Study On The Application Of Ionic Liquids In The Preparation Process Of Onion Essential Oil

The onion is a bulbous plants of the genus Allium in the lily family, It was used all overthe world not only as a kind of food, but also as a popular remedy with a long history. Thesulfer-containing compounds produced from catalytic hydrolysis of more stable alliin byalliinase in crunched fresh onion were suggested as essential pharmacological activecompounds of onion, especially thiosulfinates（TS）, and they mainly exist in the onionessential oil. Maximum enrichment of onion essential oil is the most effective method toensure of onion function.Enrichment of sulfur-containing compounds in onion is related not only with thealliinase activity, but also closely with extraction method of onion essential oil. To avoidenzymatic hydrolysis of alliin to lachrymatory factor （LF） to evaporate by the lachrymatoryfactor synthase （LFS） in onion, in this paper, instead of onion alliinase, garlic alliinase waschosen to catalyze hydrolysis of the onion alliin. In addition, the new and high-performanceionic liquids （ILs）[BMIM]PF₆as bio-catalytic medium and extraction agent was used forpreparation and extraction of onion essential oil. Firstly, the method of spectrophotometry todetermine the content of TS was established. Then the influence factors on the process ofpreparation essential oil onion by [BMIM]PF₆and garlic alliinase were investigated. Finally,different methods were used to prepare the onion essential oil, respectively. And the chemicalconstituents of the essential oil were analyzed and compared by GC-MS method. The mainresults were as follows:1. The influence factors on determination of the content of TS by spectrophotometrywere investigated. L-cysteine can react not only with TS, but also with5,5’-two thiobis （2-nitrobenzoic acid）（DTNB） reaction, and they can generate color2-nitro-5-thiobenzoic acid（NTB）. During the experiment, TS react with excess L-cysteine at first, and then add excessDTNB to react with the remanent L-cysteine, the generated NTB with a maximum absorptionat the wavelength of412nm, the amount of DTNB involved in the reaction can be obtained bymeasuring the absorbance value, then the content of L-cysteine reacted with TS can becalculated, so that the content of TS can be obtained. The results showed that the optimumconditions for TS content detection were the pH of the color reaction system was7.5-8.5, thetemperature was25-30℃and the detection time was controlled within8min, L-cysteineaddition was3mL, TS and L-cysteine reaction time was7min. This method is simple,sensitive and high accuracy, it apply to the determination of TS not only in the onion, but alsoin the other Allium plants.2. Preparation of onion essential oil mainly includes two steps: enzymolysis and extraction. In order to improve the efficiency of enzymatic hydrolysis, this paper try to addhydrophobic ILs [BMIM]PF₆during the hydrolysis process of propreparation of onionessential oil, given full play to its function as a catalytic media and extraction solvent. Theoptimal conditions were obtained by studying on the process of enzymolysis:50g fresh onionkilled enzyme by microwave, adding50mL phosphate buffer extract solution containing[BMIM]PF₆25%and pH was7.5, and then added garlic in accordance with the enzymedosage4g garlic/100g fresh onion, beating, time is80s, enzymolysis time was100min inthe shaker （160rpm） with the temperature was40℃. The results also showed that theconcentration of TS in the catalyst system containing ILs was higher than the concentration inthe system without ILs, and the enzyme to pH and the thermal stability is also improved in thecatalytic system containing ILs. But because the viscosity is large of ILs itself, increase thetransfer resistance between enzyme and substrate, so it took a long time by hydrolysis, thisalso showed that the concentration of ILs in the system should not be too much.In order to improve the efficiency of extraction of essential oil by ILs in medium afteronion enzymolysis, ultrasonic assisted extraction technology was used in this paper. The mainaffect factors in the extracting process were investigated. The results are as follows: ultrasonicpower was150w, ultrasonic time was5min and ultrasonic temperature was35℃. ILs asextraction solvent compared with dichloromethane as extraction solvent under the sameextraction conditions in this paper, the result was that efficiency of extraction by using[BMIM]PF₆was significantly better than using dichloromethane.3. Using four methods to prepare of onion essential oil, and the chemical constituents ofthe essential oil were analyzed and compared by GC-MS method. The results showed that:The kinds and content of sulfur-containing compounds in the onion essential oil by[BMIM]PF₆and garlic alliinase were highest. In addition, the kinds and content ofsulfur-containing compounds in the onion essential oil by garlic alliinase were both higherwhether or not to use [BMIM]PF₆.