Deep Eutectic Solvent-Assisted Extraction, Partially Structural Characterization, and Bioactivities of Acidic Polysaccharides from Lotus Leaves

Abstract

Lotus leaves are often discarded as byproducts in the lotus industry. Polysaccharides are regarded as one of the essentially bioactive components in lotus leaves. Therefore, in order to promote the application of lotus leaves in the functional food industry, the deep eutectic solvent (DES) assisted extraction of polysaccharides from lotus leaves (LLPs) was optimized, and structural and biological properties of LLPs extracted by DES and hot water were further investigated. At the optimal extraction conditions (water content of 61.0% in DES, extraction temperature of 92 °C, liquid-solid ratio of 31.0 mL/g and extraction time of 126 min), the maximum extraction yield (5.38%) was obtained. Furthermore, LLP-D extracted by DES and LLP-W extracted by hot water possessed the same sugar residues, such as 1,4-α-D-GalAp, 1,4-α-D-GalAMep, 1,3,6-β-D-Galp, 1,4-β-D-Galp, 1,5-α-L-Araf, and 1,2-α-L-Rhap, suggesting the presence of homogalacturonan (HG), rhamnogalacturonan I and arabinogalactan in both LLP-W and LLP-D. Notably, LLP-D was much richer in HG fraction than that of LLP-W, suggesting that the DES could assist to specifically extract HG from lotus leaves. Additionally, the lower molecular weight and higher content of uronic acids were observed in LLP-D, which might contribute to its much stronger in vitro antioxidant, hypoglycemic, and immunomodulatory effects. These findings suggest that the optimized DES assisted extraction method can be a potential approach for specific extraction of acidic polysaccharides with good bioactivities from lotus leaves for applications in the functional food industry.

Revisiting the Physicochemical Properties and Applications of Deep Eutectic Solvents

“…Polysaccharides have shown various medicinal effects such as antioxidant, antidiabetic, antiglycation, anti-viral, anti-inflammatory, anti-coagulant, immunostimulatory, and anti-tumor properties [157,171]. Due to strong inter-and intra-molecular hydrogen bonding, the extraction of polysaccharides requires harsh treatment conditions or processes [113,114,157].…”

“…The presence of alkali in extraction can influence the activity as well as the structure of polysaccharides [173]. Again, to overcome the limitation of the extraction process or solvent system, there is a continuous search to optimize the process/solvent system to improve cost and extraction yield [157,171,173]. Ionic liquids have been extensively used for biomass dissolution and extraction, and the focus is to have a greener extraction process [113][114][115].…”

“…Ionic liquids have been extensively used for biomass dissolution and extraction, and the focus is to have a greener extraction process [113][114][115]. DESs have also been used and have shown extraction properties for multiple biomolecules such as phenolic compounds, flavonoids, and alkaloids [156,[170][171][172][173][174][175][176]. Recently, Wu et al (2021) [171] used DESs to extract polysaccharides from lotus leaves.…”

“…DESs have also been used and have shown extraction properties for multiple biomolecules such as phenolic compounds, flavonoids, and alkaloids [156,[170][171][172][173][174][175][176]. Recently, Wu et al (2021) [171] used DESs to extract polysaccharides from lotus leaves. A choline chloride-and ethylene glycol-based DES was used, and the extraction process was optimized and compared with the conventionally used hot water treatment [171].…”

Preparation, Structural Features and in vitro Immunostimulatory Activity of a Glucomannan From Fresh Dendrobium catenatum Stems

“…As pro-inflammatory cytokines, IL-6, L-1β, and IFNγ , are critical to the innate immune response of bacteria in cells (42,43). Macrophages primed with IL-6, L-1β, and IFN-γ rapidly respond to a secondary signal, resulting in their tumoricidal and microbicidal activities that are essential for adaptive immunity against viral and infections (44,45). In this study, the DCP dose-dependently and significantly enhanced the secretion of macrophage-related cytokines, such as IL-6, L-1β, and IFN-γ , in RAW264.7 macrophages within the determined concentration range of 50-200 µg/mL as compared to that in the control group cells (p < 0.05).…”