Effects of succinylation on selected physico-chemical properties of nativecasein micelles in milk

The effects of succinylation on the colloidal status of native casein micel les in skimmed raw milk were studied in dependency on the extent of succiny lation (0-100 mM succinic anhydride, corresponding to the chemical modifica tion of 0-70.6% of free a-amino nitrogen released after a 2-step enzymatic digestion of buttermilk of DH = 22.5%) and on pH (6.4, 6.7 and 6.8, respect ively). The following micellar properties were investigated: (i) concentrat ion of free or ionic calcium, (ii) the turbidity of micelles at 320 nm rela ted to the absorbance at 280 nm, (iii) surface hydrophobicity and (iv) the apparent micellar diameter. The results revealed that succinylation affecte d both, the reactive amino groups and free calcium in milk. The involved ch anges destabilized the micelle structure in dependency on the severity of t he chemical modification. It was indicated by losses in micellar turbidity and surface hydrophobicity. The implemented decrease in hydrophobicity corr esponded to a larger particle size and a tendency of dissociation with prog ressing succinylation.