Heat-induced deamidation, dephosphorylation and breakdown of caseinate

The kinetics of deamidation, dephosphorylation and protein breakdown in hea ted caseinate solutions were studied. The extent of deamidation corresponde d to the level of the amide present in asparagine. The order with respect t o concentration was 1, the order with respect to time could not be establis hed unequivocally. The temperature dependence was in accordance with a mech anism in which a succinimide intermediate was formed. The extent of protein breakdown, measured as formation of non-protein nitrogen (NPN), was also c haracterized by an order of I with respect to concentration. The temperatur e dependence was in accordance with peptide bond hydrolysis (the order with respect to time could not be established unequivocally). Formation of inor ganic phosphate and dehydroalanine was determined in heated beta-casein sol utions. More phosphate than dehydroalanine was formed, and based on literat ure results for lysinoalanine formation from dehydroalanine, it was conclud ed that hydrolysis of phosphoserine occurred more extensively than beta-eli mination of phosphoserine. The order with respect to time for dephosphoryla tion seemed to increase with temperature, possibly due to a different tempe rature sensitivity of hydrolysis and beta-elimination. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.