2.9. Antioxidant activity by DPPH assay
The DPPH radical scavenging activity of samples was measured according to a slightly modified method (Yamaguchi et al., 1998). Samples were subjected to determine the least concentration of radical scavenging. Each sample solution (0.5 ml) was added to 1 ml of a freshly prepared 0.1 mM DPPH solution dissolved in methanol. The sample was mixed and incubated in the dark at room temperature for 30 min. Absorbance of the sample was measured at 517 nm using a spectrophotometer against a control. The radical scavenging of DPPH was calculated by using the formula below: Radical scavenging activity (%)=[1−(Abs. sample/Abs. control)]×100. Then results were expressed as an IC50 value, which is the concentration of the extract that scavenges 50% of the DPPH radical scavenging activity.
2.10. Estimation of molecular mass of sericin proteins by SDS-PAGE
The molecular mass of sericin proteins was estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The separating gel and staking gel were 12.5% and 5%, respectively. The sample solution was mixed with 2x buffer and heated in hot water, then sample was loaded into the well. The electric current of 150 V, 50 mA was applied to the gel. At the end of electrophoresis, the gel was stained with silver staining technique. Standard molecular mass marker was applied for estimating the molecular mass.
2.11. Statistical analysis
All experiments were performed in triplicate and the results were expressed as mean±standard deviation (SD). One-way ANOVA using SPSS software was used to compare the mean values of each treatment. Significant differences (p