parboiled polished grains. This reduction in the concentration of polyphenols
after cooking is related to the thermal decomposition, because
phenolic compounds are affected by high temperatures
(Larrauri et al., 1997; Piga et al., 2003), as previously discussed. The
reduction in polyphenol concentration after cooking was not as
great in the parboiled grains as in the brown and polished grains because
those grains had already been through a hydrothermal process
(parboiling) before cooking with the loss of part of the phenolic compounds.
The effect of cooking was also reported by Pérez-Jiménez and
Saura-Calixto (2005). Evaluating a single sample of rice, they observed
a reduction of 84.16% in the total phenolic content after
cooking.
4. Conclusions
Together, these data suggest that there is a significant difference in
the concentration of TSPCs and in AOAs among genotypes with higher
values for the grains with red and black pericarp colors. Furthermore,
a positive and significant correlation between the TSPCs concentration
and AOA was demonstrated. Parboiling reduces the concentration
of TSPCs in the grains due to the loss of part of these
compounds in the water, thermal decomposition and, potentially, interactions
with other components. Additionally, the reduction in
TSPCs concentration is related to the lower AOA of these grains. Cooking
also reduces the concentration of phenolic compounds, mainly in
brown and polished grains, due to thermal decomposition.