Stability and Antioxidant Activity Analysis of Buckwheat Bran Flavonoids and Preparation of Chitosan Blend Films

Ultrasonic-assisted extraction of buckwheat bran flavonoids (BBF) was used. The effects of pH, temperature, light condition and metal ions on the stability of flavonoids were determined. The antioxidant activity of flavonoids in vitro was analyzed by DPPH·, iron reductive force, ABTS⁺·, superoxide anion and other methods. The buckwheat bran flavone-chitosan blend films (BBF-CS) were prepared using BBF and chitosan (CS) as materials. The effects of adding BBF (0, 5, 10, 15, 20 mL) on the thickness, opacity, chroma, solubility and mechanical properties of the blend films were determined. The results showed that BBF was suitable for storing in a weak acid (pH5~7) environment under normal temperature and avoiding the contact of Ca²⁺, Fe³⁺and Cu²⁺. In vitro antioxidant activity assay revealed that BBF had significant scavenging capacity for DPPH, ABTS⁺ free radicals and superoxide anion, with the maximum scavenging rate of 92.1% and 87.7%, 53.81%, respectively, and the absorbance value of reducing power for iron ion reached 3.54. Compared with CS film, BBF-CS blend films had higher thickness, opacity and yellowness, while L^* value, total color difference, water content, solubility, tensile strength and elongation at break was lower. The method is stable and feasible, and can be used to extract BBF with strong antioxidant activity, will provide a basis for the subsequent development of BBF-CS blend films in food active packaging resources.