Saffron Processing Wastes as a Bioresource of High-Value Added Compounds: Development of a Green Extraction Process for Polyphenol Recovery Using a Natural Deep Eutectic Solvent

Abstract

The current investigation was undertaken to examine saffron processing waste (SPW) as a bioresource, which could be valorized to produce extracts rich in antioxidant polyphenols, using a green, natural deep eutectic solvent (DES). Initially, there was an appraisal of the molar ratio of hydrogen bond donor/hydrogen bond acceptor in order to come up with the most efficient DES composed of L-lactic acid/glycine (5:1). The following step was the optimization of the extraction process using response surface methodology. The optimal conditions thus determined were a DES concentration of 55% (w/v), a liquid-to-solid ratio of 60 mL g−1, and a stirring speed of 800 rounds per minute. Under these conditions, the extraction yield in total polyphenols achieved was 132.43 ± 10.63 mg gallic acid equivalents per g of dry mass. The temperature assay performed within a range of 23 to 80 °C, suggested that extracts displayed maximum yield and antioxidant activity at 50–60 °C. Liquid chromatography-mass spectrometry analysis of the SPW extract obtained under optimal conditions showed that the predominant flavonol was kaempferol 3-O-sophoroside and the major anthocyanin delphinidin 3,5-di-O-glucoside. The results indicated that SPW extraction with the DES used is a green and efficient methodology and may afford extracts rich flavonols and anthocyanins, which are considered to be powerful antioxidants.

A Green Extraction Process for Polyphenols from Elderberry (Sambucus nigra) Flowers Using Deep Eutectic Solvent and Ultrasound-Assisted Pretreatment

“…Diffusivity may be increased by raising R L/S [27]; however, the optimum R L/S found for polyphenol extractions with DES may vary from 29.5 [28] to as high as 100 mL g −1 dm [29,30]. The optimal R L/S determined for EBF (60 mL g −1 ) is in accordance with recent studies on polyphenol extraction with DES from saffron processing wastes (60 mL g −1 ) [15] and hop (59 mL g −1 ) [13].…”

“…On the other hand, optimization of polyphenol extraction has shown that, in some cases, low S S (300 rpm) may favor increased extraction yield, as opposed to higher S S (900 rpm), which apparently was hindering in this regard [30]. In other recent examinations, the findings indicated quite the opposite [15,29]. Since the phenomena associated with the effect of S S may be related with factors such as the nature of the solid material, the solid particle diameter, the solute (polyphenols species), the viscosity of the liquid phase (solvent), etc., the actual effect of S S on extraction yield would be a subject of case experimentation.…”

“…A series of DES composed of L-lactic acid (hydrogen bond donor-HBD) and glycine (hydrogen bond acceptor-HBA) was synthesized, based on a previous method [15]. Accurately weighted amounts of both HBD and HBA were placed into a round-bottom glass flask and heated moderately (80 • C) in oil bath for approximately 120 min, until the formation of a perfectly transparent liquid.…”

“…Chromatography was performed based on a recently reported methodology [15]. A Shimadzu CBM-20A liquid chromatograph (Shimadzu Europa GmbH, Germany), equipped with a SIL-20AC auto sampler and a CTO-20AC column oven, was used.…”

“…S S is a variable with crucial role in solid-liquid extraction, and it has been proven that careful S S setting could provide higher extraction yields [27,31]. In a recent study where S S was considered as one of the variables for constructing experimental design, it was found to exert a statistically significant effect on the polyphenol extraction yield [15]. It has been proposed that appropriately set S S may create sufficient turbulence in the extraction tank to increase mass transfer rate.…”