D-limonene and L-menthol as model flavors were encapsulated in gum arabic or modified starch wall materials by spray drying. The water activity (a_w) played an important role in the release rate of the encapsulated flavor. In the case of the water-insoluble flavor, D-limonene, the release rate increased with the a_w up to around 0.50 and then decreased to a minimum release rate at the a_w of around 0.70-0.80. The release rate increased again with high a,. That could be explained by the change of structure of the capsule wall materials. On the other hand, for the partially soluble flavor (L-menthol), the release rate increased monotonously with the increasing a_w. This might be because of the solubility of L-menthol. For partially water-soluble flavors, dissolved flavors can increasingly diffuse through the wall matrices with increasing a_w. The release rate was controlled by the water adsorption by wall matrices and by the flavor solubility.
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