Gelation behavior between Nicandra physalodes (Linn.) Gaertn. pectin and Ca2+ is governed by degree and pattern of methylesterification

Abstract

Nicandra physalodes (Linn.) Gaertn. Pectin (NPGP) is a new type of natural low methoxy pectin (LMP), however, the relatively poor gelling capacity of NPGP and neutral calcium limits its applicability in the food industry. In this study, we improved the gelling capacity of NPGP, and the impact of the degree and pattern of methyl esterification on NPGP gelation behavior triggered by neutral calcium was investigated. To achieve this goal, NPGP was treated with pectin methyl esterase (PME, 30 °C, pH 4.5) for various time. This modification decreased the degree of methyl esterification (DM) and generated different patterns of methyl ester distribution, quantified as the degree of blockiness (DB). The obtained PME-NPGPs possess the ability to form self-supporting gels in the presence of CaCl2, with the highest gel hardness being 331.98 g. By estimating the DM and quantifying the DB of PME-NPGP, the DB value of PME-NPGP was increased from 17.74% to 31.84% with DM decreasing from 33.09% to 17.37%, indicating a shift toward a more blockwise distribution of nonmethylated GalA in NPGP. Additionally, adsorption isotherms for Ca2+ on de-esterified NPGP were determined, enabling the quantification of its cation binding capacity and interaction energy. Reducing DM and increasing DB of NPGP were found to enhance NPGP's binding capacity to Ca2+. This research provides an important foundation for NPGP food processing, and the obtained PME-NPGP can be promising in the fields of food gel and drug delivery.