High temperature vacuum steam distillation process to purify and increase the frylife of edible oils

#The field of this invention is the processing of edible fats and oils.

#This invention relates to a process for increasing the frylife of edible oil. The process involves heating the oil at very high temperature under vacuum for a short time while stripping the oil with steam or inert gas to remove components from the class of tocopherols, tocotrienols, sterols (preferably cholesterol), trace pesticides and other trace quinone-type structures, herein described as materials deleterious to frylife.

#In order to build superior taste into edible oil products, they must undergo certain processing steps. The most important, from a finished flavor standpoint, is deodorization. Deodorization is a moderately high temperature vacuum steam distillation process used to remove volatile odoriferous compounds from edible fats and oils. These odoriferous compounds are more volatile than the fats and oils, so they can be separated by use of a stripping agent such as steam. High temperature and low pressure increase the relative volatility of these compounds. Since the senses of taste and smell are closely linked, deodorization improves the flavor of the product as well as the odor. The finished product is ideally a bland oil.

#Soybean oil is heat bleached and vacuum steam distilled using the continuous deodorization apparatus described in U.S. Pat. No. 3,542,653 to Lowrey et al., issued Nov. 24, 1970. The apparatus is set up in the same manner as described in the example in the Lowrey et al. patent with the exception that a separate vessel for heat bleaching is used (instead of using an annular heat bleaching unit) and a heating source is installed to heat oil overflowing from the heat bleaching apparatus to the continuous deodorizer to a temperature of from 550.degree. F. (288.degree. C.) to 565.degree. F. (296.degree. C.). The oil prior to entering the equipment has been refined, absorptively bleached with bleaching earth, hydrogenated to an iodine value of 107 and deaerated to a level of about 0.08% by volume of dissolved oxygen.

#Oil to be heat bleached, at a temperature of about 480.degree. F. (249.degree. C.), is introduced into the lower portion of the heat-bleaching chamber, below the oil distributor, at a rate of 1000 pounds (about 21 cubic feet) per hour. This provides a residence time of the oil within the heat bleaching chamber of about 11 minutes, during which the oil rises in the separate heat bleaching chamber in approximate plug flow.

#After heat bleaching, the oil is forced into a shell and tube heat exchanger in which hot therminol at approximately 650.degree. F. (343.degree. C.) on the shell side heats the soybean oil on the tube side from 480.degree. F. (249.degree. C.) to between 550.degree. F. (288.degree. C.) and 565.degree. F. (296.degree. C.) in less than about 2 minutes. The oil is then forced to the upper portion of the vacuum steam distillation apparatus. The oil is then allowed to flow downward through the packing material, requiring from 1 to 2 minutes to do so. This causes contact of the oil and a countercurrent stream of steam, under a vacuum of approximately 7 mm Hg, in an amount of about 0.5% by weight of the oil, which is introduced into the lower portion of the packed deodorization chamber. The combination of stripping parameters results in a stripping factor of 2.5 and compensates deleterious to frylife are removed through the volatilization of these materials in the oil, while residence time at this high temperature is minimized and few, if any, higher molecular weight materials or other side products form as a result of the high temperature processing. After passing through the packed vacuum steam distillation chamber the oil is immediately quenched to below 370.degree. F. (188.degree. C.). Heat bleached, vacuum steam distilled and quenched oil is withdrawn from the lower portion of the packed vacuum steam distillation chamber, while steam and volatilized components deleterious to frylife are withdrawn from the upper portion of the packed vacuum steam distillation chamber through the oil entrainment separator and vapor line to the steam ejector system.