Calcium cation triggers and accelerates the gelation of high methoxy pectin

The gelation of high methoxyl (HM) pectin has been found to be affected by Ca2+, but the acting mechanism of the Ca2+ in the gelation is still unclear. In order to explore the role of Ca2+ in the gelation of HM pectin, aqueous systems composed of HM pectin and CaCl2 were investigated in comparison with alginate-CaCl2 systems through a Ca2+-concentrating gelling process (CCGP) that is our newly developed gelation method based on water evaporation. A HM pectin solution (1%) formed gels in the presence of Ca2+ (2.72 mu mol/mL) during water evaporation manifesting the participation of Ca2+ in the CCGP of HM pectin. Additionally, the same amount of Ca2+ induced more dramatic changes in the flow index n, consistency index k, and loss angle delta of the HM pectin samples than those of the alginate samples suggesting that the molecular interactions of HM pectin are likely strengthened by Ca2+. After similar percentages of water were evaporated, the HM pectin-Ca2+ sample showed a delta value of 29 degrees while the delta value of the Ca2+-free HM pectin sample was 65 degrees, indicating that Ca2+ triggers and accelerates the gelation of HM pectin. The absence of an optimal concentration ratio of HM pectin to Ca2+ and the high Ca2+ content released from the HM pectin gel suggest that the structuring of HM pectin molecules by Ca2+ is realized through a non-specific binding and an electrostatic screening effect facilitating their hydrophobic interactions during CCGP to form gels. (C) 2013 Elsevier Ltd. All rights reserved.