| The planting area and yield of Walnut in China headed in the world,which plays an important role in the industrial structure adjustment and the increase of peasants' income.The loss rate in postharvest walnuts caused by insect was 20%?25%.It has become an urgent problem to control the insect in walnut post-harvest,to ensure the quality and to reduce the loss,At present,chemical fumigation is the most effective way to kill walnut storage pests.however,it has been banned because of its harm to human health and the ozone in the atmosphere.High energy radiation and electron beam killing methods were limited by high disposal cost and quality deterioration.The effect of microwave killing on insect is not good because of inadequate penetration depth and uneven heating.For walnut with large monomer size,low water content and uneven texture,it is very important to develop green insecticidal technology that combines insecticidal and quality with no chemical residue.Wen 185 and the major pests,Corcyra cephalonica and Indian meal moth were chosen as the research objects in this task.Based on the study of electromagnetic thermal properties and life rules of walnut and insect,the insecticidal action of post-harvest pests and storage quality in walnut were detected by radio frequency heating.In order to avoid eggs hatching and stop occurrence of insect.The details are as follows:(1)Terminal open circuit coaxial probe technology had been used to analyze the correlation among water content,temperature,frequency and dielectric properties of walnut kernel,calculate the penetration depth of electromagnetic wave at a specific frequency,and comparative the dielectric properties of the Corcyra cephalonica and Indian meal moth.(2)An insect heating plate system was used to analyze the thermal resistance of insect and eggs.The effect of electric heating plate and radio frequency combined with hot air on killing insect was studied,and the mechanism of radio frequency disinfestation was analyzed.(3)The color kinetics of walnut with heat treatment was constructed,and the feasible technological parameter of radio frequency disinfestation was determined by combining with the thermal death kinetics.(4)A single batch treatment technology for insect control in walnut was developed to optimize plate spacing for radio frequency heating,forced air cooling method and heating uniformity,to evaluate of the effects of radio frequency insecticides on storage quality and stability of walnut.(5)A continuous RF heating system was used to study the relationship between the lethal rate of insect and heating uniformity of the equipment,heating efficiency and processing quantity,which was aimed at discuss the possibility of industrialization of RF insecticide.The main results were described as follows:(1)Dielectric loss showed notable attenuation with increasing frequency,when the walnut moisture level was>8%and frequency was<100MHz.The loss factor of walnut kernel in radio frequency band was significantly lower than that of pest.RF had selected heating effect on walnut and insect.(2)The Corcyra cephalonica was more thermal-resistant than Indian meal moth,while the fifth-Instar larva were the most thermal-resistant stages.The minimum holding time detected were 150,50,10,2.5 and 15,10,5,2.5minutes of the fifth-Instar larva and eggs,when the required mortality was 100%under the condition that the respectively temperature of 44,46,48 and 50? with the heating rate of 5?/min.The thermal death kinetics of the Corcyra cephalonica was obtained ultimately.Under the selected heating conditions,the effect was mainly caused by the thermal effect of radio frequency treatment,but the non-thermal effects was not significant.(3)The color change of walnut during heat treatment was described by the first order kinetics.With the increase of heating temperature and holding time,the color values L*and b*decrease gradually.Compared with Corcyra cephalonica,the z value and activation energy of walnut are higher,heat resistant and less discoloration.(4)With 27.12MHz radio frequency treatment,turning over and mixing twice,heating at 55 ? by hot air and keeping for 5-6 min,stacking thickness<27cm as the technological parameters,the larva and eggs of Corcyra cephalonica can be completely killed before storage of walnut at the same time.When the insecticidal treatment quantity was 261.2kg/h,the average heating efficiency of the system was 68.8%.(5)RF could effectively kill the Corcyra cephalonica.The detection of 3 quality indexes(peroxide value,free fatty acid value and color)of walnuts insecticidal and post-storage showed that RF treatment had no significant effect on walnut quality and storage stability. |
PDF Full Text Request