Extraction of silk flavonoids and carotenoids from Thai silk waste and their antioxidant activities

Abstract

At present, there have been widespread studies on the extraction of silk proteins as well as their applications. This thesis aims to study silk pigments, the other component of the silk, which was interesting no less than its protein. Silk pigments are composed of antioxidative substances such as carotenoids and phenolic compounds, particularly flavonoids. The results in this study showed that the complete removal of the pigments of Thai yellow Nangnoi silk waste, could be achieved by repeated batch extraction 5 time with ethanol at 80oC in a closed pressure vessel. The extracts exhibited the amounts of total carotenoids and flavonoids of 0.7 and 5.1 mg/g dry weight, respectively. Of these amounts, more than 60% of carotenoids contents and 70% of flavonoids contents were located on silk fibroin layer (an inner core protein). The constituents of this extract were then analyzed using high performance liquid chromatography (HPLC) and it was found that the carotenoid called lutein is the major component of the extract. Due to the fact that carotenoids and flavonoids are associated with the medicinal functions, we investigated extraction of these pigments using two benign solvents, which are ethanol and subcritical water to determine the suitability of the solvents for extraction of these pigments. The experimental results revealed that ethanol is the suitable solvent for extraction of carotenoids while subcritical water is suitable for flavonoids extraction. For extraction of caroteinoids, ethanolic was used as extraction solvent to determine the effect of temperature (50-79 ํC) and extraction time (2-12 hours), and the result exhibited that the amount of carotenoids increased with increasing temperature and extraction time. For flavonoids, subcritical water extraction was carried out at 120-150 ํC for 10-60 min to determine the effects of subcritical water temperatures and extraction times on the yield, and the results showed that the amount of flavonoids decreased with the increasing subcritical water temperature and the extraction time due to decomposition at such conditions. Besides the amount of the pigments, the antioxidant activity of the silk extracts were determined and it was found that the concentration of the silk pigment extract that exhibit the 50% reduction of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid), (ABTS) free radicals was as small as 15.6-23.3 [micro]g/ml.