Determination of the Degree of Unsaturation in Essential Oils

Abstract

Being widely used, medicinal products based on vegetable oils require strict regulation and evaluation of quality attributes, determination of shelf-life periods, and monitoring of storage conditions. The most common testing method for unsaturated compounds in vegetable oils is the iodine value determination, which has a range of limitations. An alternative method for determining the degree of unsaturation is based on epoxidation.The aim of the study was to evaluate the possibility of determining the degree of unsaturation of terpenoids and essential oils using peroxycarboxylic acids.Materials and methods. The authors performed epoxidation of linalool, myrcene, and lemon oil with peroxydecanoic and peroxyoctanoic acids, followed by iodometric titration of the excess acid.Results. The study demonstrated the possibility of measuring the degree of unsaturation of the selected essential oil and terpenoids using peracid epoxidation. The authors developed a procedure for determining the iodine value of essential oils and calculated the iodine values of linalool, myrcene, and lemon oil. Epoxidation proceeded as a second-order reaction. The authors obtained the following reaction rate constants: 3.9 L×mol–1×min–1 for linalool (298 К), 1.76 L×mol–1×min–1 for myrcene converting to monoxide (298 К), 0.044 L×mol–1×min–1 for myrcene epoxide converting to diepoxide (298 К), and 3.9 L×mol–1×min–1 for lemon oil (297 К).Conclusions. The suggested procedure involving peracid titration for rapid and efficient determination of the degree of unsaturation (iodine value) provides a potential basis for developing a quantification method for total unsaturated bioactive compounds in essential oils.

Keywords

• terpenoids
• epoxidation
• peroxy acid
• linalool
• myrcene
• lemon oil
• unsaturation test
• titrimetry
• iodine value
• essential oils