Heat-induced gelation, rheology and stability of oil-in-water emulsions prepared with patatin-rich potato protein

Abstract

The heat treatment after non-aseptic homogenization is sufficient to ensure the microbiological safety of the product, but such a sequence of processes may affect the technological suitability of protein-stabilized emulsions. In this study, we investigated the heat-induced gelation of oil-in-water emulsions prepared with patatin-rich potato proteins (EPs) and the effect of heating to 85 °C on their final properties (the appearance, rheology and stability). Low-fat and high-fat EPs of 3.2 and 30% (w/v) oil, respectively, were prepared in a two-stage high-pressure homogenizer using pressures of 50 MPa and 5 MPa in the first and second stages before heating with or without 0.1 M NaCl addition. Multi-speckle diffusing wave spectroscopy and oscillatory rheology techniques were used to monitor the molecular and macroscopic dynamics of heat-induced EPs gelation. The results showed that both, the oil content and the salt addition play a critical role in the dynamics of EPs gelation as well as in creating properties of heated and unheated emulsions, regardless of the cycles number (one or three passes through a two-stage homogenizer) of HPH pre-processing. The protein denaturation temperature in EPs ranged from 58.1 °C to 60.2 °C, but it was shifted towards lower values in the presence of salt. Heating the low-fat EPs with 3.2% (w/v) oil resulted in their transformation at 69 °C into weak gels of homogeneous structure, strong shear thinning and thixotropy and good stability against creaming. In contrast, flocculated high-fat EPs with 30% (w/v) oil formed already at 64°C64heterogeneous gels of viscoelastic solid character and poor stability due to the tendency to syneresis.