Antioxidant Capacity of Lignin and Phenolic Compounds from Corn Stover

Corn stover, remaining after maize production, is produced worldwide. Despite being a residue, it contains bioactive compounds. Phenolic acids and lignin from maize plants were quantified to assess the possibility of valorization of this biomass. Extracts of the dry stem, root, cob, husk, leaf and grain of the maize plant were prepared using ethanol and alkaline hydrolysis. These were further subjected to acid hydrolysis to extract lignin and subsequently evaluated for their total phenolic content (TPC) and antioxidant capacity using two methods: measurement of the scavenging capacity against DPPH radical (2,2-diphenyl-1-picryl-hydrazyl) and the oxygen radical absorbance capacity (ORAC). The extracts showed a TPC of 219.67–1420.94 mg EAG 100 g−1. The antioxidant capacity of the extracts by DPPH scavenging was 1.11–11.75 mmol ET g−1, and their ORAC was 15.43–591.41 µmol ET g−1. Two phenolic acids (p-coumaric and ferulic acid) were identified in the samples using UPLC–PDA. The total lignin content (4.88–32.12%), TPC (3.4–16.9 mg EAG 100 g−1) and antioxidant capacity by DPPH scavenging (1.8–2.55 mmol ET g−1), as well as ORAC (0.8–3.9 µmol ET g−1), of the maize organs were assessed. The results suggest that corn stover is a potential source of natural antioxidants.