Stability of cloudy apple juice colloidal particles modeled with the extended DLVO theory

Abstract

Cloudiness of turbid or opalescent apple juice is provided by particulate material that remains in suspension (Genovese et al., 1997). This cloud has beenmodeled to consist of negatively charged pectin wrapped around a core of positively charged protein (Yamasaki et al., 1964; Endo, 1997). Particle sizes above 0.5 mm are unstable and settle out (Beveridge, 2002). Below this range, particles are colloidal in nature and follow Brownian motion. These colloidal particles are retained in suspension as a result of their small size, mutual charge repulsion, and the protective effect of pectin (Beveridge, Pectin acts as a protective colloid in turbid juices, retarding the coagulation and precipitation of small insoluble particles. Pectin slows aggregation by coating the particles, preventing the close-enough approach of one to another needed for the formation of hydrogen bonds or effective dipole interactions. In addition, it may give particles a large enough charge that significant electrostatic repulsion takes place between particles (Van Buren, 1989). However, the colloidal mechanism of particle stabiliz- ation in cloudy juices is still unclear.