processes and the use of newer adsorbents in the pretreatment steps for physical refining. References may be made to the development of various types of degumming processes. Alcon process was developed to attain the trading specifications of soybean oil by water -degumming (Kock, M., in Proceedings of Second ASA Symposium on Soybean Processing, American Soybean Association, 1981). Later it was extended to steam refining of oils (Penk, G., Paper presented at the ISF-AOCS World Congress, in Tokyo, 1988). Dry degumming method was slightly modified by replacing a part of the bleaching earth by a synthetic silica hydrogel, Trisyi (Welsh, W.A. and Parent, Y.O., Eur. Pat. EP 0185 182, 1986) to get an oil fit for physical refining. A variety of modifications of the acid degumming was also suggested (Mag, T.K. and Reid, M.P., U.S. Patent 4,240,972, 1980; Carlson, K.F., in Bailey's Industrial Oil and Fat products. Vol. 4., fifth edition, ed. by Y.H. Hui, John Wiley & Sons Inc., New York, 1996). Superdegumming was developed by Unilever (Segers, J.C, Fette Seifen Astrichum., 84, 1982, 543) and later modified by others (Kaji, T., Eur. Pat. EP 0269, 277, 1988; Van de Sande, R.L.K.M. and Segers, J.C, Eur. Pat. EP 0348004, 1989). Another group of scientists had developed total degumming process, popularly known as TOP degumming (Dijkstra, A.J. and Van Opstal, US 4,698,185, 1987). It was claimed that this process was useful to reduce phosphorus and iron level to attain the quality of the oil which might go for physical refining (Dijkstra, A.J., in Proceedings of World Conference on Oilseed Technology and Utilization, held in Budapest, Hungary, ed. by T.H. Applewhite, AOCS, Champaign, Illinois, 1993, 138). Two major developments in the recent years in degumming technologies are enzymatic degumming and membrane degumming. The enzymatic degumming, known as EnzyMax process was developed by enzyme producer Rohmand contractor Lurgi (Penk, E., et al., Eur. Pat. EP. 0513709, 1992). It was claimed that this process may reduce the phosphorous level close to 4 ppm irrespective of the quality of the starting material (Dijkstra, A.J., Proc World Conference On Oilseed Technology and Utilization, held in Budapest, Hungary, Ed. By T.H. Applewhite, AOCS, Champaign, Illinois, 1993, 1380). However, data are not available for rice bran oil. Commercial scale operations are being explored now mainly for soybean oil. Membrane degumming is still in its infancy and commercial production is yet to commence. The major drawback of the known degumming methods lies in the fact that those could not be applicable to physical refining of rice bran oil. In the case of crude rice bran oil all these degumming methods, including enzymatic degumming failed to produce an oil of low phosphorus content suitable for physical refining. The simultaneous dewaxing/degumming method developed in this laboratory (Kaimal, T.N.B., et al, Indian Patent No. 183,639,2000) also could not achieve the requirements of the physical refining of rice bran oil. The present authors traced the difficulties in achieving this to the presence of novel phosphorus containing glycolipids (unpublished observation). The main objective of the present invention is to provide a pretreatment process for physical refining of rice bran oil which obviates the drawbacks of the other pretreatment processes as detailed above. Another object of the present invention is to remove the wax present in crude rice bran oil to acceptable levels. Still another object of the present invention is to reduce the free fatty acid content of the oil to a level that will drastically reduce the refining loss. Statement of Invention Accordingly the present invention provides a pretreatment process for rice bran oil so as to provide an oil suitable for physical refining and which process consists essentially of (a) removal of the glycolipids, more specifically the phosphorus containing glycolipids by ttreatment of the crude oil with an alcoholic solvent exemplified by ethanol and isopropanol containing appropriate quantities of water so as to reduce the solubility of the triglycerides of the oil in the alcoholic solvent and in a ratio ranging from 1:1 to 1:5 such that the glycolipids are extracted completely into the solvent and which treatment is carried out at 25-30°C and separation of alcohol-soluble and alcohol insoluble phases after settling at a suitable temperature below this temperature for 5 to 20 h (b) treatment of the alcohol-insoluble phase at 25-30°C once or twice with hot water (~95*'C) (2-50% w/v), separating the precipitated waxes and gums and (c) subjecting the product to conventional bleaching operation using activated bleaching clays and/or carbon to yield an oil containing 4-6 ppm of residual phosphorus content. Details of the invention It is observed that, unlike other vegetable oils, rice bran oil can hold its own volume of water separating out from the oil. This is a unique feature and a very strong emulsion can be formed easily by mixing hot water with crude rice bran oil. This behavior was utilized to evolve a process where simultaneous degumming and dewaxing could be achieved for rice bran oil (Kaimal, T.N.B, et. al, Indian Patent No 183,639, 2000). The process was found to be efficient, economic and convenient to remove both the gums and waxes in a single step. However, the resultant phosphorus content was not low enough for physical refining of the oil. The phosphorus content is not reduced to below 45 ppm where as, phosphorous content of less than 20 ppm is essential before bleaching to attain the quality of oil for physical refining (Cmolik, J and Pokomy, J., Eur. J. Lipid Sci. Technol. 102, 2000, 472). In a variation of the method, in the present invention, the crude rice bran oil was subjected to an initial alcohol treatment, followed by the simultaneous degumming and dewaxing and then bleaching. The quality of oil obtained after bleaching was found to be amenable for physical refining. In another striking observation, it was found that the main difficulties in obtaining rice bran oil of low phosphorus content suitable for physical refining, arise from the presence of phosphorus containing glycolipids, identified for the first time in this investigation (Paper to be commimicated). Crude rice bran oil has an unusually, high content (about 6%) of glycolipids. Though various types of complex glycolipids have been described in literature (Fujino, Y. et al, Chem. Phys. of Lipids, 17, 1976, 275), the presence of these phosphoglycolipids in rice bran oil has escaped the attention of the earlier researchers. The difficulty in producing an oil of low phosphorus content by degumming points to these compounds which are unaffected by known degumming methods. In the present invention, the solubility of polar lipids (phospholipids and glycolipids) in the polar hydrophilic solvents like alcohols, where these molecules form an extensive hydrogen bonding, was utilized to reduce the phosphorus level of the pretreated oil to such an extent that it can go for bleaching and subsequently for physical refining. During the solvent partition most of the free fatty acids, phospholipids and glycolipids (in particular, phosphorus containing glycolipids) migrate from non-polar lipid pheise into polar solvent phase. Ethanol and isopropanol are suitable solvents for this step. This results in the removal of more than 50% of phosphatides, near total removal of glycolipids and 60-75% of FFA from the oil. In the simultaneous degumming/dewaxing step which follows the extraction step, further removal of phosphatides and glycolipids takes place, whereby the phosphorus content in degummed and dewaxed oil is reduced to near 10 ppm. During this process substantial amount of wax is also removed along with phosphatides. This is followed by conventional bleaching step, where the residual phosphorus and wax content is reduced further to about 4-6 ppm thus satisfying the critical requirements of physical refining. The following examples are given by way of illustrations and therefore, should not be construed to limit the scope of the present invention. Example: 1 One himdred grams of crude rice bran oil having initial phosphorus content of 358 ppm, free fatty acid content of 7.98%, oryzanol content of 1.35% and having a color value of 32.6Y + 5.2R + 0.2B (inlcm. Cell, Lovibond) was extracted with isopropanol containing 12% water (w/w). The oil and isopropanol-water mixture was taken in the ratio of 1:2 (w/v). The oil was mixed with two hundred milliliter of the isopropanol-water mixture in a separating funnel of five hundred milliliter capacity. The content was shaken thoroughly for thirty minutes to ensure proper mixing. Then the mixture was kept for settling in the refrigerator at lO^C for five hours. TTie two layers formed were separated. The layer which was insoluble in isopropanol was taken for further investigation. The insoluble oil layer was desolventized first on a rotary evaporator, followed by further desolventization at 110°C for about Ihr. under high vacuum to remove traces of solvent. The weight of the oil obtained was 88.2 grams. The analytical data showed that the free fatty acid content was reduced to 2.88%, the phosphorus content also was reduced to 179.5 ppm and most of the oryzanol was retained (1.24%). In the next step of the invented process, the simultaneous degumming and dewaxing of the insoluble oil was done as described in the earlier patented process (Kaimal, et al., Indian Patent No 183,639, 2000) with only 5% water (w/v). After simultaneous degumming and dewaxing it was found that the phosphorus content of the oil was drastically reduced to 10.2 ppm. There was no change in FFA content and Oryzanol content and the colour was found to be 29.4 Y+ 5.0R+ 0.2B (detemined in 1 cm. cell, Lovibond). In the third step of the invented process the oil was subjected to conventional bleaching with 3% bleaching earth (Tonsil) and 0.5% activated carbon under high vacuum at 110°C for an hour. The resultant oil after filtration was found to have the phosphorus content of 4.7 ppm. This oil is amenable for physical refining. Example: 2 In a similar experiment ethanol (Ethyl alcohol) was used as extracting solvent instead of isopropanol. In this experiment also, one hundred grams of crude rice bran oil having initial phosphorus content of 358 ppm, free fatty acid content of 7.98%, oryzanol content of 1.35% and having a color value of 32.6Y + 5.2R + 0.2B (in 1 cm. Cell, Lovibond) was taken and this was extracted with ethanol. The oil was mixed with two hundred milliliter of the ethanol in a separating funnel of five hundred milliliter capacity. The content was shaken thoroughly for thirty minutes to ensure proper mixing. Then the mixture was kept in the refrigerator at lO^C for five hours. The two layers formed were separated. The layer that was found to be insoluble in ethanol was taken for further investigation. The insoluble oil layer was desolventized first on a rotary evaporator, and was followed by further desolventization at 110°C for about Ihr. under high vacuum to remove traces of solvent. The weight of the oil obtained was 79.6 grams. The analytical data showed that the free fatty acid content was reduced to 2.64%, the phosphorus content also was reduced to 186.5 ppm and the oryzanol content was found to be 1.18%. In the next step of the invented process, the simultaneous degumming and dewaxing of the insoluble oil was done as according to the process described by Kaimal, et, al (Indian Patent No 183,639, 2000) with only 5% water (w/v) as in Example 1. After simultaneous degumming and dewaxing it was found that the phosphorus content of the oil was reduced to 10.8 ppm. There was no change in FFA content and Oryzanol content and the colour was found to be 30.2 Y+ 5.0R+ 0.2B (detemined in 1cm. cell, Lovibond). In the third step of the invented process the oil was subjected to conventional bleaching with 3% bleaching earth (Tonsil) and 0.5% activated carbon under high vacuum at 110°C for an hour. The resultant oil after filtration was found to have the phosphorus content of 5.8 ppm. This oil is quite good for physical refining. Example: 3 In another experiment of a comparatively larger sample size, one thousand grams of crude rice bran oil having initial phosphorus content of 455 ppm, free fatty acid content of 17.52%, oryzanol content of 1.68% and having a color value of 36.2Y + 6.1R H- 0.2B (in 1 cm. Cell, Lovibond) was subjected to partioning with an azeotropic mixture of isopropanol and water (12% w/w of water) as described in Example 1. The oil was mixed with two liters of the azeotropic mixture of isopropanol and water in a separating funnel of five liters capacity. The content was shaken thoroughly for thirty minutes to ensure proper mixing. Then it was kept for settling at 10°C for five hours. The two layers formed were separated. The layer, which was insoluble in isopropanol, was taken for further investigation. The insoluble oil layer was desolventized first on a rotary evaporator, and ftirther desolventized at 110°C for about Ihr. under high vacuum to remove traces of solvent as mentioned earlier. The weight of the oil obtained was 878.2 grams. The analytical data showed that the free fatty acid content was reduced to 6.55%, the phosphorus content also was reduced to 196.5 ppm and most of the oryzanol was retained (1.38%). In the next step of the invented process, the simultaneous degumming and dewaxing of the insoluble oil was done as described earlier by using 5% (w/v) of water. After simultaneous degumming and dewaxing it was found that the phosphorus content of the oil was drastically reduced to 13.4 ppm. 1 e was no change in FFA content and oryzanol content and the colour was four a be 33.4 Y+6.2R+0.2B (detemined in 1 cm. cell, Lovibond). In the third step, the oil was subjected to conventional bleaching with 3% bleaching earth (Tonsil) and 0.5% activated carbon under high vacuum at 110°C for an hour. The resultant oil after filtration was found to have the phosphorus content of 6.2 ppm. Table-1 Characteristic Properties of Rice Bran Oil Samples (Table Removed) * same sample was taken for processing with isopropanol and ethanol at 100 grams scale Notes: 1. The color readings were recorded on Lovibond Tintometer at 45°C. 2. Phosphorus content was determined according to the lUPAC method No. 2.421. 3. The free fatty acid content of oils are determined by AOCS method Ca-5a-40. 4. Oryzanol content is determined by the method described by Rogers, E. J. et al, in Journal of American Oil Chemists' Society, Volume 70, No. 3 (1993), 301. Table-2 Characteristic of Oil Samples Insoluble in Isopropanol/Ethanol (Table Removed) Table-3 Characteristic of Oil Samples Insoluble in Isopropanol/Ethanol and then Degummed and Dewaxed with 5% Water (Table Removed) Table-4 Characteristics of the Oil Samples (Insoluble in Isopropanol/Ethanol, Degummed, Dewaxed, and Bleached) (Table Removed) The main advantages of the present invention are: !. The present method provides a novel pretreatment process for the physical refining of crude rice bran oil which, otherwise, is not amenable for physical refining. 2. During simultaneous dewaxing and degumming process, a substantial reduction of waxes along with residual gums takes place, thus, the processing steps were reduced 3. A further advantage of current method is the considerable reduction of free fatty acid in the oil. 4. Alcohol fractionation of the oil produces a small fraction from which the biologically active glycolipids can be economically separated. and so on. We Claim: 1. A process for preparation of improved rice bran oil having characteristic such as herein described which process consists essentially of (a) removal of the glycolipids, more specifically the phosphorus containing glycolipids by treatment of the crude oil with an alcoholic solvent preferably by ethanol and isopropanoi containing appropriate quantities of water in a ratio ranging from 1 : 1 to 1 : 5 at 25 - 30°C and separating alcohol-soluble and alcohol insoluble phases after settling for 5 to 20 h (b) treatment of the alcohol-insoluble phase at 25-30C once or twice with hot water ( 95C) ( 2-50% w/v), separating the precipitated waxes and gums and (c) subjecting the obtained product to conventional bleaching operation using activated bleaching clays and/or carbon to yield an improved rice bran oil containing 4-6 ppm of residual phosphorous content. 2. A process as claimed in claim 1 wherein the alcohol used is either ethanol or isopropanoi. 3. A process for preparation of improved rice bran oil substantially as herein described with reference to the examples accompanying this specification.

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