Keywords: Betel leaf oil; yield; phenolic components; transformation; chavibetol acetate; 4-allylpyrocatechol diacetate; chavibetol; maximum yield

Abstract

Chavibetol 1 instead of eugenol or isoeugenol, chavibetol acetate 2 instead of eugenol acetate and 4-allylpyrocatechol diacetate 3 were unequivocally identified by us as the main phenolic compounds in Hocmon betel leaf essential oil (Piper betle L.). It was also found that oil yield and its phenolic content varied with the time of collection and the mode of leaf pretreatment. In 2011, at the 14th Asian Chemical Congress in Bangkok, we reported for the first time the transformation of 4-allylpyrocatechol diacetate 3 into chavibetol 1 resulting in a substantial decrease in oil yield and in the total phenolic content by comparison of the products which were respectively obtained by hydrodistillation in unsalted water and in NaCl saturated solution. In this communication, further experiments were performed in more details to show that this transformation would be of enzymatic origin and occurred only in the presence of betel leaf via the intermediate undistilled water soluble 4-allylpyrocatechol 4. The role of NaCl was to block effectively the enzymatic reactions, thus 4-allylpyrocatechol diacetate 3 largely remained unchanged. In unsalted water, these reactions readily occurred and concurrently produced a substantial increase of 1 and a drastic decrease of 3 while large amount of undistilled 4 led to a decrease of betel oil yield and of its phenolic content. As it was known that the antimicrobial activity of betel essential oil increased with its phenolic content, Statgraphics Centurion XVI.II was used to define the experimental conditions to provide better yield of oil which must also contain a greater percentage of the phenolic compounds and particularly the more stable 4-allylpyrocatechol diacetate 3 with respect to oxidation in view of its possible use in cosmetic products.