Valorization of okra waste: Microencapsulation of okra flower polyphenol-rich extract with maltodextrin and gum Arabic by freeze drying, spray drying, and microwave drying.

Okra (Abelmoschus esculentus (L.) (Moench.)) flowers are under valorized byproducts of okra production. They are a rich source of nutrients and have shown strong antioxidant activity. This study has optimized the extraction of phenolics, flavonoids and antioxidants from okra flowers by response surface methodology. The effect of extraction temperature (26.4-93.6°C), time (6-75 min), and solvent volume (18-102 mL) was evaluated. The optimum extraction conditions were determined as 80°C, solvent volume of 85 mL, and extraction time of 61 min. The extract prepared at optimum conditions was then microencapsulated with maltodextrin, gum Arabic, and a combination of both (1:1) using different drying techniques (freeze drying, spray drying, and microwave drying). The physicochemical properties of the resulting products were analyzed and characterized using differential scanning calorimetry, scanning electron microscopy, and infrared spectroscopy. The drying method impacted the polyphenol levels and bioaccessibility, physical powder properties, and surface characteristics of the resultant product, while the microencapsulation method mainly impacted the polyphenol content, glass transition temperature, and polyphenol bioaccessibility to a lesser extent. Microencapsulation with maltodextrin resulted in powders with significantly higher quercetin-3-glucoside (90-100 mg/kg), and epicatechin (480-580 mg/kg) content. The combination of freeze drying with maltodextrin microencapsulation provided the highest content of various polyphenols and bioaccessibility, as well as a very low water activity (0.038 ± 0.000). However, the powder was less free-flowing compared to microwave drying and tended to have a lower solubility. Consequently, the optimum drying and microencapsulation method will be a compromise between the different importance afforded to each of the aforementioned parameters.