Antioxidant Capacity and Content and Nutritive Potential of Palmer Amaranth, An Indigenous Weedy Species

Palmer amaranth (Amaranthus palmeri), a broadleaf, summer annual, is a common and competitive weed of row crop production in the Midsouth and SE states. However, Palmer amaranth has developed resistance to four herbicide mechanisms of action, the most important being the EPSPS-inhibitors (glyphosate). Currently, glyphosate-resistant Palmer amaranth populations occur on more than 2 million Ha of agronomic land, prompting some growers to question the nutritive potential of the species in hopes of finding an unconventional use for this pest. The goals of this study were to: 1) explore the phytonutrient content of Palmer amaranth and 2) compare it to other human and animal food sources common to the SE US.  Freshly harvested tissues of greenhouse grown Palmer amaranth, kale, turnip greens, millet and rye were ground under liquid nitrogen and extracted  (1:10 w/v) in 60 MeOH:37 H2O: 3 formic acid for 1 hr at 37°C, then clarified by centrifugation. Antioxidant capacity was determined using two methods: 1) DPPH radical scavenging assay and 2) total phenolics using Folin Ciocalteu’s reagent, while antioxidant content was determined using HPLC-DAD. Peaks were quantified using standard curves and expressed as chlorogenic acid (330 nm), quercetin 3-galactoside (350 nm) and cyandin 3-galactoside (520 nm) equivalents. Results from the DPPH and FC assays suggest that Palmer amaranth has as high an antioxidant capacity as some common human and animal foods. With respect to percent (%) DPPH scavenging: Palmer (51%) > turnip (48%) > kale (46%) > millet (40%) > rye (29%). With respect to total phenolics content (gallic acid equivalents; mg/L): rye (137) > millet (127) > Palmer (91) > kale (84) > turnip (77). HPLC data showed that Palmer amaranth contains high levels of hydroxycinnamic acids (µg/g chlorogenic acid equivalents) with contents of turnip (3723) > millet (3408) > rye (3136) > Palmer (2785) > kale (1502). Currently, studies are being performed to better characterize the nutritive potential (antioxidant, protein and fiber content, etc) of Palmer amaranth relative to spinach, collards, India turnip, redleaf amaranth, millet and rye, and at different developmental stages. Indigenous leafy amaranths are crucial to food security in many regions of the world including: sub-Saharan Africa, Southeast Asia, India, China, and the Caribbean. A lack of knowledge regarding production practices, harvest methods, animal preference, and nitrate accumulation, plus growers’ negative perceptions, will need to be overcome before its use as an alternate crop can be explored fully.