Drying Characteristic Of Peach Pomace And The Impact Of ICPD Treatment On Pectin Extraction

In this study,the drying charateristics of peach pomace during hot air drying(HAD),infrared radiation drying(IRD)and vacuum drying(VD)were investigated,and the mathematical models of corresponding drying method were established.The characteristics of moisture diffusivity and glass transition during HAD and IRD process were also investigated.Furthermore,the instant controlled pressure drop(ICPD)was used as pre-treatment mothed prior to drying of peach pomace.The impact of ICPD treatment on the pectin fractions(water-soluble pectin,WSP;chelator-soluble pectin,CSP;Na2CO3-soluble pectin,NSP)and pectin extraction were studied.The extraction parameters of pectin from peach pomace were optimized by RSM design.The main conclusions are as follows:1.The three drying methods all belong to the falling rate drying process,in which the rate of IRD was the highest.All drying processes of peach pomace were fitted by five thin-layer drying models,which indicated that the Midilli et al.model was the best model to describe the drying process.The value of effective moisture diffusivity of IRD was higher than those of HAD and VD,and the activation energy of VD was the highest.Under VD condition,the retention of polyphenol was the highest and the total color difference(?E)was the lowest,but they were not significantly different from the values of IRD.Compared to HAD and VD,IRD therefore is a more effective drying method for peach pomace.2.The moisture migration was mainly through diffusion during the falling rate drying process of peach pomace,and the values of moisture diffusion rate during IRD were higher than those during HAD in all drying stages.It could be included from the state diagram of glass transition and inner-center temperature curve that the center temperature of samples increased rapidly under IRD compared with HAD in the initial stage of drying.The center of samples was in a rubbery state and less casehardening,which was more conducive to diffusion of internal moisture and mass and heat transfer.3.Effect of ICPD treatments on the content of WSP,CSP,and NSP from peach pomace were not significant.The content of Gal A in WSP was decreased while increased in CSP.Degree of esterification(DE)decreased significantly for CSP,while there was non-obvious influence on DE of WSP at 90? but significant reduction at105?.In addition,the three main monosaccharides including Gal,Ara,and Rha would increase in WSP but decrease in CSP and NSP.The linearity of WSP molecules decreased and CSP molecules increased after ICPD treatments.It can be seen depolymerization in WSP from the elution curve,but not in CSP and NSP obviously.4.The optimal pectin extraction conditions from peach pomace were determined by response surface optimization.The p H of 1.3,temperature of 93.87°C and heating time of 141.96 min were determined as optimal conditions with a maximum yield of13.84%,which was close to the predicted value(13.70%).ICPD treatment can effectively improve the extraction yield of pomace pectin and reduce the viscosity of pectin.