Preliminary Research On The Purification Of Main Components In Spearmint Oil By Molecular Distillation

With development of the research on green food, the safe natural products withphysiology function are paid much more attention. Mentha spicata L., a species ofLabiatae, contains essential oil mainly composed of carvone and limonene. The spearmintoil is used as medicine for the treatment of expelling, inflammatory, hemostasis andantalgesic, widely applied in fields of food, medicine, daily necessities, cosmetics andtobacco. The oil is frequently used in drink, candy, toothpaste and tobacco in the form ofspice. Therefore, research on extraction and purification of components from spearmint oil,on the one hand, provides theoretical guidance for industrial production of carvone andlimonene, and on the other hand, is significant on the comprehensive exploitation ofspearmint oil.Herein, a new method, molecular distillation, was utilized to obtain the carvone andlimonene from spearmint oil. As compared with traditional methods of normal distillation,vacuum distillation and supercritical carbon dioxide, this method circumvents theirdisadvantages such as long operation time, high distillation temperature and lowseparation efficiency. The main studies are as follows:A HPLC method was established for the determination of carvone and limonene inspearmint oil, using methanol as external standard. The limonene and carvone wereseparated on a C18column (4.6mm250mm,5μm) using methanol–water (75︰25, v/v)as mobile phase at a flow rate of1.0mL/min, the UV detection wavelength was set at200nm and the column temperature was25℃. Under these conditions, the obtainedstandard curves for limonene and carvone showed good linear dependence of peak areaon concentration.Relative density, the solubility and the stability of the spearmint oil were alsodetermined and investigated. The results indicated the unsuitability of raw material forhigh temperature heating due to their thermal sensitivity. This demonstrated thatpurification of components from spearmint oil by molecular distillation was necessary. The separation and purification of carvone and limonene from spearmint oil with themethod of molecular distillation were investigated. The effect of separation conditions,including evaporation temperature, operating pressure, roller-wiped speed and feed flow,on separation were discussed respectively. Through orthogonal test, the optimum processconditions for yield and purity of target products were obtained. Under optimalconditions through short path distillation, the related results showed that the purity ofcarvone and limonene were increased to86.42％and76.35％, and their yields were81.71％and81.29％respectively.Based on the results of single factor experiments, the research on the purity and yieldof limonene and carvone by the two-element quadratic regression orthogonal compositeexperiments was carried out with constant roller-wiped speed (200r/min) and feed flow(2.0g/min). The effect of evaporation temperature and the distillation pressure onseparation was discussed. Concluded from results, the optimal conditions for the purity oflimonene were determined to be as following: the highest purity of82.52％can beobtained at evaporation temperature of27.9℃and distillation pressure of4.9mbar and thehighest yield of92.05％was obtained at evaporation temperature of58.4℃anddistillation pressure of6.4mbar. On the other hand, the highest purity and yield forcarvone were83.61％and90.14％respectively.