This work studies saliva foam, and the effect of in vitro orally-processed model foods on this foamy state. It reaches an estimation on the volume fraction of air trapped as bubbles in the saliva of healthy young volunteers, a value close to 0.3. So air bubbles and foam state might be intrinsic colloidal properties of saliva, with implications on its physiological and physicochemical definition and role. It then studies the capacity of mucin to stabilize model saliva, and the role of food protein (here sodium caseinate) to influence this foaming and the resulting foam stability during oral processing in in vitro systems. Synergistic effects are observed between mucin and caseinate in foams in terms of their foaming capacity and foaming stability. These are discussed in relation to their water-air dynamic interfacial tension, while the bubbles are observed with confocal microscopy. The effects of replacement of mucin with caseinate, hence the relevant transitions in interfacial composition, are studied in high internal gas volume fraction foams, with sodium caseinate producing relatively thicker foams, and mucin bringing about higher long-term stability. The above are brought together and discussed in relation to the temporal evolution of foam during the oral processing of foods.
