Optimization of Microwave-assisted Extraction of Anthocyanins from Adzuki Bean Seed Coat by Response Surface Methodology and Its Stability

The adzuki bean seed skin was taken as testing material to extract anthocyanins. The solvent extraction method, microwave extraction method, ultrasonic extraction method, enzymatic extraction method and other combined method processes were investigated. On the basis of single factor test, the response surface analysis was used to optimize the best extraction protocols and experimental conditions. At the same time, the effect of pH, light, temperature, food additives, and metal ions on the stability of anthocyanin in adzuki bean seed skin was studied. The results showed that the best extraction method was microwave-assisted solvent extraction, the impact of various factors on effect of anthocyanins extraction primary and secondary order of material-liquid ratio > microwave power > microwave time, the best extraction conditions were: Material-liquid ratio 1:30 (g/mL), microwave power 463 W, microwave time 42 min, the anthocyanin content of the adzuki bean seed skin obtained under this condition was 32.08 mg/100 g. Anthocyanins from adzuki bean seed skin was stable under acidic conditions with pH<5, but poor stability under conditions of light time greater than two days and temperature higher than 80℃. Food additives sucrose, glucose, sodium chloride and sodium benzoate had no obvious effect on its stability, and the addition of citric acid will increase its color function, it showed better stability in Na⁺, Mg²⁺, K⁺ion solution than that in Fe³⁺, Cu²⁺ ion solution.