Thickening effects of Ca2+ on apple high-methoxyl pectin: Dependences on Ca2+ concentration and the degree of esterification

Abstract

To explore the application potential of high-methoxyl pectin (HMP), the effects of Ca²⁺ (0.00%–0.50%, w/w) on the behavior of three apple HMPs with degrees of esterification (DE) of 60.6% (AP1), 66.1% (AP1) and 72.4% (AP3) were investigated. The results in zeta potential, turbidity, and fluorescence characteristics revealed that Ca²⁺ promoted the aggregation of HMP molecules. In steady shear measurements, the incorporation of Ca²⁺ substantially increased the viscosity and thixotropy of HMP systems and changed their shear-thinning behavior in a case-specific manner. In dynamic shear measurements, the frequency sweep revealed strong viscoelasticity of AP1 at Ca²⁺ concentrations of 0.35% and 0.50% (w/w) and defined other HMP-Ca²⁺ systems as weak gels or concentrated solutions, while the temperature sweep uncovered that the enthalpy-dominated elasticity of AP1-Ca²⁺ system, while the facultative enthalpic and entropic nature of the network formation in AP2-Ca²⁺ system. For the AP3-Ca²⁺ system, the viscous modulus was entropic, but the elastic modulus was first entropic and then enthalpic upon cooling. Fundamentally, the incorporation of Ca²⁺ substantially affected the micelles formation and network construction as well as the interactions involved in these systems. All of these changes highly depended both on the DE value of pectin and the concentration of Ca²⁺. The results concluded herein are expected to encourage the application of HMP in acid- and sugar-restricted food products.