The impact of heating and freeze or spray drying on the interface and foam stabilising properties of pea protein extracts: Explained by aggregation and protein composition

Abstract

The processing of plant protein extracts can affect the protein structure, leading to altered functional properties. In this work, we evaluated the impact of two common processes in pea protein extraction: heating and drying. Non-heated and heated (5 min at 95 °C) samples were compared, which were either freeze- or spray-dried. These processes led to alterations of the proteins, and resulted in changes of their interface and foam-stabilising properties. A mild protein extraction method was used to preserve the native protein structure during aqueous extraction, allowing the extraction of both albumin and globulin proteins. Spray-drying of these fractions led to higher surface hydrophobicity, which resulted in increased surface activity and stiffer interfacial layers at pH 3.8 and 7.0. The heating step induced aggregation of the globulins, while albumins remained soluble. Here, we demonstrated that the albumins had a dominant effect on the interfacial (rheology and ellipsometry) and foaming properties after heating, as the globulin aggregates were too large for effective interface stabilisation. A similar mechanism was also shown at pH 3.8, where the globulins precipitated, as the pH was close to their pI, while albumins remained soluble. Again, the albumins dictated the interfacial properties, leading to highly stable foams after removing the insoluble globulins. We have shown marginal differences in protein functionality after freeze- or spray-drying. More importantly, the changes in soluble protein composition dictate the protein functionality after heating or pH shifts.