Influence of calcium on pectin methylesterase behaviour in the presence of medium methylated pectins

Pectins account for one of the major polysaccharides of plant cell walls and are commonly used in the food industry as gelling and stabilising agents. Pectin methylesterase (PME) can alter pectin structure and affect their gelling properties by de-esterifying galacturonic acid. Previously, we reported different behaviours of plant and fungal PMEs on high methylated pectins in solution or during the gelling process (Slavov et al., 2009). In the present study, the behaviour of the two PMEs is studied on a medium methylated pectin in solution, i.e. in the absence of calcium, or during the gelling process, i.e. in the presence of calcium. Only slight modifications were observed for Aspergillus aculeatus PME behaviour between the two conditions. On the opposite we show a role of calcium on the processivity of orange PME: the processivity decreases in the presence of calcium.