JRM JRM JRM Journal of Renewable Materials 2164-6341 2164-6325 Tech Science Press USA 25844 10.32604/jrm.2023.025844 Review Research Progress on Structure and Bioactivity of Longan PolysaccharideResearch Progress on Structure and Bioactivity of Longan PolysaccharideResearch Progress on Structure and Bioactivity of Longan Polysaccharide JiXiaolong 1# ZhangShuli 1# JinXueyuan 2 YuanXin 1 ZhangSiqi 1 GuoXudan 3guoxudan123@126.com ShiFengcheng 4shifc@sctobacco.com LiuYanqi 1 College of Food and Bioengineering, Zhengzhou University of Light Industry, Henan Key Laboratory of Cold Chain Food Quality and Safety Control, Henan Collaborative Innovation Center for Food Production and Safety, Zhengzhou, 450001, China School of Clinical Medicine, Hainan Vocational University of Science and Technology, Haikou, 571126, China Basic Medical College, Hebei University of Chinese Medicine, Hebei Higher Education Institute Applied Technology Research Center on TCM Formula Preparation, Hebei TCM Formula Preparation Technology Innovation Center, Shijiazhuang, 050200, China Key Laboratory for Harmful Components and Tar Reduction in Cigarette of Sichuan Province, Chengdu, 610000, China Corresponding Authors: Xudan Guo. Email: guoxudan123@126.com; Fengcheng Shi. Email: shifc@sctobacco.com

#These authors contributed equally to this work

 30 11 2022 11 4 1631 1642 0182022 05102022 © 2023 Ji et al. 2023 Ji et al. This work is licensed under a Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Longan originates from southern China and has high nutritional and health value. Recent phytochemistry and pharmacology studies have shown that polysaccharides are a main bioactive component of longan. Longan polysaccharides possess antioxidant, anti-aging, anti-tumor, immunomodulatory, and other bioactivities. Hot-water extraction, ethanol precipitation, and ultrasonic extraction are generally used to extract water-soluble longan polysaccharides. However, the relationship between the structure and bioactivity of longan polysaccharides remains unclear, requiring further investigation. The aim of this review is to evaluate the current literature focusing on the extraction, purification, structural characterization, and biological activity of longan polysaccharides. We believe that this review would provide a useful bibliography for further innovation and a basis for using longan polysaccharides in functional food.

 Longan polysaccharides structural characterization bioactivity Introduction

Longan (Dimocarpus longan Lour.) is a valuable subtropical plant that is largely distributed in Southeast Asia, such as China, Vietnam, and Thailand [1]. The history of Longan in China is more than 2000 years. The plant has white flesh with a sugar content greater than 18%. It is rich in dietary fiber, vitamins, polysaccharides, and other substances needed by the human body. Longan has several medicinal values in traditional Chinese medicine, including spleen nourishment and strengthening, QI and blood replenishment, stomach strengthening, and muscle building [2]. In the ancient Chinese book “Qiminyaoshu,” it is recorded that “longan was one puzzle, one flounder.” The plant is also listed as an important tribute food in ancient times. The cultivation area and output of longan in China account for more than 50% of those in the world, and the general longan industry in China is in Guangdong Province. According to the China Food Information Center Report in 2018, China’s longan output was 2.03 million tons as of that year, and the harvest area was 288,000 hectares.

Modern research has found that longan can eliminate free radicals, reduce blood sugar, regulate the immune system, fight cancer, and promote intellectual development [3]. Numerous benefits of longan are derived from different chemical ingredients, such as polysaccharides, lipids, polyphenols, and flavonoids [4]. Recently, longan polysaccharide has attracted considerable attention because of its rich and diverse known biological activities, and it is a large class of bioactive components on the scientific network. Longan polysaccharide is attracting increasing research attention because it inhibits glycosylation reactions and possesses antioxidant, immunomodulatory, antitumor, and anti-inflammatory activities.

However, little is yet understood about the structure-activity relationship of longan polysaccharides. Hence, this review not only introduces the basic information about longan polysaccharides, but also comprehensively discusses and summarizes its structure-activity relationship. We believe this paper would provide a basis for future research as well as the innovation and application of longan polysaccharides in functional foods.

 Extraction and Purification Methods

Although plant polysaccharides have a wide range of sources, all plant polysaccharides have similar extraction methods. The extraction process is the most critical step in the preparation of longan polysaccharides [5]. The choice of extraction method is influenced by the physical and chemical properties of the components as well as the extraction environment and interfering substances [6,7]. Currently, the research on the extraction process of longan polysaccharides is based on hot water extraction (Fig. 1), which is the simplest existing method. However, the method can only extract polysaccharides outside the plant cell wall, leading to the relatively low polysaccharide extraction rate and time wastage of the method. In a study [8] involving the extraction of longan polysaccharide by hot-water extraction combined with ethanol precipitation, the extraction temperature was 90°C, the reduced pressure concentration temperature was 65°C, and the finished polysaccharide was obtained after decolorization and drying with hydrogen peroxide. The extraction rate of longan polysaccharides was 3.41%. In another study involving the use of ultrasonic extraction [9] under the conditions of 120 W, 22 min, 60°C, and 241 W, 18 min, 51°C, longan polysaccharide had a higher recovery and 2, 2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical scavenging ability. The extraction temperature was 60°C, the ultrasonic power was 161.414 W, the extraction time was 31.111 min, the liquid material ratio was 19.9697, and the theoretical maximum extraction rate of polysaccharide was 19.96%. Here, the extraction rate of polysaccharides was higher than that of traditional hot-water extraction. These auxiliary extraction methods have been used for improving the extraction efficiency of longan polysaccharides, shortening the extraction time, and reducing material waste [10].

Extraction process of longan polysaccharides

Crude polysaccharide extracts typically contain large amounts of protein [11], and the proteins must be removed by an appropriate process to improve the purity of polysaccharide products [7,12]. The Sevag method and trichloroacetic acid method are generally used to deproteinize crude polysaccharides [13]. Decolorization was performed with hydrogen peroxide before further purification by ion exchange chromatography, and gel filtration chromatography was performed. The semi-pure longan polysaccharides were fractionated and purified by DEAE cellulose column chromatography, and then the polysaccharide fractions were further separated and purified by the Sephadex G-100 column. Finally, UV scanning and Sephadex G-100 column chromatography were used. Wang et al. used a DEAE cellulose column to elute with a flow rate of 0.5 mL/min, and two symmetrical peaks, Lps-1 and Lps-2, appeared on the elution curve. Both peaks were eluted in the linear elution process of NaCl, indicating that longan polysaccharide is an acidic heteropolysaccharide without neutral sugar [8]. The Sephadex G-100 column chromatography was then performed. The results showed that Lps-1 separated two components—Lps-1-A and Lps-1-B—while Lps-2 only washed out a single peak, indicating that Lps-2 was relatively pure. In addition, a small protein elution peak was also detected in the range of the Lps-2 elution curve, further indicating that Lps-2 was a sugar protein complex [14].

This paper reviews the purification and separation methods of longan polysaccharides. The crude extraction of longan polysaccharide was performed by ultrasonic-assisted extraction, and the purified longan polysaccharide was obtained after protein removal, decolorization, ethanol precipitation, centrifugation, and freeze-drying, DEAE cellulose column chromatography, filtration, Sephadex G-100 column chromatography, dialysis, and freeze-drying [15,16] were also performed.

 Physiochemical and Structural Features of Longan Polysaccharides

The main aspects of the physicochemical and structural characteristics of plant polysaccharides are the monosaccharide composition, molecular weight, sequence of monosaccharides, configuration of glycosidic bonds, types of glycosidic bonds, and positions of glycosidic bonds [17,18]. Many studies have separated various monosaccharides and chemical structures from longan fruits [19].

Monosaccharide Compositions

Glycosidic bond hydrolysis, derivatization, gas chromatography (GC), and high-performance liquid chromatography (HPLC) detection are often used to quantify monosaccharide compositions [20]. Owing to the variety of extraction and purification processes, detected monosaccharides also differ but are mainly composed of rhamnose, xylose, arabinose, and galactose in different proportions [21]. Han separated two kinds of polysaccharides (FLP and DLP) from fresh longan and dry longan and found that DLP was composed of rhamnose, mannose, glucose, and galactose in a molar ratio of 2.0:1.0:1.0:10.5, with an average molecular weight of 1.06 × 107 g/mol; similarly, FLP was composed of mannose and glucose with a molar ratio of 0.59:1 and an average molecular weight of 1.31 × 107 g/mol. Different kinds of longan polysaccharides might have different monosaccharide compositions and molar ratios. More monosaccharides can also be found in the future through advances in scientific and technological development [22].

 Average Molecular Weights

Several studies on longan polysaccharides have determined the average molecular weight of polysaccharides using HPLC and high-performance gel permeation chromatography [23]. Yang et al. [24] used gel permeation chromatography to determine the molecular weight of longan polysaccharide (PLFB) to be 4.2 × 105 Da. In various studies, the average molecular weight of longan has been in the approximate range of 104–107 Da.

 Chemical Structures

Only a few studies have investigated the chemical structure of longan polysaccharides. In a study [9]. Longan polysaccharide (PLFP) was extracted from different longan peels by hot water extraction. By removing the protein and conducting analyses by gas chromatograph, it was found that the monosaccharide composition was composed of L-arabinofuranose (32.8%), D-glucopyranose (17.6%), D-galactopyranose (33.7%), and D-galacturonic acid (15.9%). The analysis results showed that the backbone consisted of →5)-L-Araf-(1→, →6)-D-Glcp-(1→, →3)-D-Galp-(1→, →3)-D-GalpA-(1→ and →6)-D-Galp-(1→ with a molar proportion of 2:1:1:1:1.

Longan pulp polysaccharide was extracted using hot water (LP-H), superfine grinding (LP-S), and superfine grinding-assisted enzymatic treatments (LP-SE). All three LPs contained similar glycosidic linkage of →3)-α-L-Araf-(1→, →3, 6)-β-D-Galp-(1→, and α-L-Rhap-(l→, whereas they each contained specific glycosidic linkage of →4)-β-D-Glcp-(l→, →4)-β-D-Galp-(1→, and →5)-α-L-Araf-(1→ in LP-H, LP-S, and LP-SE, respectively [14].

 Biological Activities

Longan polysaccharide research and analyses have provided insight into their antioxidant, immunomodulatory, antitumor, anti-inflammatory, and anti-glycated activities [25,26].

Antioxidant Activity

Natural substances are important sources of antioxidants, and many polysaccharides have antioxidant activity [27,28]. Antioxidant activity is an important index for detecting plant polysaccharides [29,30]. Many studies have verified the antioxidant activity of longan polysaccharides. Yang et al. studied the antioxidant substances in longan. Under the condition of microwave-assisted extraction, the scavenging rates of DPHH free radical and hydroxyl free radical of longan polysaccharide were 62.45% and 54.36%, respectively [24]. Jiang et al. used the DPPH free-radical scavenging method to detect the free radical scavenging activities of crude longan polysaccharide (LSP), extracted macromolecular longan polysaccharide (LSP1), and small-molecule longan polysaccharide (LSP2) [31]. When the concentration of longan polysaccharide (LSP) reached 700 (g/mL), the scavenging activity of DPPH radical increased with the increasing concentration of longan polysaccharide (LSP), whereas (LSP3) showed a lower antioxidant activity than that of (LSP1) and (LSP2). This result is similar to the previous report that crude polysaccharides have a better antioxidant effect than purified polysaccharides. The relationship between the structural characteristics of polysaccharides and antioxidant activity remains unclear [32].

 Immunomodulatory Activity

Natural active polysaccharides can participate in various immune responses [33]. Mental stress can directly affect the immune state of the body through the pituitary thymus axis, and long-term mental stress leads to a decline in human immune function [34,35]. Therefore, immune regulation is important. Rong et al. [36] isolated longan polysaccharides (LPD2) from longan pulp, and the effect of (LPD2) on macrophage phagocytosis was determined. LPD2 at 6.25–50 μg/mL enhanced phagocytosis in a dose-dependent manner (P < 0.05). Meanwhile, the effect of LPD2 on macrophage phagocytosis was not inhibited by PMB (P > 0.05). The use of a 50 μg/mL LPD2 treatment increased phagocytosis to 205.1 ± 9.3% of the control group, indicating that LPD2 significantly enhanced the phagocytic activity of macrophages. Tong et al. [37,38] found that longan polysaccharide enhanced the phagocytosis of macrophages; when the polysaccharide concentration was 100–400 μm/mL, macrophage phagocytosis was negatively correlated with polysaccharide concentration [20]. Longan polysaccharide influences immune activity, and different processing methods have varying effects on the immunoregulatory activity of longan polysaccharides (Fig. 2) [39].

Possible molecular mechanism of (LPD2) activating macrophages Antitumor Activity

The antitumor mechanism of polysaccharides can be divided into two categories: first, it improves the immune function of the body by activating the immune system, activating lymphocytes and macrophages, promoting cytokine secretion, and activating complement, as well as by indirectly playing an antitumor role. Second, it affects the growth cycle, ultrastructure, signal transduction pathway in tumor cells, and biochemical characteristics of the tumor cell membrane [40,41]. Zhong et al. [42] used longan polysaccharide (UELP) prepared by the ultrasonic extraction process to conduct in vivo tumor inhibition and in vivo immune experiments on S180 tumor-bearing mice. The results showed that UELP significantly enhanced the delayed type allergy and phagocytosis of peritoneal macrophages, considerably enhancing the proliferation of splenic lymphocytes. The in vivo tumor inhibition results also showed that UELP had a strong S180 tumor inhibition effect, and the highest tumor inhibition rate was 95.08%. The in vitro antitumor experiment showed that longan chitosan inhibited the growth of tumor cells BELE-7404, SKVO3, and MCF-7, as well as an antitumor effect [43].

 Anti-Inflammatory Activity

Polysaccharides with anti-inflammatory effects can regulate one or more inflammatory mediators secreted by inflammatory cells, balance the levels of pro-inflammatory factors and anti-inflammatory factors in inflammatory sites, and affect all stages of inflammation development [44]. Chen et al. [45] conducted a study using Euphoria longan Steud (Lour.) as a fruit and traditional Chinese medicine with the function of anti-inflammatory and immune regulation. The results of inflammatory responses induced by middle cerebral artery occlusion in rats were published. Compared with the model group, polysaccharides of E. longan Steud (Lour.) reduced the neurological function score, brain water content, infarct volume, myeloperoxidase (MPO) activity, tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) level. Polysaccharides of E. longan Steud (Lour.) had a protective effect on cerebral ischemia/reperfusion injury, and the mechanism might be related to the reduction of MPO TNF-α and IL-1β mediated inflammatory response in the brain [45].

 Anti-Glycosylation

Glycosylation refers to the combination of the amino group of protein and the aldehyde group of sugar [46]. The first stage of the non-enzymatic reaction of proteins with glucose yields bases and products, which undergo oxidation and molecular rearrangements into irreversible glycosylation products. Yang et al. [47] demonstrated the inhibitory effect of longan polysaccharide (PLFP) on the formation of advanced glycation end products. Longan polysaccharide and aminoguanidine with the same concentration (0.5 mg/mL) had higher anti-glycation activity than that of aminoguanidine in four weeks. The differences between PLFP and aminoguanidine might be due to their inhibition mechanism. The anti-glycosylation activity of PLFP is likely due to its antioxidant activity and the existence of a special structure. Therefore, further studies are necessary to better understand the structure and anti-glycosylation activity of longan polysaccharides.

 Correlation of Structure, Content, and Biological Activity

The bioactivity of polysaccharides is closely related to their chemical composition and structures [48–50]. However, no clear relationship between the activity and structure of longan polysaccharides has been identified [51,52], leaving room for speculation.

The chemical structure of polysaccharides has a considerable impact on their biological activities [53]. Table 1 summarized the main structural characteristics of longan polysaccharides, such as molecular weight, monosaccharide composition, chemical structure, and biological activity. For example, fresh longan polysaccharides (FLP) and air-dried longan polysaccharides (DLP) have been used as raw materials for structural and immunomodulatory activity comparisons. The ratio of 1, 3 chain residues of longan polysaccharides may increase during the drying process and have a greater impact on the immunomodulatory activity of longan polysaccharides [54,55]. The effects of alkali dissociation on the immune regulation of longan polysaccharide (LPI) can significantly enhance the proliferation of splenocytes and cytotoxicity of NK cells due to its micro-dissociated spherical conformation or single helix chain [56]. The results showed that the single helix chain could play an important role in the activation of lymphocytes and NK cells.

Polysaccharides isolated from longan fruit pulp (Longyan)
No. Compound name Molecular weight Monosaccharide composition Structures Biological activities Reference
1 LPS-N 1.38 × 104 Da Xyl and Glc in ratio of 1:1.9 Anti-inflammatory [3]
2 PLFB 4.2 × 105 Da Ara, Glc, Gal, and GalA in the ratio of 3.28:1.76:3.37:1.59 Backbone consisted of →5)-L-Araf-(1→, →6)-D-Glcp-(1→, →3)-D-Galp-(1→, →3)-D-GalpA-(1→ and →6)-D-Galp-(1→ Anti-glycated [9]
3 LP-2 1.08 × 105 Da Glc Backbone composed of β-(1→6)-linked-Glcp Antioxidant [10]
4 LPIIa 1.593 × 105 Da Rha, Ara, Xyl, Man, Glc, and Gal Backbone composed of (1→3,4)-linked-α-Rhap, (1→4)-linked-β-Galp, (1→6)-linked-β-Galp and (1→3,6)-linked-β-Galp Anti-inflammatory [11]
5 ASPs I Xyl, Ara, Glc, and Gal Composed of →3)-Xylp-(1→ and →3, 4)-Xylp-(1→ Immunomodulation [12]
6 LP1 1.1 × 105 Da Glc, GalA, Ara, and Gal in the ratio of 5.39:1.04:0.74:0.21 Backbone of →4)-α-D-Glcp-(1→4)-α-D-GalpA-(1→4)-α-D-Glcp-(1→4)-β-D-Glcp-(1→, side chains composed of →2)-β-D-Fruf-(1→2)-L-sorbose-(1→ attached to the O-6 position of the α-D-Glcp Antitumor agent [13]
7 LP-HLP-SLP-SE 2.38 × 105 Da2.28 × 105 Da1.90 × 105 Da Rha, Ara, Man, Glc, and Gal Glycosidic linkage of →4)-β-D-Glcp-(l→Glycosidic linkage of →4)-β-D-Galp-(1→Glycosidic linkage of →5)-α-L-Araf-(1→ Cell proliferation [14]
8 LPg1LPx1 1.06 × 107 Da1.31 × 107 Da Rha, Man, Glc, and Gal in the ratio of 0.2:0.21:1:0.2Man and Glc in the ratio of 0.59:1 Immunomodulation [16]
9 LYRP2 1.1 × 105 Da Glc Main chain β-D-(1→3)-Glcp, and branches with β-D-(1→3)-Glcp-β-D-→1)-Glcp and β-D-(1→4)-Glcp-β-D-1)-Glcp in which 1-linked Glcp terminal residues ImmunomodulationAntitumor [17]
10 LSP Ara, Gal, Glc, and Man Major components of →6)-Galp-(→1, Glcp-(→1 and →6)-Glcp-(1→ glycosidic linkages Antioxidant [31]
11 LYP2 Glc, Ara, and GalA, sorbose in ratio of 5.39:1.04:0.74:0.21 Composed of →4)-α-D-Glcp-(1→4)-α-D-GalpA-(1→4)-α-D-Glcp-(1→4)-β-D-Glcp-(1→ and branches with →2)-β-D-Fruf-(1→2)-L-sorbose-(1→, which was (1→6)-linked to α-D-Glcp ImmunomodulationAntioxidant [35]
12 LPD2 9.64 × 106 Da Ara, Man, Glc, and Gal in the ratio of 0.25:0.49:1:0.5 Backbone composed of (1→4)-β-Glcp and (1→6)-β-Manp. Immunomodulation [36]
13 LPIa 1.47 × 105 Da Rha, Rib, Ara, Xyl, Man, Glc, and Gal in the ratio of 0.99:1.37: 34.61:1.48:1.73: 5.86:55.16 Composed of→3)-α-Araf-(1→, →3, 6)-β-Galp-(1→, α-Araf-(1→ and →5)-α-Araf-(1→ Immunomodulation [43]
14 FLP 1.31 × 107 Da Man and Glc in the ratio of 0.59:1 Composed of →6)-α-D-Glcp-(1→ Immunomodulation [57]
DLP 1.06 × 107 Da Rha, Man, Glc, and Gal in the ratio of 0.2:0.21:1:0.2 Composed of →6)-α-D-Glcp-(1→, →3)-β-D-Glcp-(1→, →3)-β-D-Galp-(1→ and →3)-α-L-Rhap-(1→ Cell proliferation
Conclusions and Views

Longan polysaccharides can be effectively extracted by ultrasonic and hot-water extraction and ethanol precipitation, which has a better effect than that of simple hot-water extraction. Longan polysaccharides possess important biological activities, including antioxidation, immune regulation, antitumor, anti-inflammatory, and anti-glycosylation activities. Recently, scientific researchers have extensively investigated the extraction, structures, and biological activity of longan polysaccharides. However, the structure of longan polysaccharides is diverse and complex, and the relationships between the biological activity and chemical structure of polysaccharides are not clear, creating the need for further exploration. Thus, in-depth research in this area is needed to understand the functions of longan polysaccharides more comprehensively. Moreover, as the research on longan polysaccharides has been accelerated recently, further in vivo animal research and clinical experiments are required to determine the impact of longan polysaccharides on the human body.

Funding Statement: We thank the National Natural Science Foundation of China (32201969, 82204668), Natural Science Foundation of Henan Province (212300410297), Hebei Natural Science Foundation (H2022423376), Basic Research Plan of Higher Education School Key Scientific Research Project of Henan Province (21A550014), Doctoral Research Foundation of Zhengzhou University of Light Industry (2020BSJJ015), and Science and Technology Research Project of Higher Education in Hebei Province (QN2020233).

Conflicts of Interest: The authors declare they have no conflicts of interest to report regarding the present study.

 References Liu, X., Luo, Y., Zha, C., Zhou, S., Liu, L. et al. (2015). Rheological properties of polysaccharides from longan (Dimocarpus longan Lour.) fruit. International Journal of Polymer Science, 2015, 1–5. DOI 10.1155/2015/168064. Bai, Y., Huang, F., Zhang, R., Dong, L., Jia, X. et al. (2020). Longan pulp polysaccharides relieve intestinal injury in vivo and in vitro by promoting tight junction expression. Carbohydrate Polymers, 229, 115475. DOI 10.1016/j.carbpol.2019.115475. Liu, Y. L., Chen, Y., Zeng, Y. J., Zhang, S. T., Zhang, Z. H. et al. (2021). Molecular characterization of miRNA genes and their expression in Dimocarpus longan Lour. Planta, 253 (2), 41. DOI 10.1007/S00425-021-03564-W. He, Y. (2011). Study on the preparation technology and antioxidant activity of longan polysaccharide. Chinese Academy of Agricultural Sciences. DOI 10.7666/d.y1932729. Chaiklahan, R., Srinorasing, T., Chirasuwan, N., Tamtin, M., Bunnag, B. (2020). The potential of polysaccharide extracts from Caulerpa lentillifera waste. International Journal of Biological Macromolecules, 161, 1021–1028. DOI 10.1016/j.ijbiomac.2020.06.104. Lin, Y., Lin, H., Wang, H., Lin, M., Chen, Y. et al. (2020). Effects of hydrogen peroxide treatment on pulp breakdown, softening, and cell wall polysaccharide metabolism in fresh longan fruit. Carbohydrate Polymers, 242, 116427. DOI 10.1016/j.carbpol.2020.116427. Ji, X., Peng, B., Ding, H., Cui, B., Nie, H. et al. (2021). Purification, structure and biological activity of pumpkin polysaccharides: A review. Food Reviews International. DOI 10.1080/87559129.2021.1904973. Wang, X. Y. (2009). Extraction, purification, and antioxidant activity of longan polysaccharide. Jimei University, China. DOI 10.7666/d.y1748509. Yang, B., Jiang, Y., Zhao, M., Chen, F., Wang, R. et al. (2009). Structural characterization of polysaccharides purified from longan (Dimocarpus longan Lour.) fruit pericarp. Food Chemistry, 115 (2), 609–614. DOI 10.1016/j.foodchem.2008.12.082. Mayuree, K., Tamonpatch, P., Nattaya, L. (2019). Dendrobium orchid polysaccharide extract: Preparation, characterization and in vivo skin hydrating efficacy. Chinese Herbal Medicines, 11 (4), 400–405. DOI 10.7666/d.y1286695. Zhong, K., Wang, Q. (2010). Optimization of ultrasonic extraction of polysaccharides from dried longan pulp using response surface methodology. Carbohydrate Polymers, 80 (1), 19–25. DOI 10.1016/j.carbpol.2009.10.066. Jiang, G., Prasad, K. N., Jiang, Y., Yang, B., Jia, Y. et al. (2009). Extraction and structural identification of alkali-soluble polysaccharides of longan (Dimocarpus longan Lour.) fruit pericarp. Innovative Food Science & Emerging Technologies, 10 (4), 638–642. DOI 10.1016/j.ifset.2009.06.006. Jiang, J., Meng, F. Y., He, Z., Ning, Y. L., Li, X. H. et al. (2014). Sulfated modification of longan polysaccharide and its immunomodulatory and antitumor activity in vitro. International Journal of Biological Macromolecules, 67, 323–329. DOI 10.1016/j.ijbiomac.2014.03.030. Huang, F., Hong, R., Zhang, R., Yi, Y., Dong, L. et al. (2019). Physicochemical and biological properties of longan pulp polysaccharides modified by Lactobacillus fermentum fermentation. International Journal of Biological Macromolecules, 125, 232–237. DOI 10.1016/j.ijbiomac.2018.12.061. Yi, Y., Huang, F., Zhang, M. W., Zhang, R. F., Deng, Y. Y. et al. (2013). Solution properties and in vitro antitumor activities of polysaccharides from longan pulp. Molecules, 18 (9), 11601–11613. DOI 10.3390/molecules180911601. Lan, H. B. (2016). Structural characterization and immunomodulatory activity of longan polysaccharides. Hainan University, Haikou, China. Li, H. H., Mi, Y., Duan, Z. G., Ma, P., Fan, D. D. (2020). Structural characterization and immunomodulatory activity of a polysaccharide from eurotium cristatum. International Journal of Biological Macromolecules, 162, 609–617. DOI 10.1016/j.ijbiomac.2020.06.099. Hou, C., Yin, M., Lan, P., Wang, H., Nie, H. et al. (2021). Recent progress in the research of Angelica sinensis (Oliv.) diels polysaccharides: Extraction, purification, structure, and bioactivities. Chemical and Biological Technologies in Agriculture, 8 (1), 13. DOI 10.1186/s40538-021-00214-x. Yi, Y., Liao, S. T., Zhang, M. W., Zhang, R. F., Deng, Y. Y. et al. (2011). Immunomodulatory activity of polysaccharide-protein complex of longan (Dimocarpus longan Lour.) pulp. Molecules, 16 (12), 10324–10336. DOI 10.3390/molecules161210324. Yi, Y., Zhang, M. W., Liao, S. T., Zhang, R. F., Deng, Y. Y. et al. (2012). Structural features and immunomodulatory activities of polysaccharides of longan pulp. Carbohydrate Polymers, 87 (1), 636–643. DOI 10.1016/j.carbpol.2011.08.034. Yang, C., He, N., Ling, X., Ye, M., Zhang, C. et al. (2008). The isolation and characterization of polysaccharides from longan pulp. Separation and Purification Technology, 63 (1), 226–230. DOI 10.1016/j.seppur.2008.05.004. Han, M. M. (2018). Study on the structure-activity changes of longan pulp polysaccharides under different maillard reaction systems. Wuhan University of Light Industry, China. DOI 10.27776/d.cnki.gwhgy.2018.000145. Niu, L. (2012). Establishment of nutritional components and polysaccharide analysis method of longan meat. Guangxi University, China. DOI 10.7666/d.y2159907. Yang, B., Jiang, Y., Zhao, M., Shi, J., Wang, L. (2008). Effects of ultrasonic extraction on the physical and chemical properties of polysaccharides from longan fruit pericarp. Polymer Degradation and Stability, 93 (1), 268–272. DOI 10.1016/j.polymdegradstab.2007.09.007. Zhou, W. J. (2021). Research and development on the prebiotic activity and nutritional meal powder of longan, medlar and jujube polysaccharides. Wuhan University of Light Industry, China. DOI 10.27776/d.cnki.gwhgy.2021.000322. Han, M. M., Yi, Y., Wang, H. X., Huang, F. (2017). Investigation of the mallard reaction between polysaccharides and proteins from longan pulp and the improvement in activities. Molecules, 22 (6), 938. DOI 10.3390/molecules22060938. Zha, C. J. (2013). Rheology, structural identification and free radical scavenging activity of longan polysaccharide. Huazhong Agricultural University, China. DOI 10.7666/d.y2393993. Yang, B., Zhao, M., Prasad, K. N., Jiang, G., Jiang, Y. (2010). Effect of methylation on the structure and radical scavenging activity of polysaccharides from longan (Dimocarpus longan Lour.) fruit pericarp. Food Chemistry, 118 (2), 364–368. DOI 10.1016/j.foodchem.2009.04.128. Wang, T. (2018). Effects of drying on the structure and properties of longan pulp protein/polysaccharide complex. South China Agricultural University, Guangzhou, China. Mu, S., Yang, W. J., Huang, G. L. (2021). Antioxidant activities and mechanisms of polysaccharides. Chemical Biology & Drug Design, 97, 628–632. DOI 10.1111/cbdd.13798. Jiang, G., Wen, L., Chen, F., Wu, F., Lin, S. et al. (2013). Structural characteristics and antioxidant activities of polysaccharides from longan seed. Carbohydrate Polymers, 92 (1), 758–764. DOI 10.1016/j.carbpol.2012.09.079. Huang, X. Y. (2019). Effects of drying methods on physicochemical and functional properties of longan pulp polysaccharides. Wuhan University of Light Industry, China. DOI 10.27776/d.cnki.gwhgy.2019.000095. Wang, J. (2016). Preparation of acetylated and carboxymethylated longan polysaccharide and its antioxidant and immunomodulatory activities. Guangxi Medical University, China. DOI 10.7666/d.D01000336. Wen, Y. Z. (2017). Study on the immunomodulatory effect of longan polysaccharide. Hainan University, Haikou, China. Ning, Y. L. (2013). Studies on the preparation, immunomodulatory and antioxidant effects of phosphoesterification and longan meat polysaccharides with different molecular weights. Guangxi Medical University, Nanning, China. Rong, Y., Yang, R., Yang, Y., Wen, Y., Liu, S. et al. (2019). Structural characterization of an active polysaccharide of longan and evaluation of immunological activity. Carbohydrate Polymers, 213, 247–256. DOI 10.1016/j.carbpol.2019.03.007. Tong, H. (2014). Studies on immune regulation and anti-aging effect of longan polysaccharide LGP50 and LGP50S-1. Jinan University, Jinan, China. Jiang, J. (2014). Study on the preparation technology, immunomodulatory effect and toxicological safety of compound longan polysaccharide formula. Guangxi Medical University, Nanning, China. Yi, Y., Zhang, M. W., Liao, S. T., Zhang, R. F., Deng, Y. Y. et al. (2012). Effects of alkali dissociation on the molecular conformation and immunomodulatory activity of longan pulp polysaccharide (LPI). Carbohydrate Polymers, 87 (2), 1311–1317. DOI 10.1016/j.carbpol.2011.09.014. Huang, X. F. (2011). Preliminary study on sulfation modification and in vitro antitumor activity of longan polysaccharide before and after modification. Guangxi Medical University, Nanning, China. Rong, Y. (2019). Study on the role and mechanism of longan polysaccharide in activating macrophages. Hainan University, China. DOI 10.27073/d.cnki.ghadu.2019.000540. Zhong, K., Wang, Q., He, Y., He, X. (2010). Evaluation of radicals scavenging, immunity-modulatory and antitumor activities of longan polysaccharides with ultrasonic extraction on in S180 tumor mice models. International Journal of Biological Macromolecules, 47 (3), 356–360. DOI 10.1016/j.ijbiomac.2010.05.022. Qin, J. H. (2010). Preliminary study on isolation and activity of longan chitosan. Guangxi Medical University, China. DOI 10.7666/d.y1683389. Hou, C., Chen, L., Yang, L., Ji, X. (2020). An insight into anti-inflammatory effects of natural polysaccharides. International Journal of Biological Macromolecules, 153, 248–255. DOI 10.1016/j.ijbiomac.2020.02.315. Chen, J., Sun, X. D., Wang, Y., Zhou, L. M. (2010). Effect of polysaccharides of the Euphoria longan (Lour.) Steud on inflammatory response induced by focal cerebral ischemia/reperfusion injury in rats. Food and Agricultural Immunology, 21 (3), 219–225. DOI 10.1080/09540101003605072. Zheng, S. Q., Jiang, F., Gao, H. Y., Zheng, J. G. (2010). Preliminary observations on the antifatigue effects of longan (Dimocarpus longan Lour.) seed polysaccharides. Phytotherapy Research, 24 (4), 622–624. DOI 10.1002/ptr.2963. Yang, B., Zhao, M., Jiang, Y. (2009). Anti-glycated activity of polysaccharides of longan (Dimocarpus longan Lour.) fruit pericarp treated by ultrasonic wave. Food Chemistry, 114 (2), 629–633. DOI 10.1016/j.foodchem.2008.09.099. Li, X., Chen, S., Li, J. E., Wang, N., Liu, X. et al. (2019). Chemical composition and antioxidant activities of polysaccharides from Yingshan Cloud Mist tea. Oxidative Medicine and Cellular Longevity, 2019, 1915967. DOI 10.1155/2019/1915967. Liu, H. J. (2020). Longan pulp polysaccharide superfine grinding enzymatic hydrolysis assisted extraction and its physicochemical properties and biological activity. South China Agricultural University, China. DOI 10.16429/j.1009-7848.2020.03.015. Ji, X., Hou, C., Shi, M., Yan, Y., Liu, Y. (2022). An insight into the research concerning Panax ginseng C. A. Meyer polysaccharides: A review. Food Reviews International, 38 (6), 1149–1165. DOI 10.1080/87559129.2020.1771363. Zhang, J., Yang, G., Wen, Y., Liu, S., Li, C. et al. (2017). Intestinal microbiota is involved in the immunomodulatory activities of longan polysaccharides. Molecular Nutrition & Food Research, 61 (11), 1700466. DOI 10.1002/mnfr.201700466. Yang, B., Zhao, M., Jiang, Y. (2008). Optimization of tyrosinase inhibition activity of ultrasonic-extracted polysaccharides from longan fruit pericarp. Food Chemistry, 110 (2), 294–300. DOI 10.1016/j.foodchem.2008.01.067. Yi, Y., Liao, S. T., Zhang, M. W., Shi, J., Zhang, R. F. et al. (2011). Physicochemical characteristics and immunomodulatory activities of three polysaccharide-protein complexes of longan pulp. Molecules, 16 (7), 6148–6164. DOI 10.3390/molecules16076148. Huang, Z. S. (2008). Study on the anti-dementia effect and mechanism of longan ginseng polysaccharide. Guangxi Medical University, Nanning, China. L, L. (2010). Protective effect of longan ginseng polysaccharide on liver and kidney injury in fluorosis rats. Guangxi Medical University, China. DOI 10.7666/d.y1683316. Huang, F., Hong, R., Zhang, R., Dong, L., Bai, Y. et al. (2019). Dynamic variation in biochemical properties and prebiotic activities of polysaccharides from longan pulp during fermentation process. International Journal of Biological Macromolecules, 132, 915–921. DOI 10.1016/j.ijbiomac.2019.04.032. Gan, T., Feng, C., Lan, H., Yang, R., Zhang, J. et al. (2021). Comparison of the structure and immunomodulatory activity of polysaccharides from fresh and dried longan. Journal of Functional Foods, 76, 104323. DOI 10.1016/j.jff.2020.104323.