Separation and Purification Technology 62 (2008) 444–448 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Extraction of flavonoids and carotenoids from Thai silk waste and antioxidant activity of extracts Chattip Prommuak a , Wanchai De-Eknamkul b , Artiwan Shotipruk a,∗ a Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Patumwan, Phayathai Road, Bangkok 10330, Thailand b Department of Pharmacognosy, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Patumwan, Phayathai Road, Bangkok 10330, Thailand article info Article history: Received 15 January 2008 Received in revised form 20 February 2008 Accepted 24 February 2008 Keywords: Carotenoids Flavonoids Bombix mori Antioxidant activities Extraction Silk waste abstract Extraction of carotenoids and flavonoids from yellow Thai silk waste was investigated. The total recovery of 0.7mg carotenoids and 5.1mg flavonoids/g dry weight was obtained by ethanol extraction. Differ- ent 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 IC 50 values (15.6–23.3 g/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. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Silk waste is a part of the cocoons of silkworms (Bombyx mori) that is difficult to unreel. In Thailand, a large amount (36.6 tons) of this by-product is produced annually. Despite their unsuitability for silk textile production, the composition of silk waste is similar to that of good silk, which is composed of an inner core protein (75–83%) called fibroin that is surrounded by a glue-like protein called sericin (17–25%). Other components include waxes, hydro- carbons, and pigments. Several studies are currently being conducted on extraction, fabrication, and utilization of silk sericin and fibroin proteins [1–6]. Sericin has been found to have antioxidant activity [3,5], and is used for various applications such as cosmetics, functional biomaterials, and medicines. The more fibrous fibroin protein is utilized as functional biomaterial especially for tissue engineer- ing. In many applications, sericin and fibroin need to be made into soluble forms, which could be achieved by using acid or alkali catalyzed process. Fibroin could be solubilized in mix- tures of aqueous solution of salts and organic solvents such as CaCl 2 /H 2 O/EtOH [7], or by use of enzymes as active agents ∗ Corresponding author. Tel.: +66 2 218 6868; fax: +66 2 218 6877. E-mail address: artiwan.sh@chula.ac.th (A. Shotipruk). [8]. In addition, it has been demonstrated that subcritical water (SW) could potentially be used for solubilization of sericin and fibroin from silk waste into useful protein and amino acids [9–10]. Other than sericin and fibroin, Thai silk, particularly the yel- low Nangnoi silk, contains a significant amount of pigments, which are mostly associated with carotenoids and flavonoids [11–12]. Both of these pigments are generally found in fruits and vegeta- bles, and are remarkably reported as highly efficient antioxidants. Flavonoids have several pharmacological activities such as car- diotonic, anti-inflammatory, and anti-microbial activities [13–14], while carotenoids are associated with the prevention of cancer and cardiovascular disease [15]. In previous studies [11], the major carotenoid in yellow silk was reported to be oxygenated silk carotenoid (xanthophyll), lutein (80% of total carotenoids), which has been reported as an excellent agent to protect against vision loss [16–17]. Although a number of recent studies have been conducted to identify different constituents of silk pigments [11,12], the quan- titative analysis has not been well documented. In this study, the total amount of high value pigments, particularly carotenoids and flavonoids, in Nangnoi silk waste samples were determined. Then extractions of carotenoids and flavonoids from silk waste were conducted to examine the suitable extraction conditions using two environmentally benign solvents, such as ethanol and 1383-5866/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2008.02.020