Emulsifiers from Yellow Split Peas

Abstract

Extracts with emulsifying capacity have been extracted from split peas (Pisum sativum). At pH 7 and extract concentrations above 0.75 g L⁻¹ s, stable emulsions were produced, with droplets of tens μm. At higher concentrations (2 g L⁻¹ s) bridging flocculation occurs, with the flocs breaking up into μm-sized particles upon SDS addition, reaching sizes comparable to those obtained by oilve compost emulsifiers. At even higher concentrations, depletion flocculation is observed due to unadsorbed extracts. The extract cannot emulsify at pH 3. In all cases, the interfacial tension is quickly reduced (at a higher degree at pH 7) due to the fast adsorption of small-molecular surfactants. Within 10 s further reductions are observed, as macromolecules are adsorbed, forming steric layers at the oil – water interface at pH 7. At pH 3 the adsorption of the macromolecules reduces the interfacial tension to a smaller extent, and is followed by a slower (over 100 s) rearrangement at the interface. Coupled with a change in zeta potential from 10.8 ± 0.6 mV at pH 7 down to 4.1 ± 2.2 mV at pH 3, these phenomena render the interfacial layer at pH 3 unable to stabilize against coalescence. Size exclusion chromatography of the extract, the emulsion serum and the cream layer highlight the preferential adsorption of specific biopolymers at the interface and confirm the hypothesis of the sequential adsorption and interfacial rearrangements. Fourier transform infrared spectra show that proteins are preferably adsorbed at the interface, while polysaccharides remain at the bulk phase.