Effects of heat treatment on the rheological properties and structure characteristics of pectin in cloudy peach juice

In this study, fresh squeezed peach juice were investigated for changes of rheological properties and pectin structure induced by different heat treatments, including pasteurization at 65 ℃ for 30 min, 95 ℃ for 5 min and ultra high temperature treatment (UHT) of 110 ℃ for 3 s.Compared with the untreated peach juice, after heat treatment (60 ℃, 30 min) the viscosity of peach juice had increased, after heat treatment (95 ℃, 5 min and UHT) the viscosity of peach juice had decreased; Compared with the untreated peach juice, after the three heat treatments, peach juice turbidity has increased (p < 0.05) , peach juice suspension stability did not show significant change (p > 0.05) , the degree of esterification of pectin in peach juice showed significantly increments, from 82.87% to 96.17% (p < 0.05) , the molecular weight had increased after the ultra high temperature treatment (UHT) , from 267.17 kDa to 331.08 kDa.The relationship between the two stability indexes of peach juice and the two indexes of pectin and the PME enzyme showed different degrees of correlation.The characteristic functional group of pectin was changed, significant response of COO^-, vibration suggested enhancement of the degree of esterification of pectin.Scanning electron microscope analyses indicated that the morphology of peach pectin appeared unifrom network structure.Moreover, PME activity were inactivated from 0.041 U/m L to 0.018 U/m L. The rheological properties and structure of pectin were changed by heat sterilization, which provided guidance for the development of cloudy peach juice processing technology and quality properties.