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The influence of linear alcohols on the formation of inclusion complexes between d-limonene and IX-, fJ-, or y-cyclodextrin has been examined at a low water content using a micro-aqueous method. In the presence of alcohols, particularly methanol and ethanol, the formation of inclusion complexes between d-limonene and fJ-or y-cyclodextrin is enhanced. The alcohol included in the cyclodextrin at the low water content was replaced with d-limonene as the water content increased. This implies that these alcohols would behave like water and activate the inclusion reaction between d-limonene and fJ-or y-cyclodextrin. On the contrary, the formation of d-limonene complexes with IX-cyclodextrin is inhibited by the presence of alcohols except for methanol. By means of the apparent water content, the amount of d-limonene complex in fJ-and y-cyclodextrin correlated well with a single sigmoid curve.Cyclodextrins (CDs) are homogeneous cyclic oligosaccharides, which can include various guest molecules in their hydrophobic cavity. Many kinds of volatile and unstable materials have been formed into stable complexes with CDs by maximizing this capability, thus enhancing their stability to oxygen, heat, or light. The most important application of CDs in the food industry is the powder encapsulation of volatile food ingredients to prevent the loss of flavors and essences. Since the inclusion complex can stabilize unstable and/or volatile substances against oxidation or exposure to heat or light, CDs are used to put many food flavors and fragrances in a powder state. They are also useful for improving the solubility of medicines.There are several ways of preparing powdered complexes of guest ingredients with CDs.1) Furuta et al. 2) proposed an efficient method for encapsulating d-limonene, in which liquid d-limonene was kneaded directly with fJ-CD in a twin screw kneader at a very low moisture content (between 10 and 20% on a dry basis). However, the influence of the water content on the formation of inclusion complexes should be examined. Furthermore, from a practical perspective, it is also useful to understand the influence of third components such as alcohols on the formation of inclusion complexes, because the use of organic solvents is often inevitable during the complexing of compounds that are very insoluble in water. There have been several studies upon the effects of the presence of organic solvents such as alcohols on the formation of inclusion complexes between guest molecules and CDs in solution. Pena et al. 3) and Zung et al. 4) have extensively examined the role of several alcohols in the formation of an inclusion complex between pyrene and fJ-or y-CD in aqueous solution. They reported that the apparent formation constant of the complex between the fJ-or y-CD and pyrene increased dramatically in the presence of alcohols. Similar phenomena were reported by Schuette t To whom correspondence should be sent. et al. 5) for the binding strength between fJ-CD and acridine.Masui 6 ) reported that in the presence of methanol,...