Abstract
Waste resulting from edible plants is considered one of the best sources of valuable phytochemicals. A promising approach for using these appreciated wastes is extracting precious medically important constituents, for example, free quercetin. Two new cost-effective and green extraction methods are introduced in the present study: ultrasound-assisted glycerol extraction (UAGE) and microwave-assisted extraction (MAE). These extraction protocols are optimized using factorial design to define the highest yield of extraction, and HPLC-UV at 370 nm was used as a method of yield analysis. Quercetin remained stable during the whole process in both extraction protocols. A standard addition technique was performed to quantify quercetin in different extracts and eliminate the matrix effect. In UAGE and MAE, extraction yields were 16.55 ± 0.81 and 27.20 ± 1.55 mg/1g from red onion scales on a dry base, respectively. The amount of quercetin extracted using MAE was superior to UAGE in terms of time and yield. A greenness assessment of the offered studies compared to previously published relevant extraction methods was performed using the analytical eco-scale assessment method (ESA) and national environmental methods index (NEMI). MAE showed to be a greener method with a higher ESA score and a greener NEMI pictogram.
Highlights
Onion has been reported as one of the major sources of dietary flavonoids worldwide, which are the main source of the total antioxidant activity of onions [1,2]
Quercetin is naturally found as a free aglycone or a glycosidic form as conjugated to one or more sugar molecules [8]
This study aims to develop green, simple, high yield, time and cost-saving protocols to extract quercetin from red onion scale-waste and optimize microwave-assisted extraction (MAE) and Ultrasound-Assisted Glycerol Extraction (UAGE) methods using a factorial design to determine the conditions that resulted in the highest yield of quercetin
Summary
Onion has been reported as one of the major sources of dietary flavonoids worldwide, which are the main source of the total antioxidant activity of onions [1,2]. In terms of economic importance, onion ranks second among all vegetables after tomatoes [3]. One of the great sources of natural antioxidants is dry onion scales that are thrown away as wastes. A possible approach for using these valuable wastes is extracting precious medically important constituents, for example, free quercetin [4,5,6,7]. Quercetin is naturally found as a free aglycone or a glycosidic form as conjugated to one or more sugar molecules [8]. Extraction is the central stage in the qualitative and quantitative analysis of natural products [1]. This study has an apparent eco-friendly approach and contracts with the green chemistry concepts for the extraction process
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