Research On Radio Frequency Pasteurization Technology Of Chili Powder

Microbial contamination is a vital obstacle needed to overcome for food safety of spice seasoning.Due to the lack of effective pasteurization technology and unified national standards,the health and security conditions of spice seasoning which sells on the market is difference.However,in recent years,a series of food safety incidents which caused by spice seasoning make people to know microbial contamination of spice seasoning again.Radio frequency pasteurization technology is a new type of electromagnetic heating pasteurization technology.It is very suitable to pasteurization of solid condiments because of high heating efficiency,good uniformity and high penetration depth,and it extremely has the potential to become a new mode of commercial application solid condiments pasteurization.Chili powder was selected as the research object.Dielectric properties,temperature distribution,heating model,the fatality rate of microbial and the quality evaluation after pasteurization were successively researched in the process of radio frequency pasteurization.The detailed research contents were completed as follows:(1)Dielectric properties of chili powder were measured between 8 and 3000 MHz using an open-ended coaxial-line probe technique at 4 bulk densities,4 moisture contents and 6 temperatures.Dielectric properties prediction model of chili powder were established with moisture content and temperature under 27.12 and 2450 MHz.(2)In order to obtain the temperature distribution of chili powder,infrared thermal imager and optical fiber temperature measurement system were used in the process of radio frequency heating to monitor the temperature of chili powder.The heating model of electrode gap,moisture content and sample thickness was established.(3)A pilot-scale 27.12 MHz,6kW RF system was used.Experiments combined with 3 electrode gaps,3 moisture contents and 4 temperatures were done to select optimal pasteurization process.(4)The difference of efficiency and the quality after pasteurization between RF and dry heating pasteurization were researched.The main results were described as follows.(1)Dielectric constant and dielectric loss factor of chili powder decreased as the frequency increased between 8 to 3000 MHz.This phenomenon became obviously when moisture content(4%<W<15%)and temperature(25<T<100℃)increased.Under a certain frequency,dielectric constant and dielectric loss factor didn’t appeared fixed rules as the bulk densities changed.But it increased as the moisture content and temperature increased.Penetration depth decreased as the frequency,moisture content and temperature increased.(2)The temperature distribution of chili powder in the process of RF heating as follows: In the horizontal direction,it appeared as an edge heating phenomenon,and temperature increased from the centre to the edge.In the vertical direction,it appeared that the sample temperature of lower part was significantly higher than that of the upper part.The hot temperature was at the geometric centre of the sample.Cold spot appeared at the sample surface.Averaged temperature of chili powder increased linearly between 20 to 100℃.Uniformity index began to decrease quickly when the temperature reached 80℃.(3)The fatality rate of total number of colonies and mold of chili powder increased as temperature increased.When the final temperature reached 80℃ or above,the effect of pasteurization was meet the requirements of national standards.The effect of RF pasteurization was not obvious in different electrode gaps and moisture contents.(4)The pasteurization rate of RF pasteurization was more than 10 times of dry heating pasteurization in the same condition.The color of chili powder was not obvious,and the group of RF treatment was more closed to control on the volatile odor after RF and dry heating pasteurization.