Water Solubility of Essential Oils from Coniferous Needles with Special Reference to Effect on Germination and Antitermite Activity

Abstract

The needle essential oils of Pinus thunbergii and Cryptomeria japonica were analyzed by GC and GC/MS, and the water solubility and the bioactivities of the oils and their components were examined. In addition, relationships between solubility and bioactivity were investigated. The needle oils of P. thunbergii and C. japonica exhibited solubilities of 26.2 and 21.9 （mg/L）, respectively. For components, α－, β－pinene had low solubilities of 1.7 and 2.1 （mg/L）, respectively, and α－terpineol and terpinen－4－ ol had high solubilities of 70.7 and 81.1 （mg/L）, respectively. The water solubility of oxygenated monoterpenes was greater than those of needle oils and monoterpene hydrocarbons. With regard to germination rates of radish seeds, after 1 day of the test, when the concentration of the needle oils and the components were 5 ppm, the rates from needle oils （P. thunbergii and C. japonica）, α－terpineol and terpinen－4－ol were 11.9, 4.8, 0 and 2.4 （%）, respectively, and controlled low. In relating termite （Reticulitermes speratus） mortality, lethal concentration of 50% （LC50 ） of needle oils （P. thunbergii and C. japonica）, α－terpineol and terpinen－4－ol were 60.3, 34.8, 8.6 and 6.3 （ppm）, respectively. Bioactivi- ties of oils and the components were recognized. Thus, for oils and the components, the increased wa- ter solubility corresponded well with the decreased germination rate and LC50 of termites. It was sug- gested that water solubility and the bioactivities of needle oils are affected by those of oxygenated monoterpenes （α－terpineol and terpinen－4－ol）