Application of Gas-Liquid Partition Chromatography to the Study of Volatile Flavor Compounds

Small amounts of compounds of bacterial and of chemical origin are not usually detected in milk products by ordinary chemical methods.Gasliquid partition chromatography will, in some cases, remove this quantitative barrier and make it possible to more easily classify off-flavors.Editor.Until recently, the separation of small quantities of volatile mixtures was frequently difficult and sometimes not possible.Unless chemical means of separation could be used, micro-fractionating devices were required.These demand certain minimal quantities, and if the boiling points of the volatiles are not sufficiently diverse, considerable efficiency is lost.About 15 years ago, Turner (15) suggested the principles of gas chromatography.Martin and Synge (10) extended these principles to volatiles and suggested the process of gas-liquid partition chromatography.Various workers (1-~, 12, 14, 15) have applied these techniques to hydrocarbon analyses, and others (5-9, 11, 12) have investigated such diverse materials as fatty acids, amines, alcohols, aldehydes, and ketones.The method shows promise for the study of natural flavor compounds because of the small amounts of material required and the high degree of resolution achieved.Work reported below illustrates the application of the method to a study of volatile compounds present in commercial starter distillate.The selection of starter distillate as a starting material was influenced both by its availability and by the desirability of establishing a correlation between specific chemical compounds and flavor characteristics in cultured dairy products. METHODS AND PROCEDURE Gas-liquid partition chromatography apparatus.Although the theoretical treatment of the gas chromatography apparatus is somewhat involved (7, 8, 15), the governing principles can be simplified.In the simplest sense, the apparatus consists of a long tube filled with inert granular material coated with a nonvolatile immobile liquid.The temperature of the column is adjusted so that the materials to be separated possess suitable vapor pressures.If a mixture of volatile materials is placed on one end of the column and the tube is swept with an inert carrier gas, the rate of a particular component through the column will be, in part, a function of its relative vapor pressure.As a component works its way through the column, passing from one oil-covered granule to the next, the number of times that it dissolves, evaporates, and redissolves is tremendous.