Ultra-stable pickering emulsions stabilized by zein-cellulose conjugate particles with tunable interfacial affinity

Abstract

Designing solid particles with desirable interfacial affinity from plant-based ingredients is a key area in sustainable food production. Here, a chemical approach is introduced to fabricate conjugate particles by combining a water-insoluble plant protein (zein) and a hydrophilic polysaccharide (cellulose) through Schiff-base reaction. Zein assembles and precipitates into anisotropic particles after forming conjugates with cellulose. The wettability of conjugate particles at the interface can be precisely engineered by adjusting the ratio of the hydrophobic and hydrophilic components. The three-phase contact angle of a water droplet sitting on the substrate made of particles can be adjusted in a range from around 130°–40° when they are submerged in corn oil. The interfacial absorption kinetics of conjugate particles shows 2 to 4 times improvement than the particles made from sole material sources. The optimal polymer ratio is found to be 1:1.5 and 1:2 (zein:cellulose) for the corn oil-water system. In association with the enhanced interfacial affinity, emulsions stabilized by conjugate particles exhibit superior stability against droplet coalescence and bulk phase separation when going through the isoelectric point of the protein (around pH 6), high ionic strength, long-term storage, and thermal treatment. It has been found that 0.5 wt% conjugate particles are enough to stabilize emulsions containing more than 60 vt% oil.