Non-covalent buckwheat protein-rutin complexation for improved functional biopolymer film-forming powder using physical mixing process and dialysis techniques

There is a paucity of information on research relating to rutin and buckwheat protein (BWP) interactions, particularly regarding the non-covalent bonding of buckwheat protein, which remains underexplored. This study investigated the extent of coupling of rutin (2% and 4%) with BWP over 0–4 h using a physical mixing process and dialysis techniques (3.5 kDa tube pore size). Standard methods were used to quantify unbound rutin in the dialysate, total phenolic content (TPC) of the dialyzed freeze-dried film-forming solution (FFS) using rutin equivalents, and antioxidant potential of the FFS. A dose-dependent increase in calculated total bound rutin amount for 2% and 4% inclusion was observed with values of 98.56–111.17 mg and 198.17–232.56 mg, respectively. The 4% rutin FFS showed the highest total phenolic content by an increase of 240.04% - 577.37%, while 2% rutin FFS had 202.68% - 493.53% increase (p < 0.0001). This indicates that the increase in total phenolic content is a function of the formation of buckwheat protein-rutin associations in the BWP film-forming solution. FTIR analysis demonstrated insignificant protein backbone distortion. The study suggests that forming a stable protein-rutin complex depends on multiple environmental factors, particularly pH, temperature, and ionic strength, which mediate the strength and type of protein-polyphenol interactions.