Interaction of pectin and casein micelles

The influence of pectin (low methoxyl-LM, low methoxyl amidated-LMA, high m ethoxyl-HM) on the stability of milk was investigated using the dynamic lig ht scattering and viscosimetric methods. At pH 6.7, a depletion flocculatio n of the casein micelles was observed. This mechanism involves the exclusio n 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 separa tion occurs in agreement with the theoretical predictions. At pH 5.3 the pectin molecule adsorbs onto the casein micelles; at low conc entrations of pectin, a bridging flocculation is observed. On increasing th e 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 i nteraction between protein and polysaccharide, different 'instabilities' ar e observed. (C) 2000 Elsevier Science Ltd. All rights reserved.