Two rice cultivars with different p

Two rice cultivars with different pericarp colors were selected for investigating the effect of storage on
the concentration of rice phenolic compounds and antioxidant activity (AOA). The concentration of total
phenolic compounds in the free fraction of the dark brown rice (DBR) was 355.4 mg GAE per 100 g rice,
which was 9.3 times higher than light brown rice (LBR), and a similar trend was also found in AOA
between the two cultivars (32.4 versus 4.0 mmol TE per g rice). The concentration of phenolic compounds
present in the free fraction was higher than that in the bound fraction in DBR, whereas the proportion of
phenolic compounds between the free and bound fractions was the reciprocal in LBR, indicating that the
concentration and distribution of phenolic compounds in rice are phenotype-specific parameters.
Phenolic compounds present in the free fraction showed significantly higher AOA compared to the
phenolic compounds in the bound fraction based on the same mass, which implies that the structure and
profile of phenolic compounds between the two fractions may differ. The ageing process induced
changes in the amount of phenolics, flavonoids and proanthocyanidin extracted from both cultivars, with
storage at 37
C leading to a 15e20% reduction in the concentration of these compounds present in free
and bound fractions. This suggests that phenolic compounds in the two fractions are both involved in the
chemical reactions that occurred during the rice ageing process. There was also a significant reduction in
AOA (P < 0.001) when rice was stored at 37
C for 6 months. The plausible mechanism for the reduction
in AOA might be due to the decomposition of the antioxidant compounds during rice ageing.