Studies on Phytochemistry and Antioxidant Capacity of Nine Hibiscus sabdariffa Accessions

Hibiscus sabdariffa is considered a potential horticultural and pharmaceutical crop, yet there is limited information on beneficial traits of cultivars and germlines. We examined nine H. sabdariffa accessions for their horticultural traits, phytochemistry, and antioxidant capacity. Calyx, the main part of horticultural interest, was examined for its color, fresh weight, length, and width. Both calyx and leaf tissues were studied for phytochemical and antioxidant properties. Anthocyanins, chlorogenic acid, and quercetin were analyzed using high-performance liquid chromatography. Total phenolic content and total flavonoid content were determined by the Folin–Ciocalteu assay and the aluminum chloride assay, respectively. Antioxidant activity was examined by free radical scavenging assays, using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radicals. The study showed that three accessions (PI 265319, PI 275414, and PI 500706) had red calyces (“red”), and four accessions (PI 256039, PI 275413, PI 291128, and PI 500713) had light green calyces tinged with red (“light green–red”). Two accessions with light green calyces (“light green”) were PI 273389 and PI 500724. The average weight of calyces was the greatest with PI 291128 (13.2 g) followed by PI 275413 (11.4 g) and PI 275414 (10.9 g). Calyx length ranged from 18.7 to 60.4 mm, and the width ranged from 17.8 to 34.8 mm. Among four anthocyanins in calyx, delphinidin 3-sambubioside and cyanidin 3-sambubioside were major anthocyanins with less amounts of delphinidin 3-glucoside and cyanidin 3-glucoside. The red accession PI 275414 had the highest concentration of the total anthocyanins (32.7 mg·g −1 dry weight). Chlorogenic acid concentrations were higher in calyces (13.1 to 25.4 mg·g −1 ) than in leaves (0.7 to 2.0 mg·g −1 ), while quercetin contents were greater in leaves (3.5 to 13.2 mg/100 g) than in calyces (1.3 to 3.5 mg/100 g). Similarly, total phenolic content was higher in leaves [18.6 to 22.5 mg gallic acid equivalent/g] than in calyces (10.4 to 17.3 mg gallic acid equivalent/g). For antioxidant capacity, DPPH was higher in leaves [16.6 to 22.0 mg vitamin C equivalent antioxidant capacity (VCEAC)/g] than calyces (6.6 to 7.3 mg VCEAC/g). In contrast, ABTS antioxidant capacity was greater in calyces (8.6 to 15.7 mg VCEAC/g) than leaves (3.6 to 3.9 mg VCEAC/g). Calyx had higher contents of K and Zn, while leaf tissues had more Ca, N, Mg, S, B, Mn, and Cu. This study indicated that there is a great variation in phytochemical contents and antioxidant properties between calyces and leaves and among H. sabdariffa accessions. Because red calyx is desirable for producing herbal tea or coloring, the most interesting accession in this study was PI 275414, with the largest red fresh calyx.