Extraction Of Essential Oil From Tillering Onion And Preparation Of Its Nanocapsules

Tillered onion(Allium cepa var.aggregatum)is,widely grown and highly productive onion with a dense structure and high nutritional value.The essential oil of Allium cepa var.aggregatum contains unique onion flavour and physiologically active components,but is susceptible to environmental factors and is not stable and easy to store.In this experiment,different methods were used to extract the essential oil of Tillered onion and optimise the extraction process.The ionotropic gelation method was used to prepare tillered onion essential oil nano-microcapsules,and the performance of the nano-capsules was evaluated by particle size,scanning electron microscopy and Fourier infrared spectroscopy measurements.The experimental results were as follows :1.Determination of the extraction process of the essential oil of tillered onion:The experiment used water distillation method,ultrasonic assisted extraction method and microwave assisted extraction method to extract the essential oil of Tillered onion,and the best extraction conditions were screened out by single-factor test and optimized by using response surface.The results showed that the best extraction conditions for the essential oil of tillered onion were as follows: liquid to material ratio of 7.7 m L/g,soaking time of 3 h,soaking temperature of 31℃ and extraction time of 3.3 h.The extraction rate of essential oil of tillered onion was 0.277% under these conditions;the best extraction conditions for the essential oil of tillered onion by ultrasonic assisted extraction were as follows: liquid to material ratio of 8.2 m L/g,ultrasonic power of 280 W,ultrasonic time of 36 min and ultrasonic temperature of36℃.The best extraction method for tillered onion essential oil was: liquid to material ratio 8.2 m L/g,microwave power 401 W,microwave time 7.3 min,microwave temperature 30℃.The extraction rate of tillered onion essential oil was 0.473% under these conditions.Comparing the results of the three extraction methods,the subsequent experiment used microwave-assisted extraction method to extract the essential oil of tillered onion.2.Analysis of the composition of the essential oil of tillered onion and determination of its antibacterial effect: The composition of the essential oil of tillered onion was analysed by using gas chromatography-mass spectrometry(GC-MS).57 components were figured out in the experiment,of which 34.811% were sulphur-containing compounds.The filter paper diffusion method was used to evaluate the antibacterial activity of the essential oil of tiller onion and to investigate the effects of p H,temperature and UV irradiation time on the antibacterial activity of the essential oil.The results of the diameter of the inhibition circle and the minimum inhibition concentration(MIC)of the essential oil of tillered onion showed that the essential oil of tillered onion had the best inhibition effect on Salmonella enterica,followed by Escherichia coli and Shigella,and was moderately sensitive to Staphylococcus aureus;after the essential oil of tiller onion was heated to 60℃,the inhibition effect gradually decreased with the increase of temperature;The effect of p H on the antibacterial effect of the essential oil of tillered onion was obvious,with neutral conditions having the best antibacterial effect and acidic conditions having a better effect than alkaline conditions;UV irradiation time has no significant effect on the antibacterial effect of the essential oil.3.The nano-microcapsules were prepared by ionic gelation method with chitosan as the wall material and tiller onion essential oil as the core material.The effect of core-to-wall ratio,p H value,mass ratio of Tween-80 to essential oil and reaction time on the embedding rate of the nano-microcapsules was investigated by orthogonal test.The results showed that the optimum preparation process was as follows: core to wall ratio 0.8:1,p H 4.5,Tween-80 to essential oil mass ratio 1:1,reaction time 60 min.The average embedding rate of the nanocapsules under these conditions was 43.35% and the average particle size was 312.5 nm.From the SEM,it could be seen that the tillered onion essential oil nanocapsules showed a relatively regular round shape and the successful encapsulation of the tillered onion essential oil was confirmed by Fourier infrared spectroscopy.