Structural evolution of pea-derived albumins during pH and heat treatment studied with light and X-ray scattering

Abstract

Pea albumins are found in the side stream during the isolation of pea proteins. They are soluble at acidic pH and have functional properties which differ from their globulin counterparts. In this study, we have investigated the aggregation and structural changes occurring to pea albumins under different environmental conditions, using a combination of size-exclusion chromatography coupled with multi-angle laser light scattering (SEC-MALS) and small-angle X-ray scattering (SAXS). Albumins were extracted from a dry fractionated pea protein concentrate by precipitating the globulin fraction at acidic pH. The albumins were then studied at different pH (3, 4, 4.5, 7, 7.5, and 8) values. The effect of heating at 90 °C for 1, 3, and 5 min on their structural changes was investigated using SAXS. In addition, size exclusion of the albumins showed 4 distinct populations, depending on pH and heating conditions, with two large aggregates peaks (∼250 kDa): a dimer peak (∼24 kDa) containing predominantly pea albumin 2 (PA2), and a monomer peak of a molar mass of about 12 kDa (PA1). X-ray scattering intensities as a function of q were modeled as polydisperse spheres, and their aggregation was followed as a function of heating time. Albumins was most stable at pH 3, showing no aggregation during heat treatment. While albumins at pH 7.5 and 8 showed aggregation after heating, solutions at pH 4, 4.5, and 7 already contained aggregates even before heating. This work provides new knowledge on the overall structural development of albumins under different environmental conditions, improving our ability to employ these as future ingredients in foods.

Keywords: Albumins, structure; Heat-induced aggregation; Pea proteins; SEC-MALS; Small angle X ray scattering.