Variation in essential oil composition of rose‐scented geranium (Pelargonium sp.) distilled by different distillation techniques
The rose-scented geranium (Pelargonium sp.) cultivar ‘Kelkar’, grown in the agroclimatic conditions of the western Himalayas, was processed by various hydrodistillation methods, which revealed that water distillation of the herb gave a higher oil yield (0.16–0.22%) than the water–steam distillation (0.09–0.12%) and steam distillation methods (0.06–0.18%). The samples were analysed by GC and GC–MS to study and compare the essential oil compositions which revealed that the oil distilled by the water–steam distillation method contained a higher content of monoterpene hydrocarbons (1.7%), followed by steam distillation without cohobation and without recycling (1.5%). A higher content of sesquiterpene hydrocarbons (4.4%) was found in cumulative oil followed by ‘direct oil’ (4.2%) obtained by steam distillation with cohobation and without recycling of hydrosol, followed by the water–steam distillation method (3.4%). ‘Decanted oil’, recovered from redistilling the hydrosol obtained by steam distillation with cohobation and without recycling, contained maximum monoterpene cyclic ethers (1.1%) and carbonyl content (9.9%), closely followed by water–steam distillation method (1.1% and 7.2%, respectively). Steam distillation without cohobation and without recycling of hydrosol yielded essential oil with a higher percentage of esters (21.1%), followed by ‘direct oil’ (16.6%). Lower ester content (5.3%) was noticed in ‘decanted oil’, followed by oil distilled by steam distillation with cohobation and with recycling (11.8%) and oil distilled in a Clevenger apparatus by the water distillation method (12.2%), whereas maximum total alcohols were found in the ‘decanted oil’ (75.1%), followed by oil from the Clevenger apparatus (72.8%) and steam distillation with cohobation and with recycling (69.1%). A lower alcohol content was found in the ‘direct oil’ (55.2%) closely followed by ‘cumulative oil’ (55.8%). The variation in total alcohol and ester contents in geranium oil samples, distilled by using different processing techniques on pilot scale distillation, is mainly due to hydrolysis of some volatile constituents. This was further supported by acid values of the oils, along with other physicochemical properties, such as speciﬁc gravity, optical rotation, refractive index, solubility in alcohol, ester value with cold and hot methods, estimation of ester content as geranyl formate and geranyl tiglate, ester number after acetylation, and ester number after formylation with aceto-formic acid and formic acid. Methods have been standardized and proposed for distillations of speciﬁc quality, e.g. ester-rich and alcohol-rich geranium oils, to meet different requirements of the industry. Copyright © 2004 John Wiley & Sons, Ltd.