Seasonal Changes in the Composition of Scots Pine (Pinus sylvestris L.) Oleoresin, Measured by the NMR Method

Abstract

Seasonal changes in the composition of Scots pine oleoresin were analyzed by 1H and 13C NMR spectroscopy. Due to favorable weather conditions (positive temperatures on the sampling dates throughout the year) samples for each of the 12 months were obtained and studied. Chloroform (CDCl3) solutions of oleoresin were investigated. Eight resin acids: abietic, dehydroabietic, isopimaric, levopimaric, neoabietic, palustric, pimaric, and sandaracopimaric acids, as well as six monoterpenes: camphene, limonene, myrcene, α-pinene, β-pinene, and terpinolene, were identified and quantified. It was revealed that the amounts of the oleoresin released and its constituent α-pinene decreased at low temperatures. Other monoterpenes were not detected within the measurement accuracy in this period of time. It was supposed that monoterpenes, formed in smaller amounts during the period of pests’ anabiosis, play the key role in the control of coniferous insect pests. The contents of dehydroabietic, isopimaric, neoabietic, pimaric, and sandaracopimaric acids were found to vary insignificantly throughout the year. An interrelation between the amounts of abietic, levopimaric, and palustric acids in the oleoresin composition was revealed. The observed interrelation was supposedly associated with low-temperature catalytic reactions of levopimaric acid isomerization leading to predominant formation of abietic acid. It was suggested that these processes should be taken into account to avoid errors in determining the contents of these acids in the oleoresin even in the case of statistical analysis.