A COLLOIDAL APPROACH OF MILK ACIDIFICATION BY GLUCONO-DELTA-LACTONE

Colloidal techniques (laser Doppler electrophoresis, particle size analysis, and capillary viscosimetry) were used in combination with a turbidimetric method to study milk acidification by glucono-delta-lactone. In agreement with a previous paper (1), micellar phenomena as a whole can be related to the turbidimetric observations, and it appears possible to hypothesize a logical development of milk acidification at the micellar level. The observed electrokinetic and hydrodynamic comportment of micelles can be explained by the presence of an outer hairy layer. Then, as for renneting, ethanol, or thermal milk treatments, the micellar destabilization by acidification could largely depend upon the collapse of this outer hairy layer. Thermal motion should be a major factor for aggregation of particles because increasing temperature leads to increasing frequency of particle encounters. Casein solubilization from low temperature and acidification seems to act as an additional micellar destabilizing factor.