Chemical composition and antioxidant activity of essential oils obtained from the leaves of two different sweet potato varieties.

The sweet potato (Ipomoea batatas (L.) Lam.) is a tuberous root cultivated and consumed worldwide. However, its leaves are often neglected as a foodstuff. A better understanding about the chemical composition and biological properties of these leaves could make feasible its use as an unconventional food plant (UFP). Thus, the aim of this study was to evaluate the chemical composition and antioxidant potential of the essential oils obtained from the ground dry leaves of two different varieties of sweet potato (NSEY and CNRA) harvested in Seropédica (Rio de Janeiro, Brazil). Essential oils were isolated by hydrodistillation (100oC, 4 hours) and its components were analyzed by GC/MS and GC/FID. The antioxidant activity of these essential oils was evaluated by ABTS assay. The major compound found in both varieties was 4,8,8-trimethyl-2-methylene-4-vinylbicyclo[5.2.0]nonane [NSEY = [(24.01 ± 1.04)%; CNRA = (21.57 ± 1.84)%]. β-elemene was also present in both varieties in considerable amounts [NSEY = (11.21 ± 0.62)%; CNRA = (7.13 ± 1.13)%]. Based on quantitative data, δ-guaiene [(16.47 ± 0.43)%], valencene [(13.42 ± 0.84)%], and palmitic acid [(4.08 ± 1.58)%] were also considered important volatile compounds for NSEY samples, while γ-cadinene [(18.83 ± 3.00)%], 1,4-dimethyl-3-(2-methyl-1-propenyl)-4-vinyl-1-cycloheptene [(11.36 ± 3.03)%], and spathulenol [(6.25 ± 5.29)%,] were relevant for CNRA. The IC50 values found for the NSEY and CNRA essential oils were 2.43 ± 0.12 and 2.28 ± 0.02 mg/mL, respectively. No statistical differences (p>0.05) were found between these essential oils regarding their antioxidant potentials. The mean IC50 value estimated for all the combined samples (2.36 mg/mL) was 84.3 times bigger than that found for Trolox (IC50(ABTS) = 0.028 mg/mL). Therefore, these essential oils can be inferred as weaker antioxidants than Trolox. So far, this is the first attempt at identifying and quantifying volatile compounds from essential oils of sweet potato leaves in Brazil.