Vegetable Oils & Fats:
Vegetable Oils are obtained from a variety of seeds, grains and nuts. Most common types of oil-bearing seeds and nuts are Canola, Castor, Coconut, Corn (Maize), Cottonseed, Mustard, Olive, Palm, Palm-Kernel, Peanut (Groundnut), Rapeseed, Safflower, Soybean, and Sunflower. Other major specialty oils are obtained from Almond, Avocado, Cashew, Grapeseed, Jatropha, Pecan, Pine, Shea, and Walnut.
Animal Oils and Fats:
Animal Oils are obtained from a variety of animals. Most common types of oils and fats include Chicken-Fat (Chicken), Fish-Oil (Fish), Lard (Pigs), and Tallow (Cows). Each one of these oils and fats comes in edible and non-edible categories and multiple grades within each category.
Cleaning and Drying:
The plant feedstock must be cleaned so that foreign matters are removed. This applies particularly to sand/silicate and iron which may damage the preparation plant equipment.
Mechanical preparation:
Most of raw materials needs to be broken to reduce the particle size to ensure proper cooking and flaking. They are then heated in cooking / conditioning equipment and their moisture further controlled in addition to be softened before the next mechanical operations. After cooking, heated grits are flaked so that the oil cells are broken and the oil more readily available for further solvent extraction or mechanical pressing.
Pressing:
Oilseeds containing above 20 to 25% (rapeseed, sunflower seeds, cottonseeds...) are generally pressed mechanically in order to extract most or part of the oil available in the feedstock. This operation is done through full pressing for maximum oil recovery leaving up to 5 to 10% in the final cake which is marketed as such or through a low-pressure pre-pressing operation producing a cake with higher residual oil content which is then recovered in the solvent extraction plant.
Dehulling:
Oil extraction plants produce a solid finished product in addition to the extracted oil; this product (cake or meal) is normally used as an important component for animal feed recipes.
Depending on the meal destination, its protein content often needs to be increased and its fiber content minimized. Such characteristics are generally achieved through decortication or dehulling operations that separate the outer part of the feedstock before extracting the oil.
Extraction:
In the solvent extractor, solids (Flakes from the flaking machines or cakes from the pre-presses) are conveyed through the equipment while a mixture of hexane and oil (miscella) is sprayed counter-current. The extractor produces therefore de-oiled solids containing solvent and miscella.
De-solventization:
De-oiled solids coming out of the extractor are conveyed to a dedicated equipment that completely removes the remaining solvent while preserving the meal quality: the de-solventizer. This apparatus is usually combined with additional sections for drying and cooling the meal to the required storage and market parameters.
Miscella distillation:
Solvent contained in the miscella is completely removed under vacuum and optimum temperature for preserving oil quality.
The solvent from the distillation as well as the one removed at meal de-solventization stage are then recycled to the extractor.
Solvent recovery:
Since the air entering the process together with material fed to the extractor is laden with solvent when it is removed from the plant it first passes through a specially designed absorption column to limit emission to an acceptable level.
Meal treatment:
The extracted meal is often subject for further treatment, including grinding to obtain the required granulometry or pelletizing to reduce its volume.
Oil Refining:
Vegetable and Animal Oils and Fats have impurities such as Moisture, Solids (Insolubles), Gums (Lecithins), Free-Fatty Acids (FFA), Waxes, and Compounds of Sodium, Potassium, Magnesium, Calcium, and other metals. These impurities must be removed to improve the functionality of the oils. Other characteristics of oils (such as Color, odor, and taste) are also considered impurities by modern consumers. These impurities are removed in a series of steps such as degumming (to remove gums), neutralizing (to remove FFA), bleaching (to remove color), deodorizing (to remove odor and taste), and dewaxing or winterization (to remove waxes).
RBD Oil:
Refined Vegetable Oil is commonly called Refined, Bleached, and Deodorized (RBD) oil. As described earlier, these are the three main steps in the refining process; although additional steps are required in most cases.
Chemical Refining:
In Chemical Refining, Vegetable Oil is treated with caustic lye for separation of free fatty acids from oil. This is a conventional process that can be applied to all oils. A byproduct of alkali refining is soap-stock, which is used for manufacture of low-quality washing soap. Alternately, the soap-stock can be treated with acid to recover fatty acids. The waste-water from refinery requires extensive treatment. This can be avoided by alternate Physical Refining process.
Physical Refining:
In Physical Refining, Vegetable Oil is subject to distillation to remove free fatty acids. The alkali treatment is completely avoided. This reduces the amount of waste water and eliminates production of soap. This process is becoming more popular.
Degumming:
The purpose of Degumming Vegetable Oils is to remove Gums. All oils have hydratable and non-hydratable gums.
a. Water Degumming: Hydratable gums are removed by treating oils with water and separating the gums. The gums can be dried to produce lecithin.
b. Acid Degumming: Non-Hydratable gums are removed by treating oils with acids and separating the gums.
Neutralizing:
The purpose of Neutralizing Vegetable Oils is to remove Free-Fatty Acids (FFAs). Traditionally, FFAs are treated with caustic soda (NaOH). The reaction produces Soaps which are separated from the oil. Because trace amounts of soaps remain in the oil, the oil is either washed with water or treated with Silica.
Some processors prefer not to perform caustic neutralizing. Instead, they prefer Physical Refining in which the FFAs are evaporated from the oil under high temperature and vacuum. This process can be combined with deodorization step described under FFA stripping.
Physical Refining process is preferred because (a) it does not produce soaps; (b) it recovers fatty acids that provide better cost recovery; (c) there is smaller yield loss compared to caustic refining—especially for oils with higher FFAs; and (d) it is a chemical-free process.
Bleaching:
The purpose of Bleaching is to remove color pigments contained in Vegetable Oils. The oil is treated with Bleaching Clays that adsorb the color pigments. The clay is filtered and the clean bleached oil is stored for further processing.
Deodorizing:
The purpose of Deodorizing Vegetable Oils is to remove odor substances. The oil is subjected to steam distillation under high temperature and vacuum to evaporate all odor substances. The resulting deodorized oil is almost bland and tasteless.
FFA Stripping
As mentioned previously, the Deodorizing equipment can be modified to achieve Physical Refining. Since the conditions for deodorization and physical refining are almost identical, the modified equipment can be employed to achieve deodorization as well as physical refining.
Fatty-Acid Recovery:
Fatty-Acids are evaporated (distilled) in FFA Stripping. The Fatty-Acid vapors are condensed by direct contact with liquid Fatty-Acids to recover the evaporated Fatty-Acids. The distillation and condensation of Fatty-Acids is accomplished under very high vacuum to lower the boiling point of Fatty-Acids and prevent them from oxidizing.
Dewaxing/Winterizing:
The purpose of Winterization Vegetable Oils is to remove waxes especially in those oils that contain waxes. Such oils are subjected to chilling and filtration to remove waxes and other high melting point substances.
Winterizing is also used to separate the unsaturated fats from unsaturated fats—especially in Palm Oil or other saturated fats. The chilling process solidifies the saturated fats; thus enabling separation via filtration.
Hydrogenation:
Vegetable Oils have varying degrees of saturation levels. Some food products can only be prepared in saturated oils & fats. Hence, some food companies hydrogenate vegetable oils to produce desired level of saturation in the Oils & Fats. Vegetable oils can be hydrogenated under high temperature and pressure in the presence of a catalyst.
Bakery Fat:
The bakery industry uses hydrogenated oil (i.e., shortening). However, the shortening for bakery application should be of smooth texture. Granular texture, while desired in vanaspati ghee, leads to bleeding of fat in bakery products. Hence, hydrogenated oil is cooled under controlled conditions to get a product with smooth plastic texture suitable for the bakery industry.
Lecithin:
Gums (Lecithin) present in Vegetable Oils are valuable emulsifier and an additive in prepared foods. Hence, it may be profitable to recover them for sale to food companies. The degumming process described above produces a mixture of gums, oil, and water. The mixture of gums, oil, and water is introduced in a thin-film evaporator operating under vacuum to remove water. The resulting dry mixture of gums and oil is sold as crude dry gums or lecithin. The main design concerns are that the evaporation of water should be quick and take place under higher vacuum to prevent charring and discoloring of gums.
Soap-Splitting (Acidulation):
The caustic neutralization process described above produces Soap Stock—a mixture of Soaps (Fatty-Acid Salts), Oil, and Water. Soap Stock, by itself, is a low value by-product—usually a waste product. However, it contains considerable amount of Fatty Matter, which may be profitably recovered for sale as a higher-value product. This is accomplished by converting Soaps into Fatty Acids by reacting with an Acid. The resulting product is a mixture of Fatty Acids and Oil (commonly called Acid Oil).
Glycerolysis:
The physical refining process described above produces Fatty Acid Distillate—a mixture of Fatty Acids and Oil. The value of the Distillate may be enhanced by converting Fatty Acids into Oils through Glycerolysis. This is accomplished by reacting Fatty Acids with Glycerin to produce Oil. The resulting product is dried to recover oil for sale as a higher-value product.
GMP:
Good manufacturing practice also implies the following: the use of stainless steel equipment; the careful deaeration at < 100°C before heating to the final stripping temperature; the use of oxygen-free steam; and strict feedstock specifications (typically: Fe 0.1, Cu 0.01, P S, bleaching earth 5 mg/kg oil max.).
Investigations in which oil was maltreated under extreme conditions determined the effects of temperature (240-300°C) and time (30-180 min.) during "physical refining" of soybean oil (degummed with phosphoric acid and lightly bleached, but still containing 20 mg P, 0.35 mg Fe and 0.05 mg Cu per kg oil). A strong effect of temperature on the formation of trans fatty acids and polymeric compounds. Time also has a significant effect. At 280-300°C, there was evidence for appreciable inter- or intra-esterification (increase in the content of saturated fatty acids at the 2-position of the triacylglycerols); substantial amounts of conjugated fatty acids were formed as well. The shaded areas indicate the usual range of processing conditions required for physical refining (270°C for 30 mins. 250°C for 1 h; 240°C for 2 h; 220°C for 3 h). Under these conditions, all changes induced by the high temperature treatment appear to be relatively minor.
Major Edible Oils & Fats Equipment Manufacturers:
Technochem builds esterification, trans-esterification, methanol rectification, degumming, bleaching, deodorizing, dewaxing, and oil-refining plants. De Smet Engineers & Contractors is a major engineering and contracting firm involved in all steps of the production of vegetable oils from oilseeds crushing for the construction of Edible Oils Plants.
Alfa Laval, Chempro, Silverson, and Zink Hamworthy are major edible oil process equipment manufactures, and Desmet Ballestra is a major technology provider
Conclusions:
Commercial refining produces fats and oils that can be of high quality and have the characteristics of bland taste, clear color, good keeping quality and frying stability. Commercially-refined fats and oils are free from known contaminants extracted from the raw agricultural products. Temperature, time and pressure must be carefully controlled during industrial refining. Oil products should be properly stored, transported and packaged to maintain quality and consumers must assume responsibility for not abusing oils and fats within households.
Industry can design almost any fat or oil for a specific application by the use of various modification processes, such as hydrogenation, interesterification, fractionation or blending. Hydrogenation typically reduces essential fatty acid content and creates various fatty acid isomers, both cis and trans. The wide flexibility available to industry through the selection of raw materials and different modification processes allows for the production of oils at the lowest cost possible, an important aspect of food production.