The physicochemical properties of inulin, including its solubility, are influenced by several factors such as its source, chemical composition, functional groups, chain length, and DP [32]. At room temperature, short-chain inulin (low MW and DP values less than 10) is freely miscible in water; however, as the chain length increases, solubility decreases rapidly. Solubility of native inulin, as a function of temperature, generally increases from 6% (at 10°C) to a range of 33–35% (at 90°C). However, when the temperature is increased above a certain limit, solubility increases due to the breaking of intermolecular hydrogen bonding and the formation of crystalline regions [1, 32, 33]. “The solubility of inulin depends on the solvent,” Gupta et al. (2019) [32]. Inulin is slightly soluble or insoluble in alcohols, such as methanol, ethanol, and propanol [1, 32]. However, inulin exhibits distinct physicochemical properties that influence its behavior in different solvent systems [1, 32, 34].

Inulin also exhibits gelation at higher concentrations, forming a gel structure upon shearing that depends on the chain-length distribution and concentration. Additionally, the formation of water-insoluble inulin fragments may contribute to the gel's structural characteristics [33]. Inulin also has a higher concentration, which gives it gelling ability, depending on the normal chicory inulin concentration (> 25%), long-chain inulin concentration (> 15%), or longer-chain inulin. The inulin can also be sheared using a homogenizer/rotor-stator mixer after it has fully dissolved in water or an aqueous solvent. When inulin is sheared in water, it forms a white, creamy gel matrix that can be added to water-containing foods to replace up to 100% of the fat [35].

The gelling property of inulin can be considerably affected by the inulin concentration, the total amount of dry matter, and the shearing conditions (temperature, time, speed, and pressure), as well as the type of shearing device used. Within the pH range 4 to 9, the gelling property of inulin is independent of pH. Inulin exhibits gel-forming properties and can contribute to gel formation at relatively high concentrations [33].

The interaction between the dissolved inulin molecules normally leads to the formation of inulin gels. Additionally, a previous study showed that undissolved microcrystals coexist with gels. The strength of the gels can be enhanced by the interaction of the microcrystals with the solvent and inulin particles, forming a discontinuous structure [31, 34]. In comparison to its lower-molecular-weight counterparts, high-molecular-weight inulin displays significantly superior gelation properties. The low DP also raises the possibility that it will not form a gel [36].

The sweetness and DP of inulin are strongly correlated. Short-chain inulin fractions, otherwise called FOS, are good sugar substitutes in reduced-calorie foods. These have a mild sweetness, approximately 30–35% that of sucrose. Inulin-type fructans and short-chain FOS possess functional properties that make them suitable for use as fat and sugar replacers and texture modifiers in food products [37, 38]. On combining with high-intensity sweeteners such as aspartame and acesulfame, these fractions serve as bulking agents. These enhance mouthfeel and optimize formulations [39–41]. On the other hand, long-chain inulin primarily contributes to gelling and texturizing properties rather than flavor enhancement. It is poorly soluble and has little sweetness [42]. Inulin is particularly suitable for products focused on glycemic control and weight management. It offers about 1.5 kcal/g and encourages prebiotic effects [14, 32, 42, 43]. Short-chain inulin has more monosaccharides and disaccharides, so the physicochemical properties of inulin sweeteners depend mainly on DP: the lower the DP, the sweeter the sweeteners [1]. Inulin is widely used in food processing for its excellent moisture-attracting properties [44]. Inulin lacks a distinct melting point; instead, it undergoes thermal degradation at elevated temperatures (typically above 135–160°C), depending on its DP and moisture content.

Temperature and concentration are the factors that influence the viscosity of the inulin solution. Viscosity increased without forming a gel as concentrations increased from 1% to 10%. Inulin solubility enhances when the temperature exceeds 80°C; as a result, its viscosity also decreases. Lin et al. (2024) [19] found that the viscosity of inulin obtained from artichokes, chicory roots, and asparagus decreased at high temperatures, highlighting its excellent physicochemical properties and potential future applications in the food industry. Moreover, the increased capacity for water binding in long-chain inulin results in higher viscosity at higher concentrations. Fat-mimicking gels can be formed from long-chain inulin by raising the concentration to a sufficient level (above 10–20%) [37].

Being partially hydrolyzable in a very acidic environment via β (2→1) bonding between fructose molecules, inulin can hydrolyze and decompose in high-temperature, solid-acid systems, albeit remaining stable at 100°C. The main factors influencing inulin stability are pH, temperature, dry matter concentration, and processing duration. Although inulin is relatively stable at pH > 4.0, acid-induced hydrolysis of β (2→1) links can occur under acidic conditions (pH < 4.0), particularly at high temperatures and during extended processing durations [45]. Water content is deemed insignificant for inulin stability, even in high-temperature and high-acid environments. The high hygroscopic nature of inulin can bind free water, reduce water activity, and thereby improve food shelf life [40]. Table 2 represents the physicochemical and functional properties of inulin.

There are three major steps in the conventional process for extracting inulin: extraction, purification, and drying [52, 53]. Before the extraction for surface area optimization, inulin-rich materials are cleaned, dried, and mechanically pre-treated (pulped or sliced) [36]. Based on Azwanida et al. (2015) [54], solvent selection is an important factor in extracting bioactive compounds from plant materials, and different solvents such as water, ethanol, methanol, and their mixtures may be considered depending on the extraction objectives. The process was performed using a hot plate with magnetic stirring at 250 rpm for 24 hours at room temperature, after the burdock root powder was mixed with each of the above solvents in a 1:10 active: total solvent mass ratio. The extraction process was performed in a flask immersed in a water bath attached to a reflux apparatus for 60 min in boiling water, as described by Temkov et al. (2015) [55], who used distilled water as the solvent. For the purification process, the solution after extraction was concentrated, and then 5% Ca(OH)₂ at 50–60 ºC for 30 min was added to remove impurities (pectin, protein, and cell wall materials). By this method, the pH of the solution rose from 5–6 to 10–12. The solution was centrifuged at 4,000 rpm for 15 min, and the precipitate was removed. The yellow supernatant was mixed with 10% phosphoric acid (pH 8–9) at 60°C for 2–3 h. The method was repeated twice. In the next step, to remove the colored material, the solution was mixed with activated carbon at 40°C for 30 min. The treated solution was filtered (Whatman No. 1) and dried by rotary evaporation [56, 57].

The extraction process can be influenced by several factors, including temperature, extraction time, pH, and the solid-to-liquid (S/L) ratio [1, 52, 58]. Depending on the plant used and the processing conditions, these parameters should be further optimized [32]. It is known that the solubility of inulin increases significantly with higher temperatures. In contrast to near-neutral pH, inulin hydrolyzes more quickly at acidic pH (pH < 4.0), particularly when combined with high temperatures and extended processing or storage times [45]. As noted in that study, hydrolysis reduces DP and triggers Maillard reactions that can hinder subsequent purification steps [59]. The conventional method was necessary due to the greater use of inulin. This method has now shifted to several non-traditional ones. The current method for extracting inulin has been replaced with many non-traditional approaches.

Inulin and oligofructoses, however, are known to be largely unaffected by the process of hydrolysis or absorption by the upper part of the gastrointestinal tract (GIT). In fact, as mentioned above, they cause fermentation by the gut microflora. On the other hand, a proper prebiotic should possess certain qualities, such as resistance to hydrolysis or absorption in the upper part of the GIT, leading to fermentation by gut microflora and promoting beneficial bacteria present in the colon [71]. Inulin is increasingly added to various foods to stimulate the growth of bifidobacteria in the human gut, as reported in previous research [72, 73]. Inulin is increasingly added to various foods to stimulate the growth of bifidobacteria in the human gut, particularly in dairy products [74].

Inulin has also been used as a prebiotic in low-fat prebiotic desserts and various dairy products. Inulin, used as a prebiotic, reduces both fat and sugar content by 12% without affecting consumer acceptability [74]. Since inulin is fermented in various regions of the large intestine, with short-chain inulin being fermented in the proximal colon compared to long-chain inulin, which is fermented in a relatively distal colonic part, there have been a few nutritional studies that recommend a combination of short- and long-chain inulin for enhanced fermentability or prebiotic activity. A 50:50 combination of short- and long-chain inulin offers several additional advantages for enhancing probiotic activity, including boosting gas reduction while maintaining probiotic properties.

As stated in [72, 75], prebiotics may provide health benefits, including improved mineral bioavailability and potential support for bone health. By enhancing the valorization of intestinal microflora enzymes, such as lactobacilli and bifidobacteria, these prebiotics provide a range of health-related benefits to individuals. A greater percentage of these prebiotics can be utilized to add the desired functionality to foodstuffs [76]. For instance, short-chain prebiotics effectively enhance crispness and browning in a product, as they have properties similar to those of sugars. In contrast, long-chain prebiotics are proposed as substitutes for fats in a product.

The health benefits of minerals depend on the body’s ability to absorb them effectively and efficiently [52]. The prebiotic capability of inulin enhances the bioavailability of minerals such as calcium, magnesium, and iron [40, 77]. Short-chain fatty acids (SCFAs) increase mucosal growth and surface area for the absorption of minerals by promoting colonic fermentation. They also lower luminal pH by producing acidic compounds, thereby improving solubility and facilitating paracellular diffusion [40, 52]. As such, the ion-exchange and calcification reactions, facilitated by the acidic pH, enhance bioavailability and subsequent mineralization.

Inulin and oligo-fructose enhance mineral absorption. The colonic fermentation of inulin yields SCFAs and organic acids, which in turn reduce the pH of the large intestine. Calcium must be ionized before it can be absorbed, whether it is present in food as a free mineral or as a complex with other components. The pH enhances calcium bioavailability. It stimulates calcium absorption by passive diffusion in the small and proximal portions of the large intestine. The ion-exchange mechanism also enables SCFAs to affect calcium absorption [78]. Inulin and oligofructose increase transcellular active calcium transport by modulating the vitamin D receptor and enhancing calbindin D9k. Rising butyrate yield or polyamine formation can also favor mineral incorporation. Cell proliferation and intestinal absorption can also be stimulated by inulin and oligofructose. Among others, the study by Abed et al. (2016) [79] observed that chicory inulin, a soluble fiber, can facilitate calcium absorption, enhance bone mineral density, and mitigate the effects of osteoporosis. Moreover, the production of lactic acid and SCFAs during inulin fermentation can facilitate a decrease in intestinal pH, increased solubility of water-soluble mineral salts, and increased absorption of copper, magnesium, zinc, and calcium ions by the organism. In contrast to common fibrous components, which have high phytic acid concentrations, inulin has been observed to facilitate mineral absorption, particularly calcium ions [80].

Inulin increases the functionality of the GIT, the growth of beneficial bacteria, the prevention of harmful bacteria, the motility of the intestines, the prevention of constipation and diarrhea, and the augmentation of the host’s tolerance. Inulin also supports beneficial gut bacteria in producing SCFAs and other metabolites. These SCFAs and other metabolites enhance the activity of bacterial enzymes and the production of end products [33]. Dose levels play an important role in inulin gastrointestinal tolerance in humans; tolerant levels vary among different individuals. In tolerant humans, excess inulin and FOS can trigger mild to moderately intense gastrointestinal symptoms despite being safe and tolerated products in the human body. The rapid fermentation of non-absorbed fructans in the colon increases gas and osmotic pressure, leading to symptoms such as bloating, flatulence, abdominal pain, and diarrhea [13, 81, 82]. Healthy humans can safely consume up to 40 g of inulin daily, but gastrointestinal symptoms may vary [82, 83].

Diabetics, as well as obese and overweight individuals with health conditions, should not exceed a daily inulin dose of 20–25 g. Not more than 10 g/day for those with peritoneal dialysis [84]. A fermentable fiber supplement, such as inulin, taken at 5–15 g/day helps preserve a normal gut microbiota balance in the elderly. However, high doses can provoke gastrointestinal disturbances in some vulnerable individuals, especially in those with irritable bowel syndrome, ulcerative colitis, or food allergies [13, 82]. Well-tolerated moderate inulin dietary supplements, ranging from 2 to 10 grams daily, are generally harmless in pediatric cases. More at varying levels. While initial inulin consumption may cause constipation or loose bowel movements, a regular inulin dose helps maintain bowel regularity while preserving the normal balance of the gut microbiota. Inulin supplementation was reported to increase fat-free (non-adipose) mass in obese pediatric patients, whereas adiposity and fat mass were not significantly affected [82, 85].

High triglyceride levels can be reduced by consuming inulin. In post-absorptive conditions, inulin and FOS decrease blood levels of very low-density lipoprotein (VLDL) and triglycerides [86]. Inhibiting triglyceride formation, thereby lowering lipogenesis and colonic fermentation of SCFAs, inulin, and oligofructose decreases cholesterol by suppressing triglyceride formation [6]. Acetate is converted to cholesterol in the liver after being taken in by the colon mucosal lining. Enzymes involved in cholesterol and triglyceride synthesis were inhibited by propionates, thereby increasing lipogenesis. Hence, the acetate: propionate ratio determines the triglyceride-lowering activity. Compared to fiber-free diets, 1–5% chicory extract and 5% inulin have been shown to decrease cholesterol, lipids, and bile secretion. Prebiotics may influence gut microbiota and are associated with metabolic health, including lipid metabolism [87].

Inulin has been researched as a dietary strategy to enhance glycemic control. Preclinical studies have reported that they reduce hyperglycemia by reshaping the gut microbiota, increasing SCFA production—mainly propionate—improving insulin sensitivity, and decreasing inflammation [52, 88–91]. Therefore, the consumption of inulin has been studied in very few studies, which suggest its impact on glycemia and insulinemia. Inulin’s zero glycemic index makes it highly desirable for diabetics. Thus, inulin, as well as FOS, has been shown to be useful for stabilizing glycemic response and to have potential effects on lipid metabolism by binding bile salts in the small intestine [92].

Inulin is a mixture of polymers of fructose with a DP, usually enriched in long-chain products. Due to its particulate gel-forming properties when mixed with water, inulin alters the texture and provides a fat-like mouthfeel to meals. Fat replacers may be combined; examples include those based on lipids, proteins, and carbohydrates. Fat replacers can also be used in meal replacements, meat products, sauces, and soups to produce low-fat products with a luscious and creamy mouthfeel and a water-controlled texture [104, 105]. Sausage fat, texture, and appearance can be reduced by adding inulin. Fructan analysis was used to assess the heat- and processing-stability of inulin [106]. Another study has demonstrated that fermented chicken sausages using inulin as a fat substitute remain stable for 45 days when stored at 4°C without loss of physicochemical, microbiological, or sensory properties [107]. Fat substitution and acceptable flavor can be achieved with a combination of 15% inulin in biscuits [108].

Low-fat dairy products benefit from inulin’s improved mouthfeel properties. Long-chain inulin makes low-fat yogurt smoother. Because inulin has a slight sweet or bland flavor and no effect on viscosity, its low concentration does not alter food properties [77]. Inulin modifies the texture of dairy products due to its distinct properties. Inulin modifies the texture and flavor of dairy products. The extent of polymerization determines the properties of inulin. Oligofructose, the short-chain, has a sweet taste that is less soluble compared to the original short-chain fructose. The sweet nature of inulin enhances its mouthfeel. The original inulin has higher viscosity and solubility than the long-chain inulin, according to [109].

Inulin-type fructans are appropriate sugar substitutes. FOS and oligofructose are superior sugar replacers to inulin-type prebiotics of higher MW and longer chains, which are less soluble. These shorter-chain oligomers are much more soluble than sucrose. They behave like glucose syrup or sugar and have a sweetness of 35–55% sucrose. Inulin from dahlia tubers can be extracted with hot water, obtaining an 8–10% sugar that is slightly sweet. Other processing procedures are available for making a high-quality sugar substitute. Through inulin enzymatic hydrolysis, a powder or an oligofructose syrup is produced, containing free sugars. Sucrose FOS produces a good-tasting inulin-like prebiotic. Most of the oligofructose syrups and powders are less sweet than table sugar. Mixing with powerful sweeteners is a way of obtaining the required sweetness. This oligofructose synergizes with powerful sweeteners, therefore making it useful in food. Thus, it enhances the sweetness of powerful sweeteners and suppresses their aftertaste. Inulin and strong sweeteners have been used collectively to replace sugar. It masks the sweetness and the aftertaste of acesulfame-K and aspartame. It is therefore apparent that customers who use FOS or oligofructose are using something more than just sugar. Of course, free sugars contribute to the sweetness of inulin-type prebiotics. Inulin and FOS have attracted interest in the food industry for their potential prebiotic and health-promoting properties [110].

The technical and dietary advantages of inulin make it a suitable choice for use as an essential ingredient in a diet, primarily providing dual benefits: enhanced organoleptic qualities and nutritional attributes [111]. As a fiber constituent, inulin primarily improves taste and texture. In breakfast cereals and bakery items, inulin offers significant improvement as compared to alternative fibers. Supplementing baked products with inulin not only helps retain moisture but also keeps them fresh longer while improving crispiness. Its solubility enables the integration of fiber into aqueous media, including drinks, dairy products, thickened beverages, and table spreads. A study conducted with institutionalized adults who received inulin in thickened beverages found increased fiber intake, improved bowel movements, and a 13% increase in weighted stool frequency [112].

Inulin is a carbohydrate-based fat substitute or dietary fiber that exhibits prebiotic properties, hence making it a helpful addition to food as it gels with water. Lactic acid bacteria in yogurt starter cultures ferment it in the colon and not in the small intestine. This supports the development of beneficial bacteria, enhances calcium and magnesium absorption, supports immune function, and reduces cholesterol and blood lipids. In addition, the fermentation of inulin may produce SCFAs such as acetate, propionate, and butyrate, which colon cells prefer as energy sources. Inulin imparts a fat-like mouthfeel and texture to water-based foods, such as dairy. Adding inulin as a fat substitute did not affect PH (P > 0.05). Fat substitutes did not inhibit the culturing of yogurt starter microorganisms. Storage reduced the PH of yogurt significantly. Higher inulin concentrations reduced color score and appeal. Yogurt’s sensory acceptability was maintained when inulin was added at low levels (1%), but as the inulin level increased, the yogurt’s taste, smell, and overall acceptability decreased [113].

Akın et al. (2007) [114] also showed that the inulin did not affect the sensory properties of prebiotic ice cream. The low-fat ice cream became denser than the control due to reduced fat content and the incorporation of inulin. The reduction of fat content affected the yellowness (b*) of the low-fat ice creams, but the incorporation of inulin did not affect the redness (a*) of low-fat ice creams. The low-fat ice cream containing inulin showed a significant reduction in melting resistance compared to the control ice cream.

The melting profile of inulin-free low-fat ice cream was similar to that of ice cream containing inulin. Inulin-containing samples were much softer than inulin-free low-fat ice cream samples [115]. Inulin had no influence on the taste of probiotic ice cream (P > 0.05). Meanwhile, inulin increased viscosity, the time to first dripping, and the complete melting time, but did not affect taste [114]. Inulin lowered freezing-point depression and modified texture and rheology of ice cream, improving its chewiness, flow consistency, and pseudoplasticity. These quality changes may have been due to competition for water, interaction between inulin and milk protein, or both factors [116]. The addition of 2.5% and 5% inulin to low-fat ice cream enhanced its characteristics, including texture, body, and flavor (P < 0.01). Low-fat ice cream containing 2.5% or 5% inulin could melt more evenly, enhancing its texture. Texture could be one of the factors that gives low-fat ice cream with 2.5% and 5% inulin a better body. As a fat substitute, inulin alters physical properties, including texture, and sensory attributes, including “smoothness,” which is related to “hardness” [117].

In aqueous solutions, inulin produces particle gels with a creamy, fat-like consistency. Depending on the inulin concentration (dry matter content), the thermodynamic characteristics and melting transitions of these inulin gels change [35]. Heat-treated sausages could leverage their heat stability for use as both a fat substitute and a probiotic [103]. As a fat substitute, such as inulin, will help stabilize sausage filling, which would otherwise experience increased water loss during heat treatment, thereby affecting its sensory attributes. Also, inulin can be used to replace fats in foods without altering their palatability. In chicken sausages, adding 3% garlic-containing inulin gels decreased fat content from 13.67% (control) to 4.47–4.85%. Garlic inulin was concluded to be beneficial in enhancing taste and acceptability; thus, it can be applied as a substitute for fat [118].

Textural, rheological, and sensorial attributes of bread are more significant in terms of technology than others. Inulin at 5.7% concentration did not affect the taste of white bread as a fat substitute, as reported in studies. Inulin, with its strong water-binding properties, has great potential to improve bread technology. Inulin acts as a protective agent for proteins, preventing ice crystal recrystallization in dough during freezing. Hydrogen bonding in inulin, along with its hydrophobic interactions with proteins, helps retain gluten. For example, frozen dough with 2.5% long-chain inulin showed a protective effect for gluten proteins compared with bread containing 5% short-chain inulin. Previous inulin has a higher density in gluten. In gluten-free bread dough, long-chain inulin can replace gluten due to its gel-forming properties, potentially enhancing bread technology [119]. Through reduced starch gelatinization and reduced water absorption, inulin could interact with disulfide bridges and CO₂ retention in dough. Another crucial component for controlling staling rate is inulin inoculum, which partially shifts water [120]. Table 3 summarizes the application of inulin in food products.