On the mechanism of stabilisation of acidified milk drinks by pectin

Acidified milk drinks (AMDs) need a stabiliser, e.g. a high methoxy pectin if whey formation is to be avoided. In this work the pectin added to AMDs in order to stabilise them was investigated in terms of effective and non-effective fractions, corresponding to a fraction adsorbed onto casein micelles and a fraction of pectin dissolved in the serum. It turns out that in acidified milk systems of practical concentration less than 20% of the pectin added is directly interacting with casein micelles. The remaining 80% is involved in a network with casein/pectin complexes but plays no role in stabilising the final product. This excess fraction is, however, crucial in effecting sufficient pectin adsorption during the mixing process of yoghurt and pectin solution. Stability in AMDs of practical milk concentrations is concluded to be at least partially associated with the existence of a network of pectin-coated casein micelles. Adsorbed pectin is found to be adsorbed irreversibly. Non-adsorbed pectin is immobilised in a weak network consisting of pectin-coated casein micelles and non-adsorbed pectin.