Interaction of pectin and casein micelles

The influence of pectin (low methoxyl—LM, low methoxyl amidated—LMA, high methoxyl—HM) on the stability of milk was investigated using the dynamic light scattering and viscosimetric methods. At pH 6.7, a depletion flocculation of the casein micelles was observed. This mechanism involves the exclusion of the polymer pectin chains from the space between colloidal particles (casein micelles), which induces an effective attractive interaction between the colloidal particles. If the attraction is strong enough a phase separation occurs in agreement with the theoretical predictions. At pH 5.3 the pectin molecule adsorbs onto the casein micelles; at low concentrations of pectin, a bridging flocculation is observed. On increasing the pectin concentration further the casein micelles become fully coated and attraction between the particles is lowered. On increasing the pH from 5.3 to 6.7, pectin desorbs. These experiments thus show that depending on the interaction between protein and polysaccharide, different ‘instabilities’ are observed.