Availability of free and bound phenolic compounds in rice after hydrothermal treatment

• The rice may be a source of phenolic compounds even after preparation for consumption.
• Highest free phenolic levels were represented by chlorogenic and p-coumaric acids.
• Highest bound phenolic levels in rice were represented by ferulic acid.
• The hydrothermal treatment reduced the content of phenolic in most of rice samples.
• The hydrothermal treatment affected negatively the antioxidant activity.

This study evaluated the effect of hydrothermal treatment on the phenolic content (by spectrophotometry and HPLC-UV) and its antioxidant activity in polished, parboiled and whole rice (by DPPH radical measurement), aiming to estimate the functional contribution resulting from the consumption of this cereal. Principal component analysis (PCA) was performed to verify the effect of treatments. After the hydrothermal treatment, only the free phenolic compounds of parboiled rice were not significantly affected while, for the other rice samples, this percentage was reduced with treatment (p < 0.05). The highest free phenolic contents were represented by chlorogenic and p-coumaric acids and the bound phenolic compounds were represented by ferulic acid. A distinction between the free and bound compounds assessed by PCA and a tendency of phenolic acids to remain in the untreated sample was observed. The ability to sequester free radicals was negatively affected by the hydrothermal treatment. It was estimated that the population consumes around 37.4, 77.8 and 57.7 mg/day of phenolic compounds in its polished, parboiled and whole form respectively, indicating that rice may be an important source of these compounds even after preparation for consumption.