Inulin Gels Research Articles

Rheological and Micro-Rheological Properties of Chicory Inulin Gels.

As a soluble fiber, inulin is present in many plants and has many applications in food and non-food products. In this work, we investigated the rheological properties of inulin dispersions at seven concentrations. The linear viscoelastic properties of inulin were determined using a conventional mechanical rheometer. At 25 wt%, inulin exhibited fluid-like viscoelastic liquid behavior. However, when concentrations were ≥27.5 wt%, inulin exhibited gel-like viscoelastic properties. The viscoelastic properties (moduli and viscosities) increased with increasing inulin concentration. The high-frequency linear rheological properties of inulin were also investigated using the modern light scattering technique, diffusion wave spectroscopy (DWS). The diffusion wave spectroscopy (DWS) measurements showed the amplitude of complex moduli (|G*(ω)|) of inulin gels (≥27.5 wt%) to be proportional to ½ power law of the frequency, which suggests inulin gels behave similarly to flexible polymers. The non-linear steady shear experiments demonstrated that inulin exhibited shear-thinning behavior that was well fitted by a power law constitutive model. The trend of the power law exponent from the experiments indicated that the shear-thinning extent for inulin was greater as the inulin concentration increased. The results of this work indicated that the properties of inulin gel can be manipulated by altering its concentration. Therefore, the desired inulin product can be designed accordingly. These results can be used to direct further food and non-food applications, such as wound healing materials for inulin gels.

Thermal and Modern, Non-Thermal Method Induction as a Factor of Modification of Inulin Hydrogel Properties.

The aim of the study was to compare the properties of inulin hydrogels obtained with different methods, e.g., the traditional-thermal method and new, non-thermal methods, used in food production, like ultrasonic, high-pressure homogenization (HPH), and high hydrostatic pressures (HHPs). It was found that each of the compared induction methods allowed for obtaining inulin hydrogels. However, the use of non-thermal induction methods allows for obtaining a gel structure faster than in the case of thermal induction. In addition, hydrogels obtained with new, non-thermal methods differ from gels obtained with thermal treatment. They were characterized by higher stability (from 1.7 percent point-of-stability parameters for HHP 150 MPa to 18.8 for HPH II cycles) and in most cases, by improved microrheological properties-lower solid-liquid balance toward the solid phase, increased elasticity and viscosity indexes, and lowering the flow index. The gels obtained with the new, non-thermal method were also characterized by a more delicate structure, including lower firmness (the differences between thermal and non-thermal inductions were from 0.73 N for HHP at 500 MPa to 2.39 N for HHP at 150 MPa) and spreadability (the differences between thermal and non-thermal inductions were from 7.60 Ns for HHP at 500 MPa to 15.08 Ns for HHP at 150 MPa). The color of ultrasound-induced inulin gels, regarding the HPH and HHP technique, was darker (the differences in the L* parameter between thermal and non-thermal inductions were from 1.92 for HHP at 500 MPa to 4.37 for 10 min ultrasounds) and with a lower a* color parameter (the differences in the a* parameter between thermal and non-thermal inductions were from 0.16 for HHP at 500 MPa to 0.39 for HPH II cycles) and b* color parameter (the differences in the b* parameter between thermal and non-thermal inductions were from 1.69 for 5 min ultrasounds to 2.68 for HPH II cycles). It was also found that among the compared induction methods, the high-pressure technique has the greatest potential for modifying the properties of the created inulin hydrogels. Thanks to its application, depending on the amount of applied pressure, it was possible to obtain gels with very different characteristics, both delicate (i.e., soft and spreadable), using HHP at 150 MPa, and hard, using HHP at 500 MPa, the closest in characteristics to gels induced with the thermal method. This may allow the properties of hydrogels to be matched to the characteristics of the food matrix being created.

Garlic Inulin as a Fat Replacer in Vegetable Fat Incorporated Low-Fat Chicken Sausages.

Inulin is a non-digestible carbohydrate and a prebiotic that can also act as a fat replacer in various foods. This study examined the effect of replacing vegetable oil with garlic inulin on the quality traits of chicken sausages. Water-based inulin gels were prepared using garlic inulin or commercial inulin to imitate fats in chicken sausages. Chicken sausages were prepared separately replacing vegetable oil with water-based inulin gels to reach final inulin percentages of 1, 2, and 3 (w/w). The control was prepared using 3% (w/w) vegetable oil with no inulin. The physicochemical properties and thiobarbituric acid reactive substance (TBARS) value of prepared sausages were analyzed over 28-d frozen storage. Sausages with 2% garlic inulin recorded higher flavour and overall acceptability scores (p<0.05). Ash, moisture, and protein contents of the sausages were increased with increasing levels of inulin while fat content was reduced from 13.67% (control) to 4.47%–4.85% (p<0.05) in 3% inulin-incorporated products. Sausages incorporated with 2% inulin had lower lightness (L*) values than the control (p<0.05). Water holding capacity (WHC) was similar (p>0.05) among the samples. During storage L* value, pH, and WHC decreased while redness (a*) and yellowness (b*) values increased in all the samples. In addition, TBARS values were increased during the storage in all samples within the acceptable limits. In conclusion, garlic inulin can be used successfully as a fat substitute in sausages without altering meat quality parameters.

Effects of Pressure Level and Time Treatment of High Hydrostatic Pressure (HHP) on Inulin Gelation and Properties of Obtained Hydrogels.

The aim of this study was the evaluation of the influence of different HHP levels (150 and 300 MPa) and time treatment (5, 10, 20 min) on the gelation and properties of hydrogels with different inulin concentration (15, 20, 25 g/100 g). High-pressure treatment, in tested ranges, induces inulin gels and allows obtaining gel structures even at a lowest tested inulin content (i.e., 15 g/100 g). Selecting the pressure parameters, it is possible to modify the characteristics of the created hydrogels. The use of higher pressure (i.e., 300 MPa) allows to increase the stability of the hydrogels and change their structure to more compressed, which results in higher yield stress, lower spreadability, harder and more adhesive structure. For example, increasing the inulin gelling induction pressure (concentration 20 g/100 g) from 150 to 300 MPa with a time treatment of 10 min resulted in an increase in yield stress from 38.1 to 711.7 Pa, spreadability force from 0.59 to 4.59 N, firmness from 0.11 to 1.46 N, and adhesiveness from −0.06 to −0.65 N. Extending the time treatment of HHP increases this effect, but mainly when higher pressure and a higher concentration of inulin are being used. For example, extension of time treatment at 300 MPa pressure from 5 to 20 min resulted in an increase in yield stress from 774.8 to 1273.8 Pa, spreadability force from 6.28 to 8.43 N, firmness from 1.87 to 2.98 N, and adhesiveness from −0.94 to −1.27 N. The obtained results indicate the possibility of using HHP to create inulin hydrogels tailored to the characteristics in a specific food product.

Effect of high hydrostatic pressure on formation and rheological properties of inulin gels

The aim of the study was to determine the possibility of using high hydrostatic pressure (HHP) for induction of inulin gels and to compare properties of the obtained gels with gels induced traditionally by thermal or shear force treatment. HHP (500 MPa) induced inulin gelation regardless of the time treatment (5–20 min) and inulin concertation (20–25 g/100 g). Obtained by HHP gels differ from traditional gels, had different microstructure and distribution of primary particles. In consequences HHP gels, comparing with thermally and mechanically induced ones, were less firm and spreadable and were characterized by a higher yield stress and lower L* colour parameter. Those properties may allow using inulin gels for creating new, innovative products, than those made with traditionally induced inulin gels. It was also found that exposure time to HHP was not deteriorating physical properties of inulin gels, what gives opportunity to preserved product with inulin gels by HHP.

Interactions between whey protein and inulin in a model system.

Inulin is a commonly used prebiotic ingredients for functional food formulation. The effect of inulin on the gelation properties of whey protein was investigated using whey protein and inulin (WP/inulin) and polymerized whey protein and inulin (PWP/inulin) mixtures at different levels of protein (4-8%, w/v) and inulin (1-5%, w/v). WP/inulin mixture was prepared by heating protein and inulin together while the latter by heating protein alone and then mixed with inulin. Both mixtures were analyzed for turbidity, zeta potential, particle size, and rheological properties. Dispersions became more opaque with increasing protein but there was no significant difference between the two mixtures. A small shift towards larger size and significantly decreased negative zeta potential with increasing inulin addition (1-5%) were observed for both mixtures. WP/PWP and inulin mixtures exhibited a shear thinning behavior. Transition temperature of whey protein increased with inulin addition. WP/PWP and inulin mixtures were induced into cold-set gels by calcium and the gels were analyzed for hardness. Hardness of WP/PWP and inulin gels increased with the increasing inulin. Results indicated that interactions between whey protein and inulin had impact on the gelation properties of whey protein regardless the way inulin added.

Alteration of the structural properties of inulin gels

In this work, inulin particle gels, prepared with a type of long chain inulin, were examined in terms of their structural properties and mechanical response, depending on the applied shear rates and temperature during gel preparation. The results are interpreted on the basis of a particle gel model, which takes into account the varying gel structure, depending on the sample preparation parameters. X-ray measurements of the inulin powder, used for the experiments, revealed a mostly amorphous powder. The temperature profiles for the sample preparation, chosen from 25 °C to 60 °C with constant stirring at 600 rpm, yielded viscoelastic particle gels with decreasing hardness. By application of high shear rates (7000 rpm) at the same temperature conditions, the gel hardness was increased. Time resolved X-ray scattering experiments during gel formation provided information about the crystallization kinetics and examination of the inulin gels, using static light scattering, confirmed that the final gel particle size depends on the sample preparation temperature. Thus, the results show a high sensitivity of the structural and textural properties of inulin gels to the variation of applied temperature and shearing during sample preparation. Those findings allow the controlled alteration of large scale structures and thus of the textural properties in food systems containing inulin.

Fractals in crystallizing food systems

The present paper reviews and discusses the possible influences of irregular random fractal formation on crystallizing food systems, such as triacylglycerols (fats) and inulin (oligofructoses). In both cases the crystallization process is driven by selective processes. Triacylglycerols consist of three different fatty acids, mostly of different length and saturation degree, inulin of oligofructose molecules of a broad molecular weight distribution. The structure formation, which can be at several stages `fractal’, determines part of the processes in chocolate preparation and in the use of inulin gels, for providing nice mouthfeel during oral processing. The common physics during crystallization is also relevant for using inulin as fat replacer.

The effect of replacing pork fat of inulin on the physicochemical and sensory quality of guinea fowl pate.

Potentially, pâtés could be a functional food and are an important source of proteins, vitamin A, B complex vitamins and iron. Unfortunately, one problem in pâtés is the high level of animal fat, about 30%. Pâté with low-fat guinea fowl meat and animal fat replaced with inulin can result in this product being classified as a pro-health food. The objective of the present study was to determine the effect on pâté with guinea fowl meat of reducing its pork back fat content (about 1/3, 2/3 and 100%) and the adding inulin as a partial fat substitute. The effects on the pâté's chemical and physicochemical composition, as well as on its textural characteristics and sensory properties were analysed. On the day after production, the following took place: chemical analysis: cooking loss, moisture, protein, total fat, total calories, the pH, lipid oxidation were analysed; physical analysis: colour parameters, texture profile analysis and sensory evaluation were analysed. The pâté prepared with inulin gels as fat replacers had a fat content reduced (up to 82%), and decreased (up to 58%) energy value. The fat reduction and addition of inulin gels decreased hardness and chewiness, but the pâté's appearance, taste and odour, as well as overall quality were similar to the control (full-fat samples). The study demonstrated that inulin can be used in guinea fowl pâtés as a total fat replacer and a potential source of prebiotic.

Structure, rheological, textural and thermal properties of potato starch – Inulin gels

This paper presents studies on the structure, rheological, textural and thermal properties of potato starch + inulin gels at widely differentiated overall concentration and proportions of both gel components. The increase of polysaccharides concentration changed viscoelastic properties and firmness of gels, compared to control samples. Noticeable differences were observed at 6% concentration of starch and 25% of inulin. DSC suggested that gelatinization of potato starch with inulin produced the binary gel of the common network, that could resulted from the competition of both components for water (caused by high affinity of these polysaccharides to water molecules), which was a key factor influencing starch gelatinization and affected properties of the obtained gels.

Factors affecting inulin crystallization after its complete dissolution

In this study, we analyzed inulin crystallization during one year after its complete dissolution and an effect of inulin crystal seeds concentration on rheological and textural properties of inulin gels. 20% and 25% solutions of three different inulins, one native and two high performance (crystal and amorphous), were prepared by heating at 100°C for 5min. During one year of storage at 20°C, inulin did not form a gel structure, but only precipitates and a crystal layer on the walls of the containers. Addition of crystal seeds (0.02–2%) caused formation of gel structure. Minimal concentration of the crystal seeds necessary to form a strong inulin gel was 0.4%. Crystallographic structure of inulin powder did not have an influence on the formed gels. The obtained results allow inulin gelation to control which can be crucial in novel foods, the structure of which is based on inulin.

Effect of heating temperature on rheological properties of inulin gels

Effect of heating temperature on rheological properties of inulin gels

Crystallization and melting of inulin crystals. A small angle X-ray scattering approach (SAXS)

Summary — Bulk crystallization of the biopolymer inulin from concentrated solutions results in the same macroscopic and microscopic morphologies as those found for synthetic polymers. Optical and electron microscopy confirm the lamellar nature of the crystals and their arrangement into stacks of lamellar crystals in superstructures like axialites and spherulites. There is evidence for the occurrence of folded chain lamellar crystals. These findings justify the attempt to explore the crystallization and melting of inulin by investigating the morphology of inulin crystals by time-resolved small angle X-ray scattering. The thickness of the lamellar crystals observed by SAXS varies with the degree of supercooling — dynamically or isothermally — as observed for synthetic polymers crystallized from the solution. The complex melting behaviour of polydisperse inulin, crystallized from the concentrated solution, as observed by DSC, and previously desribe by the present authors, can be explained by the occurrence of thin lamellae with lower thermal stability (endotherms I and II) together with thicker lamellae composed of the longer chains with a higher melting temperature (endotherms III and IV), the latter lamellae being able to thicken upon annealing by recrystallization or solid state reorganisation. The broad range of molar masses proper to the samples, the different crystallization conditions (temperature, isothermal and dynamic cooling and melting) account for fractionation and the presence of partially overlapping populations of lamellar stacks with different lc‘s and hence different thermal stabilities. The reported experiments are a basis for the exploration of the semi crystalline nature of inulin gels.

Amorphous and crystal inulin behavior in a water environment

The aim of present study was rheological analysis of gels obtained from different kinds of high performance inulins and analysis of an effect of crystal seeds addition on inulin gel formation. Inulin gels (20%) were produced at different temperatures. Wide-angle X-ray scattering allowed for monitoring the crystallographic changes in used inulins. A light microscopy enabled to register the inulin particles reaction in water during the first seconds. Amorphous inulin forms, in contrast to crystal one, stable crystal structure in water at 20 °C. The presence of crystal seeds is essential to form gel structure at temperatures above 70 °C. These crystal seeds occur naturally as not dissolved inulin particles (at 72 °C) or must be added when the inulin solution is heated at 100 °C. Five per cent of a crystal or amorphous inulin added to a cooled preheated inulin solution allows forming a stable gel structure.

Effect of thermal and mechanical factors on rheological properties of high performance inulin gels and spreads

The aim of this study was analysis of a number of factors affecting the rheological properties of high performance inulin gels and spreads in comparison with commercial products. Inulin gels (20%, 25%, 30%), commercial and inulin model spread (20% canola oil, 20% inulin, 3% emulsifier) were analysed. Inulin particles in water environment absorbed water which caused an increase in viscosity of the inulin suspensions. Different temperatures of preparation, cooling rates and viscosity increase which appeared during the stirring of inulin suspensions did not significantly change the rheological parameters of the final gels in contrast to heating rates ( p ⩽ 0.05). In spite of rigid laboratory conditions high standard deviation for hardness and apparent viscosity showed how difficult the process of an inulin crystallization is to control. Rheological properties of inulin model spread exhibited thixotropic and shear thinning behaviour which made it similar to commercial spread. The applied structure destruction step in the manufacturing process should be applied to make inulin model spread comparable to commercial spreads.

Effect of thermochemical treatment on the structure of inulin and its gelling properties

SummaryThe aim of this study was to investigate rheological properties of inulin gels and the changes in the inulin structure after heating the high polymerised inulin (DP ≥ 23) solutions at different pH. The 20% inulin solutions were heated at pH 3, 5 and 7 at 60 and 80 °C followed by 21 h storage at 5 and 25 °C. Rheological properties evaluation indicated that the increase in the heating time and temperature significantly (P ≤ 0.05) influenced on the inulin structure. Reducing sugars, cryoscopy and HPLC analysis revealed that chemical structure of inulin is stable in neutral and slightly acidic conditions (pH 5). Gelation of the high polymerised inulin solution after heating at pH 7 and 80 °C could be inhibited after dissolving the inulin crystallites which act like seeding crystals. At lower temperatures in which, not all crystallites were dissolved; it was feasible for the solutions to form firm inulin gels.

Physicochemical characterization and stability of inulin gels

The ability of three commercial inulins (Raftilose ®P95, Frutafit IQ®, and Frutafit TEX®) with different chemical composition (oligo-polysaccharides profile) to form gels (at 25 and 50 °C) was evaluated. Raftilose®P95 (rich in mono-disaccharides) did not form gels, Frutafit IQ® (mainly oligosaccharides) gelatinized in the 30–60% w/w concentration range and Frutafit TEX® (mainly long-chain saccharides) in the 20–40% w/w range. Textural and thermal properties of the gels were studied and their stability was evaluated during storage at 4 °C. Frutafit TEX® gels (both fresh and during storage) were harder, more adhesive, and less cohesive than Frutafit IQ® gels (40% w/w). At 40% w/w, Frutafit TEX® gels had a significantly higher amount of freezable water than Frutafit IQ®, and the DSC thermogram line shapes indicated that ice melting was more uniform and occurred at higher temperatures in Frutafit TEX® than in the Frutafit IQ® gels. Ice melting profile was not significantly affected by both gelification temperature and storage time. Frutafit IQ® gels were more stable than Frutafit TEX® gels during storage.

Textural, rheological and microstructural properties of imitation cheese containing inulin

The possibility of using shear-induced inulin gels or heated inulin solutions to replace fat in imitation cheese was investigated. Imitation cheeses with a moisture content of 54 g/100 g were manufactured by replacing 0 (control, 21.7 g fat/100 g cheese), 23% or 63% of the fat with shear-induced inulin gel. Imitation cheeses with 54 g and 56 g moisture per 100 g cheese were also manufactured by replacing 63% of the fat with a heated inulin solution or a shear-induced inulin gel (both 25 g/100 g), respectively. No differences were observed between cheeses manufactured with the heated inulin solution or shear-induced inulin gel. The addition of inulin did not affect the cheese melt. The inulin-containing cheeses at 54 g moisture per 100 g had increased ( P < 0.05) hardness but the 56 g moisture per 100 g had similar hardness to the control. Values of G′ and G″ decreased with increasing temperature but at temperatures >55 °C increased for cheeses containing the higher level of inulin. Electron micrographs showed that inulin addition seemed to reduce the level of honeycomb structures evident in the protein matrix relative to the control. It is concluded that inulin can be used to replace up to 63% of the fat in imitation cheese and that the preferred method of addition is as a heated inulin solution.

Influence of crystallisation conditions on the large deformation rheology of inulin gels

The large-deformation rheology of inulin gels was investigated and interpreted in terms of solubility, crystallisation, and aggregation data. The gels are characterised by a strong overshoot peak in the stress–strain curve, characteristic for (non-plastic) work softening behaviour. More concentrated inulin gels tend to be firmer but are also less plastic. It is hypothesised that inulin molecules depositing during the later stages of the crystallisation/gelation process contribute most to the overshoot peak in the stress–strain curve.

Rheological properties of inulin–waxy maize starch systems

The rheological properties of mixed systems of inulin and waxy maize starch (WMS) were studied, as a model of carbohydrate–carbohydrate interactions in foods. Steady shear and oscillatory rheological properties were analyzed using a strain-controlled rheometer. Steady shear data were satisfactorily fitted to the Carreau model. The data were also fitted to the Herschel–Bulkley model. Concentrated inulin gels presented static and dynamic yield stresses. Phase inversion from a WMS-continuous system to an inulin-continuous system, manifested as a sudden change in rheological properties, was observed in samples with a total polymer concentration ≥30% (w/w, w.b.). In order to validate the oscillatory rheological data, some samples were subjected to stress relaxation experiments and both types of data were compared, showing a satisfactory agreement. The Cox–Merz rule, which relates steady shear and dynamic material functions, was not followed by most of the samples. An extended Cox–Merz rule was applied to the analysis of concentrated inulin gels.