Effect of Watermelon ( Citrullus lanatus ) Extract on Carbohydrates-Hydrolyzing Enzymes In Vitro

Hindering the absorption of glucose through inhibition of intestinal carbohydrate-hydrolyzing enzymes is an efficient strategy for reducing hyperglycemia. The purpose of this study was to examine the effect of watermelon flesh extracts (WFE), rind extract (WRE), skin extract (WSE), and citrulline on intestinal carbohydrate-hydrolyzing enzymes and to identify their bioactive compounds. WSE showed higher bioactive compounds and total phenolic content than WFE and WRE. WFE, WRE, and WSE demonstrated dose-dependent inhibition against carbohydrate-hydrolyzing enzymes. WFE, WRE, and WSE inhibited α-glucosidase by 40~45% at a concentration of 60 mg/mL whereas 80 mg/mL citrulline showed a similar inhibitory effect. WRE and citrulline showed IC 50 values of 0.02 and 0.01 mg/mL for maltase and sucrase, respectively. Citrulline at 20 mg/mL exhibited higher glucoamylase and pancreatic α-amylase inhibition than WFE, WRE, and WSE at the same concentration. Citrulline and WRE showed similar IC 50 values for glucoamylase and α-amylase compared to 1 mg/mL acarbose. This study suggests that watermelon, including its byproduct parts possibly due to citrulline, has the potential for carbohydrate-hydrolyzing enzyme inhibition that is beneficial to reducing postprandial hyperglycemia.