Energy Saving Drying Technology And Quality Control Of Allium Fistulosum L.

The volume of dried Green onion is significantly reduced,which show that they are more conducive to transportation.At the same time,the dried Green onion could be stroage without special storage methods such as modified atmosphere and cold storage.Also,preservatives are not needed.Therefore,it is one of the important processing methods for Green onion.At present,the drying of Green onion mostly adopt the method of hot air drying with constant temperature,which consumes a lot of energy.Also,the quality could not be ensured.Drying with variable temperature is an improvement over traditional hot air drying with constant temperature.Drying with variable temperature could effectively save time and energy and help to provide more products with stable quality.This subject selected Green onion as raw materials to study the drying rate,energy consumption value and color difference value of Green onion after hot air drying at different temperatures,loadings and cut lengths.The single-factor experimental results were used to determine the process parameters of the response surface,and the energy consumption value,color difference value and rehydration ratio under the process conditions were studied.The low-field nuclear magnetic technology was used to detect the migration of three kinds of water inside the Green onion during the drying process,and a temperature-changing scheme for the Green onion was prepared.Quantitative qualitative research on flavor substances was conducted on fresh Green onion,constant temperature hot air dried Green onion,and variable temperature hot air dried Green onion.The main results of this study are as follows:1.Effects of single factor experiment on the quality of Green onion.The single-factor experiment of hot air temperature,loading capacity and cutting length was conducted.The indexes that had a greater influence on the drying rate and dry base moisture content curve were temperature and loading capacity.The color difference variance of Green onion showed the same trendy with the change of temperature and loading capacity,which was inconsistent in the change of cutting length.Energy consumption decreased with the increase of the loading capacity and increases with the length of the cut section.As the temperature increased,a parabolic trend that decreased first and then increased.The comprehensive color difference and energy consumption value determined the range of the response surface at the drying temperature of 55-65oC;the length of the cut section was 5-11mm,and the loading capacity was 0.5-1 kg/m~2.2 Response surface optimization of drying process of Green onion.The response surface experiment was used to optimize the hot air temperature,loading capacity,and length of the cut section,so that the minimum energy consumption and color difference,and the maximum rehydration ratio.Among them,the optimal parameters obtained were as following using energy consumption as the main indicator.drying temperature was59.19oC,loading capacity was 2.35 kg/m~2,and cutting length was 5 mm.Under the condition,the model predicted a rehydration ratio of 4.95,a color difference of 2.25,and an energy consumption value of 1.88 kwh/kg.3.Variable temperature drying experiment of Green onion based on LF-NMRBased on the response surface experiment and low-field nuclear magnetic resonance technology,the design of the temperature-changing drying process of Green onion.The overall temperature change range of the Green onion.Drying with variable temperature process was designed to be 80-60-40oC,and the cooling range was about 20oC at each stage.In addition,the drying time at each temperature state was determined by the low-field nuclear magnetic T2 inversion map to ensure scientific experimental design according to the law of moisture change.Finally,a temperature change plan of 80oC(1 h)-60oC(1.5 h)-40oC was determined,and the proposed three-stage temperature change could save energy by 20%compared with the optimal constant temperature drying.4.Effects of constant temperature and variable temperature drying on the flavor of Green onion.The flavor substances in fresh onions were quite different from those after drying.The main flavor substances in fresh onions were methyl sulfide(41%)and thioacetate(29%).But these substances basically disappeared after drying.Different drying processes had different effects on sample flavor.The main flavors of Green onion after hot air drying with constant temperature and hot air drying with variable temperature were close to each other,all of which were 4-ethylphenol,ethyl acetate,3-methyl butyraldehyde,3-methylthiopropanal and other substances.However,after drying with variable temperature hot air,the content of4-ethylphenol was about twice that of constant temperature drying,and the content of ethyl acetate was about 3 times that of constant temperature drying.After constant temperature drying,the content of 3-methylthiopropionaldehyde was 70%higher than that of variable temperature The content of 3-methylbutyraldehyde was about 2 times that of Drying with variable temperature.