| Pepper powder belongs to the low water activity material and is an important condiment in people's daily life.In recent years,unsafe incidents caused by low water activity products have been increasing,so it's particularly important to find a reliable sterilization technology for such products.Radio frequency is a new type of sterilization technology,which has the advantages of good heating effect,fast speed,so can be used as one of the effective ways to sterilize pepper powder.At present,although most scholars have conducted radio frequency sterilization on materials,in order to avoid secondary pollution after sterilization and re-packaging,this paper aimed at sterilizing pepper powder packaged with EVOH / PA film,and studied the best process parameters of pepper powder under radio frequency.And the performance index of EVOH / PA film was measured to study the influence of radio frequency on the performance of packaging film.At the same time,in order to improve the heating effect of pepper powder,this paper measured the thermal physical characteristics of pepper powder,established and verified the radio frequency(RF)heating model of pepper powder.The main research results are as follows:(1)Changed the device electrode plate spacing(25 mm ? 40 mm),the water content of pepper powder(9.2%,11.4%,13.1%,15.3%),and studied the influence of two factors on the heating rate of pepper powder at the same time.The results show that the heating rate of pepper powder decreases as the plate's distance increases;as the water content increases,the heating rate of pepper powder increases.Studied the colony numbers inside pepper powder and the effect of radio frequency on the performance of EVOH / PA film at different temperatures(50 ?? 80 ?);performed storage tests on the packaging at the optimal sterilization temperature to study.The total number of colonies inside the pepper powder.The results show that the optimal sterilization temperature of pepper powder is 80 ?,and the total number of colonies don't change significantly after storage.Radio frequency has no significant effect on the mechanical properties,barrier properties and microscopic surface of the film.(2)Selected seven kinds of temperature(25 ?? 80 ?),three kinds of water content(9.1%,11.4%,13.1%),and measurement of heat physical properties and establishment of regression equations.The results showed that as the moisture content and temperature of the material increase,the thermal conductivity and specific heat capacity of pepper powder increase.When the water content and temperature of pepper powder change,the dielectric constant and dielectric loss also are affected.The theoretical equation of RF heating was deduced,and the COMSOL model was established and verified.The results showthat due to the electric field deflection during heating,a large temperature difference appeared in the corners and center of the pepper powder,which causes uneven heating of pepper powder.(3)Changed the sample moisture content(5%,10%,15%,20%),sample size(length 150 mm-750 mm,width 90 mm-450 mm,thickness 20 mm-60 mm),the results showed that as the water content increases,the heating uniformity decreases;when the surface area of the material is about 37% of the upper plate area,the heating uniformity is the worst.Changed the horizontal and vertical position of the material heating,and changed the electrode plate spacing(80 mm,100 mm,120 mm).The results showed that,at the same position,increasing the electrode plate spacing is beneficial to improve the uniformity;the beat heating position is the central position between the parallel plates.The effects of three external packaging media(PP,PEI,PA)at four thicknesses(1 mm,2 mm,3 mm,and 4 mm)on heating uniformity were studied,and the influence of fillet radius on heating uniformity was studied.The results showed that when the polyamide(PA)with a thickness of 2 mm is selected,the heating uniformity is the best,and as the radius of the outer packaging medium fillet increases,the heating uniformity improves. |
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