Preparation and characterization of antioxidant flavonoid-enriched extract from saffron by-product: a combination of ultrasound-assisted extraction and macroporous resin purification

The stigma of saffron, a precious spice widely used in the world, takes only 7.4% (w/w) of the total weight of the flower, resulting in wasting the rest 92.6% of the flower. The utilization of the waste saffron floral bio-residues (SFB) has hence attracted people's attention. In this paper, ultrasound-assisted extraction (UAE) associated with macroporous resin (MPR) purification step was successfully applied to enrich antioxidant flavonoid in SFB extract for the first time, resulting in significant increase in flavonoid content compared with other extraction method reported in literatures. The yield of the extract was up to 10%, and the content of kaempferol-3-O-sophoroside (KS) in the obtained extract was more than 50%, which was much higher than the total flavonoid content (2.05-19.2%) reported in other literatures. UAE procedure was optimized by studying the influence of parameters, e.g., extracting solvent, time, temperature and sample-solvent ratio, based on contents of KS and delphinidin-3,5-di-O-glucoside (DG) and the antioxidant activity of the extract. Further enrichment of flavonoid was achieved by D-101 MPR with optimum purification conditions. Furthermore, 52 flavonoids, 8 alkaloids and 10 polyols were identified or putatively characterized from the SFB extract using UPLC-MS, and the contents of KS and DG were determined to be 501.90 and 22.01 mg/g, respectively. Besides, the SFB flavonoid extract showed good antioxidant activities with IC50 33.79 mu g/mL for DPPH scavenging effect and 39.65 mu mol/mg trolox for ORAC values