Emulsification properties of alkaline soluble polysaccharide from sugar beet pulp: Effect of acetylation and methoxylation

Abstract

In our previous study, an alkaline soluble polysaccharide (ASP2), nearly non-methoxylated and non-acetylated, was prepared from the depectinized sugar beet pulp. Although displaying modest emulsion stabilizing properties, ASP2 had poor properties against calcium-induced droplet aggregation, which narrows its potential applications in food. This study aimed to overcome this limitation via esterifying ASP2 with methanol and acetic anhydride with carboxyl and hydroxyl groups of GalA residues, respectively. The results showed that the physicochemical properties, such as molecular weight, zeta-potential, neutral sugar (NS) content, etc., varied with degrees of methoxylation and acetylation. Emulsifying properties of methoxylated ASP2 (M-ASP2), acetylated ASP2 (A-ASP2), methoxylated-acetylated ASP2 (MAA), and acetylated-methoxylated ASP2 (AMA) were evaluated. Results showed that in an oil-in-water emulsion system containing 10% w/w MCT and 1% w/w emulsifier, A-ASP2 showed the best emulsifying activity as indicated by the lowest d4,3 (0.29 μm), followed by M-ASP2 with a d4,3 of 0.51 μm, while the emulsifying activities of MAA (5.25 μm) and AMA (11.1 μm) were unexpectedly worse than ASP2 (0.61 μm).The stability of A-ASP2-stabilized emulsion was comparable to that of original ASP2 but significantly better than others. M-ASP2 effectively inhibited calcium-bridged droplet aggregation, with a relatively small mean droplet size of 0.53 μm. Methoxylation or acetylation could solely enhance the hydrophobicity of ASP2, while dual modification resulted in deteriorated emulsifying properties.