Variety and Year Impact on Phenolic Content of Arkansas-Grown Sweetpotato Leaves

Abstract

Abstract Objectives Sweetpotato leaf (SPL) is a natural source of phenolic compounds with potential utility as an antioxidant. The study aimed to measure the impacts of the years on SPL total phenolic content and antioxidant capacity and to identify and quantify the individual phenolic compounds. Methods Sweetpotato leaves in 2018 (27 varieties) and 2019 (24 varieties) were grinded and lyophilized. Phenolic compounds were extracted with 70% ethanol from SPLs. Total phenolic content was determined by Folin-Ciocalteu method and antioxidant potential was determined by DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging assay. Five SPL samples with statistically highest antioxidant capacity were identified and quantified by HPLC. All statistical analyses were carried out by SAS software using ANOVA. Statistical significance was accepted at P < 0.05. Results The average of total phenolic contents in 2018 SPL samples was 43 ± 13 mg gallic acid equivalent (GAE)/g dry weight (DW) SPL whereas in 2019, it was 53 ± 9 mg GAE/g dry weight SPL. Antioxidant capacity in 2018 was 110 ± 75 µmol Trolox equivalent (TE)/g dry weight SPL whereas in 2019, it was 132 ± 32 µmol TE/g dry weight SPL. SPL1 had the highest antioxidant potential, followed by SPL9, SPL3, SPL28, and SPL11 (P < 0.05). The concentrations of major identified phenolics from the five SPL samples (#1, 9, 3, 28, and 11) in dry weight of SPL were: chlorogenic acid at 3.05 ± 0.35 mg/g, 5-monocaffeoylquinic acid (CQA) at 0.71 ± 0.06 mg chlorogenic acid equivalent (ChAE)/g, 4-CQA at 0.99 ± 0.07 mg ChAE/g, 3,4-diCQA at 1.22 ± 0.18 mg ChAE/g, 3,4,5-triCQA at 1.2 ± 0.18 mg ChAE/g, and 3,5-diCQA at 15.5 ± 4.05 mg ChAE/g. 3,5-diCQA, the predominant phenolic, was present in the highest amounts in SPL1. Conclusions The results showed that sweetpotato leaves collected in 2019 contained higher total phenolics and antioxidant capacity than the ones collected in 2018. Phenolic compounds have strong antioxidant activity in Arkansas-grown sweetpotato leaves. This study warrants further investigation of sweetpotato leaves to be utilized as an antioxidant. Funding Sources The work was supported by USDA-NIFA.