The influence of pH and calcium ions on the gelation of low methoxy pectin from potato

In this study, pectin was extracted from potato with the hydrolysis of cellulose, as well as its acid-induced and Ca²⁺-induced gelation behavior was investigated, too. The gelation process of unhydrolyzed pectin might be used as a model for studying the gelation behavior and characteristic of pectin within the cell wall. The results showed that potato pectin solution (3%) could form a gel state at a minimal concentration of 0.25% CaCl₂ or a maximum pH value of 4.60. Furthermore, acetic acid-induced and CaCl₂-induced gels were both concentration-independent. Specifically, the gel strength increased with decreasing levels of pH and increasing concentrations of CaCl₂. Moreover, CaCl₂-induced gels exhibited superior gelation characteristics with a higher storage modulus (7.2 Pa), larger fractal dimension (2.58), smaller porosity (12.11%), shorter relaxation time T₂, and a denser gel network structure. This disparity stemmed from different mechanism: acetic acid provided H⁺ to combine with free carboxyl groups on the pectin chains, reducing the repulsion between pectin molecules, narrowing chain spacing, and fostering hydrogen bond formation; whereas CaCl₂ promoted gelation primarily via the information of the "egg box" structure involving non-covalent bonded calcium bridges. This research could provide a theoretical basis for acid-induced and Ca²⁺-induced gelation of unhydrolyzed pectin extracted from the cell wall.