1. Field of the Invention
This invention pertains to a process for the extraction of oils from grain materials such as rice bran, wheat mill feed, rapeseed, amaranth and similar grains. The process not only provides a method of oil extraction, but provides for the separation of saturated from unsaturated oils. A specially designed apparatus is used to achieve this separation. Use of the process not only provides the extracted oil, but also enables production of a number of grain products having low residual oil contents, which products have particularly desirable food and feed characteristics.
The process for oil extraction applicable grain materials can also be applied to crushed or flaked vegetable matter and to grain-based food products which are somewhat porous, such as chips, noodles and crackers.
2. Background of the Invention
It is known that the best and easiest oilseed to process is soy bean. Rapeseed have also been processed on the kind of equipment used to process soy bean; however, they have been ground, cooked, and rolled into flakes to provide an extractable bed. Generally rapeseed flakes can be run only at a much slower rate than soy beans. The resultant rapeseed and rapeseed residual material after oil removal, called "Marc", cannot readily be used as meals for animal feeding due to the presence of trypsin inhibitors, high euric acid and high glucosinolates.
The process and apparatus of the present invention can be used to process oil seeds such as soy bean and safflower; however, the process was designed particularly for obtaining oil from grain materials such as rice bran, wheat mill feed, rapeseed and amaranth (as well as similar grains). These grain materials do not have as high an oil content as soy bean and safflower and have not been economically competitive as an oil source prior to the present process. Typically, oil seeds contain from about 15 percent to about 40 percent by weight oil. Grains of the kind described above contain only from about 4 percent to about 20 percent by weight oil, and prior to the method of the present invention, processing of grain materials having this low oil content was not competitive with processing of oil seeds. The present oil extraction method makes possible not only the extraction of oil from grain materials, but further extraction of additional oils from crushed or flaked vegetable materials previously oil extracted using a less efficient method of extraction, such as crushed peanuts or olives. The present oil extraction method also enables additional oil extraction from grain-based products such as chips, noodles and crackers, by way of example and not limitation.
In addition to having a lower oil content, the grains frequently require special processing in preparation for oil removal, and when a grain oil source such as rice bran is used, the rice bran itself has a limited shelf life before the oils begin to degrade, due to particularly active enzymes present in the bran. Thus, there are particular handling requirements and processing requirements necessary to enable the use of such grain materials as a source for edible oils.
Most oil seeds are extracted by soaking them in liquid Hexane. The hexane and oil mixture, is called "Miscella". The oil is then separated from the miscella by a process of distillation, and the hexane solvent is recovered for recycle use in the separation process. The Marc which remains after removal of the oil from the seeds is generally a powder and contains substantial amounts, up to about 40 percent, of hexane. The Marc is then "dried" to recover the residual hexane. Recovery of the hexane from the Miscella and from the Marc are both energy intensive processes and require extensive capital equipment.
As previously discussed, rapeseed have been processed on soy bean equipment; they have been ground, cooked and rolled into flakes prior to oil extraction. Even then, the process rate in oil seed processing equipment was marginally cost effective compared with soy bean. Other potential grain material sources of oil include wheat mill feed, amaranth, and rice bran, for example. Wheat mill feed is the material removed from wheat during milling. Twenty percent or more of all the world's wheat ends up as mill feed. Most of this goes into pet food and animal feed. Amaranth, another potential source of oil, known in the midwest as "pig weed", grows wild. The amaranth cultivars, i.e. the plants and hybrids are available to anyone through the U.S.D.A. Wheat mill feed and amaranth can both be extruded into an extractable pellet because they contain sufficient amounts of starch and sugars. The pellets can be processed on standard soy bean equipment, but the hexane solvent typically used for extraction also extracts large quantities of green chlorophyll so that the oil is difficult to refine as well as being dark green, almost black in color. Rice bran requires a particularly specialized process. The rice bran cannot easily be flaked or made into an extrudable pellet because of lack of starch and the presence of sucrose. Rice bran can be extruded if corn starch is added, but the sucrose can caramelize if heated in the presence of air, giving a dark hue to the oil product. Rice bran can be extracted with hexane using an extractor of the type used to process soy beans, but this process is comparatively slow, energy intensive and expensive when compared to soy beans.
There are numerous known apparatus and processes for extracting oil from vegetable matter. Examples of these are described below in references which were uncovered during a review of background art related to the present invention.
U.S. Pat. No. 2,448,729 to A. K. Ozai-Durrani, issued Sep. 7, 1948, describes a method of processing rice bran and rice polish to separate therefrom the valuable vegetable oil content thereof. The rice bran or polish or mixtures of the two is subjected to an agglomeration step immediately, or within a relatively short time interval, after the bran and polish have been removed from the rice grain. The natural sugars, starches and glutens of the rice bran are partially soluble in water and are used to aggregate the material into porous aggregates suitable for oil extraction processes. Typically the aggregate material is extruded into elongated relatively thin strips. The aggregated rice bran or polish in then extracted using a vegetable oil solvent, preferably hexane, under a reduced pressure or in the presence of an inert gas such as nitrogen or carbon dioxide, and at a maximum temperature of about 140.degree. F. to avoid decomposition of the vitamin and food values of the material.
U.S. Pat. No. 2,538,007 to E. B. Kester, issued Jan. 16, 1951, discloses a method for stabilization of brown rice, and particularly for the prevention of rancidity in brown rice. The brown rice, in a hulled condition, consisting of the endosperm, the germ, and the bran layers, is stabilized by extracting the "free oil" (oil which can be extracted without grinding the rice) using a solvent such as benzene, carbon tetrachloride, butane, hexane octane, and mixtures of hydrocarbons such as gasoline, petroleum ether, Stoddard solvent, benzene, naphtha, and other fat-containing solvents.
U.S. Pat. No. 2,727,914 to E. A. Castrock et al., issued Dec. 20; 1955, describes the solvent extraction of rice bran to produce bran oil. In particular, the rice bran is subjected to a mild heat treatment to make the oil more easily extractable. The rice bran particles are cooked while controlling their moisture content so that, at least at an early stage, the particles contain between about 14% to 26% by weight moisture. The cooking temperature is increased from about 170.degree. F. to about 235.degree. F. in the final stage, at which time the moisture content has decreased to between about 6% to about 18%, by weight. The resulting bran particles are then exposed to a relatively cool atmosphere conducive to the evaporation of moisture until they undergo a substantially uniform decrease in temperature to below about 130.degree. F. and a moisture content ranging from about 2% to about 4%. The treated rice bran particles are then mixed with a solvent for rice bran oil and the resulting slurry is filtered to separate the rice bran particles from the miscella. Solvents recommended for extraction include commercial hexanes, methylpentanes and trichloroethylene.
U.S. Pat. No. 2,829,055 to A.K. Ozai-Durrani, issued Apr. 1, 1958, pertains to a method of treating rice paddy or hulled rice grains to remove the rice oils and fats from the bran and polish coatings of the rice. The process for removing the rice oil content of the bran coating on dehulled rice grains comprises immersing the whole grains in a solvent consisting of a low specific gravity petroleum fraction for a time interval at a temperature less than the boiling point of the solvent, to obtain extraction of the significant portion of the rice oil content of the bran coating. In another embodiment of the invention, the removal of the hulls from the rice paddy is accomplished as a sequence of the defatting treatment. The rice paddy is extracted with an organic solvent, and the majority of the solvent, containing oils, is removed. The solvent is removed by drainage, with residual solvent being removed from the rice grains either by vacuum distillation, or by heating the grains to a temperature above the boiling point of the solvent, or by exposing the grains to a current or blast of air. The solvent-containing paddy is then shocked by suddenly increasing the temperature by between about 10.degree. C. and 50.degree. C. to substantially the flash point of the solvent and then igniting the solvent with a flame or spark, to burn the hulls, which fall from the rice kernel, leaving the kernel intact and unbroken.
U.S. Pat. No. 3,261,690 to T. B. Wayne, issued Jul. 19, 1966, relates to improvements in the milling of rice and barley which greatly reduces the breakage of rice grains during the milling. In general, the bran is milled from brown rice in the presence of a solvent effective to extract fatty components from the rice and germ. The bran may be softened with a liquid bran-softening agent used in combination with a volatile organic solvent effective to extract fatty components from the bran and germ. Examples of softening agents include non-toxic oils such as highly refined mineral oils and edible vegetable oils, as well as naturally occurring or synthetic esters of glycerol, propylene glycol, polypropylene glycol or sorbitol with fatty acids. Among preferred extraction solvents are low boiling, highly refined petroleum fractions such as n-hexane and n-heptane. In addition, polar solvents such as alcohols and ethers may be used. Chlorinated hydrocarbons may also be used.
U.S. Pat. No. 3,271,160 to G. A. Kopas et al., issued Sep. 6, 1966 describes a process for preparing feed from undecorticated oil free safflower seed residue. The safflower seeds are crushed or otherwise broken open to get access to the oil inside them, which oil is solvent extracted using known techniques, preferably with hexane. The improvement provided by the invention is that the meat of the residual seed materials, after extraction, can be separated from the hulls by subjecting the relatively dry residual seeds to impact--either pneumatically or by shooting it in an air stream through a gun at a target or mechanically, as in a vertical or horizontal impact mill or similar device. Since the meat particles are fractured more than the hulls, a classification by size alone can be used to separate the products into markedly different protein content compositions.
U.S. Pat. No. 3,852,504 to Mihara et al., issued Dec. 3, 1974, describes a process for complete separation of constituents of rice-bran and the like. All the constituents of seeds and brans of cereal grains, especially rice bran, are recovered by mixing the same with an excess of an aqueous acid solution, pulverizing the mixture, separating an emulsified solution of the dissolved phytin and the protein bonded with the oil dispersed in the acid solution from the solid residue. The solid residue is screened to separate crude fiber-containing substances from a starch-rice fraction.
U.S. Pat. No. 4,808,426 to Strop et al., issued Feb. 28, 1989, describes a process for extraction of vegetable oil from an oil bearing material such as soy bean, corn and the like. The process comprises adding at least one reagent and an oil, of preferably the same type as will be extracted from the oil bearing material, to the oil bearing material to form a slurry mixture. The reagent preferably comprises a reagent for cleaving the chemical bond of the non-hydratable phospholipids, thereby converting the non-hydratable phospholipids into hydratable phospholipids. Typically this reagent is an acid. The slurry is heated at a preselected temperature for a period of time, preferably under a partial vacuum. Subsequently, the resultant oil is extracted from the slurry mixture. This process reduces the phospholipid and trace metal content in the oil extracted from the oil bearing material.
U.S. Pat. No. 4,353,837 to R. W. Barnes, issued Oct. 12, 1982, describes a method for continuous azeotropic processing of vegetable and protein material for the extraction of oil. Particles of oil-bearing protein are continually fed into the top of a vertical column containing perforated plates; the protein particles progress downward in the column while vapor of an oil solvent/water azeotrope progresses up the column. A turbulent miscella pool is formed above the top plate in the column, with a vapor atmosphere of solvent and water being maintained above the pool. Miscella is withdrawn from the pool and the oil is separated therefrom. This patent discloses no specific examples and no particular solvent system is specified for use in the method.
U.S. Pat. No. 5,035,910 to J. D. Jones et al., issued Jul. 30, 1991, pertains to separation of oilseed components in solvent phase. In particular, oilseed, particularly whole Canola.RTM. seed, is separated under non-oxidizing conditions, in a non-aqueous solvent system, into high quality oil and proteinaceous flour food components, and a seed coat meal (hull) byproduct. Maceration in a solvent, sequential liquid cyclone separations, and recovery of components and solvent all take place in completely enclosed liquid flow-through systems with solvent recycle, in a relatively short time. Flaking, cooking and pressing of the Canola.RTM. seed is not required.
U.S. Pat. No. 5,047,254 to T-C Lee, issued Sep. 10, 1991, describes a process for the recovery of edible oil from cereal products. The oil content of rice bran is stabilized by simultaneous high temperature high pressure treatment. Such a treatment also improves the yield obtainable when such oil is extracted from rice bran by solvent extraction. The bran is pretreated prior to extraction of oil by subjecting the bran to 100.degree. C. to 200.degree. C. and at least 500 psi for from 5 to 20 seconds in the absence of added moisture. The pelletized product produced is then extracted using known solvent extraction methods.
U.S. Pat. No. 5,069,923 of E. S. Hubbard et al., issued Dec. 3, 1991, pertains to an apparatus for the processing of grains, and more particularly to a means for expanding raw, whole seed amaranth and extruded half products of cereal grains such as corn, wheat and oats. The expanded or popped grain products are produced in a manner which results in a more nutritious food product that the food product produced by previously-known methods of grain product expansion. The amaranth or other half products of cereals or grains are expanded in a apparatus including: a first container for receiving a food product suitable for expanding; a second container having a wall defining a chamber for the food product, the wall having multiple perforations therethrough, substantially uniform in size and sufficiently small to prevent passage of the unexpanded food product therethrough; and a transfer means for moving the food product from the first container to the second container at a uniform rate. The apparatus also comprises an agitation means in the second chamber for agitating amaranth (the food product) contained in the chamber. Means are also provided for heating air to a temperature sufficient for popping the raw amaranth and for supplying the heated air to the chamber through the perforations, thus to expand at least a substantial portion of the raw amaranth contained in the chamber. Finally, a separating means receives an output of the second container, and separates the expanded amaranth from raw, unpopped amaranth and other matter.
U.S. Pat. No. 5,077,071 to H. R. Strop, issued Dec. 31, 1991, discloses a process for extracting oil from oil-bearing materials, such as vegetable oil bearing seeds and plant materials. The process comprises adding crude oil, water and a reagent to the oil-bearing materials to form a slurry. Subsequently, a resultant oil is extracted from the slurry. The process provides for treating the oil bearing materials in a screw extruder. In addition, the process teaches sparging the slurry with steam to remove impurities contained therein. A substantially toxic-free feed is obtained by maintaining the oil-bearing materials in acid reagents for about 5 minutes to hydrolyze glucosinolates to carbon dioxide and ammonia. The ammonia and carbon dioxide are subsequently stripped therefrom.
U.S. Pat. No. 5,091,116 to R. G. Krishnamurthy et al., issued Feb. 25, 1992, describes an improved method for treatment of edible oils such as soybean oil and cottonseed oil to improve its stability, flavor, and/or to deodorize the oil. The method comprises the steps of: deoxygenating the oil, heating the deoxygenated oil to a temperature in the range of from about 325.degree. F. to about 550.degree. F., continuously conducting the heated, deoxygenated oil through a nitrogen contacting zone and continuously introducing substantially oxygen-free nitrogen in a countercurrent manner through the heated oil at about atmospheric pressure conditions for a time period of at least about 5 minutes and cooling the oil under oxygen excluding conditions to provide a deodorized vegetable oil. A deoxygenated, unsaturated vegetable oil can be blended with a hydrogenation catalyst and contacted with hydrogen to reduce the number of unsaturated bonds of triglyceride components of the oil, while simultaneously deodorizing the oil.
As one can see, looking at the references listed above, there are numerous possibilities for removing oil from vegetable matter and, in particular, from grains. Each of the possibilities has advantages and disadvantages. The present invention provides a very economical method of extracting oil from materials having a low oil content, such as grains, pre-extracted vegetable matter and grain-based food products. Further, the present invention provides a method of separating the extracted oil into at least two fractions, one fraction which contains principally saturated components and at least one other which contains principally unsaturated components. The separation achieved by the method is unexpected in view of the known art and provides a highly desirable oil product, which is low in saturated components.