Effects of different drying methods on the proximate composition, antioxidant activity, and phytochemical content of Hibiscus sabdariffa L. Calyx

Abstract

The study investigated the impact of freeze drying (FD), cabinet drying (CD), and sun drying (SD) on the proximate composition, phytochemicals, and antioxidant activity of roselle calyx. The proximate composition, phytochemicals, and antioxidant activity of the roselle calyx were determined by the AOAC method and the free radical-scavenging DPPH technique, followed by the spectrophotometric method, respectively. The samples were frozen and condensed at -40 to -60 °C in the FD and then dried at 20 °C for 20–30 h, and in the CD and SD, it was done at approximately 65 °C and 30 °C, respectively. CD retained the least moisture (p < 0.05) and had the highest (p < 0.05) carbohydrate content (38–49 %). There was a substantial difference (p < 0.05) in the ash, protein, and fat content of the provided samples using different drying processes. The TPC of FD, CD, and SD of roselle calyx had 64.70 ± 1.33, 32.23 ± 1.36, and 25.84 ± 1.85 mg GAE/g, respectively. The TFC of FD, CD, and SD dried roselle calyx was 65.41 ± 2.02, 41.64 ± 3.12 and 27.60 ± 1.83 mg QE/g, respectively. The phytochemicals and antioxidant activity of roselle calyces were found to be significantly higher (p < 0.05) in FD compared to CD and SD. Finally, FD should be considered an appropriate drying procedure for retaining excellent qualities.

Keywords

• Antioxidant activity
• Bioactive compounds
• Drying methods
• Nutritional composition
• Roselle