Calcium and acid induced gelation of (amidated) low methoxyl pectin

A systematic study is made of the gelation of low methoxyl pectin (LMP) and partially amidated low methoxyl pectin (ALMP) as a function of pH and Ca2+ concentration. Sol–gel state diagrams are obtained that characterize the pectin systems. Acid induced gelation is found to occur below pH 3.5 while Ca2+ induced gelation is most effective for fully charged chains (pH>4.5). In an intermediate pH range between pH 2 and 3.5 both types of gelation occur. High amounts of added Ca2+ are found to destabilize the solutions, leading to the formation of increasingly heterogeneous athermal gels or precipitation. Amidation is found to enhance acid induced gelation without significantly modifying the sensitivity to Ca2+. Spontaneous association is observed even in the absence of Ca2+ for fully charged pectin, leading to the formation of very weak gels. The influence of the pectin concentration was investigated.