Extraction and Quantification of Phenolic Compounds in Maize

Plants accumulate hundreds of thousands of specialized metabolites that participate in their interactions with the environment. Among these compounds, phenolics represent a large class, and they play important physiological roles, such as providing a first barrier against pathogens, cues to pollinators, and radiation protection. Maize is one of the most important crops worldwide for food, animal feed, and biofuels, and it has the potential to accumulate different phenolics in vegetative tissues as well as in seeds. Recent studies have identified a large number of phenolic compounds—with a diversity of chemical decorations—in different maize tissues, but these likely represent just a fraction of the metabolic diversity of maize. In this protocol, we describe a specific method for the extraction and quantification of maize phenolic compounds by ultra-high-pressure liquid chromatography–tandem multiple reaction monitoring mass spectrometry (UHPLC-MRM-MS/MS) analysis. We provide detailed instructions for the extraction of phenolics using acidic methanol, and for the quantification of 33 different compounds in maize stems, including flavonoids, phenolic acids, and lignin precursors.