Relevance of enantiomeric separations in food and beverage analyses

Abstract

A series of new derivatized cyclodextrins have been developed for use as chiral stationary phases in capillary gas chromatography. As a result, a large number of the enantiomeric components in food and beverage products can be resolved relatively quickly and easily. The study focuses on compounds other than amino acids (e.g., malic acid, lactic acid, tartaric acid, esters, alcohols, lactone flavors or fragrances, and so on). The ability to separate and quantitate enantiomers at low levels should be useful for detecting adulterated products, for evaluating fermentation processes, and for the accurate characterization of enantiomeric flavor components, growth regulators, pesticides, and herbicides as well as their chiral environmental degradation products and metabolites. A large number of the organic components of foods and beverages are chiral molecules. In addition, a significant number of additives, flavors, fragrances, preservatives, growth regulators, fumigants, pesticides, herbicides, and so on used in the industry also are chiral molecules. Chiral or enantiomeric molecules are known to rotate plane polarized light, and they cannot be superimposed on their mirror image isomer. It is well-known that enantiomers have exactly the same physical and chemical properties in an isotropic environment. This can make it very difficult to separate them from one another or even to discern that there is a mixture of the two. An equimolar mixture of two enantiomers is referred to as a racemic mixture or racemate. Most synthetically produced chiral compounds are racemates. Spectroscopically (polarimetry, circular dichroism, or optical rotatory dispersion), racemates appear to be achiral. When the various organic components of food and beverage products are analyzed, it is rare to consider the enantiomeric makeup of the chiral components. However, Sandra et al. (1984) and Kuneman et al. (1988) pointed out the value of separating L- and D-amino acids because the presence of the synthetically produced D enantiomer could be used to detect adulterated fruit juices. Indeed, the identification of adulterated consumer products is one of a number of important areas where enantiomeric separations can make a significant contribution. Table I lists a few of the areas in which enantiomeric separations may be relevant to food science. For example, amino acids are not the only components of foods and beverages that can be analyzed to identify adulterated products. There are a variety of chiral organic acids, alcohols, diols, esters, lactones, aldehydes, and ketones that not only are useful but also may be more specific markers than some amino acids. Consequently, we will focus on compounds other than amino acids, such as malic acid, lactate esters, tartaric acid, and butylene glycol. Fermentation processes sometimes can alter the enantiomeric excess of certain solutes in addition to producing