Phosphorus-31 nuclear magnetic resonance study on adsorption behavior of caseinate in triacylglycerol-in-water emulsions

P-31 NMR was used to study the adsorption behavior of caseinate in triacylglycerol-in-water emulsions. The droplet size and surface areas of caseinate-stabilized emulsion are closely related to the oil/protein ratio in emulsions. The line widths of P-31 NMR spectra of the protein in emulsion increased with increase of the amount of protein adsorbed at an oil-in-water interface. Thus, the restriction of the phosphoserine residues of caseinate was correlated with the interaction between protein and triacylglycerols on the interface. The droplet size of the emulsion became larger with increasing carbon number of saturated triacylglycerols but became smaller when unsaturated triacylglycerol was used as an oil phase. Broadening of P-31 NMR spectra also suggested the possibility of a conformational change of caseinate induced by varying the temperature and molecular species of triacylglycerols at the interface.