Experiments were designed and conducted to simulate volatiles retention partially during a drying process by creating a thin layer feed system and drying it by hot-air at 40 and 50℃. Volatiles carriers used were maltodextrin (40 and 60%, WWB) and skim milk (40%). A mixture of volatile compounds made up of pentanol, benzaldehyde, D-limonene, was added to the carriers in the beginning at a higher concentration of 5000 ppm and in some cases three more volatiles were used, including butyl acetate, pentyl acetate and 2,5-dimethyl pyrazine, each at a concentration of 50 ppm. The volatile contents of the feed materials just before and after drying was determined by Liken-Nickerson simultaneous distillation and concentration followed by GC-MS analysis. The results showed that volatiles were seriously lost during the first 80 min at 40 ℃ for all three volatiles in a 40% maltodextrin feed, after that, as drying continued, D-limonene seemed to cease loss but pentanol and benzaldehyde lost continuously. The same situation was observed at 50℃ drying but with the volatiles retention lower than that of at 40℃ drying. For the 40% skim milk feed, with the exception of D-limonene (presented the highest retention), volatiles loss occurred during the slow drying process. During the whole drying trial of 40% maltodextrin, drying was maintained in the constant rate period of drying and most of the volatiles showed a great loss in this period. However, when 60% of maltodextrin was applied, no distinct volatiles loss was observed for all of the 6 volatiles, because the selective diffusion mechanism was effective at the concentration from very beginning, which is corresponding to the falling rate period of drying. It was concluded that, the selective diffusion mechanism is not completely applicable during the drying process of a thin layer feed system in terms of volatile retention.
