Study On Characteristics And Quality Of Vacuum Drying Of Corn

Corn dryness is prone to different degrees of quality damage and internal tissue damage.In the study of corn dry quality,it is rarely associated with the preservation of nutrients in corn.Therefore,this paper proposes to use nutrient content preservation combined with commonly used evaluation indicators for corn drying.Microwave vacuum drying technology and vacuum pulsation technology were used to study the drying characteristics and quality of corn.The internal microstructure was observed by scanning electron microscopy to explore the internal mass transfer process.From the influence analyzed through the microstructure on quality,use the response surface method to optimize the queuing scoring method and entropy weight.The method established comprehensive evaluation index to optimize the process parameters of corn drying,which solved the problem of nutrient preservation in corn drying,improved the quality and drying efficiency of dried corn,andreduced energy consumption.(1)Study on drying characteristics:The drying kinetic curves of microwave vacuum drying and vacuum pulsation drying in corn were studied.The results showed that vacuum pulsating drying and microwave vacuum drying were slow drying,and the temperature had the most significant effect on the drying characteristics of corn.When the drying temperature,vacuum degree and microwave power were appropriately raised,it was found that the drying speed and time can be improved by density,vacuum pulsation ratio and reduction of loading.The analysis showed that the microwave vacuum drying intensity is stronger than the vacuum pulsation,and the drying time is also obviously shortened.From the effective diffusion coefficient of water,moisture diffusion,dry activation energy Ea in microwave vacuum drying was higher than vacuum pulsation,which indicated microwave vacuum drying was more benefical.(2)Study on drying quality characteristics of corn:The content of nutrients(protein,starch,fat),energy consumption and crack rate of corn samples were evaluated.The results showed that microwave vacuum drying with temperature below 55?was better than vacuum pulsation drying than natural air drying.The presence of vacuum conditions maintained the corn nutrients well.When the temperature is higher than 60?,the nutrients inside the corn will be obviously damaged.The higher the vacuum,the lower the temperature,the less the load,the longer the vacuum retention time,the better the quality of the corn,and the higher the quality with the increase of the power density.After the reduction.From the analysis of variance,microwave vacuum drying had a more significant effect on the dry nutritional quality of corn.With the increase of temperature and microwave intensity,the vacuum degree was reduced,the vacuum holding time is decreased and the load and the crack ratewas increased.During the drying process of corn,the soft endosperm of corn had obvious bulgng,the color was light,and the drying was excessive.The greater the intensity,the more pronounced the expansion of the protrusion,the more serious the color loss,and the higher the temperature,the more severe the microwave vacuum drying than the vacuum pulsation.(3)Study on the microstructure of corn drying:Microscopic scanning electron microscopy was used to observe the surface structure and morphology of corn surface.It showed that the drying strength and the mesh structure of corn epidermis were significantly different.The greater the drying strength,the more obvious the dent of the corn skin mesh structure,and the results of vacuum pulsation and microwave vacuum were similar with the increase of capillary channel width;the surface of starch granules had multiple planes and edges,the surface structure was tight,the edges were smooth,.With the increase of drying strength,the more serious the microcrack,the surface of some starch granules pitted,and gradually appeared holes.Structure,some particles had swelling,but no obvious surface burst phenomenon.When the temperature was 65?,some of these starch particles were constantly collapsing.The starch structure wound be transformed into a space-crossing network-like macromolecule,whichgelatinized.The pressure in the vacuum pulsation drying chamber was continuously cyclically changed,and the microscopic pores of the material were continuously squeezed and expanded,and the micropores were deepened.(4)Corn drying response surface optimization:Based on the research on the drying characteristics and quality of corn,it was found that microwave vacuum drying is more suitable for corn drying.The results of response surface optimization showed that the optimal process parameters of corn were:vacuum degree-90KPa,temperature 56.98?,power density 0.8W/g.The comprehensive score reached 7.65.At this time,the oil content was 3.80%,the protein content was 7.42%,the drying rate was 0.77,the energy consumption was2318kJ,and the crack rate was 15.20%.The comprehensive score YZ regression model equation is:Y_Z=-79.026+2.472A+0.0875B+13.549C-0.001AB-0.116AC-0.073BC-0.02A~2+0.0007B~2-0.24C~2(A-temperature;B-vacuum degree;C-power).