Effects of pH and anthocyanin concentration on color and antioxidant activity of Clitoria ternatea extract

Clitoria ternatea flower is commonly used in Thailand as a source of natural coloring for food and cosmetics. Its color pigments are mostly comprised of anthocyanins which show high antioxidant activity and ability to change color according to pH. These benefits can be applied to produce innovative products such as antioxidant beverages and intelligent films which can sense pH change. Thus, to evaluate possibility of the applications, changes in color, antioxidant activity and color acceptance of crude anthocyanin extracts had been evaluated over a pH range of 3 to 9 and different anthocyanin concentration from 10 to 20 mg/100 mL of the extract using response surface methodology. As a result, pH was a major factor influencing both color and antioxidant activity, while anthocyanin concentration showed only a minor influence. Although color acceptance was not significant, the change in color of extracts was apparent; for instance, the color of the extract was red in acidic solution, blue in neutral solution and green in basic solution. Furthermore, the antioxidant activity showed high activity at acidic pH and gradually decreased as pH increased to basic value. Consequently, the optimum point yielding highest antioxidant activity in this study was at pH 3 and 20 mg/100 mL anthocyanin concentration.