Total polyphenols and antihyperglycemic activity of aqueous fruits extract of Abelmoschus esculentus: Modeling and optimization of extraction conditions

Abstract

Aqueous fruits extract of Abelmoschus esculentus (L.) Moench (Malvaceae) has been used traditionally in several communities to alleviate elevated blood glucose levels. However, optimized extraction conditions have not been reported. Thus, this study determined the optimal extraction conditions for extracting polyphenols from A. esculentus fruits and evaluated antihyperglycemic activity in vivo. Extraction time, temperature, and solid-to-solvent ratio were optimized using Response Surface Methodology (RSM). Total polyphenols and flavonoids were quantified using the Folin-Ciocalteu and aluminium chloride colorimetric methods, respectively. The fingerprint and quantification of quercetin—a major flavonoid with an antihyperglycemic effect was done using the chromatographic method. The antihyperglycemic activity was determined in a high-fat diet-Streptozotocin rat model. The rats were assigned to five groups (n = 6): Group 1 and 2 were normal and diabetic control received distilled water 1 mL/100g; Treatment group 3 and 4 received standardized A. esculentus fruit extract (AEFE) at a dose of 100 and 200 mg/kg, respectively; Group 5 received 5 mg/kg glibenclamide. All treatments were given orally for 14 days. Measurements of fasting plasma glucose (FPG) and body weight were done weekly. The RSM quadratic model predicted total polyphenols of 22.16 mg GAE/g DW. At optimal conditions of a solid-to-solvent ratio of 5%, extraction time 1 h, and extraction temperature of 70C, confirmation experiments yield 20.2 [95% CI; 16.7 to 27.6] mg GAE/g DW, implying the model successfully predicted total polyphenols. The extract HPLC fingerprint showed 13 characteristic peaks with 0.45 ± 0.02 μg/g DW of quercetin. Compared with diabetic control, the standardized AEFE reduced FPG level dose-dependently (P < 0.001) with an EC50 of 141.4 mg/kg. Together, at optimal extraction conditions, extract with a high content of total polyphenols and good antihyperglycemic activity can be obtained. Studies are needed to identify additional polyphenolic compounds and determine their antidiabetic effects.