Effect of enzymatic de-esterification and RG-I degradation of high methoxyl pectin (HMP) on sugar-acid gel properties

The influence of RG-I domains on high methoxyl pectin (HMP) sugar-acid gel properties has rarely been reported. In our work, HMP was modified by enzymatic de-esterification and degradation of RG-I domains to compare and analyze the relationship between the structure and final sugar-acid gel properties. The results showed that the degree of esterification (DE) of REP (pectin degraded by rhamnosidase) and GEP (pectin debranched by galactosidase) was the same as that of untreated HMP, whereas the DE of PMEP (pectin de-esterified by pectin methyl esterase) decreased from 59.63 % to 54.69 %. The monosaccharide composition suggested no significant changes in the HG and RG-I structural domains of PMEP. In contrast, the percentage of RG-I structural domains of REP and GEP dropped from 37 % to about 28 %, accompanied by a reduction in the proportion of the RG-I backbones and side chains. The rheological characterization of sugar-acid gels demonstrated an enhanced gel grade for PMEP and a weakened one for REP and GEP. Moreover, we constructed a correlation relationship between the fine structure of pectin and the properties of the sugar-acid gels, confirming the critical contribution of the RG-I region (especially the neutral sugar side chains) to the HMP sugar-acid gels.