Pineapple and Banana Pectins Comprise Fewer Homogalacturonan Building Blocks with a Smaller Degree of Polymerization as Compared with Yellow Passion Fruit and Lemon Pectins: Implication for Gelling Properties

摘要

Pectins are viewed as multiblock cobiopolymers of different pectic polysaccharides, notably, homogalacturonan (HG) and rhamnogalacturonan I (RG I). Furthermore, on the basis of HGs isolated from different (pectins from) dicot cell walls, HG is supposed to have an average degree of polymerization (DP) of ～100 irrespective of the plant source. To validate or invalidate these suppositions, pectins from both monocot (pineapple and banana) and dicot (yellow passion fruit and lemon) cell walls were examined. The results show that all the extracted pectins comprise HGs as well as type I and II arabinogalactan side chain-containing RGs I, but of significantly (p < 0.05) different relative proportions; lemon pectin being the richest in HGs, followed by yellow passion fruit pectin. The HG building blocks of each pectin are homogeneous with respect to the molecular size but have a significantly (p < 0.05) reduced length in monocot pectins (59—67) compared to dicot ones (93—102). Lemon pectin displayed the highest degree of esterification (DE), viscosity-average molecular weight (M_v), and gelling ability, whereas with similar DEs and a higher M_v, banana pectin exhibited a lower gelling ability than yellow passion fruit pectin. It is concluded that both the HG amount and DP strongly influence the gelling properties of pectin.