Effects of Processings and Complexation on Solubility, Antioxidant and Antibacterial Properties of Buckwheat Polyphenols

To take better advantage of buckwheat polyphenols, processings including extrusion, steam explosion, microwave, roasting, superheated steam, ultrasound and enzymolysis treatment were applied to buckwheat bran to release more bioactive polyphenols. Polyphenols were extracted and characterized, and rutin was identified as the predominant compound. To further improve the properties of buckwheat polyphenols, rutin was selected as the target polyphenol and a formation of its ionic cross-linking complex was proposed. Rutin was loaded on chitooligosaccharide as Rutin-COS with tripolyphosphate (TPP) as crosslinking agent, whose molecular structure and properties were investigated. Results showed that all processing significantly increased ( p < 0.05) the content of buckwheat polyphenols, up to 1.83-fold increase. The composition of polyphenols was altered, and their antioxidant (up to 15% increase) and antibacterial activities were significantly enhanced ( p < 0.05). Among all the processings, extrusion and superheated steam showed the best effect. For Rutin-COS complex, the encapsulation efficiency was as high as 74.77% with the mass ratio of rutin and COS at 1:8. The structure of Rutin-COS was stabilized by hydrogen bonding between aromatic rings of rutin and amino and hydroxy groups of COS in the network formed by COS and TPP. Compared to free rutin, Rutin-COS presented better thermal stability and water solubility. The antioxidant and antibacterial activities of Rutin-COS were also significantly improved ( p < 0.05) due to the molecular interaction between rutin and COS. The combination of processing and complexation strategy for buckwheat polyphenols in this work provided new approaches to take better advantages of polyphenols of cereal foods. Graphical Abstract