Variations in quantitative and qualitative characteristics of wild marigold (Tagetes minuta L.) oils distilled under vacuum and at NTP

Essential oil of Tagetes minuta was distilled in vacuo in a mini distillation apparatus to study and compare the qualitative and quantitative characteristics vis-`a-vis oil distilled by conventional distillation technique at normal temperature and pressure (NTP),which revealed that higher oil yield (1.56%) was obtained in the oil distilled by conventional distillation technique at NTP and decreased gradually with increase in vacuum to 150mmHg (1.16%), 200mmHg (1.07%) and 225mmHg (0.91%). Concentration of monoterpene hydrocarbons (MH) was found maximum (55.3%) in the oil distilled at NTP and decreased with increase in vacuum to 150mmHg (35.2%), 200mmHg (31.4%) and 225mmHg (27.5%). On the contrary, oxygenated monoterpenes (OM) were found minimum (22.9%) in the NTP distilled oil but increased with increase in vacuum to 150mmHg (55.4%), 200mmHg (61.3%) and 225mmHg (65.3%). Sequential evolution of chemical compounds was also studied by distilling the oil at 225mmHg vacuum and found that the lipophilic effect plays an important role in distillation of MHs. Due to the high concentration of these unsaturated MHs, the oil gets polymerized easily when exposed to unfavorable conditions and this can be minimized by reducing the concentration of these compounds by distilling the plant material under vacuum thus increasing the shelf life of the oil. The physicochemical properties of the oil were also evaluated. Vacuum distilled oil samples possessed better solubility in alcohol than NTP distilled oils. The olfactory evaluation of the samples revealed that the oil distilled at NTP possessed powerful, peculiar and disagreeable odour with burnt note, whereas the oils distilled in vacuo has pleasant odour varied from powerful fruity odour without any burning note to near true-to-nature odour of the flowers with increase in vacuum. Due to these improved characteristics, the in vacuo distilled oil of T. minuta is recommended for exploring its application in high grade perfumes, flavours and other formulations