Determination of Essential Oils in Hops by Headspace Solid-Phase Microextraction

A solid-phase microextraction (SPME) method is described for the determination of the essential oils, humulene and caryophyllene, in the headspace of female hop cones and male hop lupulin samples. Optimized SPME sampling parameters for the determination of the humulene to caryophyllene (H/C) ratio for female hops (50 mg) and male lupulin (25 mg) samples include a 100 μm poly(dimethylsiloxane) SPME fiber and a 4 h sample exposure period at a temperature of 50 °C. Increasing the temperature to 90 °C or increasing the length of sample exposure at 50 °C promoted caryophyllene oxidation. In a survey of five female hop varieties, good agreement was found between the H/C ratio obtained by headspace SPME and conventional steam distillation. The H/C ratio for 10 male lupulin varieties determined by headspace SPME and pentane extraction also indicated good agreement between the two extraction methods.