Phenolic acids, anthocyanins, proanthocyanidins, antioxidant activity, minerals and their correlations in non-pigmented, red, and black rice

- Soluble-free, soluble-conjugated and insoluble-bound phenolic fractions were quantified in rice.
- Soluble conjugated phenolics and anthocyanins were negatively correlated with color parameters.
- Some soluble conjugated and insoluble bound phenolic acids had positive correlations with TPC and antioxidant activity.
- The correlation ships among the seven mineral contents were exhibited.
- Principal component analysis divided the rice samples into non-pigmented, red and black rice groups.

Soluble-free, soluble-conjugated, insoluble-bound phenolics and antioxidant activity, flavonoid (TFC), proanthocyanidins (TPAC), anthocyanins and minerals of fifteen whole rice grains with different colors were investigated. Soluble-free protocatechuic and vanillic acids were only quantified in black rice, which had the most quantities. Non-pigmented rice had no detectable conjugated protocatechuic and 2,5-dihydroxybenzoic acids both of which were found in black and red rice, respectively. The main bound phenolic acids were ferulic and p-coumaric, as well as 2,5-dihydroxybenzoic in red rice and protocatechuic and vanillic acids in black rice. Soluble-conjugated phenolics, TFC, and anthocyanins were negatively correlated with L∗, b∗, C and H° values. TPAC was positively correlated with a∗ (P < 0.01). Protocatechuic, vanillic, syringic and ferulic acids were associated with TPC and antioxidant activity in the soluble-conjugated fraction while protocatechuic and ferulic acid were correlated with those in the insoluble-bound fraction. Principal component analysis divided samples into non-pigmented, red and black rice groups.