Seasonal variation in the essential oils extracted from leaves and inflorescence of different Ocimum species grown in Western plains of India

The content and composition of the essential oils obtained from different Ocimum species varies widely based on the geographical location, growth stage and harvesting season. Hence, the variation in the essential oil content and chemical composition of the leaves and inflorescences of the different Ocimum species (Ocimum santum ‘Purple’, O. sanctum ‘Green’, O. basilicum, Ocimum gratissimum Land Race 1 & Land Race 2, Ocimum viride and Ocimum canum) growing in Western plains of India were determined for two harvesting seasons. The essential oil was extracted using hydro-distillation and chemical characterization was done on gas chromatography/mass spectrometry (GC/MS). Recovery of the essential oil ranged from 0.18% to 0.774% during pre-monsoon and 0.141–0.748% during post-monsoon. Amongst the seven Ocimum species studied, leaves recorded higher essential oil content compared with inflorescence in all species except in O. basilicum and O. canum. Further, essential oil content during post monsoon was lower compared with pre-monsoon harvest in all the species irrespective of the plant parts. Highest essential oil content was recorded in O. viride leaves (0.774%) followed by O. gratissimum LR1 leaves (0.641%) and the least was recorded in Ocimum canum leaves (0.18%). Amongst the different species analyzed, Ocimum gratisimum LR-1 was found to be the richest source of eugenol (53–89%) followed by O. santum ‘Purple’ and O. sanctum ‘Green’ and O. viride Ocimum gratisimum LR-2 was rich in methyl iso eugenol (40.26–53.21%). While, O. santum ‘Purple’ type contained considerable amount of methyl eugenol, which was absent in ‘Green’ type. O. basilicum analyzed in this study is methyl chavicol rich type (33.32–79.2%), but this compound was absent in other species. Ocimum canum was the only species rich in d-camphor (13.29–29%). The identified eugenol rich species of Ocimum were identified as cheap alternative sources of eugenol as compared with clove.