Fractal dimension and mechanism of aggregation of apple juice particles.

摘要

Turbidity of freshly squeezed apple juice is caused by a polydisperse suspension of particles from cellular tissue. After precipitation of coarse particles by gravity, only fine colloidal particles remain in suspension. Aggregation of these colloidal particles leads to formation of fractal structures. The fractal dimension is a measure of the internal density of the aggregates and depends on their mechanism of aggregation. In this study, digitized images of primary particles and aggregates of depectinized, diafiltered cloudy apple juice were obtained by SEM. Average radius of the primary particles was 40 +or- 11 nm. Max. radius of the aggregates ranged between 250 and 7750 nm. The fractal dimension of the aggregates was determined by analysing SEM images by the variogram method, obtaining an average value of 2.3 +or- 0.1. This value is typical of aggregates formed by rapid flocculation or diffusion limited aggregation. Diafiltration was found to reduce the average size and polydispersity of the aggregates, as shown by photon correlation spectroscopy. Average gyration radius of the aggregates before juice diafiltration was 629 +or- 87 nm and the average number of primary particles per aggregate was 1174.