Total Polyphenols, Flavonoids and Anti-oxidant Activity of Corn Silk (Stigma maydis) as Influenced by Drying Condition and Extraction Solvent.

Corn silk, the yellowish thread-like strands, is a waste material from corn cultivation. Corn silk bioactive components such as polyphenols and flavonoids provide benefits that can be tapped as potential natural anti-oxidant product for healthcare applications. The study aimed to determine the effect of different drying methods on colour parameters and that of different extraction solvents on total polyphenols, flavonoids and anti-oxidant activity of corn silk. Corn silk samples were either lyophilized or tray-dried at 40 and 60°C. Bioactive compounds from powdered corn silk sample were extracted using 80 per cent ethanol, methanol, water or acetone. Colour analysis revealed that tray drying caused more browning of the sample compared to lyophilizing. Significantly higher (p < 0.05) Total phenolic content (TPC) and Total flavonoid content (TFC) were observed in 80 per cent ethanolic extract of lyophilized sample (35.86 ± 0.83 mg GAE and 38.05 ± 0.22 mg RE/g sample) followed by 60°C (20.31 ± 0.19 mg GAE and 20.56 ± 0.32 mg RE/g sample) and 40°C (5.68 ± 0.04 mg GAE and 8.88 ± 0.02 mg RE/g sample) tray dried sample. In line with this, antioxidant activities by DPPH (2,2-diphenyl-1-picryl-hydrazyl), ABTS+(azinobistetrazolium sulfate cation) and FRAP (Ferric ion reducing antioxidant power) models, were also respectively affected by drying methods. TPC, TFC and antioxidant capacity was found to be in decreasing order with the corresponding solvents used: 80 per cent ethanol > methanol > aqueous > acetone. Correlation analysis presented a significantly positive correlation (p< 0.01) of antioxidant activity with TPC and TFC. The study revealed that lyophilization was the most effective drying method with highest yield of bioactive compounds in 80 per cent ethanol as the solvent. The results provide the evidence required for utilization of corn silk as a potential source of natural antioxidants. [ABSTRACT FROM AUTHOR]