Experimental Study On Rapid Measurement Of Moisture Content In Hot-air Drying Of Coprinus Comatus

Coprinus comatus is rich in nutrition,short in growth cycle,and has high water content in mature fruit bodies,so that it is not suitable for storage.Drying Coprinus comatus can not only reduce its water activity,inhibit microbial growth,improve storage period,but also preserve the nutrient content and flavor of fresh Coprinus comatus maximally.Hot air drying is one of the commonly used drying methods for Coprinus comatus.The moisture content in the drying process is an important indicator to measure the dryness and drying effect of the material.The traditional method takes a long time to measure the moisture content,and the measurement results are inferior in timeliness.Studying the rapid measurement technology of moisture concent of Coprinus comatus in hot-air dying and real-time monitoring of moisture content change during hot air drying of Coprinus comatus are essential for optimizing the control process,controlling the drying quality and judging the drying end point.Based on the previous studies,this paper summarizes several methods that can be used for the rapid measurement of moisture content of fruits and vegetables.For the defects of the prior art,a dielectric constant method and a mathematical model method were comprehensively used to design a device to rapidly measure the moisture content of Coprinus comatus in hot-air drying.A rapid measurement technology and method of moisture content of fruits and vegetables in hot air drying was proposed.The main research contents of the thesis are as follows:Based on the previous studies,this paper summarized some methods that can be used for on-line measurement of water content of fruits and vegetables,including the use of dielectric properties,nuclear magnetic resonance technology,mathematical model,hyperspectral imaging technology,CT technology and on-line weighing.Besides,the principle of measuring the moisture content of fruits and vegetables by each method is summarized.According to the principle of measuring water content by mathematical model method and dielectric constant method,using the IAP15W4K61S4 Micro Controller Unit as the main control chip and the high-precision AD7746 as the capacitive sensor,the hardware system and software system of the rapid hot air drying moisture content measuring device for fruits and vegetables were designed.It mainly consists of communication and power supply circuit,main control circuit,capacitance signal acquisition device,key input circuit,liquid crystal display and alarm device.The capacitive sensor collects the capacitive signal,and the microprocessor processes the capacitive signal and displays the final moisture content result through the LCD.The communication interface can be used for communication with the host computer,and the buzzer sends an alarm message at the end of drying or when the system is abnormal.The software system and measurement program are written in C language.The comprehensive application of dielectric constant method and mathematical model method was realized.Through the blanching pretreatment test,the best blanching pretreatment process before the hot air drying of Coprinus comatus was determined,that is,the best 15 s with water vapor blanching.After the optimal blanching pretreatment process,the optimization experiment of the hot air drying process of Coprinus comatus was carried out.Using the comprehensive scoring method for multiple indicators,combined with response surface analysis,the regression model between the comprehensive value of the index and each factor was established,and the optimal combination of process parameters was obtained.The test was carried out to verify the best hot air drying process of Coprinus comatus,namely hot air temperature 55°C,hot-air wind speed 1.35m/s,slice thickness 4 mm is the best combination of processes.Hot air drying experiments of fresh Coprinus comatus were performed on different conditions,and the thin-layer drying characteristics of Coprinus comatus were analyzed and 7 frequently-used mathematical models were used to fit the experimental data.The results showed that the Demir model is the best descriptive model for hot air drying of Coprinus comatus and can perfectly describe the hot air drying behavior of Coprinus comatus,on this basis,the mathematical model on hot air drying of Coprinus comatus was established,and the regression equation between the parameters a,b,k,n and the drying conditions in the model is obtained.At the same time,the relative dielectric of different water content was measured and analyzed.When the moisture content of Coprinus comatus is below 30%,the water content is linearly related to the relative dielectric constant.Based on this,a relative permittivitywater content calculation model is established.The result was verified under the optimal hot air drying technology.The results showed that the mathematical method or dielectric constant method could not accurately measure the water content during the hot air drying process of Coprinus Comatus.Only the combination of the two methods can accurately measure the water content during the hot air drying process,using mathematical model method in the uneven drying stage,and the dielectric constant method in the drying uniform phase.The relative error of measurement results is less than 5%.