EFFECT OF CASEIN HYDROLYSATES ON ASSOCIATION PROPERTIES OF MILK-PROTEINS AS SEEN BY DYNAMIC LIGHT-SCATTERING

Small amounts (nil, 1, 2, and 4% w/w) of tryptic (T-PEP) and chymotryptic (C-PEP) hydrolysates of casein were added to sodium caseinate (Na-CN) and beta-lactoglobulin (A) (beta-LA A) to observe their effect on association properties of the proteins. Association was studied by gel permeation chromatography (GPC) and dynamic light scattering (DLS). Structural alterations were monitored by determining the intrinsic fluorescence of the proteins with and without peptides. Model studies were conducted side by side with zwitterionic amphiphiles (sulfobetaines) of varying hydrophobicity (C:8, C:12, and C:16). The quantum yield of fluorescence was affected by the peptides indicating changes in structure. The zwitterionic amphiphiles also affected the fluorescence. Amphiphiles of low hydrophobicity decreased the quantum yield, whereas high hydrophobicity increased it. The observed changes in the quantum yield of fluorescence reflected a change in the associated states of the proteins. DLS showed that the peptides had a dissociating effect on Na-CN, whereas beta-LA A showed a tendency to associate to a larger aggregate in their presence. C-PEP was more effective compared to T-PEP, which consisted of smaller peptides.