Abstract
The polysaccharide isolated from alfalfa was considered to be a kind of macromolecule with some biological activities; however, its molecular structure and effects on immune cells are still unclear. The objectives of this study were to explore the extraction and purifying methods of alfalfa (Medicago sativa L.) polysaccharide (APS) and decipher its composition and molecular characteristics, as well as its activation to lymphocytes. The crude polysaccharides isolated from alfalfa by water extraction and alcohol precipitation methods were purified by semipermeable membrane dialysis. Five batches of alfalfa samples were obtained from five farms (one composite sample per farm) and three replicates were conducted for each sample in determination. The results from ion chromatography (IC) analysis showed that the APS was composed of fucose, arabinose, galactose, glucose, xylose, mannose, galactose, galacturonic acid (GalA), and glucuronic acid (GlcA) with a molar ratio of 2.6:8.0:4.7:21.3:3.2:1.0:74.2:14.9. The weight-average molecular weight (Mw), number-average molecular weight (Mn), and Z-average molecular weight (Mz) of APS were calculated to be 3.30 × 106, 4.06 × 105, and 1.43 × 108 g/mol, respectively, according to the analysis by gel permeation chromatography-refractive index-multiangle laser light scattering (GPC-RI-MALS). The findings of electron ionization mass spectrometry (EI-MS) suggest that APS consists of seven linkage residues, namely 1,5-Araf, galactose (T-D-Glc), glucose (T-D-Gal), 1,4-Gal-Ac, 1,4-Glc, 1,6-Gal, and 1,3,4-GalA, with molar proportions of 10.30%, 4.02%, 10.28%, 52.29%, 17.02%, 3.52%, and 2.57%, respectively. Additionally, APS markedly increased B-cell proliferation and IgM secretion in a dose- and time-dependent manner but not the proliferation and cytokine (IL-2, -4, and IFN-γ) expression of T cells. Taken together, the present results suggest that APS are macromolecular polymers with a molar mass (indicated by Mw) of 3.3 × 106 g/mol and may be a potential candidate as an immunopotentiating pharmaceutical agent or functional food.
Highlights
Alfalfa (Medicago sativa L.) is an extensively cultured, dual purpose plant that has been generally used as forage for livestock or a kind of functional food for humans due to its high-quality protein [1,2,3]and immunomodulation bioactivity [4,5]
The polysaccharides in alfalfa (APS) have been regarded as a natural alternative to antibiotics when added to animal diets because they promote growth performance and have no toxic or other side effects in animals [3,15,16]; they have been used as functional agents or foods [16,17]
Eight peaks were identified in Alfalfa polysaccharide (APS) in the order of fucose, arabinose, galactose, glucose, xylose, mannose, galactose, galacturonic acid (GalA), and glucuronic acid (GlcA) with a molar ratio of 2.6:8.0:4.7:21.3:3.2:1.0:74.2:14.9 (Figure 3, Table 1)
Summary
Alfalfa (Medicago sativa L.) is an extensively cultured, dual purpose plant that has been generally used as forage for livestock or a kind of functional food for humans due to its high-quality protein [1,2,3]and immunomodulation bioactivity [4,5]. Alfalfa (Medicago sativa L.) is an extensively cultured, dual purpose plant that has been generally used as forage for livestock or a kind of functional food for humans due to its high-quality protein [1,2,3]. Nutrients 2019, 11, 1181 polysaccharides in alfalfa, and subsequent research clarified that those polysaccharides exert immunomodulatory [6], anti-inflammatory [7,8], antioxidant/anticancer [9,10], and growth-promoting bioactivities [11,12]. The polysaccharides in alfalfa (APS) have been regarded as a natural alternative to antibiotics when added to animal diets because they promote growth performance and have no toxic or other side effects in animals [3,15,16]; they have been used as functional agents or foods [16,17].
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