chapter  5
44 Pages

Preseparation techniques in aroma analysis

I. Introduction .................................................................................................111 II. Chemical manipulation............................................................................. 113

A. Classic acid and base separation..................................................... 113 III. Column-liquid chromatography ............................................................. 123

A. Normal-phase chromatography ...................................................... 124 1. Silica gel column chromatography........................................... 124 2. Reversed-phase chromatography ............................................. 132

B. Ion-exchange chromatography ........................................................ 132 C. Isolation of thiols by ion-exchange chromatography .................. 135

IV. Preparative and multidimensional HPLC and GC.............................. 138 A. Preparative HPLC and GC techniques .......................................... 139 B. Multidimensional gas chromatography......................................... 141

1. Conventional two-dimensional GC.......................................... 142 2. Comprehensive two-dimensional GC...................................... 144

V. Summary and outlook .............................................................................. 147 References ............................................................................................................ 147

Aroma analysis is highly dynamic and fairly demanding because the aromatic composition of foods, beverages, and perfumery products are frequently quite complex. There is often the impression that we enjoy just a single aroma or flavor sensation for a particular product when there are often actually numerous volatile compounds that combine together to impart a sensory impact. Only in rare cases can the characteristic aroma of a food

product be narrowed down to one particular compound; for example, 4-hydroxy-3-methoxybenzaldehyde is given the common name of vanillin, and

trans

-3-phenyl-2-propenal is commonly known as cinnamaldehyde, owing to their association with the aromas of vanilla and cinnamon, respectively. However, the isolation of volatile compounds from natural flavor extracts has shown that, individual components frequently do not impart aromas that are reminiscent of the flavor substance [1]. Rather, a combination of particular volatile compounds is required, each at a specific concentration, for us to recognize an aroma as having a distinctly familiar odor quality.