I. Field of the Invention
The present invention relates to a process for the production of sorbitol fatty acid esters through direct esterification. More specifically, the direct esterification process of the present invention is directed to the production of mixtures of sorbitol fatty acid esters with a degree of hydroxyl substitution ranging from about 3 to about 5.5 fatty acid ester groups, which are useful as low calorie fat substitutes.
II. Description of the Prior Art
Continued concern with health problems such as obesity and arteriosclerosis, which are associated with a diet high in fat content, has led to new formulations of normally high-caloric fat-containing foods. These formulations are often referred to as “diet,” “lite” and “low calorie” and are made by replacing the normally present fat with fat substitutes, thereby reducing the fat content. It is generally known that certain sorbitol fatty acid esters and polyesters can be used as such fat substitutes.
Sorbitol fatty acid esters may be prepared by a variety of methods. These methods include transesterification of sorbitol with methyl, ethyl or glycerol fatty acid esters (U.S. Pat. Nos. 5,458,910 and 5,612,080), enzyme catalyzed direct esterification of sorbitol with fatty acids (U.S. Pat. No. 4,614,718), and acylation of sorbitol with a fatty acid chloride or anhydride.
Depending on the method by which the sorbitol fatty acid ester is made, it contains varying degrees of hydroxyl substitution and varying proportions of sorbitol anhydride esters. For example, when esterification is carried out by acylation of sorbitol with a fatty acid chloride, the product generally contains very little or no sorbitol anhydride esters. In contrast, transesterification of sorbitol with fatty acid methyl esters under basic conditions can result in a product in which about 15–20% of the sorbitol fatty acid esters are esters of sorbitol anhydrides. Additionally, depending on the method of production, the sorbitol fatty acid ester product can contain varying degrees of color. Organic solvents and bleaching agents may be required to obtain acceptably low color levels.
It is also generally known that fatty acid mono-and diesters of sorbitan and sorbide, useful as emulsifying agents, can be produced by direct, base-catalyzed reaction of sorbitol with fatty acids at elevated temperatures. Such processes are disclosed, for example, in U.S. Pat. No. 2,322,820 to Brown.
Previous methods for preparing mixtures of sorbitol fatty acid esters and sorbitol anhydride fatty acid esters with sufficiently low color values, such as are shown in U.S. Pat. Nos. 5,458,910 and 5,612,080, have involved a transesterification process comprising heating a mixture of sorbitol, an alkali metal fatty acid soap, an excess of a costly fatty acid alkyl ester, and a basic catalyst. Such processes necessarily required the use of organic solvents and bleaching agents in order to obtain acceptable product purity and color. However, use of such solvents and bleaching agents are greatly limited by environmental and governmental concerns.
It is accordingly an object of the present invention to develop a method for producing mixtures of sorbitol fatty acid esters with specified degrees of hydroxyl substitution and sufficiently low color values to enable their use as low calorie fat substitutes, without the need for organic solvents and bleaching agents, thus substantially removing these potential regulatory barriers. The present invention has the additional advantages of being more cost effective and simpler than previously known methods. Cost savings and process simplicity are realized largely through a significant reduction in the number of processing steps and the substantial elimination of the use of organic solvents.