LAYERING OF SODIUM CASEINATE SUBMICELLES IN THIN LIQUID-FILMS - A NEWSTABILITY MECHANISM FOR FOOD DISPERSIONS

Drainage and stability mechanisms of thin foam and emulsion films cont aining aqueous sodium caseinate solutions were investigated, We found that the films thin stepwise by stratification, The heights of the fil m step-transitions were in the same range as the effective size of the casein-aggregates, the so-called submicelles (about 20 nm), This show ed that microlayering of submicelles takes place in the stratifying fi lm and, at a step-transition, a layer leaves the film. The number of s teps increased with increasing caseinate concentration. Increase of te mperature accelerated the step-transitions. At a lower temperature the drainage was not only slower but the last transition was inhibited an d a final film containing a layer of submicelles formed. The stepwise film thinning process could also be stopped at high film thicknesses b y decreasing the film size, i.e., by forming smaller drops or bubbles. The stepwise thickness transition results could be explained by the t heory of ''vacancy'' mechanism. It was found that the film and the emu lsion are very stable if the drained emulsion film contains layer(s) o f submicelles. This new mechanism of microlayering in foam and emulsio n films can be important in the stability of food systems because the concentration (0.1-4 wt%) and temperature (25 - 80 degrees C) ranges w here the phenomenon was observed are similar to those found in practic al applications. (C) 1996 Academic Press, Inc.