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

Colloidal techniques (laser Doppler electrophoresis, particle size ana lysis, and capillary viscosimetry) were used in combination with a tur bidimetric method to study milk acidification by glucono-delta-lactone . In agreement with a previous paper (1), micellar phenomena as a whol e can be related to the turbidimetric observations, and it appears pos sible to hypothesize a logical development of milk acidification at th e micellar level. The observed electrokinetic and hydrodynamic comport ment of micelles can be explained by the presence of an outer hairy la yer. Then, as for renneting, ethanol, or thermal milk treatments, the micellar destabilization by acidification could largely depend upon th e collapse of this outer hairy layer. Thermal motion should be a major factor for aggregation of particles because increasing temperature le ads to increasing frequency of particle encounters. Casein solubilizat ion from low temperature and acidification seems to act as an addition al micellar destabilizing factor.