Clitoria ternatea L. flower extract inhibits α-amylase during in vitro starch digestion

This study aimed to investigate the inhibitory effect of Clitoria ternatea flower against α-amylase during simulated in vitro wheat starch digestion. The dark-blue tropical flower is used as a food colorant but its ability to modulate starch digestion has not been tested before. The aqueous extract of the flower containing anthocyanins was a competitive inhibitor against α-amylase with an IC₅₀ value (concentration of inhibitor required to reduce the enzyme activity by half) and inhibition constant, K_i, of 0.91 mg/mL and 0.75 mg/mL,
respectively. Subjecting the extract to pasteurisation (72^oC for 15 s) and boiling (for 30 min) it significantly (P<0.05) decreased the anthocyanin content as determined by a pH-shift method, although the light absorbance profile of the extract remained virtually unchanged, suggesting that the equilibrium mixture of anthocyanin species was unaffected. The thermal degradation of the anthocyanins explained the partial loss of inhibition activity of the extract, as indicated by the decrease in Michaelis-Menten constant, K_m, from 14.8 mg/mL in the
systems with unheated extract to 11.3 and 6.1 mg/mL in pasteurised and boiled extracts, respectively. The thermal treatments, however, did not change the type (competitive) of inhibition. The results from this work demonstrated the potential of C. ternatea flower extract in inhibiting α-amylase during starch digestion, which might lead to development of functional food/drink for controlling postprandial blood glucose level.