Extraction of flavonoids and carotenoids from Thai silk waste and antioxidant activity of extracts

Extraction of carotenoids and flavonoids from yellow Thai silk waste was investigated. The total recovery of 0.7 mg carotenoids and 5.1 mg flavonoids/g dry weight was obtained by ethanol extraction. Different methods for extractions of these pigments were carried out using two benign solvents: ethanol and subcritical water (SW) to determine the extraction efficiency of the solvents in various extraction conditions. For extraction of carotenoids, ethanol was suitable as extraction solvent and the amount of carotenoids increased with increasing temperature and extraction time. For flavonoids, SW extraction was suitable but the amount of flavonoids decreased with increasing SW temperature and extraction time due to decomposition at such conditions. In addition, the silk extracts were found to have low IC₅₀ values (15.6–23.3 μg/ml), the concentrations of the silk extracts that exhibit 50% reduction in 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), (ABTS) free radicals, thus indicating high antioxidant activities.