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Development of gelling properties of inulin by microfluidization
Food Hydrocolloids 24 (2010) 318–324
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Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd
Development of gelling properties of inulin by microfluidization Se´bastien N. Ronkart a, b, *, Michel Paquot b, Claude Deroanne a, Christian Fougnies c, Souhail Besbes d, Christophe S. Blecker a a
University of Lie`ge, Gembloux Agro-Bio Tech, Department of Food Technology, Passage des De´porte´s, 2, B-5030 Gembloux, Belgium University of Lie`ge, Gembloux Agro-Bio Tech, Department of Industrial Biological Chemistry, Passage des De´porte´s, 2, B-5030 Gembloux, Belgium c Cosucra Groupe Warcoing S.A., Rue de la sucrerie, 1, B-7740, Warcoing, Belgium d Unite´ Analyses Alimentaires, Ecole Nationale d’Inge´nieurs de Sfax, Route de Soukra 3038, Sfax, Tunisia b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 June 2009 Accepted 14 October 2009
In this paper, we report the impact of a microfluidic device (MicrofluidizerÒ) on the development of gelling properties of inulin – water systems. Inulin dispersions at a concentration of 2, 7 and 15%, w/w, were subjected to microfluidization treatments at 30 MPa with various numbers of circulations in the apparatus (1, 2 or 5 passes). The high shear stress treatment did not induce a chemical composition change of inulin. However, it allowed an increase of the gel-like behavior of the system as well as the viscosity of the inulin dispersion, transforming a visual aspect of the product similar to milk, to a system similar to yogurt or margarine depending on the concentration and the number of passes in the MicrofluidizerÒ. The viscosity increased with both the number of passes and the inulin concentration. Granulometry as well as optical and electronic microscopy ascertained the reduction of the particle size and the formation of a network composed of agglomerates which interacted with the solution and thus led to textural modifications. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Inulin Microfuidization Dispersion Gelation
1. Introduction Inulin is a dietary fiber chemically composed of a mixture of oligo- and/or polysaccharides constituted of fructose unit chains (linked by b-(2/1)-D-fructosyl-fructose bonds) of various length, terminated generally by a single glucose unit (linked by an a-Dglucopyranosoyl bond) (French, 1993). It is extracted from chicory root and is available as a spray-dried powder with various chemical and physical properties which depend on the process (Ronkart, Deroanne, et al., 2007; Ronkart et al., 2009). Inulin does not release fructose in the gastro intestinal tract and is thus classified as a low calorie food ingredient (Roberfroid & Delzenne, 1998). In addition to its interesting nutritional and health benefit properties, inulin is also used in food formulations for its technofunctional properties such as fat substitute, bulk agent, water retention, etc. (Blecker et al., 2001; O’Brien, Mueller, Scannell, & Arendt, 2003). The texture similar to fat can be obtained by increasing the concentration (Kim, Faqih, & Wang, 2001) and the average degree of polymerization of inulin above a critical value * Corresponding author at: University of Lie`ge, Gembloux Agro-Bio Tech, Department of Food Technology, Passage des De´porte´s, 2, B-5030 Gembloux, Belgium. Tel.: þ32 81 622303; fax: þ32 81 601767. E-mail address: [email protected] (S.N. Ronkart). 0268-005X/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2009.10.009
(He´bette, 2002; He´bette et al., 1998). He´bette (2002) showed that degrees of polymerization under 15 were insufficient to reach a supersaturation level and thus a crystallization of inulin. The formation of small insoluble inulin particles induces a gel-like texture (Kim et al., 2001). Such small particles can be produced by controlling the heating and the cooling of the dissolved inulin in order to induce nucleation and thus small insoluble crystal formation (He´bette, 2002; Lis & Preston, 1998). In such a situation, soluble inulin becomes insoluble and forms a network due to the association of polymer molecules in the polymer solution. Franck and De Leenheer (2005) reported that at a high concentration (>25% for native inulin and >15% for long-chain type inulin), inulin forms a network composed of solid crystalline particles after shearing which confers gel-like texture to it. When inulin is thoroughly mixed with water or another aqueous liquid, using a shearing device such as a rotor-stator mixer (e.g. Ultra-TuraxÒ) or a homogenizer, a white creamy structure is formed which can easily be incorporated in food to replace fat (up to 100%) (Franck, 1993). The resulting inulin – water system imitates fat extremely well, providing a short spreadable texture and a smooth fatty mouth feel (Frippiat & Smits, 1996). Although such a textural property is very important for the use of inulin in formulation (in reduced fat food), the mechanism inducing the gelling properties of inulin is not detailed in the literature, probably for confidential reasons.
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For this reason, in this paper we describe the gelling properties of an inulin dispersion treated in MicrofluidizerÒ, a tool involving transfer of mechanical energy to fluid particles under high pressure. In such an apparatus, the liquid is pumped and split into two microstreams which are impacted or collided against each other in a chamber, called the interaction chamber where shear, turbulence and cavitation forces are generated (Kasaai, Charlet, Paquin, & Arul, 2003; Korstvedt, Nikopoulos, Chandonnet, & Siciliano, 1985). It results in the reduction and control of particle size which affects the technofunctional properties of the product. It allows a modification of the dispersed or suspended material properties such as cell rupture, dispersed particle size reduction leading to nano-particles, emulsion, liposome or de-agglomeration. Microfluidic device applications have received more and more attention in food technology due to the control they give on the microstructure and thus the technofunctional properties of food (Skurtys & Aguilera, 2008). In this study, the impact of high shear stress (induced by the MicrofluidizerÒ) and the concentration of the inulin dispersion on the textural properties of inulin – water systems were investigated. 2. Materials and methods 2.1. Sample preparation and microfluidization of inulin dispersions The inulin sample used was a commercial spray-dried product extracted from chicory roots (FibrulineÒ XL) kindly supplied by Cosucra Groupe Warcoing SA (Warcoing, Belgium). Inulin dispersions (2, 7 and 15%, w/w) were prepared by pouring inulin in distilled water at 20 1 C and kept at this temperature under magnetic stirring for one hour. The inulin dispersions were submitted to one, two or five passes in a MicrofluidizerÒ (Microfluidics, MFIC Corporation) at 30 MPa. Microfluidization being a high shear treatment, it induced a temperature increase of the dispersion so the entire system was cooled with ice which allowed a constant sample temperature of 20 C. The dispersions were then left to stand for one hour prior to characterization. 2.2. Chemical composition of inulin The influence of the microfluidization treatment on the chemical composition of inulin was determined by high performance anion exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD) on a Dionex DX500 chromatographic system. For this purpose, a sample portion of the microfluidized or non-microfluidized dispersion was freeze-dried. Then, a volume of 25 ml of a 0.8 g l1 inulin solution was injected on a Dionex PA100 column at a flow rate of 1 ml min1 as described elsewhere (Ronkart, Blecker, et al., 2007). Each sample was microfluidized in duplicate, and the products were analyzed in triplicate by HPAEC-PAD. A two-way analysis of variance was conducted at a confident level of 95%.
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systems, amplitude sweeps were carried out from 0.01 to 100 Pa at 1 Hz frequency. These measurements showed that G0 and G00 had constant values from 0.1 to 10 Pa. Therefore, frequency sweeps were performed from 0.1 to 10 Hz at 1 Pa amplitude. Each sample was microfluidized in duplicate, and the rheological characterization was realized at least in duplicate. 2.4. Particle size The particle size distribution of the different inulin dispersions was determined by LASER scattering using a Malvern Mastersizer 2000 (Malvern Instruments, Malvern, UK), connected to a Hydro 2000S mixing device (Malvern Instruments) for liquid measurements with distilled water as dispersant. A sufficient amount of inulin dispersion was introduced in the sample cell of the particle size analyzer under moderate stirring. The obscuration value was comprised between 10 and 20%. The refractive index used was 1.53. Measurements were performed at room temperature in triplicate. The average particle size, expressed in mm, refers to the median diameter in volume. 2.5. Optical microscopy Observations were carried out at room temperature using an optical microscope (Nikon Eclipse E400, Kanagawa, Japan) with a 40 objective magnification. A portion of the sample was placed on a glass slide and covered with a coverslip. The software employed for visualization was Lucia (version 4.5) and pictures were taken using a Basler video camera (Vision technologies, Ahrensburg, Germany). 2.6. Scanning electron microscopy observation of freeze-dried inulin dispersions Freeze-dried inulins were dehydrated by successive 5 min immersions in increasing concentrations of ethanol/water (25, 50, 70, 80, 90, 95 and 100% v/v ethanol). The samples were then dried with carbon dioxide at critical point in a Balzers, Bal-Tec Critical Point Dryer 30 chamber (Balzers Union, Balzers, Germany) where substitution of the ethanol by liquid CO2 occurred. The temperature Table 1 Inulin chemical composition of non-microfluidized and microfluidized inulin dispersions at 30 MPa for 5 passes at a concentration of 2 and 15% (w/w). The quantification of glucose, fructose, sucrose, the different DP ranges, DPn and DPw was determined by HPAEC-PAD analysis. Each sample was microfluidized in duplicate, and the products were analyzed in triplicate by HPAEC-PAD. A two-way analysis of variance showed no difference between the samples, as p value > 0.05 for each constituent. Number of passes Inulin concentration (%, w/w) 0
2.3. Rheological properties Rheological measurements were carried out by using a Bohlin CVO 120 High Resolution controlled stress rheometer (Bohlin Instruments, Cirencester, UK) equipped with a water bath. The measuring geometry employed was cone-plate (4 , 40 mm). The samples were analyzed at a controlled temperature of 20 C. The apparent viscosity and the shear stress were recorded as a function of shear rate, ranging from 0.01 to 150 s1 with 60 measurement points acquired in a logarithmic ramp. The experiments were realized in duplicate. To investigate the viscoelastic properties (amplitude and frequency-dependent behavior) of the inulin – water
5
2 Glucose Fructose Sucrose DP 1–10 DP 11–20 DP 21–30 DP 31–40 DP 40–50 DP 51–60 DP > 60 DPn DPw
0.0 0.2 0.2 3.0 23.1 39.9 22.1 9.2 2.4 0.0 20.7 27.5
15
0.0 0.0 0.0 0.1 0.7 0.2 0.3 0.3 0.2 0.0 0.3 0.2
0.1 0.3 0.3 3.4 24.0 40.1 21.5 8.6 2.1 0.0 20.0 27.1
2
0.0 0.1 0.1 0.1 0.8 0.5 0.4 0.4 0.1 0.0 0.3 0.2
0.1 0.3 0.3 3.5 24.4 40.2 21.0 8.5 2.1 0.0 19.8 26.9
15
0.0 0.1 0.1 0.1 0.3 0.9 1.0 0.3 0.2 0.0 0.3 0.2
0.1 0.3 0.3 3.4 24.4 40.2 21.1 8.4 2.1 0.0 19.8 26.9
0.0 0.1 0.1 0.1 0.6 0.4 0.2 0.2 0.1 0.0 0.3 0.2
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(Lagoueyte & Paquin, 1998) or starch (Wang et al., 2008) by using techniques based on high shear treatments like microfluidization or homogenization. For example, Kasaai et al. (2003) ascribed the fragmentation of chitosan by microfluidization process to mechanical action and hydrodynamic parameters of the polymer such as molecular weight and concentration in solution. Although these authors observed chain scission of chitosan after 5 cycles at a pressure of 21 MPa, we did not observe inulin fragmentation in our experimental conditions (up to 5 cycles at a pressure of 30 MPa). However, Kasaai et al. (2003) pointed out by exclusion size chromatography that large macromolecules were preferentially fragmented. They calculated that chain scission of chitosan started at a molecular weight of 258 kDa, which is well above the molecular weight of the inulin used in this study (w4 kDa in average).
3.2. Rheological properties of inulin Fig. 1. Photographic representation of inulin dispersions at a concentration of 15% (w/w). Left side: microfluidized inulin dispersion after two passes at 30 MPa and one hour rest. Right side: non-microfluidized inulin dispersion after one hour rest.
was then progressively increased up to 40 C. After drying, a gold coating was applied by cathodic pulverization using a Baltec Med 20 (Balzers Union, Balzers, Germany). The samples were observed with a MEB Philips XL30 (Philips, Limeil Brevannes, France) at acceleration voltages of 10–25 kV. 3. Results and discussion 3.1. Impact of the microfluidization treatment on the chemical composition of inulin The chemical composition of microfluidized and non-microfluidized inulin dispersions is compared in Table 1. The analysis of variance of data showed that the glucose, fructose, sucrose and the different degrees of polymerization content, as well as the average degree of polymerization in number (DPn) or weight (DPw) were not influenced by the high shear treatments (p-values > 0.05, a ¼ 5%). It means that the chemical integrity of inulins was maintained after the various treatments realized in this study. This fact is important because other works emphasized the degradation of natural polymer such as cellulose (Floury, Desrumaux, Axelos, & Legrand, 2002), chitosan (Kasaai et al., 2003), xanthan gum
All inulin – water systems which were submitted to a microfluidization treatment developed gelling properties, while the untreated systems were liquid whatever the concentration used in this study (2–15%, w/w). Concerning the microfluidized inulin – water systems, the texture depended on the initial concentration and went from yogurt (2 and 7%, w/w) to margarine (15%, w/w). Such a behavior is illustrated in Fig. 1. On the left side of Fig. 1, one can observe that two passes of a 15% (w/w) dispersion in the MicrofluidizerÒ induced a gelation of the product which did not flow even if the beaker was reversed. On the opposite, a non-microfluidized inulin dispersion of the same concentration was completely flowable (texture similar to milk) as illustrated on the right side of Fig. 1. As discussed later in this paper (see microstructure of inulin – water system), such a difference is probably due to the breaking of inulin nuclei. As a consequence, gelation happened more quickly because the smaller particles that were formed reduced the critical inulin concentration required for gelation and for the formation of a porous network which improved the water holding capacity. Prior to the viscoelasticity measurements of the inulin – water systems, the linear viscoelastic region was determined. It represented the range in which the storage modulus (G0 ) and the loss modulus (G00 ) were independent of the stress/strain of the oscillation. As a start point, the amplitude sweep was performed from 0.1 to 100 Pa at a frequency of 1 Hz. This frequency is in accordance to the work of Gonzalez-Toma´s, Coll-Marque´s, and Costell (2008) who
10000 1000
G' / G' ' (Pa )
100 10 1 0.1 0.01 0.001 0.1
1 Frequency (Hz)
10
Fig. 2. Frequency sweeps of inulin – water systems at different concentrations. The inulin concentration were square: 2% (w/w), lozenge: 7% (w/w), triangle: 15% (w/w). The systems were microfluidized for 5 passes at 30 MPa (red symbols) or not microfluidized (black symbols). Storage modulus (G0 ) and loss modulus (G00 ) are represented by closed and opened symbols, respectively. (For the interpretation of the reference to color in this figure legend the reader is referred to the web version of this article).
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a
321
10 0
Shea r stress (Pa )
10
1
0.1
0.01
0.001
b
0.1
1
10 Shear rate (1/s)
100
0.1
1
10 Shear rate (1/s)
100
1000
1000
Visco sity (Pa s)
100 10 1 0.1 0.01 0.001 0.0001 1000
Fig. 3. Flow behavior of inulin – water systems at different concentrations. (a) Shear stress as a function of the shear rate; (b) viscosity as a function of shear rate. The inulin concentration were square: 2% (w/w), lozenge: 7% (w/w), triangle: 15% (w/w). The systems were microfluidized (black symbols) or not microfluidized (red symbols) at 30 MPa after 0 (closed and opened black symbols) and 5 (closed and opened red symbols) passes.
Fig. 4. We observed that the number of passes and the inulin concentration led to an increase of the viscosity of the inulin – water system. The significant increase of this viscosity was probably due to a reduction of the particle size (discussed later) which led to more
2 % (w/w)
0.3
7 % (w/w) 15 % (w/w)
0.25
Viscosity (Pa s)
investigated the viscoelasticity properties of dairy systems formulated with inulin–starch mixes. The linear region range varied with the inulin concentration but in all the samples a stress of 1 Pa was comprised within the linear viscoelastic region and was selected for the frequency sweeps. The results are illustrated in Fig. 2 and showed that at the low frequency values (up to 1 Hz), non-microfluidized inulins (2, 7 and 15%, w/w) as well as microfluidized inulins at a concentration of 2 and 7% (w/w), presented G00 values higher than G0 which characterized a liquid-like system. However, G0 of five passes microfluidized 15% (w/w) inulin is superior to the loss modulus which is characteristic of a gel-like system. These results were in agreement with the observation of the inulin–water systems illustrated in Fig. 1. Except for inulin at 2% (w/w), inulin concentration as well as the microfluidization process increased largely G0 and G00 values. Crossover of G0 and G00 were found in the 0.5–1 Hz region except for microfluidized inulin at 15% (w/w) where G0 was higher than G00 in the investigated frequency sweep (up to 10 Hz). It means that in the frequency zone investigated (0.1–10 Hz), microfluidization of inulin at 15% (w/w) led to a system with properties close to solid rather than liquid material. Flow behavior of inulin – water systems are presented in Fig. 3. For a given shear stress, the inulin concentration as well as the microfluidization treatment induced an increase of the viscosity and shear stress values. In Fig. 3a, one can observe that yield stress increased from 0.1 to 12.7 Pa when the inulin – water systems were microfluidized. Fig. 3b presents the evolution of the viscosity as a function of shear rate. The curves presented pseudoplastic behavior of the inulin – water systems because the viscosity decreased as the shear rate increased. The apparent viscosity at a given shear stress of 100 s1 was determined and presented in
0.2
0.15
0.1
0.05
0 0
1
2
5
Number of passes Fig. 4. Apparent viscosity at a shear rate of 100 s1 of non-microfluidized and microfluidized inulin dispersions at 30 MPa after 1, 2 and 5 passes at a concentration of 2, 7 and 15% (w/w).
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Fig. 5. Optical microscopy photos of non-microfluidized (a,c,e) and microfluidized (b,d,f) inulin dispersions (5 passes at 30 MPa) at a concentration of 2 (a,b), 7 (c,d) and 15% (w/w) (e,f). The scale bar represents 25 mm.
particle interactions and the formation of a network composed of solid particles which held water and inulin solubilized in it. At this point of the study, it is important to emphasize the importance of keeping the temperature of the inulin dispersion constant through the microfluidization process. Indeed, the high shear rate of the process led to an increase of the inulin dispersion temperature if the apparatus was not immersed in ice. It resulted in a decrease of the gel strength of the inulin – water system (data not shown). This fact is probably due to the partial dissolution of particles involved in the inulin – water network responsible of the water retention by the polymer. Our observations were in agreement with those of Glibowski and Wasko (2008) who pointed out that the gel hardness of inulin was lower after preheating the dispersion. 3.3. Microstructure of inulin – water system Fig. 5 illustrates optical microscopy pictures of microfluidized and non-microfluidized inulin dispersions. Microfluidized inulin dispersions showed relatively smaller and more uniform particles compared to the untreated ones. It is interesting to emphasize that
in comparison with non-microfluidized inulin dispersion, the microfluidization treatment eliminated the sandy texture of the dispersion. Kim et al. (2001) ascribed the sandy texture to large inulin particles. These findings were in accordance with our results as large particles were observed on non-microfluidized inulin dispersions whatever the concentration used in this study (Fig. 5a,c,e). So, the microfluidization process reduced the solid inulin particle size which in turn resulted in a smoother texture similar to that of yogurt or margarine depending on the inulin concentration. This sensorial property is important for developing new products for formulations when inulin is used as a fat replacer (Nowak, von Mueffling, Grotheer, Klein, & Watkinson, 2007). We observed that the reduction of the particle size was correlated to the development of the gelling properties of the inulin dispersions. This reinforced the gelation mechanism of inulin proposed by Kim et al. (2001) as well as by Bot, Erle, Vreeker, and Agterof (2004). Indeed, these authors ascribed inulin gel formation through the crowd effect of the particles which entrapped the soluble fraction of the dispersion. This phenomenon is probably amplified by the increase of the water–particle interactions due to the decrease of the particle size (Fig. 6). This was probably due to
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25 2 % (w/w) 7 % (w/w) 20
15 % (w/w)
D(0.5)
15
10
5
0 0
1
2
5
Number of passes Fig. 6. Average particle size (expressed in mm) of non-microfluidized and microfluidized inulin dispersions at 30 MPa after 1, 2 and 5 passes at a concentration of 2, 7 and 15% (w/w).
the increase of the particle specific area which increased the ability of inulin to hold more water. This hypothesis is reinforced by the observation of the decrease of the viscosity of the inulin dispersion when the temperature of the MicrofluidizerÒ was not controlled (without immerging the apparatus in ice) which inevitably reduced the density of particles in the dispersion (as they entered into solution rather than participating in the water retention). Nevertheless, the particle size reduction was not the only factor inducing inulin gelling because at a constant number of passes, the
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particle size increased in regards to the inulin concentration. This augmentation of the particle size was probably due to the formation of aggregates which were constituted of agglomerate inulin particles. In LASER granulometry, the size of an aggregate is assimilated to a spherical particle. It resulted in an augmentation of the measured mean diameter as the amount of inulin present in the dispersion increased. So, the particle size was also influenced by the number of particles in the dispersion. These conclusions are in accordance with the work of Bot et al. (2004) who observed that agglomeration of particles was responsible for the entrapment of the fluid phase in the aggregates. It avoided phase separation (liquid – solid particles) and thus allowed the formation of an inulin gel. So, a minimum inulin concentration was required to develop gelling properties. Additional information about the microstructure of the inulin – water network were gained from scanning electron microscopy after freeze-drying of the treated or untreated dispersion. The resulting electron micrographs are shown in Fig. 7. The microstructure of a microfluidized inulin dispersion consisted of particles interspaced by voids (Fig. 7c,d). It confirmed the network formation and thus the water retention in such a structure. On the opposite, the microstructure of a non-microfluidized inulin dispersion led to the superposition of lamella which was not able to retain the soluble fraction of the dispersion. The results are in accordance with the discussion of other works which ascertained by electron cryomicroscopy observations (but the data were not shown) that gel-like inulin induced by high shear is composed of a threedimensional network of insoluble inulin particles in water (Franck, 1993; Franck & De Leenheer, 2005). These authors also found that these particles were of about 100 nm in size which aggregated to form larger clusters of 1–5 mm in size without a well-defined shape. It resulted in large amounts of water being immobilized in the network, which allowed the stability of the inulin particles gel as a function of time. Our results were in accordance to these finding as a five passes in the MicrofluidizerÒ of a 2, 7 or 15% (w/w) inulin dispersion led to particle size comprised between 0.3 and 3.9 mm.
Fig. 7. Electronic micrograph of (a and b) non-microfluidized and (c,d) microfluidized inulin dispersions at 30 MPa and two passes at a concentration of 15% (w/w).
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4. Conclusions The application of a high shear device on dispersed particles in water induced the modification of their textural properties. In the case of inulin, the development of thickening properties of inulin – water systems was observed when the dispersions at different concentrations were subjected to microfluidization treatments at 30 MPa with various numbers of circulations in the apparatus. Depending on the concentration of the dispersion, it allowed, without a modification of the chemical composition of the polymer, an increase of the viscosity of the inulin – water systems, transforming a texture similar to milk to a texture similar to yogurt or margarine. Such properties were due to a decrease of the particle size and the formation of a network composed of agglomerates interacting with the solution which led to such textural modifications. These results have practical repercussions if the formulation in which inulin is incorporated is submitted to a high shear treatment like homogenization, mixer, etc. because it will lead to textural modifications of the food product. In addition, a given gelling characteristic can be obtained with less inulin if the system is treated by such techniques, which will reduce the cost of the food formulation. Acknowledgments Financial support was provided for this study by the Walloon Region of Belgium (DGTRE) and Cosucra Groupe Warcoing SA. The authors are grateful to Mrs Lynn Doran for technical assistance. References Blecker, C., Chevalier, J.-P., Van Herck, J.-C., Fougnies, C., Deroanne, C., & Paquot, M. (2001). Inulin: its physicochemical properties and technological functionality. Recent Research and Development in Agricultural & Food Chemistry, 5, 125–131. Bot, A., Erle, U., Vreeker, R., & Agterof, W. G. M. (2004). Influence of crystallization conditions on the large deformation rheology of inulin gels. Food Hydrocolloids, 18, 547–556. Floury, J., Desrumaux, A., Axelos, M. A. V., & Legrand, J. (2002). Degradation of methylcellulose during ultra-high pressure homogenization. Food Hydrocolloids, 16, 47–53. Franck, A. (1993). Rafticreming: the new process allowing to turn fat into dietary fibre. In FIE 1992 Conference proceedings (pp. 193–197). Maarssen: Expoconsult Publishers.
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Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd
Development of gelling properties of inulin by microfluidization Se´bastien N. Ronkart a, b, *, Michel Paquot b, Claude Deroanne a, Christian Fougnies c, Souhail Besbes d, Christophe S. Blecker a a
University of Lie`ge, Gembloux Agro-Bio Tech, Department of Food Technology, Passage des De´porte´s, 2, B-5030 Gembloux, Belgium University of Lie`ge, Gembloux Agro-Bio Tech, Department of Industrial Biological Chemistry, Passage des De´porte´s, 2, B-5030 Gembloux, Belgium c Cosucra Groupe Warcoing S.A., Rue de la sucrerie, 1, B-7740, Warcoing, Belgium d Unite´ Analyses Alimentaires, Ecole Nationale d’Inge´nieurs de Sfax, Route de Soukra 3038, Sfax, Tunisia b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 June 2009 Accepted 14 October 2009
In this paper, we report the impact of a microfluidic device (MicrofluidizerÒ) on the development of gelling properties of inulin – water systems. Inulin dispersions at a concentration of 2, 7 and 15%, w/w, were subjected to microfluidization treatments at 30 MPa with various numbers of circulations in the apparatus (1, 2 or 5 passes). The high shear stress treatment did not induce a chemical composition change of inulin. However, it allowed an increase of the gel-like behavior of the system as well as the viscosity of the inulin dispersion, transforming a visual aspect of the product similar to milk, to a system similar to yogurt or margarine depending on the concentration and the number of passes in the MicrofluidizerÒ. The viscosity increased with both the number of passes and the inulin concentration. Granulometry as well as optical and electronic microscopy ascertained the reduction of the particle size and the formation of a network composed of agglomerates which interacted with the solution and thus led to textural modifications. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Inulin Microfuidization Dispersion Gelation
1. Introduction Inulin is a dietary fiber chemically composed of a mixture of oligo- and/or polysaccharides constituted of fructose unit chains (linked by b-(2/1)-D-fructosyl-fructose bonds) of various length, terminated generally by a single glucose unit (linked by an a-Dglucopyranosoyl bond) (French, 1993). It is extracted from chicory root and is available as a spray-dried powder with various chemical and physical properties which depend on the process (Ronkart, Deroanne, et al., 2007; Ronkart et al., 2009). Inulin does not release fructose in the gastro intestinal tract and is thus classified as a low calorie food ingredient (Roberfroid & Delzenne, 1998). In addition to its interesting nutritional and health benefit properties, inulin is also used in food formulations for its technofunctional properties such as fat substitute, bulk agent, water retention, etc. (Blecker et al., 2001; O’Brien, Mueller, Scannell, & Arendt, 2003). The texture similar to fat can be obtained by increasing the concentration (Kim, Faqih, & Wang, 2001) and the average degree of polymerization of inulin above a critical value * Corresponding author at: University of Lie`ge, Gembloux Agro-Bio Tech, Department of Food Technology, Passage des De´porte´s, 2, B-5030 Gembloux, Belgium. Tel.: þ32 81 622303; fax: þ32 81 601767. E-mail address: [email protected] (S.N. Ronkart). 0268-005X/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2009.10.009
(He´bette, 2002; He´bette et al., 1998). He´bette (2002) showed that degrees of polymerization under 15 were insufficient to reach a supersaturation level and thus a crystallization of inulin. The formation of small insoluble inulin particles induces a gel-like texture (Kim et al., 2001). Such small particles can be produced by controlling the heating and the cooling of the dissolved inulin in order to induce nucleation and thus small insoluble crystal formation (He´bette, 2002; Lis & Preston, 1998). In such a situation, soluble inulin becomes insoluble and forms a network due to the association of polymer molecules in the polymer solution. Franck and De Leenheer (2005) reported that at a high concentration (>25% for native inulin and >15% for long-chain type inulin), inulin forms a network composed of solid crystalline particles after shearing which confers gel-like texture to it. When inulin is thoroughly mixed with water or another aqueous liquid, using a shearing device such as a rotor-stator mixer (e.g. Ultra-TuraxÒ) or a homogenizer, a white creamy structure is formed which can easily be incorporated in food to replace fat (up to 100%) (Franck, 1993). The resulting inulin – water system imitates fat extremely well, providing a short spreadable texture and a smooth fatty mouth feel (Frippiat & Smits, 1996). Although such a textural property is very important for the use of inulin in formulation (in reduced fat food), the mechanism inducing the gelling properties of inulin is not detailed in the literature, probably for confidential reasons.
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For this reason, in this paper we describe the gelling properties of an inulin dispersion treated in MicrofluidizerÒ, a tool involving transfer of mechanical energy to fluid particles under high pressure. In such an apparatus, the liquid is pumped and split into two microstreams which are impacted or collided against each other in a chamber, called the interaction chamber where shear, turbulence and cavitation forces are generated (Kasaai, Charlet, Paquin, & Arul, 2003; Korstvedt, Nikopoulos, Chandonnet, & Siciliano, 1985). It results in the reduction and control of particle size which affects the technofunctional properties of the product. It allows a modification of the dispersed or suspended material properties such as cell rupture, dispersed particle size reduction leading to nano-particles, emulsion, liposome or de-agglomeration. Microfluidic device applications have received more and more attention in food technology due to the control they give on the microstructure and thus the technofunctional properties of food (Skurtys & Aguilera, 2008). In this study, the impact of high shear stress (induced by the MicrofluidizerÒ) and the concentration of the inulin dispersion on the textural properties of inulin – water systems were investigated. 2. Materials and methods 2.1. Sample preparation and microfluidization of inulin dispersions The inulin sample used was a commercial spray-dried product extracted from chicory roots (FibrulineÒ XL) kindly supplied by Cosucra Groupe Warcoing SA (Warcoing, Belgium). Inulin dispersions (2, 7 and 15%, w/w) were prepared by pouring inulin in distilled water at 20 1 C and kept at this temperature under magnetic stirring for one hour. The inulin dispersions were submitted to one, two or five passes in a MicrofluidizerÒ (Microfluidics, MFIC Corporation) at 30 MPa. Microfluidization being a high shear treatment, it induced a temperature increase of the dispersion so the entire system was cooled with ice which allowed a constant sample temperature of 20 C. The dispersions were then left to stand for one hour prior to characterization. 2.2. Chemical composition of inulin The influence of the microfluidization treatment on the chemical composition of inulin was determined by high performance anion exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD) on a Dionex DX500 chromatographic system. For this purpose, a sample portion of the microfluidized or non-microfluidized dispersion was freeze-dried. Then, a volume of 25 ml of a 0.8 g l1 inulin solution was injected on a Dionex PA100 column at a flow rate of 1 ml min1 as described elsewhere (Ronkart, Blecker, et al., 2007). Each sample was microfluidized in duplicate, and the products were analyzed in triplicate by HPAEC-PAD. A two-way analysis of variance was conducted at a confident level of 95%.
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systems, amplitude sweeps were carried out from 0.01 to 100 Pa at 1 Hz frequency. These measurements showed that G0 and G00 had constant values from 0.1 to 10 Pa. Therefore, frequency sweeps were performed from 0.1 to 10 Hz at 1 Pa amplitude. Each sample was microfluidized in duplicate, and the rheological characterization was realized at least in duplicate. 2.4. Particle size The particle size distribution of the different inulin dispersions was determined by LASER scattering using a Malvern Mastersizer 2000 (Malvern Instruments, Malvern, UK), connected to a Hydro 2000S mixing device (Malvern Instruments) for liquid measurements with distilled water as dispersant. A sufficient amount of inulin dispersion was introduced in the sample cell of the particle size analyzer under moderate stirring. The obscuration value was comprised between 10 and 20%. The refractive index used was 1.53. Measurements were performed at room temperature in triplicate. The average particle size, expressed in mm, refers to the median diameter in volume. 2.5. Optical microscopy Observations were carried out at room temperature using an optical microscope (Nikon Eclipse E400, Kanagawa, Japan) with a 40 objective magnification. A portion of the sample was placed on a glass slide and covered with a coverslip. The software employed for visualization was Lucia (version 4.5) and pictures were taken using a Basler video camera (Vision technologies, Ahrensburg, Germany). 2.6. Scanning electron microscopy observation of freeze-dried inulin dispersions Freeze-dried inulins were dehydrated by successive 5 min immersions in increasing concentrations of ethanol/water (25, 50, 70, 80, 90, 95 and 100% v/v ethanol). The samples were then dried with carbon dioxide at critical point in a Balzers, Bal-Tec Critical Point Dryer 30 chamber (Balzers Union, Balzers, Germany) where substitution of the ethanol by liquid CO2 occurred. The temperature Table 1 Inulin chemical composition of non-microfluidized and microfluidized inulin dispersions at 30 MPa for 5 passes at a concentration of 2 and 15% (w/w). The quantification of glucose, fructose, sucrose, the different DP ranges, DPn and DPw was determined by HPAEC-PAD analysis. Each sample was microfluidized in duplicate, and the products were analyzed in triplicate by HPAEC-PAD. A two-way analysis of variance showed no difference between the samples, as p value > 0.05 for each constituent. Number of passes Inulin concentration (%, w/w) 0
2.3. Rheological properties Rheological measurements were carried out by using a Bohlin CVO 120 High Resolution controlled stress rheometer (Bohlin Instruments, Cirencester, UK) equipped with a water bath. The measuring geometry employed was cone-plate (4 , 40 mm). The samples were analyzed at a controlled temperature of 20 C. The apparent viscosity and the shear stress were recorded as a function of shear rate, ranging from 0.01 to 150 s1 with 60 measurement points acquired in a logarithmic ramp. The experiments were realized in duplicate. To investigate the viscoelastic properties (amplitude and frequency-dependent behavior) of the inulin – water
5
2 Glucose Fructose Sucrose DP 1–10 DP 11–20 DP 21–30 DP 31–40 DP 40–50 DP 51–60 DP > 60 DPn DPw
0.0 0.2 0.2 3.0 23.1 39.9 22.1 9.2 2.4 0.0 20.7 27.5
15
0.0 0.0 0.0 0.1 0.7 0.2 0.3 0.3 0.2 0.0 0.3 0.2
0.1 0.3 0.3 3.4 24.0 40.1 21.5 8.6 2.1 0.0 20.0 27.1
2
0.0 0.1 0.1 0.1 0.8 0.5 0.4 0.4 0.1 0.0 0.3 0.2
0.1 0.3 0.3 3.5 24.4 40.2 21.0 8.5 2.1 0.0 19.8 26.9
15
0.0 0.1 0.1 0.1 0.3 0.9 1.0 0.3 0.2 0.0 0.3 0.2
0.1 0.3 0.3 3.4 24.4 40.2 21.1 8.4 2.1 0.0 19.8 26.9
0.0 0.1 0.1 0.1 0.6 0.4 0.2 0.2 0.1 0.0 0.3 0.2
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(Lagoueyte & Paquin, 1998) or starch (Wang et al., 2008) by using techniques based on high shear treatments like microfluidization or homogenization. For example, Kasaai et al. (2003) ascribed the fragmentation of chitosan by microfluidization process to mechanical action and hydrodynamic parameters of the polymer such as molecular weight and concentration in solution. Although these authors observed chain scission of chitosan after 5 cycles at a pressure of 21 MPa, we did not observe inulin fragmentation in our experimental conditions (up to 5 cycles at a pressure of 30 MPa). However, Kasaai et al. (2003) pointed out by exclusion size chromatography that large macromolecules were preferentially fragmented. They calculated that chain scission of chitosan started at a molecular weight of 258 kDa, which is well above the molecular weight of the inulin used in this study (w4 kDa in average).
3.2. Rheological properties of inulin Fig. 1. Photographic representation of inulin dispersions at a concentration of 15% (w/w). Left side: microfluidized inulin dispersion after two passes at 30 MPa and one hour rest. Right side: non-microfluidized inulin dispersion after one hour rest.
was then progressively increased up to 40 C. After drying, a gold coating was applied by cathodic pulverization using a Baltec Med 20 (Balzers Union, Balzers, Germany). The samples were observed with a MEB Philips XL30 (Philips, Limeil Brevannes, France) at acceleration voltages of 10–25 kV. 3. Results and discussion 3.1. Impact of the microfluidization treatment on the chemical composition of inulin The chemical composition of microfluidized and non-microfluidized inulin dispersions is compared in Table 1. The analysis of variance of data showed that the glucose, fructose, sucrose and the different degrees of polymerization content, as well as the average degree of polymerization in number (DPn) or weight (DPw) were not influenced by the high shear treatments (p-values > 0.05, a ¼ 5%). It means that the chemical integrity of inulins was maintained after the various treatments realized in this study. This fact is important because other works emphasized the degradation of natural polymer such as cellulose (Floury, Desrumaux, Axelos, & Legrand, 2002), chitosan (Kasaai et al., 2003), xanthan gum
All inulin – water systems which were submitted to a microfluidization treatment developed gelling properties, while the untreated systems were liquid whatever the concentration used in this study (2–15%, w/w). Concerning the microfluidized inulin – water systems, the texture depended on the initial concentration and went from yogurt (2 and 7%, w/w) to margarine (15%, w/w). Such a behavior is illustrated in Fig. 1. On the left side of Fig. 1, one can observe that two passes of a 15% (w/w) dispersion in the MicrofluidizerÒ induced a gelation of the product which did not flow even if the beaker was reversed. On the opposite, a non-microfluidized inulin dispersion of the same concentration was completely flowable (texture similar to milk) as illustrated on the right side of Fig. 1. As discussed later in this paper (see microstructure of inulin – water system), such a difference is probably due to the breaking of inulin nuclei. As a consequence, gelation happened more quickly because the smaller particles that were formed reduced the critical inulin concentration required for gelation and for the formation of a porous network which improved the water holding capacity. Prior to the viscoelasticity measurements of the inulin – water systems, the linear viscoelastic region was determined. It represented the range in which the storage modulus (G0 ) and the loss modulus (G00 ) were independent of the stress/strain of the oscillation. As a start point, the amplitude sweep was performed from 0.1 to 100 Pa at a frequency of 1 Hz. This frequency is in accordance to the work of Gonzalez-Toma´s, Coll-Marque´s, and Costell (2008) who
10000 1000
G' / G' ' (Pa )
100 10 1 0.1 0.01 0.001 0.1
1 Frequency (Hz)
10
Fig. 2. Frequency sweeps of inulin – water systems at different concentrations. The inulin concentration were square: 2% (w/w), lozenge: 7% (w/w), triangle: 15% (w/w). The systems were microfluidized for 5 passes at 30 MPa (red symbols) or not microfluidized (black symbols). Storage modulus (G0 ) and loss modulus (G00 ) are represented by closed and opened symbols, respectively. (For the interpretation of the reference to color in this figure legend the reader is referred to the web version of this article).
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a
321
10 0
Shea r stress (Pa )
10
1
0.1
0.01
0.001
b
0.1
1
10 Shear rate (1/s)
100
0.1
1
10 Shear rate (1/s)
100
1000
1000
Visco sity (Pa s)
100 10 1 0.1 0.01 0.001 0.0001 1000
Fig. 3. Flow behavior of inulin – water systems at different concentrations. (a) Shear stress as a function of the shear rate; (b) viscosity as a function of shear rate. The inulin concentration were square: 2% (w/w), lozenge: 7% (w/w), triangle: 15% (w/w). The systems were microfluidized (black symbols) or not microfluidized (red symbols) at 30 MPa after 0 (closed and opened black symbols) and 5 (closed and opened red symbols) passes.
Fig. 4. We observed that the number of passes and the inulin concentration led to an increase of the viscosity of the inulin – water system. The significant increase of this viscosity was probably due to a reduction of the particle size (discussed later) which led to more
2 % (w/w)
0.3
7 % (w/w) 15 % (w/w)
0.25
Viscosity (Pa s)
investigated the viscoelasticity properties of dairy systems formulated with inulin–starch mixes. The linear region range varied with the inulin concentration but in all the samples a stress of 1 Pa was comprised within the linear viscoelastic region and was selected for the frequency sweeps. The results are illustrated in Fig. 2 and showed that at the low frequency values (up to 1 Hz), non-microfluidized inulins (2, 7 and 15%, w/w) as well as microfluidized inulins at a concentration of 2 and 7% (w/w), presented G00 values higher than G0 which characterized a liquid-like system. However, G0 of five passes microfluidized 15% (w/w) inulin is superior to the loss modulus which is characteristic of a gel-like system. These results were in agreement with the observation of the inulin–water systems illustrated in Fig. 1. Except for inulin at 2% (w/w), inulin concentration as well as the microfluidization process increased largely G0 and G00 values. Crossover of G0 and G00 were found in the 0.5–1 Hz region except for microfluidized inulin at 15% (w/w) where G0 was higher than G00 in the investigated frequency sweep (up to 10 Hz). It means that in the frequency zone investigated (0.1–10 Hz), microfluidization of inulin at 15% (w/w) led to a system with properties close to solid rather than liquid material. Flow behavior of inulin – water systems are presented in Fig. 3. For a given shear stress, the inulin concentration as well as the microfluidization treatment induced an increase of the viscosity and shear stress values. In Fig. 3a, one can observe that yield stress increased from 0.1 to 12.7 Pa when the inulin – water systems were microfluidized. Fig. 3b presents the evolution of the viscosity as a function of shear rate. The curves presented pseudoplastic behavior of the inulin – water systems because the viscosity decreased as the shear rate increased. The apparent viscosity at a given shear stress of 100 s1 was determined and presented in
0.2
0.15
0.1
0.05
0 0
1
2
5
Number of passes Fig. 4. Apparent viscosity at a shear rate of 100 s1 of non-microfluidized and microfluidized inulin dispersions at 30 MPa after 1, 2 and 5 passes at a concentration of 2, 7 and 15% (w/w).
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Fig. 5. Optical microscopy photos of non-microfluidized (a,c,e) and microfluidized (b,d,f) inulin dispersions (5 passes at 30 MPa) at a concentration of 2 (a,b), 7 (c,d) and 15% (w/w) (e,f). The scale bar represents 25 mm.
particle interactions and the formation of a network composed of solid particles which held water and inulin solubilized in it. At this point of the study, it is important to emphasize the importance of keeping the temperature of the inulin dispersion constant through the microfluidization process. Indeed, the high shear rate of the process led to an increase of the inulin dispersion temperature if the apparatus was not immersed in ice. It resulted in a decrease of the gel strength of the inulin – water system (data not shown). This fact is probably due to the partial dissolution of particles involved in the inulin – water network responsible of the water retention by the polymer. Our observations were in agreement with those of Glibowski and Wasko (2008) who pointed out that the gel hardness of inulin was lower after preheating the dispersion. 3.3. Microstructure of inulin – water system Fig. 5 illustrates optical microscopy pictures of microfluidized and non-microfluidized inulin dispersions. Microfluidized inulin dispersions showed relatively smaller and more uniform particles compared to the untreated ones. It is interesting to emphasize that
in comparison with non-microfluidized inulin dispersion, the microfluidization treatment eliminated the sandy texture of the dispersion. Kim et al. (2001) ascribed the sandy texture to large inulin particles. These findings were in accordance with our results as large particles were observed on non-microfluidized inulin dispersions whatever the concentration used in this study (Fig. 5a,c,e). So, the microfluidization process reduced the solid inulin particle size which in turn resulted in a smoother texture similar to that of yogurt or margarine depending on the inulin concentration. This sensorial property is important for developing new products for formulations when inulin is used as a fat replacer (Nowak, von Mueffling, Grotheer, Klein, & Watkinson, 2007). We observed that the reduction of the particle size was correlated to the development of the gelling properties of the inulin dispersions. This reinforced the gelation mechanism of inulin proposed by Kim et al. (2001) as well as by Bot, Erle, Vreeker, and Agterof (2004). Indeed, these authors ascribed inulin gel formation through the crowd effect of the particles which entrapped the soluble fraction of the dispersion. This phenomenon is probably amplified by the increase of the water–particle interactions due to the decrease of the particle size (Fig. 6). This was probably due to
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25 2 % (w/w) 7 % (w/w) 20
15 % (w/w)
D(0.5)
15
10
5
0 0
1
2
5
Number of passes Fig. 6. Average particle size (expressed in mm) of non-microfluidized and microfluidized inulin dispersions at 30 MPa after 1, 2 and 5 passes at a concentration of 2, 7 and 15% (w/w).
the increase of the particle specific area which increased the ability of inulin to hold more water. This hypothesis is reinforced by the observation of the decrease of the viscosity of the inulin dispersion when the temperature of the MicrofluidizerÒ was not controlled (without immerging the apparatus in ice) which inevitably reduced the density of particles in the dispersion (as they entered into solution rather than participating in the water retention). Nevertheless, the particle size reduction was not the only factor inducing inulin gelling because at a constant number of passes, the
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particle size increased in regards to the inulin concentration. This augmentation of the particle size was probably due to the formation of aggregates which were constituted of agglomerate inulin particles. In LASER granulometry, the size of an aggregate is assimilated to a spherical particle. It resulted in an augmentation of the measured mean diameter as the amount of inulin present in the dispersion increased. So, the particle size was also influenced by the number of particles in the dispersion. These conclusions are in accordance with the work of Bot et al. (2004) who observed that agglomeration of particles was responsible for the entrapment of the fluid phase in the aggregates. It avoided phase separation (liquid – solid particles) and thus allowed the formation of an inulin gel. So, a minimum inulin concentration was required to develop gelling properties. Additional information about the microstructure of the inulin – water network were gained from scanning electron microscopy after freeze-drying of the treated or untreated dispersion. The resulting electron micrographs are shown in Fig. 7. The microstructure of a microfluidized inulin dispersion consisted of particles interspaced by voids (Fig. 7c,d). It confirmed the network formation and thus the water retention in such a structure. On the opposite, the microstructure of a non-microfluidized inulin dispersion led to the superposition of lamella which was not able to retain the soluble fraction of the dispersion. The results are in accordance with the discussion of other works which ascertained by electron cryomicroscopy observations (but the data were not shown) that gel-like inulin induced by high shear is composed of a threedimensional network of insoluble inulin particles in water (Franck, 1993; Franck & De Leenheer, 2005). These authors also found that these particles were of about 100 nm in size which aggregated to form larger clusters of 1–5 mm in size without a well-defined shape. It resulted in large amounts of water being immobilized in the network, which allowed the stability of the inulin particles gel as a function of time. Our results were in accordance to these finding as a five passes in the MicrofluidizerÒ of a 2, 7 or 15% (w/w) inulin dispersion led to particle size comprised between 0.3 and 3.9 mm.
Fig. 7. Electronic micrograph of (a and b) non-microfluidized and (c,d) microfluidized inulin dispersions at 30 MPa and two passes at a concentration of 15% (w/w).
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4. Conclusions The application of a high shear device on dispersed particles in water induced the modification of their textural properties. In the case of inulin, the development of thickening properties of inulin – water systems was observed when the dispersions at different concentrations were subjected to microfluidization treatments at 30 MPa with various numbers of circulations in the apparatus. Depending on the concentration of the dispersion, it allowed, without a modification of the chemical composition of the polymer, an increase of the viscosity of the inulin – water systems, transforming a texture similar to milk to a texture similar to yogurt or margarine. Such properties were due to a decrease of the particle size and the formation of a network composed of agglomerates interacting with the solution which led to such textural modifications. These results have practical repercussions if the formulation in which inulin is incorporated is submitted to a high shear treatment like homogenization, mixer, etc. because it will lead to textural modifications of the food product. In addition, a given gelling characteristic can be obtained with less inulin if the system is treated by such techniques, which will reduce the cost of the food formulation. Acknowledgments Financial support was provided for this study by the Walloon Region of Belgium (DGTRE) and Cosucra Groupe Warcoing SA. The authors are grateful to Mrs Lynn Doran for technical assistance. References Blecker, C., Chevalier, J.-P., Van Herck, J.-C., Fougnies, C., Deroanne, C., & Paquot, M. (2001). Inulin: its physicochemical properties and technological functionality. Recent Research and Development in Agricultural & Food Chemistry, 5, 125–131. Bot, A., Erle, U., Vreeker, R., & Agterof, W. G. M. (2004). Influence of crystallization conditions on the large deformation rheology of inulin gels. Food Hydrocolloids, 18, 547–556. Floury, J., Desrumaux, A., Axelos, M. A. V., & Legrand, J. (2002). Degradation of methylcellulose during ultra-high pressure homogenization. Food Hydrocolloids, 16, 47–53. Franck, A. (1993). Rafticreming: the new process allowing to turn fat into dietary fibre. In FIE 1992 Conference proceedings (pp. 193–197). Maarssen: Expoconsult Publishers.
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