Fractal dimension and mechanism of aggregation of apple juice particles

BENITEZ, ELISA INES ; LOZANO, JORGE ENRIQUE; GENOVESE DIEGO BAUTISTA

FOOD SCIENCE AND TECHNOLOGY INTERNATIONAL

SAGE PUBLICATIONS LTD

Lugar: Los Angeles; Año: 2010 vol. 16 p. 179 - 186

1082-0132

Turbidity of freshly squeezed apple juice is produced by a polydisperse suspension of particles coming from the cellular tissue. After precipitation of coarse particles by gravity, only fine-colloidal particles remain in suspension. Aggregation of colloidal particles leads to the formation of fractal structures. The fractal dimension is a measure of the internal density of these aggregates and depends on their mechanism of aggregation. Digitized images of primary particles and aggregates of depectinized, diafiltered cloudy apple juice were obtained by scanning electron microscopy (SEM). Average radius of the primary particles was found to be a equal to 40±11 nm. Maximum radius of the aggregates, RL, ranged between 250 and 7750 nm. Fractal dimension of the aggregates was determined by analyzing SEM images with the variogram method, obtaining an average value of Df equal to 2.3. This value is typical of aggregates formed by rapid flocculation or diffusion limited aggregation. Diafiltration process was found to reduce the average size and polydispersity of the aggregates, determined by photon correlation spectroscopy. Average gyration radius of the aggregates before juice diafiltration was found to be Rg equal to 629 nm. Average number of primary particles per aggregate was calculated to be N equal to 1174.