Effects Of Low-Temperature Plasma Pretreatment On Drying Kinetics And Storage Characteristics Of Corn Kernels

As the main food crop in our country,the storage security of corn is related to national economy and people's livelihood.Corn is prone to mold effects and spoilage during storage and transportation owing to its high moisture content after harvested,which needs to be dried in time to achieve safe storage.So far,corn drying methods used in China mainly include natural drying and hot-air drying,but these methods are limited by low drying efficiency,large energy consumption,loss of nutrition after drying,and deterioration of sensory quality.Therefore,it is of great significance to explore a new drying technology which can improve drying efficiency and ensure drying quality.In this study,low-temperature plasma technology was used to pretreat corn kernels.Through the analysis of corn apparent structure and chemical composition evolution after treatment,the plasma action mechanism was explored,and the effects of different plasma conditions on corn drying kinetics were also studied to optimize the drying process parameters.On this basis,the impact of this technology on the storage characteristics of corn after drying was further studied.The main work of the research are as follows:(1)Surface topography of the plasma-pretreated corn kernels was visualized via scanning electron microscopy,atomic force microscopy,fourier transform infrared spectroscopy and x-ray photo electron spectroscopy.The results show that the plasma has an etching effect on the corn surface.Plasma pretreatment can change the surface topography of corn kernels with some micro-holes and cracks.With the increase of the pretreatment power or pretreatment time,the micro-holes and cracks of corn kernels become deepen and denser,the surface roughness increased.Oxygen-containing groups such as-OH,-COOH,C=O and C-O were accessed on the surface of plasma-pretreated corn kernels.The oxygen to carbon ratio(O/C)atomic ratio increased with the plasma pretreatment power or pretreament time.(2)Thin-layer drying after plasma pretreatment of corn kernels was tested.The effects of pretreatment time,pretreatment power,and drying temperature on the drying performance and kinetics of corn kernels were studied.The plasma pretreatment increase the effective diffusion coefficient of corn kernels.With the increase of the pretreatment power,the effective moisture diffusion coefficient of corn kernels increases;With the extension of the pretreatment time,the effective moisture diffusion coefficient first increases and then decreases;Plasma pretreatment enhances the drying rate and shortening the drying time more effectively for the corn kernels with lower activation energy;After pretreatment power of 500 W for 30 s at 37.5?,drying time was shortened by a maximum of 21.52%,and the drying rate was increased by 8.15%.(3)Optimization of plasma pretreatment of corn kernels hot-air drying process using response surface method.The responses were drying time and drying rate.The optimal pretreatment conditions are drying temperature at 52.5?,pretreatment time of 50 s and plasma power of 500 W,drying time was 1.33 h,which was 33.50%shorter than the control group;the drying rate was 3.5359(g/g?h^-1),which was25.61%higher than the control group.(4)Experiments were carried out to explore the effects of cracking rate and starch yield on corn kernels of hot-air drying after low-temperature plasma pretreatment.The results show that the plasma pretreatment time,plasma pretreatment power or drying temperature had no significant effect on the stress crack rate and starch yield of dried corn kernels.The stress crack rate of corn kernels was 1.13%to 5.80%and starch yield was 60.78%to 70.36%in the test ranges.Under the optimal process parameters,stress cracking rate and starch yield of corn kernels were 5.74%and63.12%,which were increased by 33.50%and 25.61%compared with the control group.(5)Aspergillus flavus and Aspergillus parasiticus were selected as the research objects,and the changes of mold growth during storage on corn during drying were investigated.The results show that the growth rates of Aspergillus flavus and Aspergillus parasiticus with different moisture content(16%,19%and 22%)increase first and then stabilized with the extension of storage time,and rise with the increment of corn moisture contents or drying temperature.The increase in neither plasma pretreatment power nor pretreatment time significantly affect the growth of mold during corn kernels storage.Plasma pretreatment has no adverse effect on storage characteristics and ensures the quality of dried corn kernels.Plasma pretreatment drying can effectively accelerate the drying rate and shorten the drying time.This technology does not cause damage or change to the internal com ponents of corn kernels,and has no adverse effect on the storage performance of corn after drying.