Methods for refining vegetable oils and byproducts thereof

Details Methods for refining vegetable oils and byproducts thereof Methods for refining vegetable oils and byproducts thereof

2000-02-29

2001-01-09

Carr, Debroah D. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Fatty compounds having an acid moiety which contains the...

Reexamination Certificate

active

06172247

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to improved methods for refining vegetable oils and byproducts thereof. More particularly, this invention relates to improved processes for producing vegetable oils having reduced content of impurities such as free fatty acids and phosphatides. This invention also relates to an improved process for deodorizing lecithin. This invention additionally relates hydrolyzed lecithin, deodorized lecithin and deodorized vegetable oil obtained by improved processes of the invention.
BACKGROUND OF THE INVENTION
Organic Acid Refining
Vegetable oils are typically obtained by pressing or extracting the oil seeds of plants such as corn or soybeans. Properly processed vegetable oils are suitable for use in many edible oil and fat compositions destined for human consumption. Such edible oils and fats include salad oils, cooking oils, frying fats, baking shortenings, and margerines. In addition to being widely used in edible oils and fats, vegetable oils are also increasingly utilized in important industrial products such as caulking compounds, disinfectants, fungicides, printing inks, and plasticizers.
Vegetable oils primarily consist of triglycerides, but several other compounds are also present. Some of these additional compounds, such as diglycerides, tocopherols, sterols, and sterol esters, need not necessarily be removed during processing. Other compounds and impurities such as phosphatides, free fatty acids, odiferous volatiles, colorants, waxes, and metal compounds negatively affect taste, smell, appearance and storage stability of the refined oil, and hence must be removed. Carefully separated, however, some of these additional compounds, particularly the phosphatides, are valuable raw materials. It is therefore important to select a vegetable oil purifying method that maximizes removal of impurities but does so in a way that least impacts the compounds removed.
Vegetable oil impurities are typically removed in four distinct steps of degumming, refining, bleaching, and deodorizing. Of these four steps, degumming removes the largest amount of impurities, the bulk of which are hydratable phosphatides. Refining primarily removes non-hydratable phosphatides, soaps created from the neutralization of free fatty acids, and other impurities such as metals. Bleaching then improves the color and flavor of refined oil by decomposing peroxides and removing oxidation products, trace phosphatides, and trace soaps. Soybean oil bleaching materials include neutral earth (commonly termed natural clay or fuller's earth), acid-activated earth, activated carbon, and silicates. Deodorizing is the final processing step and prepares the oil for use as an ingredient in many edible products including salad oils, cooking oils, frying fats, baking shortenings, and margerines. The deodorizing process generally comprises passing steam through refined oil at high temperature and under near vacuum conditions to vaporize and carry away objectionable volatile components.
Vegetable oil refining, also known as neutralization or deacidification, essentially involves removing free fatty acids (FFA) and phosphatides from the vegetable oil. Most refining operations employ either alkali refining (also termed caustic refining) or physical refining (also termed steam refining). Of these two refining methods, alkali refining predominates.
For either refining method, an optional but preferred first step is a conventional water degumming process. Degumming refers to the process of removing hydratable phosphatides and other impurities such as metals from vegetable oils. Crude vegetable oils contain both hydratable phosphatides (HPs) and non-hydratable phosphatides (NHPs). A simple degumming process comprises admixing soft water with the vegetable oil and separating the resulting mixture into an oil component and an oil-insoluble hydrated phosphatides component (frequently referred to as a “wet gum” or “wet lecithin”). The NHPs, generally considered to be calcium and magnesium salts of phosphatidic acids, are largely unaffected by water and remain soluble in the oil component.
Normally, refiners also must introduce chelating agents following degumming processes to remove metal compounds from crude vegetable oil, which typically contains calcium, potassium, magnesium, aluminum, iron and copper. Left in place, these metal impurities form salts of phosphatidic acid, thereby contributing to the NHP content. Moreover, metal contaminants, especially iron, can darken oil during deodorization, and even small amounts of iron that do not affect the oil's color can nevertheless dramatically reduce stability of refined oil.
Treating crude vegetable oil with soft water produces a degummed oil and a phosphatide concentrate containing the hydratable phosphatide fraction. This phosphatide concentrate subsequently can be removed from the degummed oil by a convenient method such as centrifugal separation. Phosphatide concentrates coming from centrifugal separation will generally contain up to about fifty percent by weight water, and typically will contain from about twenty-five to about thirty percent by weight water. In order to minimize chances of microbial contamination, phosphatide concentrates must be dried or otherwise treated immediately. Dried phosphatide concentrates can be profitably sold as commercial lecithin. Degummed oil is further refined to remove NHPs and other unwanted compounds.
Mineral acid also is sometimes added during the water degumming process to help minimize the NHP content of degummed oil. The acid combines with calcium and magnesium salts, enabling phosphatidic acids to migrate from the oil to the water phase, thus eliminating them from the crude oil. However, using mineral acid during degumming is inappropriate when seeking to recover gums intended for use as lecithin because the presence of mineral acid will cause darkening of the lecithin.
In alkali refining, free fatty acids and gums are removed from crude or degummed oil by mixing the oil with a hot, aqueous alkali solution, producing a mixture of so-called neutral oil and soapstock (also termed refining byproduct lipid), which is an alkaline mixture of saponified free fatty acids and gums. The neutral oil is then separated from the soapstock, typically by centrifugation. The soapstock has commerical value due to its fatty acid content but must be processed further in order to render it salable. The neutral oil is further processed to remove residual soap.
Soapstock is treated in a process called acidulation, which involves breaking or splitting the soap into separate oil and aqueous phases through addition of a mineral acid such as sulfuric acid to reduce the pH to approximately 1.5, followed by thorough heating and mixing. Because the aqueous phase is heavier than the oil phase, the acidulated soapstock is separated from the oil by gravity or centrifugation. The separated oil (termed acid oil) has essentially the composition of the neutral oil and is drawn off, washed with water to completely remove mineral acid and sludge, and sold, usually as an animal feed supplement. The remaining aqueous phase (termed acid water) is the final waste product and can either be used in other processes or neutralized before being discarded.
The alkali refining process has several drawbacks, however, mainly related to soapstock formation. One drawback is refining losses that occur due to the soapstock's emulsifying effect, wherein soapstock acts to take up a portion of the valuable neutral oil into the aqueous soapstock solution. To minimize such emulsification losses, the crude or degummed oil is usually heated to between 158° F. and 194° F. prior to being contacted with the hot alkali solution. However, heating will not completely prevent emulsions from forming, nor will it entirely break emulsions once formed. Centrifugation forces also are insufficient to completely break emulsions of neutral oil in soapstock.
Another drawback to alkali refining is losses that occur when a portion of the neutral oil undergoes alkaline

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