The role of pectin in orange juice stabilization: Effect of pectin methylesterase and pectinase activity on the size of cloud particles

In citrus juice cloud particles impart the characteristic color and flavor, and although the chemical composition of these particles is known, the details of their stabilization are not well understood. Pectin, a major component of orange juice cloud, is thought to play an important role in juice destabilization: in the presence of the active enzyme pectin methylesterase (PME), pectin forms calcium pectate complexes and causes the precipitation of cloud particles. This research summarizes a study on the changes occurring to orange juice cloud particles after addition of pectinase and PME. The particle size of juice cloud did not change with addition of pectinase. On the other hand, at the natural pH (3.8) of the juice, the addition of PME caused aggregation of the cloud particles within a few minutes, and the amount of enzyme added affected the kinetics of the aggregation. A higher amount of enzyme was necessary to cause the same effects at pH 6.0, while at low pH (2.5) cloud particles showed faster aggregation and a higher particle size, possibly because of a decreased surface charge at this pH. The results obtained by dynamic light scattering provided evidence of a direct effect of the PME on cloud and question our current understanding of the mechanism of cloud loss. (c) 2005 Elsevier Ltd. All rights reserved.