Study On The Change Law Of Drying Quality Of Indica Rice Based On Cold Plasma Pretreatment

Paddy drying is an essential link to effectively connect the post-harvest and pre-storage.If the newly harvested paddy is not dried in time,it will be easy to cause mildew and germination.Under the background of the "Blue Sky Plan",carbon neutrality goals and Healthy China,new green and low-carbon drying technologies with high quality have been attracted more and more attention,such as heat pump drying.However,if heat pump drying was used alone,there are some disadvantages,such as long drying cycle,high environment requirements and so on.Therefore,the research on the combination of pretreatment technology and heat pump drying is of great significant to improve the drying rate for paddy and ensuring drying quality of paddy.In this paper,the effects of cold plasma technology on the micro structure and thermodynamic properties of indica rice were studied.The effects of cold plasma power,cold plasma treatment time,hot air temperature,and the ratio of tempering temperature to hot air temperature on drying characteristics and quality of paddy heat pump were studied.The mapping relationships between four test factors and key quality indicators were analyzed by Design Expert 10 software.The comprehensive analysis and evaluation method of membership degree was adopted to optimize the drying process parameters.Compared to sun drying and thin-layer hot air drying,the optimal process parameters for paddy heat pump drying after cold plasma pretreatment were obtained.The specific results are as follows:(1)Cold plasma pretreatment can reduce the enthalpy value of paddy,which will reduce the amylose content of paddy.The carbonyl and hydroxyl functional groups of paddy increased after cold plasma treatment,and the anisotropic reactive ion etching effect increased.Cold plasma pretreatment produced etching on the surface of paddy,with the increase of treatment power and time,the degree of etching was intensified gradually.(2)In the process of paddy heat pump drying,with the increase of cold plasma power,cold plasma treatment time,hot air temperature,and tempering temperature:hot air temperature,the paddy drying time was shortened,the drying rate and the effective water diffusion coefficient were increased.The activation energy of paddy heat pump drying is 47.72 KJ·mol-1.By comparing nine commonly used mathematical models of thin-layer drying for agricultural products,it is found that Weibull I model is the best model to characterize the drying dynamic characteristics of rice heat pump after cold plasma pretreatment.(3)With the increase of cold plasma power and cold plasma treatment time,the cracking rate and germination rate of paddy increased,and the head rice rate、the amylose content and fatty acid value decreased.With the increase of hot air temperature,the cracking rate、amylose content and fatty acid value increased,the head rice rate and germination rate decreased,With the increase of the ratio of tempering temperature to hot air temperature,the cracking rate and germination rate decreased,and the head rice rate、amylose content and fatty acid value increased.Therefore,too high hot air temperature and tempering temperature are not conducive to maintaining the quality of dried paddy.(4)The optimum process parameters for heat pump drying of cold plasma pretreated paddy are,cold plasma power 400 W,cold plasma treatment time 60 s,drying temperature 40℃ tempering temperature:hot air temperature 1.2.Under these conditions,the initial moisture of rice is 22.60%(w.b.)to the target moisture of 13.50%(w.b.),the average drying rate of paddy is 0.056844 g·(g·h)-1,the drying time is 2.25 h,the cracking rate is 3.0%,the head rice rate is 61.355%,and the fatty acid value is 22.48 mg KOH·100g-1,respectively.Under the optimal process parameters of cold plasma pretreatment,the paddy quality was close to that of sun drying,the drying time is 9.75 h shorter than that of sun drying,and the drying rate is 0.0414 g·(g·h)-1 higher than that of sun drying.In conclusion,the application of cold plasma pretreatment technology in paddy drying can shorten the drying time and increase the drying rate.At the same time,the quality of cold plasma pretreatment paddy heat pump drying under the best process parameters is close to that of sun drying,it shows that cold plasma pretreatment technology can be used for paddy drying.