Improvement of functional properties of sunflower protein isolates near isoelectric point: Application of heat treatment

The present study was carried out to enhance the functional properties of sunflower protein isolates near isoelectric point. Protein isolates were subjected to heat treatment at 80 degrees C for 5, 15 and 25 min at three pH values (3.5, 4.5 and 5.5) and were evaluated for physicochemical and functional properties. It was observed that surface hydrophobicity and sulfhydryl content of sunflower protein isolates were lower near isoelectric point and increased with heat treatment. Highest hydrophobicity value of 123.27 was observed at pH 5.5 and heating time of 25 min. Higher particle size of 102.56 nm was observed at pH 4.5 due to aggregation of proteins and was further increased to 108.29 nm with heat treatment. SDS-PAGE analysis showed that heat treatment near isoelectric point did not cause hydrolysis of protein molecules. Heat treatment decreased the available lysine content of protein isolates at all the pH values studied. Functional properties like solubility, emulsification and foaming properties were lower near isoelectric point and showed increasing trend with heat treatment. Water binding capacity decreased with heat treatment near isoelectric point, while oil binding capacity increased with heat treatment near isoelectric point.