Effect of type and quality of milk on heat induced protein–protein interactions in khoa

The present study was carried out to evaluate the effect of developed acidity and subsequent neutralization of milk (cow/buffalo) on heat induced protein–protein interactions occurring at various stages during khoa preparation. Protein–protein interactions were studied in terms of surface hydrophobicity (Fmax), sulfhydryl (–SH) group and SDS PAGE. As milk progressed to boiling stage, increase in Fmax and decrease in –SH content was observed. Khoa prepared from cow milk had comparatively higher values for Fmax and lower values for –SH group. Fmax was observed to be highest in acidic samples followed by neutralized and fresh samples. While considering –SH group, maximum values were observed in neutralized samples followed by acidic and fresh samples of both milk and khoa. However, no visible difference was observed in SDS PAGE patterns of casein fractions isolated from different types of samples. The bands of β-lg and α-la did not resolve clearly in the khoa samples due to high heat treatment involved in its preparation, indicating intense denaturation of whey proteins especially in neutralized samples where an alkaline medium resulted in strong binding between casein and whey proteins. The quality of milk also resulted in altered heat induced protein–protein interactions in khoa.