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 70°C, 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.
Highlights
Abelmoschus esculentus (L.) Moench (Malvaceae) is synonymously known as Hibiscus esculentus L., Okra, Okro, Ochro, lady’s finger, Gumbo, Gombo, Bamia (Kiswahili), Bamie, Bhandi, Quingombo, and Quiabo
total polyphenols content (TPC) sharply decreased to a minimum of 2.1 mg GAE/g distilled water (DW) (Fig 1)
The yield of TPC increased with the increase in time up to 2 hours that gave the maximum yield of 18 mg GAE/ g DW
Summary
Abelmoschus esculentus (L.) Moench (Malvaceae) is synonymously known as Hibiscus esculentus L., Okra, Okro, Ochro, lady’s finger, Gumbo, Gombo, Bamia (Kiswahili), Bamie, Bhandi, Quingombo, and Quiabo. It is an annual herbaceous plant, believed to have originated in Ethiopia is almost cosmopolitan; cultivated in the tropical, subtropical, and warm temperate regions, the Caribbean, South America, North America, Asia, rest of Africa, and eastern Mediterranea [1]. A recent study among traditional healers and individuals with diabetes mellitus in northern Tanzania found that the fruits of A. esculentus are among the most popular vegetable plant for this disease [7]
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