Effect of heat denaturation on the adsorption of β-lactoglobulin at the oil/water interface and on coalescence stability of emulsions

The adsorption behavior of heat treated β-lactoglobulin at the oil/water emulsion interface and the coalescence stability of the emulsion droplets were studied. Heating of β-lactoglobulin (β-lg) increased its surface hydrophobicity probably due to uncoiling. The average volume—surface droplet size of all these emulsions was kept constant. The change of conformation of β-lg on progressive heating was monitored by measuring surface hydrophobicity. The amount of protein adsorbed at the oil/water interface initially decreased from 2.8 to 1.4 mg/m2 with increase of surface hydrophobicity, followed by a sharp increase to about 5 mg/m2 to form multilayers. The coalescence of emulsion droplets followed first-order kinetics and the rate constant decreased from 8 × 10−6 to 2 × 10−6s−1 as the surface hydrophobicity increased from 80 to 500. The strength of the interfacial film was determined by its resistance to removal by detergent. The film strength increased with decreased stability of the compact structure of β-lg. The proteins adsorbed in the multilayers were loosely bound and did not significantly contribute to coalescence stability. Surface hydrophobicity and film strength showed strong correlation with coalescence stability. The results indicated that conformational instability of β-lg was more important than film thickness in controlling droplet coalescence.