**5. Changes of phenolic compounds during processing (nixtamalization) of maize grain**

Nixtamalization results in multiple changes in the chemical components of the maize grain. Under the traditional process, the cooking water has high pH (∼12) which hydrolyzes the ester bond by which ferulic acid is linked to cell wall components. The grain structure that is mostly affected by this process is the pericarp, which becomes partially or fully hydrolyzed [45, 46]. As the most abundant phenolic in the grain, the hydrolysis of the ester linkage between the ferulic acid and the cell wall components causes the soluble fraction to be higher in nixtamalized maize products relative to that found in the whole grain, white maize. However, in colored maize that contains anthocyanin pigments, the soluble fraction is reduced due to the significant loss of anthocyanins [47–49]. According to the information presented in **Table 4**, in white maize grain soluble pheno‐ lics increase by about 26% when the grains are processed into tortillas, while in red maize grain, they are reduced by 20%. The magnitude of the reduction varies according to the grain color and the origin of the genetic material. The cooking of the tortilla results in an additional loss of pheno‐ lic compounds, but much less significant that resulting from nixtamalization [47].


SP: soluble phenolics; IP: insoluble phenolics; TP: total phenolics; WG: white grain; RG: red grain; BG: blue grain.

**Table 4.** Phenolic compounds in raw grain and tortillas obtained by the traditional nixtamalization process, from maize grains with different colors.

When nixtamalization is performed by the extrusion method, total phenolic losses in maize grain are lower than those resulting from the traditional method [49]. The differences were attributed to the fact that the extrusion method does not produce losses from hydrolyzed pericarp, and there is no leaching of phenolics.

Of the phenolic acids present in maize grain, the changes in ferulic acid have been monitored, as the most abundant member of this group. In white maize grain, the losses of this acid in the process of going from grain to tortillas are between 20 and 30%; nevertheless, in red maize grain they are higher and account between 44 and 60%, while in the blue maize grain they represent 18–45%, according to the information shown in **Table 4**. It is probable that the high losses of ferulic acid observed in red or blue maize grain may be a result of the maize varieties used in the studies that have a floury grain, which is very likely to occur if the maize used were native of Mexico. Floury maize generally has a thinner pericarp as compared to that of hard grains, and thus during nixtamalization the grain is hydrated faster than hard grain. Thinner pericarps could favor the hydrolysis of the ester bond that keeps the ferulic acid linked to cell wall components, and thus the acid is leached to the cooking water, known as nejayote. There are no reports on contents of ferulic acid in the nejayote of maize of different grain hard‐ ness, processed under the same nixtamalization method. In addition, when cooking times are adjusted to achieve optimal nixtamalization for each type of maize, the values of ferulic acid found in nejayote relate more to the cooking length than with grain hardness [50] and have values of ferulic acid content greater than those found in the grain and the masa for tortillas.
