Aroma retention during the drying of liquid foods

Factors detg. aroma retention during the drying of food liqs. were investigated by a model system. Slabs of an aq. soln. of partially hydrolyzed starch, contg. a small amt. of acetone, were dried in air and the percentage of acetone retained was measured. Acetone was lost almost exclusively during the \"const. rate\" period of drying and its rate of loss could be described in terms of a binary diffusion process. At high moisture contents, the rate of loss of a component from a drying soln. is mainly dependent on its volatility, while at low moisture contents the diffusion coeff. of the component becomes the detg. factor. Loss of volatile components will be only very slight if, at the onset of drying, the value of the dimensionless group BiwoKwo is sufficiently large. Here Biwo is the Biot no. for water transport and Kwo is the ratio of the equil. water concn. in the gas phase and the water concn. in the soln. to be dried. The min. value of the group necessary to ensure high aroma retention increases with increasing relative humidity of the drying air. This value is larger for a drop than for a slab and is equal to 22 for a droplet under normal spray-drying conditions