Phosphorylation of ovalbumin by dry-heating in the presence of pyrophosphate: Effect of carbohydrate chain on the phosphorylation level and heat stability

Ovalbumin (OVA) derived from egg white (N-OVA) and recombinant OVA (Re-OVA), which was essentially carbohydrate-free, expressed by Escherichia coli, were phosphorylated by dry-heating for 1 day in the presence of pyrophosphate (PP-N- and PP-Re-OVA). The phosphorus contents of N- and Re-OVA were 0.79% and 0.46%, respectively, after phosphorylation. The secondary structural change of both OVAs was small, and the midpoint temperature of both OVAs determined from the thermal unfolding curve was decreased by phosphorylation. In addition, the differential scanning calorimetry thermograms of both OVAs showed a lowering of denaturation temperature by phosphorylation. The stability of both OVA solutions after heating at pH 7.0 was improved, and the degree of stabilization was higher for PP-N-OVA than for PP-Re-OVA. This suggests that the phosphate groups introduced to the carbohydrate chain also play an important role in the heat stability of OVA.