Effects of succinylation in raw milk - modification of whey protein

The effects of succinylation reaction of whey protein on the molecular prop erties of individual proteins were studied after reaction with different co ncentrations of succinic anhydride in the range of 7-70 mM. The study is ba sed on a new spectrophotometric assay for native beta -lactoglobulin (beta -Lg) and on separations of the modified protein with FPLC fitted with 3 dif ferent columns and on electrophoresis. The extent of denaturation following succinylation depends on the substrate containing the protein as shown by the assay for native beta -Lg. The effects of succinylation on the molecular structure were elucidated usi ng raw milk serum. alpha -lactalbumin (alpha -La) is modified before it int eracts with beta -Lg. Moreover, beta -Lg formed complexes with the free kap pa -casein present in traces in the chemically modified milk serum. This is analogous to the chemically induced interaction between beta -Lg and kappa -casein at the micellar surface on succinylation of raw milk. The latter w as proved indirectly by the spectrophotometric analysis of the enzymaticall y released caseinomacropeptide (CMP) from renneted milk and by the spectrop hotometric assay of native beta -Lg. The molecular changes of alpha -La, be ta -Lg and immunoglobulin correlate with the results of the inhibited relea se of CMP and to the impaired stability of the resulting gel net work.