Heat treatment of whey proteins in the presence of anionic surfactants

Heat treatment of whey protein at pH=7.5 in the presence of three anionic surfactants (sodium dodecyl sulfate, sodium stearoyl-2 lactylate and diacetyl tartaric acid ester of monoglyceride) was studied. The effect of surfactants on whey protein denaturation level was evaluated by measuring solubility at pH=4.8 and slow reacting thiol groups. Denaturation temperature and enthalpy were determinated by differential scanning calorimetry. The resulting heat-induced whey protein–surfactant complexes were characterized by solubility profile between pH 2 and 6, hydrodynamic diameter and surface activity. During heat treatment, protein solubility at pH 4.8, slow reacting thiol groups and denaturation temperature increased with increasing surfactant/protein ratio and reached maximum values around 80 μmol surfactant per gram protein. Anionic surfactants decreased the size of heat-induced whey protein polymers. Heat-induced complexes showed low solubility between pH 4.8 and 5.4. The pH where minimal solubility occurred shifted to lower values when the surfactant/protein ratio increased. The surface tension profiles before heating showed three transitions associated with surfactant binding stages. After heating, these transitions disappeared as a result of total protein unfolding. The thermal behavior of whey proteins depended on the nature of surfactant, sodium dodecyl sulfate and sodium stearoyl-2 lactylate being the most effective.