Ultrasonic-assisted Ionic Liquid Extracts The Flavor Of The Onion

Shallot, a kind of featured spicy vegetable in Lingnan, was large-scalely planted in Fujian Province and Guangdong Province, especially, in Baiyun District and Conghua District. Generally, shallot was sold as fresh vegetable, while only a small amount was processed into dehydrated one, showing low commercial value. To achieve the extraction of flavor compounds in shallot efficiently, [BMIM]PF6, an extraction solvent that was green, safe and recyclable ionic liquids, and technical means, such as ultrasound, vacuum distillation etc. were necessary. An efficient process was established to extract flavor compounds in shallot in order to prepare essential oil and to increase its commercial value. Furthermore, test of antioxidative and antibacterial activities and stability on essential oil above were studied, and its compositions were analyzed and identified.1. The establishment of technical process to extract flavor compounds in shallot by ionic liquids.Thiosulfinates content as the main index and sensory score as the auxiliary one were used to study the influence of the factors in extraction process by ionic liquids on the extraction effect of flavor compounds. Based on the results of single factor test, orthogonal test was conducted to confirm the optimal process parameters, that is, distillation of shallot at the temperature of 55? for 100 min after crushing when solid-liquid ratio was 2.5: 1, which makes TS content and sensory score reach up to 4.01% and 9 point respectively. By comparing the 1H-NMR spectrum of intact [BMIM]PF6 with the one used and recycled repeatedly, its stable and recyclable property was further confirmed.2. The establishment of extraction process by ionic liquid with ultrasonic assisted.To improve the yield and quality of flavor compounds, ultrasound-assisted extraction was added. The optimal extraction process, condition that ultrasonic extraction at 100 w for 16 min after crushing when solid-liquid ratio was 2.5: 1, was confirmed after single factor test and orthogonal test. Under this condition, TS content and sensory score reached to 5.80% and 9 point respectively. Besides, yield, glossiness, odor, TS content, of essential oil extracted by steam distillation method and ultrasonic extraction method were compared with that by ultrasonic assisted ionic liquids extraction method, suggesting that the latter one had the best extraction effect on flavor compounds.3. The study of the biological activity and stability on essential oil.Study of antioxidative and antimicrobial activities and storage stability on essential oil drawn a conclusion that essential oil had antioxidative and antibacterial activity. Regression equation was established to evaluate its antioxidative capacity and the results were as follow: superoxide anion radical O₂^·-<lipid peroxidation <DPPH radical <hydroxyl radical ·OH. Essential oil had the strongest capacity to eliminate ·OH, and the value of IC50 reached to 0.86 mg / m L. Noticeably, essential oil were recommended to be kept in a cool, sealed and dark condition for its sensitiveness to the changes of light and temperature. Besides, test of the inhibitory effect among Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Penicillium were conducted in vitro, showing that essential oil had certain but different inhibitory effect on them, and that on Penicillium was obvious while Bacillus subtilis was weakest. Being treated by essential oil, the ultrastructural surface of bacteria tested became rough, distorted and fractured without standard shape, indicating that the inhibition mechanism of essential oil was to destroy the structure of bacteria and to affect their normal growth.4. The analysis of essential oil compositionsSuch compositional variations in essential oil extracted by traditional method, such as steam distillation method and ultrasonic extraction method, and ultrasonic assisted ionic liquids extraction method used experimentally as had been demostrated via GC-MS analysis technology showed that ultrasonic-assisted ionic liquids extraction method was superior to the other extraction process and that [BMIM]PF6was inherent with efficient extraction capacity. In addition, the main components of essential oil derived from shallot were basically identical to that of onion known from related literatures, indicating that shallot had similar compositions and characteristics to Allium plant.