The monosaccharide composition analysis process of litchi polysaccharides includes hydrolysis, separation, chemical modification, and detection analysis (Chen M. et al., 2024). At present, research on the monosaccharide composition of litchi polysaccharides is mainly focused on the analysis of the types and contents of monosaccharides (Sun et al., 2024). Litchi polysaccharides mainly consist of galactomannan (GalA), arabinose (Ara), rhamnose (Rha), galactose (Gal), glucose (Glc), xylose (Xyl), mannose (Man), and ribose (Rib), existing in varying molar ratios (Figure 3). For instance, acid hydrolysis, acetic acid acetonitrile derivatization, and gas chromatography analysis revealed that LPPBa from litchi pulp is an arabinogalactan with a molar ratio of Ara: Rha: Gal: GalA = 2.76: 0.89: 3.02: 1.00 (Yang et al., 2016). Polysaccharides from litchi pericarp are mainly composed of 65.6% Man, 33.0% Gal, and 1.4% Ara (Yang et al., 2006). The neutral heteropolysaccharide LSP-W-4 isolated and purified from litchi seeds is composed of Ara, Man, Glc, and Gal with a molar ratio of 6.33:3.88:10.35:1.00 (Wu et al., 2020).

Mw is a key parameter that influences the chemical properties and biological activity of polysaccharides (Sun et al., 2024). Several ways to express the Mw of polysaccharides exist, including Mw, number average molecular weight (Mn), viscosity average molecular weight (Mv), and Z-average molecular weight (Mz) (Wang Z. et al., 2023). The literature generally reports on Mw. The typical methods for determining the Mw of litchi polysaccharides include gel permeation chromatography (GPC) and high-performance GPC (HPGPC). Available data show that the Mw of litchi polysaccharides ranges from 5.54 kDa to 2,400 kDa (Table 2). For example, the Mw of the polysaccharide LSP-W-4 extracted from litchi seeds is 6.70 kDa, while the Mw of LP1 polysaccharide extracted from litchi fruit is 378.67 kDa (Wu et al., 2020; Zou et al., 2023). The considerable variation in the Mw of litchi polysaccharides is likely attributable to differences in the source material, processing methods, and preparation techniques employed in their extraction.

As is well known, studying the chemical structure of polysaccharides is beneficial for elucidating their biological activity and health benefits, and for developing their potential value. Yang et al. (2016) preliminarily identified the precise structure of LPPBa. Its main chain is composed of →4)-α-d-GalpA6Me-(1→ and →6)-β-d-Galp-(1→. Branch chains include α-l-Araf-(1→5)-α-l-Araf-(1→α-l-Rhap-(1→, α-l-Araf-(1→). Hu et al. (2011) discovered that the polysaccharide LCP50S-2, extracted from pulp tissues of litchi, consists of a main chain in its structure composed of (1→3)-linked β-l-rhamnopyranosyl residues, (1→4)-linked α-d-xylopyranosyl residues, (1→4)-linked β-d-glucopyranosyl residues, and (1→4) linked α-d-glucopyranosyl residues, while the side chain includes α-l-arabinopyranosyl residues and (1→6)-linked β-d-galactopyranosyl residues. These two side chains are terminated by α-l-arabinopyranosyl residues (Hu et al., 2011). Subsequently, the team further studied litchi polysaccharide (LCP50W). The backbone of LCP50W was constructed by (1→3)-linked β-l-rhamnopyranosyl, (1→6)-linked α-d-glucopyranosyl, and (1→2,6)-linked α-d-glucopyranosyl residues, and the branches may contain (1→ 2)-linked α-l-rhamnopyranosyl, (1→3)-linked α-d-galactopyranosyl, and (1→3)-linked α-l-mannopyranosyl residues. Like the side chain terminal structure of LCP50S-2, it terminated by α-l-arabinopyranosyl residues (Jing et al., 2014). Wang et al. (2015) extracted a polysaccharide from litchi named LCPA50-S1, whose main chain of its primary structure is composed of (1→4)-linked β-d-glucopyranosyl residues, (1→6)-linked β-d-galactopyranosyl, (1→3,6)-linked β-d-galactopyranosyl residues, (1→4,6)-linked α-d-glucopyranosyl residues and branched at O-6, while the side chain includes (1→2)-linked α-l-rhamnopyranosyl residues, (1→4)-linked β-d-glucopyranosyl residues, and (1→6)-linked β-d-galactopyranosyl, terminated with (1→)-linked α-l-arabinopyranosyl residues and (1→)-linked β-d-galactopyranosyl residues. The proposed structures of LCPA50-S1 are shown in Figure 4.

Diabetes is a chronic disease that severely impairs the body’s health. It has a high incidence rate and can lead to mortality. Diabetes mellitus type 2 (T2DM) is one of the most common types (Khumalo et al., 2024). A hallmark of T2DM is elevated postprandial blood glucose, which is largely influenced by the rate and extent of carbohydrate digestion. α-glucosidase is a crucial enzyme for the control of regulating glycoprotein metabolism and plays a vital role in carbohydrate digestion and absorption (Benjamin et al., 2024). It has become a promising therapeutic target for relieving postprandial hyperglycemia. Research has indicated that litchi polysaccharides inhibit α-glucosidase activity, thereby delaying carbohydrate absorption and lowering postprandial blood glucose levels (El-Nashar et al., 2024). To further explore the effects of litchi polysaccharides on α-glucosidase, Wu et al. (2020) investigated the inhibitory activity of litchi polysaccharide (LSP-W-4) against α-glucosidase from two sources: rat intestines and yeast (Saccharomyces cerevisiae). The study also examined the interaction between LSP-W-4 and α-glucosidase through kinetic enzymatic analysis. The results showed that LSP-W-4 effectively inhibited both yeast- and mammalian-derived α-glucosidases, with the most notable difference in IC₅₀ between yeast-derived α-glucosidases (66.97 μM) and mammalian-derived ones (75.24 μM). The addition of varying concentrations (0, 0.20, 0.40, and 0.60 mg/mL) of LSP-W-4 led to a linear change in absorbance corresponding to α-glucosidase concentration (0.025, 0.050, 0.100, and 0.200 U/mL). Notably, the slope of the line decreased with lower LSP-W-4 concentrations, indicating that LSP-W-4 interacts with α-glucosidase through non-covalent interactions, allowing easy removal via dilution or dialysis. These kinetic enzymatic analysis results suggest that LSP-W-4 inhibits α-glucosidase activity in a non-competitive manner, with K_M values of 0.43 mmol/L and 0.53 mmol/L for yeast and mammalian enzymes, respectively (Figure 5). These findings could provide valuable insights for the development of functional foods targeting diabetes and its complications. In addition to its effects on α-glucosidase, litchi polysaccharides also inhibit α-amylase. Experimental results revealed that litchi polysaccharides (LPPA, LPPI, LPPH, LPPF, and LPPFH) obtained through five different drying methods exhibited a dose-dependent inhibitory effect on α-amylase within the concentration range of 0–4.0 mg/mL. The inhibitory activity followed the order: LPPF > LPPFH > LPPH > LPPI > LPPA. Overall, the hypoglycemic activity of litchi polysaccharides, as evidenced by existing research, is primarily attributed to their inhibition of α-glucosidase (An et al., 2022).

Plant polysaccharides (excluding starch) are resistant to digestion in digestive fluids such as saliva, gastric juice, and intestinal fluid. Polysaccharides that cannot be hydrolyzed by the host’s enzymes pass into the intestine, where they serve as a primary carbon source for the gut microbiota. These polysaccharides can exert health benefits by selectively promoting the proliferation of beneficial gut probiotics (Zhang et al., 2022; Bock et al., 2024). Litchi polysaccharides, as a type of plant polysaccharide, possess prebiotic activity. Experimental studies on prebiotic effects have revealed that litchi polysaccharides promote the growth of various probiotic strains, including Lactobacillus plantarum, Leuconostoc mesenteroides, Lactobacillus casei, Bifidobacterium adolescentis, Bifidobacterium infantis, and Bifidobacterium longum. Zou et al. (2023) investigated the prebiotic activity of litchi polysaccharides LP1 and LP2 using four lactic acid bacteria strains: L. plantarum, Leuconostoc enterica, L. casei, and B. adolescentis. The results demonstrated that the addition of litchi polysaccharides promoted the growth of all four bacterial strains. Notably, different carbon source media significantly influenced the growth of L. mesenteroides (P < 0.05). LP2 exhibited strong prebiotic activity, enhancing the growth of L. mesenteroides, followed by fructooligosaccharides (FOS) and LP1. For L. plantarum, the growth-promoting effects of the three carbon sources were similar, with LP2 > FOS > LP1. The proliferation of B. adolescentis was also highest with LP2, followed by FOS and LP1. While the microbial growth of L. casei was comparable between FOS and LP2, LP1 showed the least effect (P < 0.05). These findings suggest that LP2 is more effective than LP1 in promoting probiotic growth, but further research is needed to elucidate the underlying mechanisms. He et al. (2022) investigated the prebiotic activity of litchi polysaccharides using three strains of Bifidobacterium through an in vitro fermentation experiment over different time intervals (0–72 h). The study used carbohydrate-free MRS broth with 0.05% (w/v) L-cysteine as the base medium, with FOS serving as the positive control. The results showed that fermentation time influenced the effect of litchi polysaccharides on the proliferation of the Bifidobacterium strains. Among the polysaccharides tested, LP-6 exhibited the most significant prebiotic effect by promoting the growth of Bifidobacterium strains (He et al., 2022).

Microbial polysaccharides can be classified into interstitial polysaccharides and exopolysaccharide based on their location in cells. Exopolysaccharides (EPS) have adhesive properties, thickening properties, and water and oil retention. They can be used as stabilizers, emulsifiers, thickeners, and applied in food processing production (Salimi and Farrokh, 2023). Research shows that litchi polysaccharides can promote the production of EPS by Weissella confusa (W. confusa). An experiment evaluated the effect of Lzp2-2 on fermented yogurt through its physicochemical properties and flavor. Adding Lzp2-2 (10 mg/mL) to the yogurt fermentation medium, the viscosity of the yogurt gradually increased with the extension of fermentation time (0, 8, 24, 48, 72 h). At equivalent amount of sucrose, the viscosity of the sucrose treatment group was lower than that of the Lzp2-1 treatment group. The EPS content in the Lzp2-2 treatment group was higher than that in the sucrose treatment group. This may be because Lzp2-2 promotes the production of EPS by W. confusa. EPS and milk protein interact to form gel network, resulting in increased viscosity of yogurt. In addition, Lzp2-2 can be hydrolyzed by glycoside hydrolases into various monosaccharides such as Gal, Glc, and Ara. Subsequently, Gal, Glc, and Ara simultaneously participate in the biosynthesis of EPS through the Wzx/Wzy dependent pathway, ABC transporter pathway, synthase dependent pathway, and sucrose-synthase dependent pathway. In the control group, only Glc in sucrose participated in the synthesis of EPS by W. confusa. So, there are differences in viscosity at the same time point. The structural characteristics of yogurt, including hardness, adhesion, adhesiveness, chewiness, and elasticity, are considered important indicators of its overall acceptability. After adding Lzp2-2, these indicators significantly improved, while the difference in cohesion was not significant. In addition, the effect of Lzp2-2 on yogurt flavor was detected using electronic nose and electronic tongue. The Lzp2-2 treatment group increased the content of sulphur, ketones, alcohols, aldehydes, nitroxide, and short-chain alkanes in yogurt. And the richness, sweetness, freshness, and acidity of the Lzp2-2 treatment group were higher than those of the control group. These may all be related to the generation of EPS by W. confusa. In summary, adding litchi polysaccharides can significantly improve the fermentation characteristics and quality of yogurt fermented with W. confusa, providing scientific reference for the rational application of litchi polysaccharides in the production of new dairy products and theoretical basis for the high value-added utilization of litchi resources (Hu et al., 2023).

Free radicals are clusters of atoms that contain one unpaired electron. Studies have shown that the occurrence, development, and prognosis of various related diseases such as heart, liver, kidney, and brain are closely related to the excessive production of free radicals or the decrease in the ability to scavenge free radicals. Antioxidants play a pivotal role in capturing and neutralizing free radicals, making them essential in defending against free radical-related diseases (Huang et al., 2017; Zhou et al., 2022). Litchi polysaccharides exhibit significant antioxidant activity, characterized by low cost and minimal side effects, positioning them as a promising focus for antioxidant research.

The antioxidant capacity of litchi polysaccharides has been evaluated using several common assays, including DPPH, ABTS, hydroxyl radical scavenging, superoxide anion radical scavenging, and reducing ability tests. Studies have shown that litchi polysaccharides, such as LCP50S-2, LCP70S-1, and LCP70W, demonstrate increased scavenging effects on DPPH and hydroxyl radicals with rising concentrations. In the DPPH radical scavenging assay, the maximum scavenging percentages of these polysaccharides reached 75.6%, 67.4%, and 44.1% of the positive control (Vitamin C), respectively. In the hydroxyl radical scavenging assay, the values were 73.9%, 65.0%, and 44.6%, respectively (Hu et al., 2011; Hu et al., 2015). Four polysaccharides (LFP-I, LFP-II, LFP-III, and LFP-IV) isolated and purified from litchi pulp tissue showed varying levels of DPPH radical scavenging at a concentration of 1.0 mg/mL. The scavenging ability followed the order: LFP-III > LFP-I > LFP-II > LFP-IV. At concentrations ranging from 0.1 to 2.0 mg/mL, the superoxide anion scavenging effects were 18.62%–67.24% for LFP-III, 17.10%–62.07% for LFP-I, 10.28%–46.24% for LFP-II, and 9.62%–44.24% for LFP-IV. In the hydroxyl radical scavenging assay, the IC₅₀ values for LFP-I and LFP-III were found to be 0.81 mg/mL and 0.65 mg/mL, respectively. In the Ferrous ion chelating assay, the chelation ability of each LFP increases with the increase of concentration. There is a good correlation between the reducing ability of all LFPs and the increase in concentration. After comprehensive consideration and analysis of existing results, LFP-III has the strongest antioxidant capacity and is worthy of further research (Kong et al., 2010). In addition, due to the closer proximity of cells to the internal environment of organisms, using cell models for antioxidant activity (CAA) research is also a commonly used method. Huang et al. (2015) compared the antioxidant activity of three litchi polysaccharides (LP4, LP6, and LP8) using an 2,2′azobis-(2-amidinopropane)-hydrochloride (AAPH) induced oxidative stress model in HepG2 cells. The order of CCA values from high to low is: LP8 (10.79 mol QE/g DW) > LP4 (9.66 mol QE/g DW) > LP6 (4.72 mol QE/g DW). The content of galactose and mannose in LP8 is higher than that in LP4 and LP6, which is the reason why it has strong cellular antioxidant activity.

Cancer is one of the leading causes of death. It not only has a direct harm to the patient’s body but also has a profound impact on the patient’s psychological and social life. Therefore, cancer prevention, early detection and treatment are particularly important. At present, the main methods for treating cancer are chemotherapy and radiotherapy (Cao et al., 2014). But these methods are susceptible to the effects of tumor cell drug resistance or radiation resistance and may have varying degrees of side effects on patients during the treatment process. Plant polysaccharides, as natural biomacromolecules, are considered promising candidate drugs for treating cancer due to their excellent anti-cancer activity and small side effects and have received increasing attention in recent years (Wang A. et al., 2023). Huang et al. (2014) investigated the inhibitory effect of litchi polysaccharides on the proliferation of tumor cells. Using tumor cell lines A549, HepG2, and MGC-803 as cell models, the in vitro anti-proliferative activity of litchi polysaccharides (100, 200, 400, and 800 μg/mL) on these three types of cells was examined. The results showed that litchi polysaccharides exhibited significant inhibitory activities against the three tumor cell lines, with inhibition rates varying between 10.69% and 38.1%, 9.34% and 40.96%, and 4.8% and 58.86%, respectively (Huang et al., 2015). The inhibitory effect of litchi polysaccharides (50–750 μg/mL LPF and LPD) on tumor cell lines A549, Hela, and HepG2 have been studied. The inhibitory effect of LPF and LPD on proliferation of A549 cells was 2.59%–30.07% and 2.56%–27.17%, respectively. Similarly, cell growth was inhibited by 4.61%–28.04% and 5.17%–35.65% when Hela cells were incubated at the tested concentrations with LPF and LPD, respectively. The inhibition rate of LPF on HepG2 cells was 0.57%–24.12%. The inhibitory percentage of LPD against HepG2 cells ranged from 3.11% to 41.37%. Briefly, both above two litchi polysaccharides have the function of inhibiting the growth of A549, HeLa, and HepG2 cells in a concentration-dependent manner (Huang et al., 2014). The experiments below suggest that litchi polysaccharides have potential for use in chemoprevention and tumor therapy; however, the specific mechanism of action requires further study.

Immunity is generally considered the primary protective mechanism against various diseases (Mirzadeh, M., Keshavarz Lelekami, A., & Khedmat, L., 2021). What current research indicates is that litchi polysaccharides play an important role in enhancing the body’s immune system, predominantly by affecting what might be characterized as immune cells and cytokines (Figure 6). Splenic lymphocyte proliferation tends to represent an important indicator to study immune response and evaluate cell activity. Wang et al. (2015) found that the concentrations of litchi polysaccharide LCPA50-S1 were 0, 31.3, 62.5, 125, 250, and 500 μg/mL, which significantly promoted spleen lymphocyte proliferation in a concentration dependent manner and promoted the production of cytokine IL-2. In addition, considering the nuanced nature of these findings, LCPA50-S1 rapidly increased NO production and TNF-α secretion in RAW264.7 cells after 24 h of stimulation. These results suggest that LCPA50-S1 may function as an immune modulator for the treatment of various immune-related diseases (Wang et al., 2015). The evidence reveals that litchi polysaccharide LCP50W can typically promote splenic lymphocyte proliferation at concentrations of 3.9–125 μg/mL. At a concentration of 3.9–250 μg/mL, NK cell killing activity can also seemingly be enhanced in what appears to be a concentration-dependent manner. IFN-γ and IL-4 are important cytokines that regulate the body’s immune response. LCP50W promotes the secretion of Th1 cytokine IFN-γ while inhibiting the secretion of Th2 cytokine IL-4. Further exploration of its mechanism reveals that LCP50W enhances the expression of T-bet and predominantly inhibits the expression of GATA-3. What can be reasonably inferred from these findings is that LCP50W possesses the potential to improve mouse immune function, which may be mediated by an effect on the Th1/Th2 balance (Jing et al., 2014). The intestine not only plays a crucial role in the process of digestion and absorption but can also be described as the largest immune organ in the body. Intestinal immunity provides a crucial pathway through which litchi polysaccharides exert their immunomodulatory effects. At a concentration of 25–100 μg/mL, litchi polysaccharide LP 1-3 can stimulate the proliferation of Mesenteric lymph node (MLN) cells and exhibit dose-dependent secretion of IL-6 and IFN-γ, indicating that they can stimulate MLN cells to regulate the intestinal immune system (Huang et al., 2016b).