Extraction and antioxidant activity analysis of total flavonoids from okra (Abelmoschus esculentus L.)

Abstract

Abelmoschus esculentus L., commonly referred to as okra, is a versatile plant with applications in medicinal, culinary, and ornamental fields. Total flavonoids (TF), a major bioactive component of okra, exhibit significant antioxidant properties and hold considerable potential in healthcare applications. Due to the critical impact of extraction efficiency and purity on TF activity, a systematic extraction process is crucial for enhancing the development and utilization of okra resources. This study systematically investigates the effects of ultrasound-assisted extraction (UAE), heat reflux extraction (HRE), and shaking water bath extraction (SWB) on TF yields from various okra tissues (seeds, flowers, leaves, and fruits). The optimal conditions for UAE were determined as follows: 90% ethanol concentration, a solid–liquid ratio of 1:40 g/mL, an extraction duration of 30 min, and an ultrasound power of 150 W, resulting in TF yields of 6.21% for flowers, 3.81% for fruits, 3.68% for seeds, and 1.94% for leaves. For HRE, the optimal conditions were identified as 75% ethanol concentration, a solid–liquid ratio of 1:40 g/mL, an extraction time of 5 h, and a temperature of 80  °C, yielding 5.87% for flowers, 3.87% for fruits, 2.56% for seeds, and 2.21% for leaves. The optimal parameters for SWB were found to be 80% ethanol concentration, a solid–liquid ratio of 1:35 g/mL, an extraction time of 1.5 h, and a temperature of 65  °C, resulting in yields of 5.28% for flowers, 4.48% for fruits, 3.16% for seeds, and 2.49% for leaves. Furthermore, the study evaluated five types of macroporous resins for TF purification, identifying HPD-100 resin as having superior adsorption capacity. Post-purification with HPD-100 resin significantly enhanced the TF’s ability to scavenge DPPH and ABTS radicals. Given the high TF content and potent antioxidant properties found in okra fruit, along with its abundant yield and extended harvesting period, okra fruit is recommended as the primary source for TF extraction and the development of related antioxidant products. The SWB method is suggested as the optimal technique for TF extraction from okra fruit.