COMPARISON OF ANTI-OXIDANT COMPOUNDS AND ANTIOXIDANT ACTIVITY OF NATIVE AND DUAL MODIFIED RICE FLOUR

Rice (Oryza sativa L.) is one of the most important cereal crops consumed in Asia and the primary staple food being consumed by nearly half of the world’s population. Black rice is getting popular recently and is consumed as a functional food. Black rice contains relatively high anthocyanin in the pericarp layer which gives the dark purple color. Black rice has a higher content of phenolic compounds as compared to white rice. The total phenolic content was four times higher in pigmented rice than in non-pigmented varieties. Heat Moisture Treatment (HMT) and enzymatic modification are essential processes prior to absorption in the human body as they affect digestibility. On the basis of these considerations, the dual modification applied in this study was a combination of heat-moisture treatment (HMT) and enzymatic modification. The samples used for the study were native and dual modified rice flour of selected white and black rice variety. The samples were termed as Native White Rice Flour (NWRF), Dual Modified White Rice Flour (DMWRF), Native Black Rice Flour (NBRF) and Dual Modified Black Rice Flour (DMBRF). The objective of this study was to determine and compare antioxidant compounds such as total phenolic content, total flavonoid content, total anthocyanins and antioxidant activity such as DPPH radical scavenging activity of native and dual modified rice flour. Results revealed that NBRF had higher total phenolic content (167.13 ± 12.90 mg GAE/100 g) and total flavonoid content (109.81 ± 10.3 mg QE/100g) when compared with other selected rice flour. Anthocyanins were not detected in white rice flour. Total anthocyanins in NBRF and DMBRF were 78.85 ± 8.42 and 72.87 ± 2.40 mg CGE per 100g respectively. It was observed that the anti-oxidant compounds decreased drastically on dual modification. Studies have shown that thermal treatment generally causes a significant reduction in the phenolic content and antioxidant capacity. Temperature and heating time had a significant impact on total anthocyanin content and total antioxidant activity. The drastic decrease in total phenolic content, flavonoid content and total anthocyanins may be due to the thermal degradation of phenolic and flavonoid compounds, as these compounds are very sensitive to heat treatments. A higher percentage of antioxidant activity was exhibited by NBRF (25.13 ± 1.92) and followed by that DMBRF (16.9 ± 1.29). A decline in antioxidant activity in DMBRF may be due to loss of anti-oxidant compounds in the water, thermal decomposition and potential interaction with other components.