Unexpected gelation behavior of citrus pectin induced by monovalent cations under alkaline conditions

Monovalent cations normally do not induce gel formation of high methoxyl pectin. Alkali (NaOH or KOH) solution is normally used for saponification of pectin, which is one of the steps for measuring degree of methoxylation. However, the present study found that the alkali (NaOH or KOH) added to high methoxyl pectin could lead to gel formation in a concentration-dependent manner, involving in monovalent cation, alkali and pectin. The gel strength of CPGs increased and the morphology structure became denser with the increase of monovalent cations and pectin concentration. It was also found that Na⁺ induced stronger gels as compared to those induce by K⁺, at the same alkaline and pectin condition. It suggested that de-esterification, charge screening, hydrogen bond changes, and electronic attraction could be responsible for the monovalent cation-induced pectin gelation under alkaline condition.