Effect of Sulfated Polysaccharides on Heat-Induced Structural Changes in beta-Lactoglobulin

摘要

The mechanism that leads to a decreased aggregation of beta-lactoglobulin in the presence of dextran sulfate and gamma-carrageenan was investigated by assessing changes in the denaturation thermodynamics and protein structure.Differential scanning calorimetry results showed that the denaturation temperature (T_P) was about 4.6 deg C higher in the presence of dextran sulfate,as compared with beta-lactoglobulin alone,whereas in the presence of A-carrageenan the difference in T_p was about 1.2 deg C.Changes in protein structure studies using near-UV circular dichroism (CD) provided support for the calorimetric results.The transition midpoint (T_m) for denaturation of beta-lactoglobulin was about 5 deg C higher in the presence of dextran sulfate than that found with beta-lactoglobulin alone and about 2 deg C in the presence o fgamma-carrageenan.Thermal modifications of the tertiary structure of beta-lactoglobulin were irreversible at temperatures above 67 deg C;the addition of dextran sulfate reduced the extent of such modifications.Far-UV CD studies indicated that the addition of dextran sulfate or gamma-carrageenan did not affect secondary structure changes of beta-lactoglobulin upon heating.These studies indicate that dextran sulfate and gamma-carrageenan can enhance the stability of beta-lactoglobulin and thereby inhibit heat denaturation and aggregation.