1. Department of Physics, IBILCE UNESP, Universidade Estadual Paulista, R. Cristóvão Colombo 2265, 15054-000 São José do Rio Preto SP, Brazil, and Laboratory of Physical Chemistry and Colloid Science, Department of Agrotechnology and Food Sciences, Wageningen University, P. O. Box 8038, 6700 EK, Wageningen, The Netherlands