Study On Ravine Radio Frequency Sterilization Technology

Raisins are world-wide dried fruit products that are rich in nutrients and are popular among consumers.Raisins are susceptible to microbial contamination during drying,transportation,etc.,such as air drying and sand,direct contact with raw materials,and pollution during transportation.Most consumers do not have cleaning habits before eating raisins,and there is a certain risk of eating.Radio frequency sterilization technology is a new type of thermal sterilization technology,which has great potential for commercial application.It can realize rapid heating of materials,and has the characteristics of large penetration depth and good heating uniformity.In this paper,raisins were selected as research objects to study the variation of dielectric properties of raisins with temperature,moisture content and frequency.The temperature distribution and heating rate of raisins under different water contents,different plate spacings and different rotation speeds were studied.According to the analysis of the results of radio frequency sterilization conditions and heat preservation test,a better sterilization process was obtained;according to the color,physical and chemical indicators and sensory evaluation,the optimal sterilization process was determined.(1)The dielectric constant and loss factor of raisins decrease in the frequency range of 1-3000 MHz,with the increase of frequency,and increase with the increase of raisin moisture content(12%-24%).It increases as the temperature(25 ° C-80 ° C)increases.RF penetration of raisins far exceeds microwaves.(2)During the RF heating process,the uniform rotation of the raisins can effectively improve the heating uniformity,but has no significant effect on the heating rate.The plate spacing has a significant effect on the RF heating rate of the raisins.The smaller the plate spacing,the faster the heating rate.The higher the moisture content,the faster the raisin heating rate,but the heating uniformity of raisins with different moisture content is different.The optimal conditions for RF heating uniformity of raisins: motor speed 40 r/min,plate spacing 160 mm,raisin moisture content 18%.(3)The higher the radio frequency sterilization temperature,the longer the heat preservation time,and the better the sterilization effect on the total number of colonies and mold in the raisins.The color of the raisins changed significantly before and after sterilization.Except for the significant reduction of vitamin C,other nutrients did not change much.(4)The optimal sterilization process is: the moisture content of the raisins is 18%.Under the condition of motor rotation speed of 40 r/min and plate spacing of 160 mm,the RF heating is about 243 s,and the material temperature rises to 70 °C.When the temperature was kept at 70 ° C for 5 min,the total number of colonies and molds could be reduced by 2 log values.