Key role of three-dimensional reticular interface membranes in the formation of single polysaccharide-stabilized high internal phase emulsions

Although the interfacial activity of polysaccharides is believed to be insufficient for their applications as individual emulsifying stabilizers, four single polysaccharides examined herein, namely sodium carboxymethyl cellulose (Na-CMC), sodium alginate (SA), high-methoxyl pectin (HMP), and low-methoxyl pectin (LMP) are shown to effectively stabilize high internal phase emulsions (HIPEs) at loadings as low as 0.1 wt% under acidic conditions, that is, at pH 0.5-5.2 (Na-CMC), 0.5-4.0 (SA), 1.0-4.2 (HMP), and 1.0-3.0 (LMP). Despite their structural differences, the four studied polysaccharides feature similar HIPE stabilization mechanisms that mainly involve the formation of three-dimensional reticular interface membrane structures with fiber branching chains. Within the pH range suitable for HIPE formation, the polysaccharides mainly exist as nanofiber network structures with a grid width of 50-100 nm but adopt flake-like and other structures at higher pH. Further insights are provided by the relationship between network membrane structures formed at the interface and the fiber network structures formed by polysaccharides in the original aqueous phase. In addition, the inferred emulsification and stabilization mechanisms are shown to be significantly different from those observed for mainstream Pickering HIPE stabilizers. Thus, our work expands the understanding of the interfacial activity function of polysaccharides, provides conceptual thinking reference and design rules for the development of simple, efficient, safe, and cheap polysaccharide-based HIPEs, and supplements and furthers the theory of HIPE stabilization.