Recent advances in inulin polysaccharides research: extraction, purification, structure, and bioactivities

Abstract

Inulin, a polysaccharide predominantly composed of fructose molecules, possesses a linear chain structure with β-(2 → 1) linkages between fructose units and usually has a glucose molecule at one end of the chain. It is not only an edible natural functional polysaccharide, but also a soluble dietary fiber, with a variety of physiological functions such as antioxidant, promoting the growth of gut flora and maintaining its homeostasis, enhancing gut immune function, promoting nutrient absorption, lowering glycemia, as well as providing anti-carcinogenic, weight loss and constipation relief. This review provides a comprehensive overview of the latest research advances in the extraction, purification, structural characterization, and bioactivities. It is intended to lay the theoretical and research foundations to enable further exploration and effective progress in the advancement towards the production of inulin.

Graphical abstract

Introduction

Inulin, also known as an inulin-type fructan, is a chain polysaccharide consisting of d-fructose linked by a β-(1–2) glycosidic linkage. The average degree polymerization (DP) of inulin typically falls within the range of 2–60 [1, 2]. Inulin with a DP less than 10 typically refers to oligosaccharides that are formed by the linkage of relatively fewer fructose units through glycosidic bonds [3, 4]. Inulin from different plant sources, with the main differences being DP and molecular weight (Mw), have similar structure and linkages types [5, 6]. Inulin has been successfully extracted from a wide range of plants, including several monocotyledonous and dicotyledonous plant families such as Liliaceae, Asteraceae and Gramineae, among which chicory is the most widely used for the industrial-scale production and extraction of inulin [7].

With its diverse range of characteristics, inulin has found its way into different industries, playing crucial roles in food, health, and biotechnology. Inulin is garnering attention as a dietary fiber. It can be used as a functional ingredient in food and beverage products, providing added value and meeting the growing demand for healthy and natural products [8, 9]. In addition, inulin has many biological activities, including the modulation of the immune system, the prevention of cancers, the regulation of abnormalities in glucose–lipid metabolism, antioxidant, weight loss and the alleviation of liver damage [10,11,12,13,14,15,16,17]. As a result, inulin is widely regarded as an excellent functional food.

As research on inulin continues to advance, new applications and insights are emerging. This exploration of inulin's properties and potential opens exciting possibilities for innovation and improvement in multiple domains. Understanding and harnessing the power of inulin can lead to the development of more sustainable and beneficial products for society. Therefore, the objective of presenting a comprehensive and in-depth review on the extraction, purification, structure, and bioactivities of inulin from plant sources is of utmost importance. By delving into the various methods of extraction, understanding the purification processes, analyzing the complex structure, and exploring the diverse bioactivities of inulin, we aim to provide a solid theoretical foundation.

Analysis of research hotspots by CiteSpace

By performing a bibliometric analysis of inulin-related literature using CiteSpace, research hotspots and development trends can be visualised. By mining the co-occurrence of keywords and other elements, popular topics can be accurately identified, helping researchers to identify the frontier research directions related to inulin and avoid repetitive research. Using CiteSpace bibliometrics, relevant articles on inulin polysaccharides from the last decade were collected from the Web of Science database, after removing duplicates, and analyzed for number, keyword classification. A total of 735 publications were included. The results of the visualization analysis showed an overall increase in the number of annual publications related to inulin (Fig. 1A). In the analysis of the literature, eight clusters were identified, mainly focused on prebiotic activity, drug delivery and fructan (Fig. 1B). “Inulin” was the keyword with the highest frequency and centrality (Fig. 1C). There were 15 burst terms, with “dendritic cells” having the highest burst strength (Fig. 1D). This clearly indicates that research on inulin is garnering an increasing amount of attention from an ever-growing number of scholars. As the understanding of inulin's unique properties and potential applications continues to expand, more and more researchers are being drawn to explore this fascinating polysaccharide.

Fig. 1

Analysis of publications on inulin polysaccharides based in web of science on CiteSpace. A Volume of articles about inulin polysaccharides, 2015–2024. B Keywords cluster maps. C Keyword co-occurrence maps. D Citation Burst maps

Extraction methods

With an increasing value and demand for inulin, the selection of efficient inulin extraction and purification methods is becoming increasingly important. It is important to note that factors such as extraction methods, plant sources and growing climates all have a significant impact on its yield, physic-chemical properties and activities [18]. Figure 2 presents information on plant sources of inulin, as well as its extraction, purification, and identification methods.

Fig. 2

Plant sources, extraction, purification, and identification of inulin

Hot water extraction

The principle of hot water extraction is based on taking advantage of the physical property that polysaccharides are easily soluble in hot water above 80 °C for the purpose of extracting inulin [19, 20]. Ning et al. employed a hot water reflux extraction process to extract inulin from dahlia at an extraction rate of 17.72% [21]. Fu et al. found that the optimum extraction conditions for extracting inulin from the vegetative flowers of Codonopsis pilosula Nannf. were as follows: 100 ℃ and a material/liquid ratio of 40 mL/g, with twice extractions for 2.5 h each, resulting in an extraction rate of 20.6% [5].

Ultrasonic extraction

Ultrasonic extraction is a contemporary extraction approach. It makes use of the distinct physical effects of ultrasound, including cavitation, mechanical vibration, and heating. The physical effect of ultrasound is used to disrupt the cell walls during ultrasonic extraction, facilitating the release of polysaccharides and increasing the efficiency of polysaccharide extraction [22, 23].

Qiao et al. obtained the optimum process of inulin extraction through a response surface analysis as follows: a material/liquid ratio of 1:30 (g/mL), the power is 600 W, an ultrasound duration of 58 min, and extraction rate of 95.81% from Chrysanthemum [24]. Chen et al. obtained the optimal process of inulin extraction from Taraxacum koksaghyz Rodin as follows: the power is 230 W, a duration of 34 min, 61 ℃, and the extraction rate was 20.14% ± 0.19% [25]. However, the ultrasonic extraction method can lead to the cleavage of sugar chains in inulin, which in turn destroys its physicochemical properties. Therefore, a proper control of the treatment power and time during ultrasonic treatment is required to ensure the yield of the goal.

Microwave extraction method

During the microwave extraction process, high-frequency electromagnetic waves are used to polarize and impact the molecules within plant cells, which in turn increases the temperature and pressure to improve the efficiency of inulin extraction [26].

Xiao et al. found that the optimum microwave-assisted extraction process for inulin in Helianthus tuberosus was a microwave treatment period for 6 min and microwave power at 450 W, yielding 12.2% inulin [27]. Zhang et al. found that a microwave treatment time of 6 min led to the highest extraction rate of inulin from Jerusalem artichoke, which was 15.35% [28]. However, improper microwave power or extraction time can lead to changes in the structure, including partial degradation resulting in decreased molecular weight and altered degree of polymerization, as well as affecting the distribution and length of side chains.

Enzyme-assisted extraction

Enzyme-assisted extraction is a technique that employs specific enzymes for the purpose of breaking down plant cell walls and thereby releasing inulin. This method is typically gentler on the extracted product, minimizing the risk of degradation or damage [29]. Domingo and others discovered that the optimal process for extracting inulin from Cynara cardunculus using pectinase is at a pH of 4.5, an enzyme ratio of 7.5 U:1 g, an extraction time of 2 h at 50 ℃. The yield of inulin was 35.30% ± 0.85%, which is 38.16% higher than that obtained by traditional hot water extraction [30]. Jiang et al. used a material–liquid ratio of 1:20, an enzyme temperature of 54 °C, a composite enzyme (papain: pectinase = 1:8) and an extraction duration of 40 min; yielding 73.30% of Chrysanthemum inulin [31]. One of the primary challenges in employing enzymatic methods lies in enzyme stability. Enzymes are frequently sensitive to environmental factors like temperature, pH value, and ionic strength. Fluctuations in these conditions can cause denaturation or inactivation of the enzymes, thereby diminishing their effectiveness.

In addition, the results of Termrittiky et al. on the extraction of inulin using an ohmic heat-assisted process showed that both wet- and dry-ground solutions for inulin tuber powders were highly conductive, and that higher field strengths induced more inulin to be leached from the cells [32].

The various extraction methods for inulin all possess their respective advantages and limitations. Ultrasound-assisted extraction provides higher efficiency and shorter extraction times; however, it may necessitate specialized equipment. Enzyme-assisted extraction can be more selective, yet it encounters challenges such as enzyme stability and cost. Traditional methods are frequently less efficient, but might be more accessible and cost-effective in certain situations.

Purification methods

Like other polysaccharides, crude inulin contains a variety of impurities such as proteins, monosaccharides, pigments. [33]. In order to obtain high-purity and high-quality inulin, it is necessary to remove the pigments and proteins from crude inulin first [34]. Proteins in crude polysaccharides are usually removed using methods such as salting-out precipitation, Sevag method, enzymatic hydrolysis or enzymatic hydrolysis + Sevag method [35, 36]. The most commonly used methods for inulin decolorization are: activated carbon, resin and hydrogen peroxide [37]. Tian et al. found that the maximum decolorization of inulin was 72% at an activated carbon level of 4%, after which the decolorization rate decreased with an increasing activated carbon dosage [38].

To obtain high-purity inulin, polysaccharides must be purified using cellulose and dextran gel column chromatography [39]. Li et al. obtained homogeneous inulin (MWP) from the crude polysaccharides of Artemisia annua by using DEAE-Sepharose and Superdex-75 column chromatography [40]. Xu et al. obtained homogeneous inulin RCOP1-2-1 from Codonopsis tangshen by employing DEAE-Sepharose fast flow ion exchange chromatography and Sephadex G-100 column chromatography [41]. Wang et al. used macro-porous adsorbent resins and a Sevag reagent, respectively, to remove pigments and proteins rom the crude polysaccharides of Arctium lappa, which were then eluted on a Sephadex-G 100 column to obtain the homogeneous inulin ALP-1 [42].

Structure

Characterization method

The biological activities of inulin are influenced by its monosaccharide ratio, Mw and DP. A deeper understanding of the inulin structure can better reveal the intrinsic links between its structure and biological activities [43]. Techniques such as high-performance liquid chromatography (HPLC) and gas chromatography–mass spectrometry (GC–MS) are used to accurately analyze the monosaccharide composition, Mw and linkage types of inulin [44]. In addition, Fourier transform infrared (FTIR) may reveal key functional groups in inulin [45], and nuclear magnetic resonance (NMR) techniques may resolve its complete structural information [46]. One-dimensional NMR includes NMR hydrogen spectra, which can determine the glycosidic linkage configuration and structural information of the heterojunction protons of inulin, and carbon spectra can confirm the relative number of sugar residues. Two-dimensional nuclear NMR techniques include homonuclear chemical shift correlation, proximal hydrocarbon correlation and remote hydrocarbon correlation, all of which can provide more comprehensive structural information [44]. Therefore, a comprehensive analysis of the inulin structure can be achieved through joint applications of multiple techniques while providing a strong foundation for in-depth analyses of its properties and functions.

Structural feature of inulin

The molecular formula of inulin is (C₆H₁₀O₅)n, where n represents the degree of polymerization and can vary from 2 to 60 or more. Inulin is a chain polysaccharide composed of d-fructose linked by β(2 → 1) glycosidic bonds, and often has a glucose residue at the end [5, 21, 47]. The structural characteristics of inulin are influenced by a variety of factors, including plant species, growing environment, harvest time, storage conditions as well as extraction and purification methods. Table 1 shows the monosaccharide composition, extraction method, Mw, DP, and biological activities of inulin from different plant sources. The structural formula of inulin is presented in Fig. 3.

Table 1 The monosaccharide composition, extraction methods, Mw, DP, and biological activities of inulin from different plant sources

Fig. 3

Structural formula of inulin: A (general formula of inulin structure), B (DLH-A) [21], C (RCOP1-2-1) [41]

Mw and monosaccharide compositions

The Mw and monosaccharide composition of inulin are mainly affected by plant species, environment, extraction methods and seasons, etc. Ning et al. obtained the high-purity inulin DLH-A from dahlia, and the results of its Mw determination as well as monosaccharide composition showed that the peak Mw of DLH-A was 3.633 kDa, whose monosaccharide ratio was Glc:Gal:Ara:Fru:Man-A = 55.7:8.2:4.4:28.6:3.2 [21]. Fu et al. isolated and purified inulin from the crude polysaccharides of Codonopsis pilosula (CPPF), which was composed of a large amount of Fru and a small amount of Glc, with an Mw of 2.810 kDa [5]. Xu et al. confirmed that inulin RCOP1-2-1 from Codonopsis tangshen Oliv. was a neutral homogeneous polysaccharide composed of fructose with a relative molecular mass of 2.58 kDa [41]. Wang et al. showed through structural characterization that Arctium lappa inulin ALP-1 was a fructan with an Mw of 5.12 kDa, whose monosaccharide composition included fructose and glucose [42].

Glycosidic linkage types and positions

Ning et al. concluded that dahlia inulin (DLH-A) was mainly composed of fructans, whose linkage mode was mainly → 1)-Fruf-(2 → . The two-dimensional spectral analysis of the HMBC of DLH-A showed that there was a linkage mode of α-d-Glcp-1 → 2-β-d-Fruf-1 → , and at the same time there were also cross peaks of H1a,1b(β-d-Fruf-2,1)-C2(β-d-Fruf-2,1), indicating that the fructose residues were in a 2,1-linkage mode. Combining methylation with monosaccharide composition, the structural formula of DLH-A can be deduced as α-d-Glcp-1 → (2-β-d-Fruf-1)19 → 2-β-d-Fruf [21]. The purification by Fu et al. yielded a Codonopsis inulin-type fructan (CPPF) which has a backbone of β-(2 → 1)-Fruf and α-d-(2 → 1). It has a DP of about 2 to 17, and Glcp is attached at the end. This CPPF shows an average DP of 6 [5]. Xu et al.’s structural characterization of inulin RCOP1-2-1 from Codonopsis tangshen Oliv revealed that the chemical structure of this component mainly consists of 2 → 1-β-d-fructose. Additionally, it contains a small amount of terminal β-d-fructose and a trace amount of terminal α-d-glucose [41]. Wang et al. determined that the structural unit of inulin ALP-1 extracted from Arctium lappa consisted of (2 → 1)-β-d-glucopyranose, linked to the terminal (2 → 1)-α-d-glucopyranose at the non-reducing end, with (2 → 6)-β-d-glucopyranose branching off the main chain [42].

Physicochemical properties of inulin

Inulin is an amorphous odorless white powder soluble in water [56], which is chemically stable under alkaline conditions and high temperatures, and the stability of long-chain inulin is superior to that of short-chain inulin [57]. Lin et al. found that inulin derived from dahlia tubers and phacelia roots showed a particulate aggregated form through scanning electron microscopy and a semi-crystalline structure through X-ray diffraction. Inulin from yam, chicory roots and asparagus showed a rough lamellar morphology and an amorphous structure [50].

Inulin has 3 molecular conformations, namely α-, β- and γ-, which have different solubility properties due to the presence of intramolecular and intermolecular hydrogen bonds. The solubility of inulin is strongly influenced by DP and external temperature. Inulin with a DP ≤ 10 is easily soluble in water, while that with DP > 10 can hardly be soluble in water, and its solubility increases significantly with an increasing temperature. However, inulin with a poor solubility but a high Mw has an increase in the solubility with an increasing temperature [58].

The excellent physicochemical properties of inulin also give it significant potential for its use in food applications: Lin et al. found that the viscosity of inulin from artichoke, chicory roots and asparagus decreased at elevated temperatures [50]. It has also been found that viscosity increases as the concentration increases, with long-chain inulin solutions forming a gel with a creamy flavor and texture at a concentration of 30% [59, 60]. The physicochemical properties of inulin sweeteners depend mainly on DP: the lower the DP is, the sweeter the sweeteners will be [17], because there are more monosaccharides and disaccharides in short-chain inulin [61]. In addition, inulin has an excellent hygroscopicity and a unique melting point, making it important in the applications in the food processing industry.

Biological activities

As a soluble dietary fiber and natural functional edible polysaccharide, inulin exhibits a variety of physiological functions. It has biological activities including promoting the growth of beneficial bacteria in the intestine, regulating blood sugar and lipids, anti-inflammatory, antioxidant, enhancing immunity, and facilitating the absorption of minerals. Biological activities of inulin are illustrated in Fig. 4.

Fig. 4

Common biological activities of inulin

Immunoregulation activity

Inulin has positive influence on the immune system of organisms by regulating the intestinal flora, reducing inflammatory reactions, and enhancing immune cell activity, thus contributing to health maintenance, and boosting immunity [62, 63].

Ning et al. discovered that dahlia inulin (DLH-A) exhibited no toxic side effects on macrophages. Concentrations of low, medium, and high (25, 50, and 125 μg/mL) levels of DLH-A enhanced the phagocytosis of RAW264.7 cells (P < 0.05). In the concentration range of 25–125 μg/mL, DLH-A also significantly stimulated the secretion of NO in RAW264.7 cells (P < 0.05), demonstrating a clear dose–response relationship. At a dose of 25 μg/mL, DLH-A could effectively promote ROS generation in RAW264.7 cells (P < 0.05), showing superior immunomodulatory activity [21].

Prebiotic effect

Due to its unique structure, inulin is not digested or degraded in the oral cavity, stomach or small bowel, but is only degraded in the colons [64]. Inulin can specifically stimulate the development of beneficial flora, thereby promoting intestinal peristalsis, increasing stool frequency and volume, as well as improving bowel functions. At the same time, inulin can inhibit the growth of harmful bacteria (like Clostridium perfringens, Campylobacter jejuni, and Salmonella) and activate the intestinal immune system, which can help the body fight against harmful pathogens while improving immunity.

Inulin increases microbial diversity, the richness of bifidobacteria and the diversity of microbiota in the gut. Birkeland et al. demonstrated that with a randomized supplementation of 16 g of inulin in early- and mid-aged men with diabetes, the diversity of juvenile bifidobacteria in feces and the fecal level of SCFAs were markedly improved [65]. Fu et al. found that inulin from the vegetative flowers of Radix et Rhizoma ginseng improved intestinal mucosal immune functions in the jejunum and ileum segments of immunocompromised mice and reduced the level of cyclophosphamide-induced intestinal mucosal inflammation [5]. Inulin supplementation boosted bacterial growth in the gut by 40-fold, according to Darjani et al. [66]. Iraporda et al. found that inulin extracted from Jerusalem artichoke tubers not only improved the growth of several Lactobacillus species, but also increased their bacterial resistance to gastrointestinal diseases [67]. Brambillasca et al. found that the lactic acid and SCFAs formed during the fermentation of inulin lowered the intestinal pH, prevented the proliferation of a variety of spoilage bacteria and indirectly reduce the production of intestinal toxins, thus maintaining good intestinal functions and relieving constipation [68]. Yang et al. found that inulin with different molecular masses promoted the proliferation of Lactobacillus plantarum, altered the rheological properties of its fermentation broth, and produced SCFAs through a simulated in vitro digestion, with 10% ethanol-deposited inulin of a small molecular mass having the best prebiotic effect [69].

Regulation of glucose–lipid metabolism

Increasing the amount of inulin in food may make the food bulkier, leading to a longer period for emptying the stomach. In addition, inulin slows down the absorption of glucose, resulting in a slower release of sugars from the body, which reduces the postprandial insulin level [70]. Inulin can also be fermented to SCFAs in the gut, which can be modulators of glucose metabolism and insulin resistance. The potential role of inulin in diabetes and obesity (Fig. 5).

Fig. 5

Possible relationship between the effect of inulin on diabetes and obesity

Inulin has bidirectional effect on blood glucose regulation, which can both lower the blood glucose of diabetics and raise blood glucose in hypoglycemics [71, 72]. Acetic acid and propionic acid, produced through the fermentation of inulin in the colons, are absorbed through colonic mucosa and transported to the liver, where acetic acid acts as a substrate for cholesterol synthesis. Propionic acid inhibits fat synthesis by interfering with enzymes involved in cholesterol and triglyceride synthesis. Meng et al. found that burdock inulin might fight against atherosclerosis by regulating the lipid balance, reducing inflammation, and activating cholesterol reverse transporters to maintain a cholesterol metabolic balance [73]. Huang et al. pointed out that the long-term administration of appropriate amounts of inulin could significantly reduce the total cholesterol (TC) and low-density lipoprotein (LDL-C) level while effectively regulating the lipid metabolism of humans and animals [74]. After adding inulin to the diets of diabetic mice, Li et al. found a significant improvement in their diabetes indicators, which was associated with the suppression of associated pro-inflammatory elements, such as interleukin-6, tumor necrosis factor-alpha (TNF-α) and interleukin-17 (IL-17) [75]. Lightowler et al. found that when inulin was added to diets, blood glucose and insulin were markedly lower in healthy adults after 40 min postprandially [76]. Yang et al. showed that inulin reduced the key regulators of cholesterol synthesis, namely sterol regulatory element binding transcription factor 2 (Srebf2), 3-hydroxy-3-methylglutaryl-CoA reductase (Hmgcr) and 3-hydroxy-3-methylglutaryl-CoA reductase (Hmgcr), with a notable rise in the excretion of total bile acids as well as neutral sterols in feces [77].

Anti-inflammatory effect

In mice with collagen-induced arthritis (CIA), Li et al. found that inulin (MWP) decreased serum levels for IL-17A and IL-6 and elevated IL-10, lowered gene expressed IL-17, and enhanced levels of IL-10 and TGF-β, suggesting that inulin modulates the systemic immune response [40]. Xu et al. found that inulin RCOP1-2-1 from Codonopsis tangshen Oliv. had good anti-inflammatory effect, which might be achieved by inhibiting activation through the TLR4/NF-κB pathway and could also be associated with the inflammatory factors TNF-α and IL-6 [41]. Wang et al. used dextran sulphate (DSS)-induced colitis mice to observe the anti-inflammatory effect of Arctium lappa inulin. The results of the effect using ALP-1 against intestinal inflammation showed that ALP-1 markedly improved the colitis-induced dysregulation of inflammatory cytokines (IL-1β, IL-6, TNF-α) along with the anti-inflammatory cytokine (IL-10) [42]. The potential anti-inflammatory action mechanism of inulin (Fig. 6).

Fig. 6

Potential anti-inflammatory action mechanism of inulin

Antioxidant activity

Inulin also shows significant antioxidant properties. It can effectively neutralize free radicals, protect cells from oxidative damage, and contribute to maintaining the health and integrity of the body. With its unique chemical structure and biological activities, inulin plays an important role in the realm of natural antioxidants [78]. Zhang et al. observed that MDA and LDH increased dramatically in IPEC-J2 cells after a treatment with H₂O₂, whereas CPPN and CTPN, the inulin from Radix and Rhizoma ginseng, could dose-dependently promote the cellular clearance of MDA and LDH, suggesting that inulin could slow down the cellular damage caused by oxidative stress [49]. Bhanja et al. found that polysaccharides and commercial inulin inhibited DPPH radicals by 75.74 ± 4.5% and 84.78 ± 1.5%, respectively, through in vitro oxidation experiments when given at 10 mg/ml. This is an indication that inulin has an excellent antioxidant capacity [79].

Promote mineral absorption

By producing inulin-mineral compounds, which are later broken down during the fermentation process in the gut flora, inulin can promote the intestinal absorption of certain metal elements and minerals, releasing the mineral elements while making them more favorable for intestinal absorption. In addition, lactic acid and SCFAs produced during inulin metabolism can not only lower the pH of the gut, but also promote the solubility of water-soluble mineral salts as well as increase the ability of the organisms on minerals like copper, magnesium, zinc, and calcium. Gharibzahedi et al. found that unlike ordinary dietary fibers, which could inhibit mineral absorption due to their high phytic acid content, inulin significantly improved and enhanced the absorption of minerals, especially calcium [80]. Feruś et al. showed that supplementing with inulin decreased the blood hepcidin level and improved iron resorption as well as balance of children and young adults affected by the celiac disease, who were not anemic [81]. Lepczyński et al. observed the modulation of gut microbiota and the stimulation of intestinal absorption of minerals through the addition of inulin-type fructans to pig diets [82]. Inulin-enriched supplements have been shown to improve gut immunity and increase mineral absorption, according to Massot-Cladera et al. [83].

Conclusions

Firstly, hot water extraction is still primarily used to extract inulin, but by combining it with other auxiliary extraction methods, the yield can be increased and a more environmentally friendly and economical extraction process can be achieved. Secondly, inulin consists of a polysaccharide polymer made up of multiple fructose connected by β(2 → 1) glycosidic linkages, and it is this structure that gives inulin its unique properties and efficacy. Thirdly, DP, chain length and molecular weight of inulin have significant effect on its properties and therefore its applications in different fields can vary. Therefore, attaching importance to the development of inulin is of great significance to promoting the food health market, improving the dietary structure, enhancing innovations of the food industry, promoting the upgrade of agriculture.

Although inulin appears to be a natural carbohydrate possessing a broad scope of biological activity, it has great potential for research and applications in life sciences, medicine, and food. However, research on inulin still faces several challenges. First, natural plants provide an abundant and affordable source of inulin, meanwhile studies have shown that the development of inulin products has a great market potential and economic significance. However, the applications of inulin in certain areas of food research require further validation of its action mechanisms. Secondly, in the future, it is still necessary to intensify research on the safety of inulin and formulate the number of additives that meet food safety standards, to provide an effective reference for the widespread applications of inulin. Thirdly, with the continuous progresses of science and technologies, it is necessary to use more advanced research methods and techniques to study the structures and properties of inulin in depth to reveal its relationship with functions and applications. Fourthly, the pharmacological effects of inulin or its action mechanisms are not yet fully understood, so it is still necessary to understand and grasp the action mechanisms and side effects of inulin in drugs as well as health care products in an in-depth and comprehensive manner. Fifthly, based on the structural characteristics of inulin, how to give it different functions and activities by changing its structure or adding specific groups to meet different needs in industry and life is also the focus of the current research. Finally, the combined use of inulin and other bioactive substances as well as the exploration of their interactions and synergies to develop more bioactive products will also be a new direction of research on inulin.