ABSTRACT
Introduction ........................................................................................................ 289
Materials and Methods ..................................................................................... 292
Results and Discussion ..................................................................................... 292
Conclusion .......................................................................................................... 298
Acknowledgments ............................................................................................. 299
References ........................................................................................................... 299
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.
