Mucoadhesion ability of protein and starch from lotus (Nelumbo nucifera Gaertn.) seeds, relative to milk casein, gelatine and gum arabic as well-recognized mucoadhesive biopolymers

This study investigated the mucoadhesive properties of two polysaccharides [lotus seed starch (LS) and gum Arabic (GA)] and three proteins [lotus seed protein (LP), casein (CA), and gelatine (G)]. Different in vitro tests were carried-out to study the biopolymeric mucin interactions including mucin adsorption assay, turbidity development over 6 hours, and viscosity increase ("force of bioadhesion"). The free thiol content of proteins was also measured as one of the underlying mechanisms for adhesion. The biopolymers were studied at different concentrations (0.25-1% for polysaccharides and 2-10% for proteins, except G, which was studied at 1-5% due to its high gelling capacity). The effect of biopolymer modification on its ability as a mucoadhesive was also studied. Proteins underwent thermal treatment (H, 85⁰C/30 min), ultrasounds (US, 50% amplitude at 40⁰C/30 min), or heating followed by ultrasounds (H+US), while polysaccharides were treated with US only. The results showed a descending order of mucoadhesion: GA > LS > CA > G > LP. GA and CA had higher mucin adsorption than LP and LS. Increasing LP concentration decreased mucoadhesion, while CA increased adhesion, peaking at 10% protein content. However, gelatine showed maximum adhesion at 3%, which declined at higher concentrations; GA and LS had optimal mucin adsorption at 0.5%, with no improvement beyond this concentration. In addition, Casein's higher thiol content correlated with stronger mucoadhesion. Intact or heat-treated gelatine had high mucoadhesion, unlike US or H+US treatments, which reduced it. However, US treatment increased LS's ability to bind mucin, while LP showed no significant changes with any treatment. Therefore, these findings suggest the potential for using mucoadhesive biopolymers in food applications to prolong retention time on the mucosa, aiding in salt reduction without compromising taste.