Ginseng polysaccharides: Structures-based classification and biological activities-A review

Abstract

Ginseng polysaccharides are primarily categorized into two group: acidic polysaccharides, which are composed of rhamnogalacturonan I and homogalacturonan domains, and neutral polysaccharides, primarily consisting of glucans. These polysaccharides exhibit valuable pharmacological activities, including immunomodulation, antitumor effects, and antioxidant properties. Numerous studies have confirmed that structural characteristics such as weight-average molecular weight, monosaccharide composition, and structural domains of ginseng polysaccharides are closely related to their biological activities. However, research on the correlation between these factors remains fragmented, lacking a systematic integration that elucidates their intrinsic connections. This paper provides a comprehensive review of the structural features and biological activities of ginseng polysaccharides, with a particular focus on their structure-activity relationships. Furthermore, it summarizes the patterns of physical, biological, and chemical transformations of ginseng polysaccharide structures and the resulting changes in their biological activity. We hope this paper provides a theoretical basis and insights for the clinical application and product development of ginseng polysaccharides.

Graphical abstract

Ginseng polysaccharides: Structures, biological activities, structure-activity relationships and structural transformation.

Highlight

• ●Systematically summarize the structural characteristics of ginseng polysaccharides.
• ●Comprehensively outline the biological activities of ginseng polysaccharides.
• ●Establish the structure-activity relationships of ginseng polysaccharides.
• ●Reveal physical, biological, and chemical transformations of ginseng polysaccharides structure and biological activity.

1. Introduction

Ginseng, known as the dried root and rhizome of the plant Panax ginseng C.A. Meyer, belongs to the Araliaceae family and is primarily distributed in East Asia [1,2]. The numerous bioactive properties of ginseng are attributed not only to its well-known ginsenosides but also to another significant active component: ginseng polysaccharides [3,4]. Ginseng polysaccharides are a class of structurally complex bioactive macromolecules derived from the dried roots and rhizomes of ginseng. Extensive research has demonstrated that ginseng polysaccharides exhibit diverse biological activities, including but not limited to immunomodulation, antitumor effects, antioxidant properties, blood glucose reduction, and anti-aging effects. These attributes hold great promise for applications in functional foods, dietary supplements, and new drug development [5,6].

Recent research has indicated that the biological activity of ginseng polysaccharides is closely linked to structural characteristics such as weight-average molecular weight (M_w), monosaccharide composition and linkage, structural domains, and higher-order structures [7]. Furthermore, physical, biological, and chemical structural transformation methods can modulate their biological activity to a certain extent [8,9]. However, the intrinsic relationship between the structural features of ginseng polysaccharides and specific biological activities, as well as the structural and activity changes occurring during the transformation process, remain inadequately elucidated. This paper systematically summarizes the structure, biological activity, structure-activity relationship, and the impact of structural transformation on the biological activity of ginseng polysaccharides, aiming to provide a scientific basis for the scientific evaluation and comprehensive utilization of ginseng polysaccharides.

2. Structure of ginseng polysaccharides

Ginseng polysaccharides are primarily composed of two types of acidic monosaccharides, namely galacturonic acid (GalA) and glucuronic acid (GlcA), along with four types of neutral monosaccharides: glucose (Glc), galactose (Gal), rhamnose (Rha), arabinose (Ara) (Fig. 1A). Based on their monosaccharide composition, these polysaccharides can be classified into two categories: ginseng acidic polysaccharides and ginseng neutral polysaccharides [10]. Ginseng acidic polysaccharides, commonly known as pectins, mainly consist of rhamnogalacturonan-I (RG-I) and homogalacturonan (HG) structural domains [7]. In contrast, ginseng neutral polysaccharides are primarily composed of glucans and arabinogalactans (AG) structural domains. These structural domains typically do not exist independently; instead, they are combined in specific ratios to form complex structures.

Fig. 1.

Structural characteristics of ginseng polysaccharides. (A) Monosaccharide composition; (B) RG-Ⅰ structural domain; (C) HG structural domain; (D) Glucans structural domain; (E) AG structural domain.

Polysaccharide structures can be categorized into four hierarchical levels. The first level, known as the primary structure, encompasses the monosaccharide composition, the sequence of monosaccharide arrangement, and the types of linkages between adjacent sugar units. The second to fourth levels correspond to higher-order structures, which involve various interactions, including hydrogen bonds, functional group interactions, non-covalent bonds, and the spatial configurations formed through further curling and folding. Currently, most studies on ginseng polysaccharides have concentrated on analyzing primary structures, while research on higher-order structures remains relatively limited.

2.1. Structure of ginseng acidic polysaccharides

2.1.1. Acidic polysaccharides rich in RG-I structural domains

The RG-I structural domain features a disaccharide backbone composed of alternating Rha and GalA. The predominant side chains consist of polymers derived from AG structural domains, galactan, and/or arabinose structural domains, which are linked to the main chain via C-4 linkages of the Rha residues [11] (Fig. 1B). White ginseng polysaccharide-0.1 M NaCl-RG (WGP-0.1-RG) has an M_w of 71.3 kDa, a monosaccharide composition of Rha: GalA: Ara: Gal = 6.8 %:8.1 %:55.8 %:29 %, a long chain consisting of the RG-I structural domain in the main chain, and α-1,5-linked arabinogalactans, β-1,4-linkage galactan, and arabinogalactan II (AG-II) in the side chains [12]. White ginseng polysaccharide-0.3 M NaCl (WGP-0.3) has an M_w of 63.35 kDa and a monosaccharide composition of Rha: GalA: Ara: Gal: Glc = 9.4 %:45.5 %:14.8 %:13.9 %:11.7 %. This polysaccharide does not exhibit a triple helix structure; instead, its backbone is composed of repeating units represented as [→3)-α-L-Rhap-(1 → 4)-α-D-GalpA-(1 → 3,4)-α-D-GalpA-(1→]. Microscopic analysis reveals an intricate structure characterized by asymmetric lamellar cracks and fissures. Additionally, WGP-0.3 exhibits aggregation due to the intertwining of molecular chains and the interactions between intermolecular and intramolecular hydrogen bonds [13].

2.1.2. Acidic polysaccharides rich in HG structural domains

The HG structural domain is characterized by a linear backbone composed of 1,4-linked GalA [14]. The hydroxyl groups at the C-2 or C-3 positions can undergo O-acetylation, while some carboxyl groups at the C-6 position may be methylated (Fig. 1C) [15]. Based on the degree of methylation (DM), HG-type pectins are generally classified into two categories: high-methyl pectins (DM ≥ 50 %) and low-methyl pectins (DM < 50 %) [16]. White ginseng polysaccharide-0.2 M NaCl-HG(WGP-0.2-HG) and white ginseng polysaccharide-0.3 M NaCl-HG(WGP-0.3-HG) have an M_w of 6.5 kDa and 16 kDa, respectively, with GalA as the predominant monosaccharide. Their DM values are 16 % and 8 %, respectively, categorizing them as low-methyl HG-type pectins [17,18]. Additionally, white ginseng polysaccharide-0.3 M NaCl b (WGPE-0.3 b) and white ginseng polysaccharide-0.5 M NaCl b (WGPE-0.5 b) have an M_w of 12 kDa and 50 kDa, with GalA contents of 62.2 % and 81.7 %, and DM values of 5 % and 27 %, respectively. These polysaccharides are similarly classified as low-methyl HG-type pectins. Notably, WGPE-0.5 b is primarily composed of HG structural domains, whereas WGPE-0.3 b contains both HG and RG-I structural domains, featuring side chains of arabinogalactan and galactan [19].

2.2. Structure of neutral polysaccharides in ginseng

2.2.1. Glucans

Ginseng glucans are comprised of several structural forms, including α-D-(1,4)-glucan, 6-branched α-D-(1,4)-glucan, 3-branched α-D-(1,6)-glucan, and unbranched α-D-(1,6)-glucan [20] (Fig. 1D). Two distinct types of neutral polysaccharides have been isolated from ginseng: enzymatic hydrolysate of white ginseng neutral polysaccharide-0.1 M NaCl (WGPNE-0.1) and enzymatic hydrolysate of white ginseng neutral polysaccharide-0.2 M NaCl (WGPNE-0.2). WGPNE-0.1 has an M_w of 80.4 kDa and a monosaccharide composition of Glc: Gal: Ara = 7.0:1.9:1.0. It is classified as a heteropolysaccharide, consisting of glucan domains along with AG-I and AG-II. In contrast, WGPNE-0.2 has an M_w of 31.5 kDa and features a backbone of (1 → 4)-α-D-Glcp, with (1 → 3)-α-D-Glcp and (1 → 6)-α-D-Glcp located at the branching points, representing a highly branched α-glucan [21]. Additionally, white ginseng acidic polysaccharide-0 M NaCl has an M_w of 1653.0 kDa, mainly consisting of Glc (98.1 %) and trace amounts of Gal (1.9 %). Its backbone is characterized by →6)-α-D-Glcp-(1 → . Congo red analysis indicates a minimal red shift, suggesting the absence of a distinct triple helix structure [22].

2.2.2. AG

The AG structural domain predominantly exists in the form of branched chains and can be classified into two types: AG-I and AG-II, based on their configuration. AG-I is characterized by a galactan chain linked by β-(1,4)-Galp, featuring one or more branches with α-(1,5)-linked L-Araf residues or a single terminal Arap residue. In contrast, AG-II has a backbone of β-(1,3)-D-Galp, with side chains consisting of 3-Galp, 6-Galp, or Ara (Fig. 1E) [23].

After hydrolyzing and purifying the water-soluble polysaccharides from ginseng using endo-polygalacturonase, two types of arabinogalactans, enzymatic hydrolysate of white ginseng acidic polysaccharide-0.07 M NaCl-AG (WGPAE-0.07-AG) and enzymatic hydrolysate of white ginseng acidic polysaccharide-0.16 M NaCl-AG (WGPAE-0.16-AG), were obtained. Although both have the same monosaccharide compositions, they differ in the ratios of their components. The monosaccharide composition of WGPAE-0.07-AG is Gal: Ara: Rha: GalA: Glc = 48.9:12.8:6.3:4.7:15.3, whereas that of WGPAE-0.16-AG is Gal: Ara: Rha: GalA: Glc = 55.9:18.6:9.5:5.0:4.0 [24].

3. The biological activities of ginseng polysaccharides

3.1. Immunomodulatory effects

The immunomodulatory effects of ginseng polysaccharides are characterized by a complex and multifaceted process. This involves the activation of macrophages, enhancement of phagocytosis, and increased production of nitric oxide (NO) and various cytokines. Additionally, ginseng polysaccharides stimulate natural killer (NK) cells, leading to the release of perforin and granzyme, and promote the maturation of dendritic cells (DCs). Moreover, they also stimulate the activation of T and B lymphocytes, as well as NK cells, thereby enhancing both innate and adaptive immunity and improving the host's immune function [25] (Fig. 2). Furthermore, ginseng polysaccharides can negatively regulate immune stress responses, alleviate the infiltration of inflammatory cells and reduce tissue damage.

Fig. 2.

Pathways of ginseng polysaccharides involved in innate immunity and adaptive immunity.

3.1.1. Activation of macrophages

Ginseng polysaccharides can activate pattern recognition receptors (PRRs)on the surface of macrophages, including Toll-like receptors (TLRs) and mannose receptors (MRs). This activation promotes macrophage proliferation and enhances phagocytic activity, as well as the production of immunomodulators such as NO, IL-1β, IL-6, and TNF. For instance, white ginseng acidic polysaccharide-0.2 M NaCl (WGPA-0.2) significantly enhances macrophage viability, increases phagocytic activity, and promotes the secretion of IL-1β, IL-6, TNF-α, and the production of NO [22]. Ginseng polysaccharides can activate macrophages via TLR2 and TLR4, triggering signaling pathways such as MAPK, NF-κB, and PI3K/AKT, which further facilitate the production of these immunomodulators [26,27].

3.1.2. Activation of NK cells

NK cells are crucial effector cells of the innate immune system. Although they do not express specific antigen recognition receptors, they possess the ability to directly kill certain target cells, including tumor cells and virus-infected cells [28]. NK cells induce target cell cytotoxicity by releasing perforin and granzyme, and by secreting cytokines such as TNF-α, TNF-β, IL-5, and IL-10 [29,30]. For example, ginseng neutral polysaccharide derived from ginseng can mitigate the inhibitory effects of 5-fluorouracil on NK cell activity [31]. Furthermore, ginseng polysaccharide has been shown to enhance the proliferation of NK cells in immunosuppressed mice and regulate the expression levels of perforin and granzyme in NK cells under immunosuppressive conditions [32].

3.1.3. Induction of dendritic cell maturation

Dendritic cells (DCs) are potent antigen-presenting cells that can recognize, uptake, process, and present antigens, thereby regulating both innate and adaptive immunity [33]. Ginseng polysaccharides activate PRRs on the surface of DCs, such as TLRs, MR, and dectin-1. This activation leads to the upregulation of co-stimulatory molecules such as CD80, CD40, CD86, and major histocompatibility complex (MHC) molecules, which are essential for initiating adaptive immune responses [22]. For instance, WGP-0.3 effectively activates DC2.4 cells through the TLR4-MyD88-NF-κB signaling pathway, resulting in a significant increase in the expression of CD80, CD86, and MHC class II [13]. Furthermore, ginseng polysaccharides act as an adjuvant that effectively activates DCs in mice, inducing a more robust IFN-γ CD8 T cell response and efficiently initiating adaptive immune responses [34].

3.1.4. Activation of lymphocytes

Lymphocytes are essential components of the immune system, encompassing T lymphocytes and B lymphocytes, which mediate cell-mediated immunity and humoral immunity, respectively. Ginseng polysaccharides have been shown to promote the proliferation and differentiation of splenic T lymphocytes into CD4⁺ T cells, which activate innate immunity, and CD8⁺ T cells, which are responsible for directly killing target cells. Additionally, ginseng polysaccharides stimulate B lymphocytes to proliferate and differentiate into plasma cells, leading to the secretion of antibodies such as IgM and IgG, thereby regulating immune responses [23,35]. For example, WGPA-0.2 enhances the proliferation and differentiation of splenic lymphocytes, increasing the ratio of CD4⁺/CD8⁺ T cells [22]. Moreover, ginseng acidic polysaccharide derived from ginseng activates the transcription factor Foxp3, promoting the generation of regulatory T cells (Tregs) and inhibiting the activation and proliferation of peripheral autoreactive T cells in the context of autoimmune encephalomyelitis [36]. Additionally, WGP-0.3 enhances the secretion of IgG, IgG1, and IgG2a antibodies, thereby increasing the neutralizing capability of antibodies and promoting humoral immunity [13].

3.2. Antitumor effects

The antitumor mechanisms of ginseng polysaccharides primarily involve the induction of tumor cell apoptosis, cell cycle blockade, inhibition of tumor invasion and metastasis, and the activation of immune regulatory responses.

3.2.1. Induction of tumor cell apoptosis

Ginseng polysaccharides can induce apoptosis in tumor cells through two classical pathways: the mitochondrial (intrinsic) pathway and the death receptor-mediated (extrinsic) pathway. As illustrated in Fig. 3, ginseng polysaccharides trigger mitochondrial-mediated apoptosis by downregulating pro-apoptotic proteins Bcl-2 family while upregulating the anti-apoptotic protein Bax. This cascade leads to the release of cytochrome c (Cytc) and the activation of caspase-9. Furthermore, ginseng polysaccharides can induce death receptor-mediated apoptosis by enhancing the expression of death receptors, such as TRAIL-R1, TRAIL-R2, and Fas, along with their ligand (FasL), which activate caspase-8. Both pathways ultimately activate caspase-3 and caspase-7, thereby promoting the apoptosis of tumor cells.

Fig. 3.

Pathways of ginseng polysaccharides induce apoptosis of tumor cells.

Ginseng acidic polysaccharide has been shown to alter the ratio of Bcl-2 family proteins and increase caspase-9 levels, thereby activating the mitochondrial-mediated apoptosis pathway. It also enhances the expression of pro-apoptotic receptors such as Fas and Fas ligand, leading to an increase in caspase-8 and triggering death receptor-mediated apoptosis. [37]. Furthermore, ginseng polysaccharide induces apoptosis in gastric cancer MGC803 cells by causing mitochondrial membrane depolarization, decreasing mitochondrial membrane potential, and increasing the expression levels of Bax and Cytc. Concurrently, it reduces Bcl-2 expression, increases cytochrome C content, and elevates reactive oxygen species (ROS) levels, indicating that polysaccharide mediates apoptosis through the mitochondrial pathway [38].

3.2.2. Inhibition of tumor cell invasion and metastasis

Disruption of the extracellular matrix (ECM), epithelial-mesenchymal transition (EMT), and tumor angiogenesis are critical processes involved in tumor invasion and metastasis. Galactose lectins are known to play a role in inducing cell migration and angiogenesis; their binding to T cell receptors promotes immune evasion, thereby facilitating tumor progression. Thus, they represent potential molecular targets for cancer therapy [39]. Studies have indicated that ginseng polysaccharides can interact with galactose lectins, exerting antagonistic effects and demonstrating anti-tumor activity.

Ginseng polysaccharide has been shown to inhibit key signaling pathways associated with EMT by reducing the levels of Twist and its downstream genes, including AKR1C2 and NF1 proteins. This action suppresses the invasion and migration of gastric cancer HGC-27 cells [40]. Additionally, the β-1,4-galactan side chains of ginseng RG-I pectin can bind to Gal-8 and Gal-3, thereby inhibiting their roles in T cell apoptosis, cell adhesion, and the migration of endothelial cells [39,41]. Additionally, ginseng pectin specifically suppresses Gal-3-mediated T cell apoptosis without affecting T cell activation [42].

3.2.3. Blockade of tumor cell cycle

Cell cycle blockade is a crucial mechanism for inhibiting tumor cell proliferation. Ginseng polysaccharides can regulate cell cycle-related proteins to disrupt the progression of the tumor cell cycle, thereby inhibiting tumor cell proliferation.

Research has demonstrated that ginseng acidic polysaccharide exerts a growth-inhibitory effect by inducing G2/M phase blockade in a concentration-dependent manner [37]. Ginseng polysaccharide can arrest MGC803 cells in the G1 phase, effectively preventing tumor cells from undergoing DNA replication and growth, while also inducing phenomena such as nuclear membrane contraction and vesicular apoptosis [38,43].

3.3. Antioxidant activity

In vitro assessment of antioxidant capacity primarily includes the measurement of free radical scavenging ability, reducing power, and metal ion chelation. Ginseng pectin polysaccharides exhibit strong metal chelation properties, whereas ginseng neutral polysaccharides display lower metal chelation capacity; both types possess antioxidant activity [44].

Ginseng polysaccharide demonstrates significant antioxidant properties in DHHP, ABTS, and FRAP assays [45]. Ginseng polysaccharide exhibits self-oxidation capabilities comparable to ascorbic acid (Vc) and displays slightly higher scavenging activity against superoxide radicals and hydroxyl radicals than Vc [46].

Oxidative stress is a process characterized by an imbalance between oxidation and antioxidant defenses [47]. Key antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), play vital roles in cellular redox processes. Ginseng polysaccharides can enhance the levels of SOD, CAT, and glutathione (GSH) while reducing oxidative stress markers such as malondialdehyde (MDA) and lipofuscin (LP), thereby protecting tissues from oxidative damage, as illustrated in Fig. 4.

Fig. 4.

Antioxidant pathways in vivo of ginseng polysaccharides.

Ginseng polysaccharides are effective in reducing levels of ROS and decreasing the production of the oxidative stress marker MDA, thereby alleviating lipid peroxidation [48]. Ginseng polysaccharides significantly enhance the activities of SOD, CAT, and glutathione peroxidase (GSH-Px), while inhibiting the mRNA and protein expression of hypoxia-inducible factor (HIF), thus mitigating lipid peroxidation in ischemia-reperfusion injury in rabbit kidneys [49]. In an in vitro oxidative stress model induced by H₂O₂ in red blood cells, ginseng polysaccharides significantly increase SOD and CAT activities while reducing oxidative markers MDA and ROS [50].

3.4. Other effects

3.4.1. Hypoglycemic effect

Elevated blood glucose levels can result in free radical damage within the body, exacerbating oxidative stress and causing significant damage [51]. Ginseng polysaccharides can inhibit the expression of free radicals, eliminate free radicals, reduce the apoptosis of pancreatic β cells, and suppress the activities of α -amylase and α -glucosidase, thereby reducing the release and absorption of glucose and improving disorders of glucose metabolism.

In a streptozotocin (STZ)-induced diabetic mouse model, ginseng polysaccharides significantly lowered MDA levels while enhancing the activities of antioxidant enzymes such as SOD and GSH-Px. Additionally, they were associated with triglycerides (TG) and total cholesterol (TC) levels. Notably, ginseng polysaccharides also contributed to increased body weight, insulin levels, and glycogen content in the mice [52]. Furthermore, ginseng polysaccharides alleviated oxidative stress in STZ-induced diabetic mice by decreasing MDA levels, increasing serum insulin, SOD, and enhancing liver glycogen content, while scavenging free radicals generated by reactive oxygen species [53]. Various ginseng polysaccharides have demonstrated the ability to inhibit α-amylase and α-glucosidase in vitro, delaying glucose diffusion and directly inhibiting glycolytic enzymes activity to help regulate blood glucose levels [45].

3.4.2. Anti-aging effects

The insulin/IGF-1 signaling (IIS) and target of rapamycin (TOR) signaling pathways are critical regulators of growth and aging in organisms. Ginseng polysaccharides have been found to inhibit both the IIS and TOR pathways, leading to a reduction in the excessive production of ROS, improving the oxidative/antioxidative balance, alleviating oxidative stress, and slowing the aging process. In addition, ginseng polysaccharides can also alleviate aging-related symptoms and improve physiological functions by restoring the intestinal barrier in aged mice [54].

Specifically, ginseng polysaccharides with RG-Ⅰ and HG structural domains can respectively inhibit the TOR and IIS pathway, promoting the activity of transcription factors DAF-16 and SKN-1, thereby delaying aging [12,55]. Additionally, ginseng polysaccharides enhance the antioxidant activity in Caenorhabditis elegans by reducing intracellular levels of lipofuscin and ROS while simultaneously increasing the activity of the antioxidant enzyme SOD, thereby exerting their anti-aging effects [56]. ginseng neutral polysaccharide can increase the abundance of A. senegalensis bacteria in the intestines of aged mice, induce indole accumulation, activate the AhR pathway, and prevent age-related intestinal barrier dysfunction and inflammation [54].

4. The structure-activity relationship of ginseng polysaccharides

The M_w, type of polysaccharide, primary structure (including domain types, structural domain side chains, monosaccharide composition, and linkage types), as well as the higher-order structure of ginseng polysaccharides, all possess structural characteristics that can influence their biological activity to varying degrees, as illustrated in Fig. 5.

Fig. 5.

The structure-activity relationships of ginseng polysaccharides.

4.1. Influence of molecular weight and distribution on bioactivities

Generally, low M_w polysaccharides are characterized by good water solubility and enhanced bioactivity, while high M_w polysaccharides often face challenges in penetrating cell membranes [57,58]. For instance, the neutral polysaccharide from ginseng, when enzymatically hydrolyzed to produce WGPNE, experiences a decrease in M_w from 13.78 kDa to 1.10 kDa. This reduction is accompanied by a notable enhancement in biological activity, particularly in antioxidant capacity and the ability to alleviate Aβ-induced oxidative stress in cells [59]. Neutral ginseng oligosaccharides (WGRPN) and ginseng neutral polysaccharide (WGPN) were extracted from ginseng residue and the ginseng root, respectively, with M_w of 1.12 kDa and 12.79 kDa. Notably, the lower M_w WGRPN demonstrated significantly stronger antioxidant, hypoglycemic, and immunomodulatory activities [60]. However, this relationship is not absolute; higher M_w ginseng polysaccharides can also demonstrate certain levels of biological activity. For example, ginseng polysaccharides enzymatic hydrolysate of white ginseng acidic polysaccharide-0.22 M NaCl-RG1 (WGPAE-0.22-RG1) (50 kDa) and enzymatic hydrolysate of white ginseng acidic polysaccharide-0.30 M NaCl-RG (WGPAE-0.30-RG) (60 kDa) showed significantly greater inhibitory effects on galectin-3 compared to enzymatic hydrolysate of white ginseng acidic polysaccharide-0.16 M NaCl-RG (WGPAE-0.16-RG) (4 kDa) and enzymatic hydrolysate of white ginseng acidic polysaccharide-0.22 M NaCl-RG2 (WGPAE-0.22-RG2) (6 kDa), with WGPAE-0.30-RG outperforming WGPAE-0.22-RG1 [61].

4.2. Activity differentiation based on polysaccharide types: neutral versus acidic polysaccharides

Uronic acids, such as GalA, are a defining feature that distinguishes neutral polysaccharides from acidic polysaccharides. Polysaccharides containing uronic acids are generally classified as acidic polysaccharides. Generally, the biological activity of acidic polysaccharides derived from ginseng is superior to that of neutral polysaccharides. In a dextran sulfate sodium (DSS)-induced colitis model, ginseng acidic polysaccharides effectively downregulate inflammatory cytokines, inhibit the TLR4/MyD88/NF-κB signaling pathway in the colon, and reduce intestinal damage, demonstrating greater efficacy compared to neutral polysaccharides from ginseng [62]. The acidic polysaccharide has been shown to stimulate insulin release and gluconeogenesis, lower blood glucose levels, and reduce SOD activity, exhibiting a stronger antidiabetic effect than neutral polysaccharides. In vitro assessments of ABTS radical scavenging, reducing power, ferrous ion chelation, and hydroxyl radical scavenging, along with in vivo evaluations of intracellular reactive oxygen species concentration and lipid peroxidation, confirm that the antioxidant capacity of ginseng acidic polysaccharides surpasses that of neutral polysaccharides [48]. This enhanced antioxidant activity is hypothesized to be due to the negatively charged GalA groups within the polysaccharides, which may exert antioxidant effects through metal chelation [44]. Conversely, some studies suggest that neutral polysaccharides may possess advantages over acidic ones. For instance, GPN from ginseng can induce apoptosis in B16F10 melanoma cells, restore the diversity of gut microbiota in melanoma-bearing mice, and upregulate levels of short-chain fatty acids (SCFAs), such as acetate and butyrate, demonstrating significant superiority over the acidic polysaccharide [63].

4.3. Relationship between the primary structure and pharmacological efficacy of ginseng polysaccharides

4.3.1. Structural domains: HG and RG as core functional domains mediating multiple biological activities

Ginseng polysaccharides, particularly those rich in HG and RG structural domains, demonstrate significant immunomodulatory and antitumor activities. In the process of inhibiting cell migration, the HG structural domain are vital for suppressing cell migration, while the RG-I structural domain provides important auxiliary and synergistic effects. These polysaccharides can activate immune cells, stimulate cytokine secretion, modulate both innate and adaptive immune responses, antagonize galactose-binding lectins, promote apoptosis in tumor cells, disrupt the cell cycle, and inhibit cell migration. Ginseng polysaccharides rich in HG structural domains exhibits a marked inhibitory effect on colon cancer cells (HT-29), inducing apoptosis specifically during the G2/M phase of the cell cycle. In contrast, polysaccharides primarily composed of ginseng amylopectin and arabinogalactan show no significant antitumor activity [64]. Furthermore, ginseng polysaccharides rich in HG structural domains can inhibit the migration of mouse fibroblasts (L929) through mechanisms of cell adhesion and spreading, with those containing RG-I structural domains demonstrating even greater inhibitory efficacy.

Notably, the biological activity of ginseng polysaccharides rich in HG structural domains is influenced by their uronic acids content and DM. The inhibitory effect on migration of ginseng polysaccharides rich in HG structural domains is enhanced with increasing GalA content [65]. Low methyl-esterified ginseng HG pectin has been shown to inhibit the insulin/insulin-like growth factor signaling pathway while enhancing the expression of anti-aging genes, thereby demonstrating potential anti-aging properties. In contrast, high methyl-esterified ginseng HG pectin and non-methyl-esterified ginseng HG pectin do not exhibit significant changes in this regard [17].

4.3.2. Side chains: composition, position, and branching degree as critical elements for biological activities

The composition, position, content, and quantity of monosaccharide side chains in ginseng polysaccharides are crucial factors that influence their biological activities. Galactan is a functional polysaccharide primarily composed of Gal. The presence of Gal side chains can enhance the antagonistic effect of RG-I-4 against galectin-3, thereby inhibiting ASF-induced cell aggregation and the binding of galectin-3 to T cells [41]. The presence of β-1,4-galactan side chains can promote the binding capacity of RG-I-rich ginseng pectin to galectin-8, inhibiting T lymphocyte apoptosis and endothelial cell migration, whereas the RG-I backbone itself does not exhibit enhanced binding activity [39]. Arabinogalactan, another functional polysaccharide primarily made up of Ara, has side chains—especially those with α-1,5-linked arabinose—that facilitate the anti-aging effects of the ginseng polysaccharide WGP-0.1-RG. This occurs through the TOR signaling pathway, which promotes the activity of transcription factors dauer formation-16 (DAF-16) and skinhead-like protein -1 (SKN-1), ultimately extending lifespan. In contrast, the main chain of WGP-0.1-RG does not exhibit any lifespan-promoting effects [12].

The positioning of the Ara residues can either enhance or inhibit the galectin antagonistic activity of the enzymatic fragments of ginseng pectin, with Ara chains generally inhibiting activity while terminal Ara of the AG-I side chain promotes it [41].

AG-I and AG-II are commonly found in the branched structures of ginseng polysaccharides and are essential for their biological activity. WGPNE-0.1 and WGPNE-0.2, derived from the enzymatic hydrolysis of neutral polysaccharides GPN from ginseng, exhibit different compositions: WGPNE-0.1 is primarily composed of glucan, AG-I, and AG-II, while WGPNE-0.2 consists solely of glucan. Notably, WGPNE-0.1 demonstrates superior immunomodulatory effects [21]. The Ara residues in the AG-II side chain of ginseng polysaccharide WGP-0.2-RG are crucial for lymphocyte proliferation and the production of NO by macrophages [66]. Furthermore, the degree of branching (DB), a crucial parameter that characterizes the quantity and distribution of polysaccharide side chains, can also reflect the biological activity of ginseng polysaccharides. For example, WGP-0.3, a highly branched acidic polysaccharide derived from ginseng, has been shown to activate lymphocytes, enhance antibody production, enhance the neutralizing capacity of antibodies, and upregulate the TLR4-MyD88-NF-κB signaling pathway in DC2.4 cells, leading to a stronger immune response [13].

4.3.3. Monosaccharide composition: monosaccharide regulating biological activity via differential pathways

The composition of monosaccharides plays a crucial role in determining the biological activity of ginseng polysaccharides. For instance, although Gal and GalA are similar in structure, the polysaccharides composed of them belong to different categories and have significant differences in physicochemical properties and biological activities. Gal is an important monosaccharide found in ginseng polysaccharides. Polysaccharides with high Gal content mostly exhibit significant immunological activity, whereas those lacking Gal show poorer immunological activity [57]. Mannose (Man) can bind to receptors on the surface of immune cells [67], thereby activating immunomodulatory activity. WGP-0.3 containing Man can promote the maturation of DCs and exhibit strong adjuvant activity, which may be closely related to the Man component it contains [13]. Uronic acids, which carry a negative charge, possess strong metal-chelating properties, and their content is related to the antioxidant capacity of the polysaccharides [7]. Generally speaking, the antioxidant capacity of acidic polysaccharides is positively correlated with the content of galacturonic acid [68]. For instance, ginseng polysaccharide with a high uronic acids content, demonstrates stronger antioxidant activity compared to which has a lower uronic acid content [69]. In addition, the carboxyl group of uronic acid is regarded as an effective electron donor for lipid-lowering activity [70]. Uronic acid exerts lipid-lowering activity by interfering with the formation of cholesterol. For instance, ginseng polysaccharides containing 14.5 % uronic acid can prevent weight and fat gain induced by a high-fat diet [71].

4.3.4. Monosaccharide linkage patterns: specific linkage patterns regulating bioactivity through conformation

The linkage patterns of monosaccharides govern the branching architecture and spatial conformation of glycan chains, which in turn direct the biological activity of ginseng polysaccharides. Specifically, Glucans containing α-glycosidic bonds favor the formation of helical folds, while Glucans containing β-glycosidic bonds predominantly adopt extended, ribbon-like conformations. Generally, Glucans containing β-glycosidic bonds exhibit greater biological activity than those with α-glycosidic bonds. Additionally, the presence of 1,3-, 1,4-, and 1,6-glycosidic linkages within the glucan structure are crucial determinants of their activity [37]. Specifically, glucans with (1 → 4) and (1 → 6) glycosidic bonds can demonstrate potent α-glucosidase inhibitory effects, thereby contributing to blood glucose-lowering properties [72]. Both GRON and GPN contain (1 → 4) glycosidic bonds, with WGRPN having a higher number of (1 → 6) glycosidic bonds compared to WGPN. Both polysaccharides demonstrate significant α-glucosidase inhibitory activity, with WGRPN showing superior effects [60].

4.4. Relationship between the higher order structure and pharmacological effects of ginseng polysaccharides

The unique spatial configuration of polysaccharides allows for the expression of active sites, enabling active fragments to exert their effects more effectively. The conformations of polysaccharides, which can include linear and helical structures, have a direct influence on their binding interactions with receptors [57,72]. Generally, polysaccharides with a triple helical structure are regarded as exhibiting various biological activities. Among the polysaccharides isolated and purified from ginseng roots, white ginseng acidic polysaccharide-0 M NaCl, white ginseng acidic polysaccharide-0.1 M NaCl, and WGPA-0.2 were identified, with only WGPA-0.2 demonstrating a triple helical structure. This particular structure can upregulate the TLR2-NF-κB-TRAF6 signaling pathway to activate macrophages, thereby enhancing immune modulation. In contrast, the other two polysaccharides, which lack a triple helical structure, displayed no significant immunomodulatory activity [22]. Additionally, enzymatic-degradation-WGP-0 (EWGP-0), obtained through enzymatic hydrolysis, demonstrates a stronger triple helical structure compared to the weaker triple helical structure of white ginseng-0M NaCl (WGP-0), and it exhibits superior antioxidant properties, neuroprotective effects, and gut microbiota modulation [59].

However, this relationship is not absolute. 20 % Ethanol Precipitate from White Ginseng Polysaccharide (WGP-20EP), 40 % Ethanol Precipitate from White Ginseng Polysaccharide (WGP-40EP), 60 % Ethanol Precipitate from White Ginseng Polysaccharide (WGP-60EP), and 80 % Ethanol Precipitate from White Ginseng Polysaccharide (WGP-80EP), extracted using gradient ethanol extraction, reveal that WGP-20EF and WGP-40EF possess a triple helical structure yet exhibit no significant immunomodulatory effects. Conversely, WGP-60EF and WGP-80EF, which lack a triple helical structure, can enhance immune indices, promote lymphocyte proliferation, and the activate NK cells and macrophages, thereby effectively modulating the immune system [57].

5. Structural transformation - structure-activity of ginseng polysaccharides

The structural transformations of ginseng polysaccharides encompass physical, biological, and chemical modifications (Fig. 6). The primary method for the physical transformation of ginseng polysaccharides is thermal processing. Unprocessed ginseng is referred to as sun-dried ginseng, also known as white ginseng, while red ginseng, steamed ginseng, and black ginseng are products of physical transformation. Specifically, red ginseng is dried after being steamed at 100 °C, and steamed ginseng undergoes steaming at 120 °C, respectively, while black ginseng is produced through a more complex process that involves nine cycles of steaming and drying [73,74]. Biological transformation includes enzymatic hydrolysis and microbial fermentation, both characterized by mild conditions and environmentally friendly practices [75,76]. Chemical transformation involves the introduction of functional groups into the polysaccharide chains, including sulfation, phosphorylation, and selenization [25]. Compared to physical transformation, biological and chemical transformation of ginseng polysaccharides have received less attention in research. Structural transformation and structure-related information of ginseng polysaccharide are summarized in Table 1.

Fig. 6.

Structural transformation of ginseng polysaccharides.

Table 1.

Structural transformation and structure-related information of ginseng polysaccharide.

Polysaccharides	Transformation methods	Mw (kDa)	Gal (%)	Glc (%)	Ara (%)	Rha (%)	Man (%)	GalA (%)	GlcA (%)	Fru (%)	Structural domain	Type	Reference
WGP-0	White ginseng	3.5	18.00	66.30	15.70	–	–	–	–	–	–	Neutral	[12], [17], [18]
WGP-0.1-RG		10	56.20	3.50	34.00	0.20	2.50	1.80	1.90	–	RG	Acid
WGP-0.2-RG		11	44.40	2.00	40.90	4.10	0.40	5.30	2.00	–	RG
WGP-0.1-HG		3.5	15.20	7.60	7.10	1.60	3.60	62.40	2.60	–	HG
WGP-0.2-HG		6.5	5.10	1.90	4.60	3.00	0.20	83.60	1.60	–	HG
WGP-0.3-HG		16	3.50	1.30	2.20	1.50	–	90.90	0.50	–	HG
WGP-0.5-HG		45	5.00	2.00	–	–	–	92.10	–	–	HG
WGP-0		12.79	–	100.0	–	–	–	–	–	–	–	Neutral	[59]
WGPNE-0.1		80.4	19.00	71.00	10.00	–	–	–	–	–	–	Neutral	[21]
WGPNE-0.2		31.5	–	100.0	–	–	–	–	–	–
WGPAE-0.15 a		17	–	100.0	–	–	–	–	–	–	–	Neutral	[77]
WGPE-0		–	2.30	94.80	2.90	–	–	–	–	–	–	Neutral	[19]
WGPE-0.1 a		110	30.90	44.30	21.90	2.10	–	–	–	–	–	Acid
WGPE-0.1 b		5.5	8.30	72.90	10.80	1.90	–	2.80	–	–
WGPE-0.3 a		430	36.50	1.20	39.70	8.30	–	13.70	–	–	RG-Ⅰ
WGPE-0.3 b		12	14.10	2.90	16.10	4.60	–	62.20	–	–	HG
WGPE-0.5 a		420	23.00	–	30.70	11.40	–	34.90	–	–	RG-Ⅰ
WGPE-0.5 b		50	5.20	4.10	5.60	3.40	–	81.70	–	–	HG
WGRP		605	12.90	46.08	14.29	1.84	–	24.88	–	–	HG,RG-Ⅰ	Acid	[38]
WGP-0.5 a		851	26.33	3.57	61.75	1.40	–	6.35	–	0.85	RG-Ⅰ	Acid	[52]
WGP-0.5 b		295	22.33	6.19	32.24	3.64	–	29.12	–	6.84	HG
WGPE-0		–	3.90	88.70	4.60	–	–	–	–	–	–	Neutral	[78]
WGPE-0.1 a		450	–	100.0	–	–	–	–	–	–
WGPE-0.1 b		62	11.20	75.50	9.90	1.10	–	2.30	–	–	RG-Ⅰ	Acid
WGPE-0.4 a		420	27.60	3.40	27.70	8.00	–	32.70	–	–	HG,RG-Ⅰ
WGPE-0.4 b		150	20.70	3.90	21.90	7.00	–	46.50	–	–	HG,RG-Ⅰ
WGPE-0.6 a		430	16.90	3.90	17.70	8.70	–	52.80	–	–	HG,RG-Ⅰ
WGPE-0.6 b		110	12.50	6.10	9.50	7.40	–	64.50	–	–	HG,RG-Ⅰ
WGP-0		–	1.87	81.11	9.74	–	–	0.95		–	–	Acid	[79]
WGP-0.1		–	21.14	36.53	10.80	–	–	5.89	1.61	–
WGP-0		13.78	–	–	–	–	–	–	–	–	–	Neutral	[59]
RGP-0	Red ginseng (100 °C)	5.65	4.92	94.26	–	–	–	–	–	–	–	Neutral	[80]
RGP-0 a		21.3	–	100.0	–	–	–	–	–	–	–	Neutral	[81]
RGP-0 b		10.2	10.60	77.90	8.80	–	–	2.70	–	–
RGP-0.1 a		21.6	11.00	77.00	10.00	2.00	–	–	–	–	–	Neutral	[82]
RGPE-a		96	30.40	–	35.00	9.50	–	18.40	–	–	RG-Ⅰ	Acid	[83]
RGP-0.5 a		886	19.96	12.29	54.57	1.92	–	10.64	–	0.62	RG-Ⅰ	Acid	[52]
RGP-0.5 b		258	18.76	1.52	8.55	6.85	–	61.55	–	2.77	HG
SGP-a	Steamed ginseng (120 °C)	20.3	32.02	5.98	16.95	–	–	6.98	2.67	–	–	Acid	[84]
SGP-b		48.6	16.56	7.65	57.97	9.96	–	6.49	0.73	–	–
SGP-0.5 a		961	31.92	13.31	30.67	2.12	–	11.27	–	2.71	RG-Ⅰ	Acid	[52]
SGP-0.5 b		339	6.62	9.36	3.65	6.71	–	68.09	–	5.57	HG
BGP-60	Blank ginseng (Nine steaming and nine drying)	28.6	22.33	77.67	–	–	–	–	–	–	–	Neutral	[82]
BGP-65		26.7	37.05	59.23	3.72	–	–	–	–	–
BGP-70		11.4	43.39	51.43	5.18	–	–	–	–	–
BGP-80		3.05	41.73	51.61	6.66	–	–	–	–	–
WGPAE-0.07-RG	Enzymolysis	5	21.20	5.90	13.00	12.80	7.20	26.80	7.40	–	RG-Ⅰ	Acid	[24]
WGPAE-0.16-RG		4	12.40	4.40	14.50	11.70	1.00	44.30	5.80	–
WGPAE-0.22-RG1		45	31.60	1.90	16.30	11.10	2.10	32.20	3.00	–
WGPAE-0.22-RG2		6	13.70	2.50	11.90	14.10	1.30	44.60	3.70	–
WGPAE-0.30-RG		60	19.50	3.00	9.20	21.80	0.40	33.80	2.20	–
EWGP-0		1.1	–	–	–	–	–	–	–	–	–	Neutral	[59]
WGPE-9 %		47.2	2.46	96.63	0.90	–	–	–	–	–	–	Neutral	[85]
S-WGPE-9 %		46.9	2.43	96.68	0.88	–	–	–	–	–
G-WGPE-9 %		46	2.50	96.59	0.91	–	–	–	–	–
I-WGPE-9 %		40.4	2.49	96.49	1.02	–	–	–	–	–
F12-WGPE-9 %	Fermentation	33.3	3.86	95.29	1.40	–	–	–	–	–
F24-WGPE-9 %		28.4	6.15	92.45	2.19	–	–	–	–	–
FGP-0		–	1.95	80.46	10.43	–	–	–	–	–	–	Neutral	[79]
FGP-0.1		–	13.31	29.15	24.33	–	–	10.28	2.76	–	–	Acid
FGP-0.2		–	16.40	45.64	32.23	–	–	1.24	0.97	–

Note: WGP-0.1 to 0.5-RG or HG, white ginseng polysaccharide-0.1 to 0.5 M NaCl-RG or HG; WGPAE-0.15 a, enzymatic hydrolysate of white ginseng acidic polysaccharide-0.15 M NaCl a; WGPE-0.1 to 0.6. enzymatic hydrolysate of white ginseng polysaccharide-0.1 to 0.6 M NaCl; WGRP, white ginseng residue polysaccharide; WGP-0.5, white ginseng polysaccharide-0.5 M NaCl; WGPE-0.1 to 0.6. enzymatic hydrolysate of white ginseng polysaccharide-0.1 to 0.6 M NaCl; WGP-0.1, white ginseng polysaccharide-0.1 M NaCl; RGP-0 to 0.5; red ginseng polysaccharide-0 to 0.5 M NaCl; SGP, steamed ginseng polysaccharide; SGP-0.5, steamed ginseng polysaccharide-0.5 M NaCl; BGP-60 to 80, 60 %–80 % Ethanol Precipitate from black ginseng polysaccharide; WGPE-9 %, enzymatic hydrolysate of white ginseng polysaccharide-9 % NaCl; S-WGPE-9 %, saliva digestion-enzymatic hydrolysate of white ginseng polysaccharide-9 % NaCl; G-WGPE-9 %, gastric juice digestion-enzymatic hydrolysate of white ginseng polysaccharide-9 % NaCl; I-WGPE-9 %, intestinal juice digestion-enzymatic hydrolysate of white ginseng polysaccharide-9 % NaCl; F12 to 24-WGPE-9 %, fermentation 12 to 24 h-enzymatic hydrolysate of white ginseng-9 % NaCl; FGP-0 to 0.2, Fermented ginseng polysaccharide-0 to 0.2 M NaCl.

5.1. Physical transformation — structure-activity relationship of ginseng polysaccharides

5.1.1. Effects of physical transformation on the structure of ginseng polysaccharides

Physical transformation primarily involves high-temperature heating, which disrupts the cell wall and membrane structures of ginseng, facilitating the extraction of high M_w ginseng polysaccharides. This process also induces hydrolysis of the polysaccharides, altering their original structure, reducing their M_w, and increasing the level of monosaccharides and oligosaccharides [8] (Fig. 7A). During high-temperature treatment, proteins responsible for transmembrane transport in the cell membrane denature, leading to the loosening of cellulose and hemicellulose structures in the cell wall. This results in the rupture of the cell wall and an increase in cellular permeability, allowing for the release and leaching of ginseng polysaccharides from both the cell interior and cell wall [86].

Fig. 7.

The impact of physical transformation on the structural characteristics of ginseng polysaccharides. (A) Molecular weight bar chart; (B) Heat map of the monosaccharide composition.

When comparing polysaccharide content in white ginseng, red ginseng, and steamed ginseng, it was observed that polysaccharide content increases with the intensity of heating, while the M_w shows an increasing trend [19,52]. This indicates that the content of ginseng polysaccharides increases with heater heating intensity. A comparison analysis of polysaccharide content among white ginseng, red ginseng, and black ginseng (which undergoes nine cycles of steaming and drying) revealed that the red ginseng contents a higher polysaccharide content than white ginseng, while black ginseng shows a decrease. This suggests a trend where the content of ginseng polysaccharides initially increases and then decreases as heating intensity is enhanced [87].

During the process of physical transformation, ginseng polysaccharides undergo significant changes in their types, structural domains, and monosaccharide compositions (Fig. 7B). Notably, the content of acidic polysaccharides in ginseng increases with the intensity of the physical transformation [88,89]. In the heating process of ginseng pectin-type polysaccharides, the contents of Gal and Ara, which are key branched components, decrease, while the content of GalA increases, with no significant changes observed in rhamnose Rha, Fru, and Glc [52]. This suggests that ginseng pectin-type polysaccharides may be more susceptible to the cleavage of side chains such as arabinogalactan and arabinose upon heating, while the RG-I and HG backbones, composed of Rha and GalA, are less likely to undergo hydrolysis. Interestingly, GalA in ginseng pectin-type polysaccharides exists in both methyl-esterified and non-methyl-esterified forms; during thermal processing, methylated GalA may convert to its non-methyl-esterified form, leading to an increased content of galacturonic acid [52].

Additionally, the surface morphology and higher-order structures of ginseng polysaccharides also change during the physical transformation process. Research indicates that ginseng-derived polysaccharides become denser and exhibit triple helix characteristics following thermal processing [9]. For example, RGP-0 obtained from red ginseng, appears in both sheet-like and irregular spherical forms, exhibiting a smooth, and compact surface with fewer voids. This layered structure provides a greater cohesive space for water molecules, enhancing its solubility and biological activity. Furthermore, the triple helix structure may be associated with the increased exposure of hydrogen bonds as a result of physical hydrolysis [80].

5.1.2. The impact of physical transformation on the biological activity of ginseng polysaccharides

Physical transformation can significantly enhance the activity of ginseng polysaccharides. Research indicates that the hypoglycemic effect of ginseng pectin increases with the intensity of physical transformation [90]. Comparisons among the polysaccharides derived from white ginseng, red ginseng, and steamed ginseng reveal that the hypoglycemic effect improve with higher processing temperatures [52]. This enhancement is likely due to the conversion of esterified GalA to its non-esterified form during thermal processing [90]. Studies have shown that polysaccharides with lower degrees of DM exhibit strong competitive inhibition of pectin, leading to a significantly reduction in α-amylase and α-glucosidase activity, thereby notable hypoglycemic effects [43].

Furthermore, the antioxidant activity of ginseng polysaccharides is also enhanced through physical transformation [90]. Steamed ginseng polysaccharides demonstrate a markedly stronger effect on oxidative stress in diabetic mice compared to red and white ginseng, indicating that physical transformation positively influences the antioxidant activity of ginseng polysaccharides [52]. Additionally, physical transformation impacts other biological activities as well. In particular, the highly methylated HG domain exhibits notable sensitivity to elevated temperatures in its anti-proliferative effects on HT-29 colon cancer cells. Ginseng pectin polysaccharides rich in the HG domain significantly enhance their anti-proliferative effects on HT-29 cells following high-temperature treatment. This enhancement includes the induction of cell cycle arrest at lower concentrations and the promotion of caspase-3-mediated apoptosis at higher concentrations [64].

5.2. Biological transformation — structure-activity relationship of ginseng polysaccharides

5.2.1. The impact of biotransformation on the structure of ginseng polysaccharides

Enzymatic hydrolysis is one of the important ways for the biological transformation of ginseng polysaccharides. By using specific enzymes to degrade polysaccharides, it has strong specificity and can precisely control the degree of hydrolysis of polysaccharides, generating stronger biological activity. The enzymatic hydrolysis of WGP-0 using a combination of β-glucanase, β-glucosidase, pectinase, and β-amylase results in chain cleavage, reduced M_w, and increased exposure of hydrogen bonds, thereby exhibiting a more pronounced triple helical structure [59]. Furthermore, different types of enzymes exhibit varying effects on the enzymatic hydrolysis of ginseng polysaccharides. Treatment with saliva or gastric juice does not result in significant changes in polysaccharide content and M_w, whereas treatment with intestinal fluid significantly decreases both polysaccharide content and M_w, potentially due to the presence of bile salts and pancreatic enzymes in the intestinal fluid [85].

Microbial fermentation represents another vital method for the bioconversion of ginseng polysaccharides, primarily involving bacteria and fungi [91]. Given that fermentation is a collective behavior of living cells in a dynamic environment, it inherently possesses a degree of complexity and variability. The fermentation of ginseng polysaccharides by Saccharomyces cerevisiae leads to an increase in the content of uronic acids [79]. Additionally, treatment of ginseng with multi-enzyme-conjugated probiotics significantly enhances the polysaccharide content in the resulting fermentation broth [92]. In contrast, during the fermentation process using fecal matter, both the polysaccharide content and M_w of ginseng polysaccharides exhibit a significant decrease over time [85].

5.2.2. The impact of bioconversion on the biological activity of ginseng polysaccharides

Enzymatic hydrolysis is a crucial method for the bioconversion of ginseng polysaccharides and is frequently used in studies of structure-activity relationships. Some studies have found that enzymatic treatment can significantly enhance the biological activity of ginseng polysaccharides. Ginseng polysaccharide EWGP-0 obtained through complex enzyme hydrolysis demonstrates a superior free radical scavenging ability compared to its non-hydrolyzed ginseng polysaccharides WGP-0, effectively alleviating Aβ-induced oxidative stress in PC12 cells [59]. Additionally, treatment of ginseng polysaccharides with α-amylase yields WGPE-9 %, which has been shown to increase the relative abundance of beneficial gut bacteria and promote gut health [85].

Microbial fermentation also plays a vital role in the bioconversion of ginseng polysaccharides, enhancing their activity post-fermentation. For example, ginseng polysaccharides fermented with Saccharomyces cerevisiae demonstrate enhanced scavenging capabilities against hydroxyl and superoxide anion radicals, and are more effective in alleviating lipopolysaccharide-induced inflammation [79]. The fecal fermentation product derived from ginseng polysaccharides can activate macrophages through the TLR4/Myd88/NF-κB signaling pathway [85].

5.3. Chemical transformation — structure-activity relationship of ginseng polysaccharides

Sulfation is a chemical modification method that involves the reaction of sulfuric reagents with polysaccharide solutions, resulting in the introduction of sulfate groups onto the polysaccharide chains. Utilizing the chlorosulfonic acid-formamide method for the sulfation of ginseng polysaccharides enhances various biological activities, including antimicrobial, prebiotic, antioxidant, and anticancer effects [93].

Phosphorylation is another chemical modification process that incorporates phosphate groups into polysaccharides. Phosphorylated ginseng polysaccharides demonstrate improved antioxidant capabilities, as evidenced by their enhanced capability to scavenge DPPH radical and hydroxyl radical [94]. Additionally, these phosphorylated ginseng polysaccharides show greater in vitro anti-inflammatory activity compared to their unmodified versions, and can regulate the TLR4/MYD88 signaling pathway, promote macrophage polarization, and restore intestinal barrier function, positioning them as promising therapeutic agents for chronic inflammatory bowel diseases [95].

Selenylation is a chemical transformation method that involves the incorporation of selenium into the hydroxyl groups of polysaccharides, leading to the formation of stable complexes [96]. The selenylation of ginseng polysaccharides using a nitric acid-selenic acid method has been shown to induce mitochondrial-mediated apoptosis in the HL-60 leukemia cell line, thereby demonstrating notable anticancer properties [97].

6. Conclusion and outlook

Ginseng polysaccharides represent a class of natural carbohydrates that exhibit significant biological activity and promising application potential. This paper reviews the structural characteristics, biological activities, structure-activity relationships, and the effects of structural transformations on the activity of ginseng polysaccharides. It has been found that factors such as relative M_w, structural type, primary structure, and higher-order structure are closely related to their biological activity. Through physical, biological, and chemical transformations, the structure and physicochemical properties of ginseng polysaccharides can be modified to degrees, thereby influencing their biological activities.

Nevertheless, several challenging remain in the research on ginseng polysaccharides: 1) Structural analysis tends to focus on primary structures such as M_w, monosaccharide composition, and structural domains, while elucidating higher-order structures presents a significant challenge; 2) The mechanisms underlying the biological activities of ginseng polysaccharides, including their antioxidant and hypoglycemic effects, still require further exploration, as many existing studies emphasize biological activities without thoroughly investigating the underlying mechanisms; 3) The depth of research into the structure-activity relationships of ginseng polysaccharides is insufficient, lacking comprehensive studies that correlate structural domains, active fragments, and biological activity, thus failing to clarify the interrelation between the structure and biological activity of ginseng polysaccharides; 4) There is a scarcity of research on the methods of structural transformation of ginseng polysaccharides, and investigations into the characterization of transformed structures and their biological activities are not sufficiently comprehensive.

In summary, research on ginseng polysaccharides still faces numerous challenges that require further exploration. It is crucial to elucidate the mechanisms of their biological activities and structure-activity relationships, with the goal of developing more efficient and environmentally friendly structural transformation methods to maximize the potential value of ginseng polysaccharides.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.