Microencapsulation Technology Of Onion Comprehensive Extract And The Effect Of Onion Drying Pretreatment

Onions(Liliaceae,Herbs)are grown all over the world.The main functional components of onions are flavonoids,sulfur compounds(onion essential oil).Another of the most valuable chemical components in onions is prostaglandin,in addition to protein and various amino acids.Functional ingredients in onions have attracted more and more attention.It is a hot research topic in recent years to use the effective ingredients of onions reasonably.In order to solve the problem of inconvenience in extraction process caused by high water content of onion,fresh onions were made into onion powder by hot air drying,freeze-drying and microwave freeze-drying.The effective ingredients were extracted from onion powder by different extraction methods.The effects of different drying methods on onion extracts were studied,and the suitable drying method for extracting the effective ingredients of onions was determined.The extracted effective ingredients were embedded in microcapsules to facilitate the extraction of onion powder.The active ingredients of onion are widely used.The main research content is as follows:(1)Through comparing the effects of different drying methods on the extraction rate,quality and extraction time of flavonoids in onion,we determined that the most economical and effective drying method was hot air drying.The extraction time of MFD onion powder was the shortest,3 h.The antioxidant activity of flavonoids extracted from AD onion powder was the highest(30.7%),but the color difference was large.FD onion powder has the highest extraction rate,but the highest energy consumption.In order to obtain onion powder which can be used to extract flavonoids from onion quickly,economically and effectively,MFD or AD method can be used to dry onion powder.(2)Comparing the effects of different drying methods(AD,FD and MFD)on the extraction of essential oil from onion,it was found that microwave freezedrying of onion powder had high yield and short extraction time.The optimum extraction conditions of onion essential oil were determined by single factor and orthogonal experiments: preparation of onion powder by microwave freeze-drying,extraction temperature was 40 C,time was 50 min.The antioxidant activity of onion essential oil was studied.It was found that onion essential oil had potential antioxidant activity.(3)The types of wall materials,core-wall ratio and solid content of onion essential oil microcapsules were studied,and the optimum technological conditions for preparing onion essential oil microcapsules were obtained: Arabic gum + ?-cyclodextrin(4:3)as wall materials,core-wall ratio was 1:4,solid content was 20%.The microcapsules prepared under the optimum conditions had the highest embedding rate,92.35%,the microstructures more in line with the requirements of preparation of microcapsules,and sensory evaluation.It is more acceptable to consumers and the quality index of microcapsules shows that they are of good quality and good storage stability.(4)Spray drying conditions of onion essential oil microcapsules were studied.The best preparation process of microcapsules was obtained by response surface optimization: emulsification temperature was 61?,air inlet temperature was 177?,feed flow was 900 mL/h,and the encapsulation rate of microcapsules reached 92.06%.The results showed that the microencapsulation of onion essential oil could play a good protective role on onion essential oil by spray drying method.The microcapsule wall material had good controlled release effect on the core material.The Avrami' s formula was applied to onion.It is feasible to analyze the release characteristics of essential oil microcapsules.