Comparison of Major Compounds in Essential Oils Steam Distilled from Fresh Plant Material of South African Hop Varieties

Apart from the importance of bittering acids in the brewing sector, hops also produce terpene-rich essential oils, recognised for their therapeutic benefits. Agri-processing practices of this crop in South Africa produce tonnes of discarded (waste) plant material that could still contain sufficient bioactive compounds to justify upcycling. This research aimed to determine the chemical composition of steam distilled essential oils from fresh hop plant material destined for disposal. Essential oils from eight hop varieties unique to South Africa were produced on industrial scale using steam distillation. Chemical profiling was performed using GC-FID and MS. A total of 208 compounds were identified and oil consisted largely of terpenes (89.04 ± 1.89%) as well as aliphatic esters and -ketones (6.1 ± 1.15%). Myrcene (27.8-48.15%) was the most abundant monoterpene and α-humulene (19.52-24.98%), β-caryophyllene (8.47-13.73%) and β-farnesene (2.08-7.57%) constituted the majority of the sesquiterpenes fraction. Experimental variety XJA2/436 had the highest myrcene fraction (48.15%) and its chemical composition was markedly different from the other varieties. The major compounds in African Queen hop oil were methyl (4Z) decanoate (0.74%), 2-tridecanone (0.77%) and β-farnesene (7.57%). Southern Dawn hop oil contained the highest fractions of 2-undecanone (1.21%) and α-humulene (24.89%) and Southern Passion hop oil contained the highest β-caryophyllene fraction (13.73%). These findings established that fresh hop vegetative biomass shows promise to be transformed into a valuable resource.