Kinetics of acid‐catalysed de‐esterification of pectin in a heterogeneous medium

Summary The rate constants of acid‐catalysed de‐esterification at 30,40 and 50°C of apple, lemon, grapefruit, orange and carrot pectins, in ethanolic hydrochloric acid show that the reaction is a pseudo first‐order reaction and is uninfluenced by the origin of the pectin. The activation parameters (ΔS*= ‐107.2±2.6 J mol‐1 K‐1; ΔH*= 74.51±0.96 kJ mol‐1) were close to those calculated by Speiser, Eddy and Hills (1945) for homogeneous acid de‐esterification of apple pectin, and thus the reaction mechanism appears to be the same as that in solution. In most cases, (except grapefruit pectin) gel strength increased with the degree of es‐terification and the duration of acid treatment: the maximum depends on the type of the pectin.