**3.2. Insoluble or bounded phenolic compounds**

Insoluble phenolics from maize grain are those obtained from alkaline hydrolysis of the sam‐ ple residue once soluble phenolics have been removed. The pH of the hydrolyzed sample is adjusted to 2 and liquid‐liquid extractions with ethyl acetate are used to recover them. The total content is quantified by the Folin‐Ciocalteau assay. They can also be analyzed by HPLC‐DAD techniques or HPLC/MS/MS for a complete identification of the different pheno‐ lics present in this fraction.

**Figure 4.** Basic structure of the anthocyanidins (aglycons) present in maize grain (adapted from Rodríguez and Wrolstad [26]).
