Adsorption and Desorption Properties of Total Flavonoids from Oil Palm (Elaeis guineensis Jacq.) Mature Leaf on Macroporous Adsorption Resins

Abstract

Three different macroporous resins (XAD7HP, DAX-8, and XAD4) were evaluated for their adsorption and desorption properties in preparing flavonoid-enriched oil palm (Elaeis guineensis Jacq.) leaf extract. The influences of initial concentration, solution pH, contact time, and desorption solvent (ethanol) concentration were determined by static sorption/desorption methods. The optimal condition for adsorption of flavonoids was achieved when the solution of the extract was adjusted to pH 7, reaching equilibrium after 1440 min at 298 K. The adsorption process was well described by a pseudo-second-order kinetics model, while the adsorption isotherm data fitted well with a Freundlich model. The adsorption by each resin was via an exothermic and physical adsorption process. Based on the static experiment results, XAD7HP was found to be the most appropriate adsorbent, while 80% ethanol was the best solvent for desorbent. Further evaluation of its dynamic adsorption and desorption characteristics on a packed glass column showed that XAD7HP could enrich the OPL total flavonoid content by a 3.57-fold increment. Moreover, UHPLC-UV/PDA and UHPLC-MS/MS analysis revealed that apigenin and luteolin derivatives were selectively adsorbed by XAD7HP. Additionally, both the crude OPL extract and the flavonoid-enriched fraction have good DPPH and NO free radical scavenging activities. Multiple interactions between the flavonoids and cross-linked polymeric XAD7HP resin through van der Waals forces and hydrogen bonding described the sorption processes. Therefore, by utilizing this method, the flavonoid-enriched fraction from crude OPL extract could be used as a potential bioactive ingredient in nutraceutical and pharmaceutical applications at minimum cost with optimum efficiency.Molecules 2020, 25, 778 2 of 17 shown to be safe for use in disease treatments based on the absence of adverse effects in several studies on rodents [5,6].Previous chemical investigations revealed that OPL extract is rich in flavonoids, mainly flavonoid O-glycosides and flavonoid C-glycosides [7]. As a class of compounds, flavonoids are well known to have positive effects on human health with reports of being hepatoprotective, antioxidative, and antidiabetic, among others [8]. Presently, there is a high demand for flavonoids globally by the nutraceutical and pharmaceutical industries, which is forecasted to reach approximately RM 4.40 billion by the year 2025 [9]. Thus, to meet requirements, the availability of simple and efficient methods for their separation and purification is needed.Conventionally, flavonoids are separated from plant matrixes by methods that require high amounts of solvents, long separation time and low recovery. These methods include solid-liquid extraction, liquid-liquid extraction, and column chromatography, either packed with silica gel or Sephadex LH-20. Macroporous resin (MAR), with the property of high cross-linkage and many permanent pores, was also utilized in the separation and purification of flavonoids, for example, separation of...

Enrichment in Antioxidant Flavonoids of Stamen Extracts from Nymphaea lotus L. Using Ultrasonic-Assisted Extraction and Macroporous Resin Adsorption

“…The optimal pH value was around 5, which resulted in an increased enrichment of the N. lotus stamen extract in total flavonoids. This result is consistent with other studies [55][56][57][58][59][60]. At a higher pH value, the flavonoid phenolic hydroxyl groups dissociated with H+ and the corresponding flavonoid anion result in lower adsorption capacity and thus a drastic reduction in the purification yield [57].…”

“…The results showed that concentration and pH of the aqEtOH solution and the temperature influenced the desorption capacity of the MPR. In the literature, most flavonoids are desorbed with an aqEtOH concentration for the desorption solution ranging from 75-100% (v/v) in agreement with the present study [54][55][56][57][58][59][60]. The pH value can change the ionization of flavonoids, which also affects their adsorption to the MPR [57].…”

“…[ 60 ]. The authors of this study pointed out the importance of adjusting the chemical nature of the MPR, but also its physical properties, to the nature of the plant extract and the compounds to be purified [ 60 ]. The ester substitution of the acrylic matrix with a lower surface area (140 m 2 /g), a lower particle diameter (250–420 μm) and a lower pore diameter (225 Å) of the DAX-8 MPR compared to the XAD-7 MPR were more suitable characteristics for the purification of total flavonoids from N. lotus stamen extract.…”

“…Acrylic MPRs, DAX-8 MPR in particular, have previously been reported for its efficacy in the enrichment of total flavonoid extracts from mature oil palm leaf (Elaeis guineensis Jacq.) [60]. The authors of this study pointed out the importance of adjusting the chemical nature of the MPR, but also its physical properties, to the nature of the plant extract and the compounds to be purified [60].…”

“…Divergent assumptions on the effect of the chemical structure (e.g., styrene, acrylic) and physical properties (such as surface area, pore diameter) of the MPR on the recovery of flavonoids were made, depending on the plant matrix [54][55][56][57][58][59][60]. In line with some recent reports [56,[58][59][60], here, better results were achieved using the moderately polar acrylic DAX-8 and XAD-7 MPRs, certainly due to the nature of the flavonoids present in the N. lotus stamen extract. Acrylic MPRs, DAX-8 MPR in particular, have previously been reported for its efficacy in the enrichment of total flavonoid extracts from mature oil palm leaf (Elaeis guineensis Jacq.)…”