Aggregation and rheological behavior of soluble dietary fibers from wheat bran

Accepted Manuscript Aggregation and rheological behavior of soluble dietary fibers from wheat bran

Qian Li, Rui Liu, Tao Wu, Min Zhang PII: DOI: Reference:

S0963-9969(17)30648-8 doi:10.1016/j.foodres.2017.09.064 FRIN 7013

To appear in:

Food Research International

Received date: Revised date: Accepted date:

2 May 2017 10 August 2017 22 September 2017

Please cite this article as: Qian Li, Rui Liu, Tao Wu, Min Zhang , Aggregation and rheological behavior of soluble dietary fibers from wheat bran. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Frin(2017), doi:10.1016/j.foodres.2017.09.064

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ACCEPTED MANUSCRIPT Title: Aggregation and rheological behavior of soluble dietary fibers from wheat bran Authors: Qian Li1, Rui Liu1,2, Tao Wu1, Min Zhang1,2,*

Affiliation: Key Laboratory of Food Nutrition and Safety (Tianjin University of Science & Technology),

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Ministry of Education, Tianjin 300457, China 2

Tianjin Food Safety & Low Carbon Manufacturing Collaborative Innovation Center,

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Tianjin 300457, China

Corresponding Author:

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Min Zhang

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Key Laboratory of Food Nutrition and Safety (Tianjin University of Science & Technology), Ministry of Education, Tianjin 300457, China

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Fax: 86-22-60912343

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Telephone: +86-22-60912343

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E-mail address: [email protected]

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ACCEPTED MANUSCRIPT Abstract The present study assesses the aggregation behavior of wheat bran arabinoxylan-rich soluble dietary fiber (SDF) fractions with diverse molecular weight and substitution in order to provide useful information to prevent the formation of a block network. In the present work, dynamic and

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static light scattering, diffusing wave spectroscopy, small amplitude dynamic rheology, atomic force microscopy, and the water-holding and swelling capacities were evaluated to assess the SDF aggregation behavior induced by intrinsic and extrinsic factors. Furthermore, the rheological behavior was explained by the physically cross-linked or interpenetrating hydrocolloid network

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established during SDF self-aggregation, dependent on its molecular structure. The results indicated that the SDF fractions exhibiting a high molecular weight and a lower substitution

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degree and di-substituted ratio led to more significant aggregation due to the formation of

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disordered tangles coupled with a more solid-like behavior. The obtained information will prove

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useful for the development of more stable and compatible SDF fractions.

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Keywords: Soluble dietary fiber; Wheat bran; Aggregation behavior; Rheological properties Chemical compounds studied in this article

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Arabinoxylans (PubChem CID: 6438923); D-Xylose (PubChem CID: 135191); L-Arabinose (PubChem CID: 439195); Ethanol (PubChem CID: 702); Phosphate-Buffered Saline (PubChem CID: 24978514); Dihydrogen oxide (PubChem CID: 962)

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ACCEPTED MANUSCRIPT 1. Introduction Dietary fiber (DF) has been defined as “the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine, with complete or partial fermentation in the large intestine” (Phillips & Cui, 2011). DFs include polysaccharides,

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oligosaccharides, lignin, and associated plant substances (Anderson et al., 2009) and have been considered as a valuable constituent of health-promoting foods, possessing advantageous nutritional and functional benefits. On the basis of solubility in water, DFs are categorized into soluble dietary fibers (SDFs) or insoluble dietary fibers. In general, SDFs have a high hydration

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capacity and swell to form viscous solutions (Corradini, Lantano, & Cavazza, 2013; Lopez Rubio et al., 2016). SDFs can also adsorb and retain substances such as water, minerals, sugars, and fats,

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among others, within its fibrous matrix, resulting in the use of SDF components (pentosans,

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pectins, gums, and some other viscous polysaccharides associated with plants) as thickening and gelling agents, foam and emulsion stabilizers, and film-forming and fat-mimetic agents (Liu et al.,

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2016). Further, these soluble fibers are widely used in food processing and cooking to modify

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texture and rheology and to influence the colligative properties of food systems, thus improving the marketability of the food product as health promoting or functional foods (Buriti et al., 2014).

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Nevertheless, the nature of SDF aggregation limits their nutraceutical and manufacturing interest (Tran & Rousseau, 2013). Furthermore, aggregation affects the stability, phase behavior, and rheological properties of SDF (Chatsisvili, Amvrosiadis, & Kiosseoglou, 2012; Watrelot, Le Bourvellec, Imberty, & Renard, 2014). According to Kohnke et al. (2008), lignins have a great influence on the self-assembly behavior and the colloidal stability of xylan fractions, which also influences the driving force of xylan accumulation and deposition on cellulose surfaces during the

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ACCEPTED MANUSCRIPT production of cellulose-based materials. The self-aggregation of soy soluble polysaccharides to form large-sized aggregates has been shown to exert an influence on the distribution of proteins in various phases of oil-in-water emulsions, thus varying the degree of oil release and emulsion stability (Durand, Franks, & Hosken, 2003). The macromolecular association and phase

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separation from solutions have been found to influence the solubility, stability and disturb the balance of initial system et al. (Falzone & Robertsonanderson, 2015; Y. Fang et al., 2015; Jacobs, Oxtoby, & Frenkel, 2014; Xu et al., 2015). Aggregation also affects the physiological activity of SDF; indeed, the immune modulatory capacity of beta-glucan has been shown to be partly

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dependent on its aggregation in solution (Haddarah et al., 2014). It is accepted that there is an equilibrium between two types of entangled-chain dynamics models in macromolecular liquids,

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where the chains extensively interpenetrate the domain of other chains and where physical

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entanglement between molecular chains is systematically related to molecular size, structure, and concentration (Graessley, 1983; Konak, Helmstedt, & Bansil, 2000; Virtanen, Holappa,

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Lemmetyinen, & Tenhu, 2002). However, the self-aggregation behavior of SDF has not been

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adequately described and more convincing experimental evidence is required to determine the mechanism of aggregation.

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Although physical techniques such as rheology and light scattering can be used to investigate the physical properties of SDF solutions, these techniques are limited. For instance, rheology is disruptive because the sample undergoes deformation during measurement, and light scattering requires the sample to be filtered to avoid dust contamination. Micro-rheology, a non-invasive light scattering-based technique, is a non-traditional technology that provides valuable insight into the structural rearrangements and mechanical responses of a wide range of materials in

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ACCEPTED MANUSCRIPT inhomogeneous systems under a range of temperatures. Micro-rheology is particularly valuable in characterizing soft materials or complex fluids, such as colloidal suspensions, polymer solutions and gels (Camassola & Dillon, 2007; Guo et al., 2014), in which inertia between particles must be considered and where no external shear must be applied considering that equilibrium thermal

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excitations drive particle motion at all frequencies. Cereal bran, as a waste product of conventional grain processing, represents a low cost source of SDFs. Thus, wheat brans have been noticed for their great potential in the processing of value-added products (Chinma, Ramakrishnan, Ilowefah, Hanis-Syazwani, & Muhammad, 2015;

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Reisinger et al., 2013). The major source of SDF in wheat bran is arabinoxylan, which consists of a β-D-(1→4)-linked xylopyranosyl (xylp) backbone, substituted with α-L-arabinofuranosyl

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(α-L-Araf) groups at O-2 or O-3. In addition to the basic molecular chain composition, SDFs in

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wheat bran have been shown to exhibit different physicochemical properties according to their molecular weight, substitution pattern, and conformation arising from their specific botanical

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origin and isolation treatment (Scheller & Ulvskov, 2010). The various physicochemical

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properties of SDFs induce different aggregation trends, and therefore technological supports are required to control the dispersion and stability of SDF-containing food systems (Franz et al., 2016;

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Shelat et al., 2010). Therefore, appropriate assessment of the distinct aggregation behavior of SDF fractions under the influence of inherent structural characteristics and extrinsic factors is urgently required. In the present work, we investigate the self-aggregation behavior of wheat bran SDF fractions as induced by intrinsic and extrinsic factors, including molecular weight and the degree of substitution, concentration, quiescence, and thermal and shear treatment. In the present work,

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ACCEPTED MANUSCRIPT dynamic (DLS) and static light scattering (SLS), diffusing wave spectroscopy (DWS), small amplitude dynamic rheology, atomic force microscopy (AFM), and the water-holding capacity (WHC) and swelling capacity (SC) were evaluated to assess the SDF aggregation behavior induced by intrinsic and extrinsic factors. The aim of this work was to suggest strategies for

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controlling the wheat bran SDF aggregation behaviors and its environmental tolerance, focusing on the effect of molecular weight and ramification level (indicated by the ratio of arabinose/xylose) of SDF, and to investigate the possible structure-related activity of these soluble fibers. 2. Materials and methods

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2.1. Sample preparation

Wheat bran was purchased from the Public Grain and Oil Food Co., LTD (Henan Province,

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China). The composition of wheat bran included 53.5% w/w of the total dietary fiber and

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contained 24.3% w/w starch, 15.7% w/w protein, 3.86% w/w lipids, 2.64% w/w ash on a dry weight basis. The fermented wheat bran was prepared by inoculating 20 g of sterilized bran

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(moisture content 60%) with pre-cultured Rhizopus oryzae pellets (10%, v/w, a species from

2 °C for 5 days.

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biology laboratory in Tianjin University of Science and Technology) and then incubating at 30 ±

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The SDFs were extracted from wheat bran at 90 °C for 3 h in an aqueous solution. Starch and protein were removed with α-amylase and protease E, respectively. The SDF extracts from natural and fermented wheat brans were further treated by α-amylase (10000 U/mL , Novozymes (China) Biotechnology Co., Ltd., Tianjin, China) at pH=7.0 and 90 °C for 30 min, alkaline protease (2000 U/mL, Novozymes (China) Biotechnology Co., Ltd., Tianjin, China) at pH=8.0 and 55 °C for 30 min, and amyloglucosidase (2000 U/mL, Tianjin Noao Science & Technology Development Co.,

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ACCEPTED MANUSCRIPT Ltd, Tianjin, China) at pH=7.0 and 60 °C for 30 min, to remove starch and protein according to the method as described in the previous work (Comino, Shelat, Collins, Lahnstein, & Gidley, 2013). Then SDF fractions from natural and fermented wheat bran were fractionated via stepwise ethanol precipitation following the experiment process as described in our previous work (Li, Liu,

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Wu, Wang, & Zhang, 2016). In brief, the lyophilized SDF (250 mg) from natural and fermented wheat bran was dissolved in 50 mL of distilled water at room temperature under constant stirring. Aliquots (5 mL) of 95% ethanol were slowly added to SDF solutions maintaining the temperature at 4 °C for 2 h; ethanol addition was repeated until a total ethanol volume of 900 mL had been

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added. The precipitated SDF samples at different ethanol concentrations were recovered by filtration and sequentially washed with 75% ethanol, 95% ethanol, acetone, and distilled water,

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followed by dialysis and lyophilization. Then, four different SDF fractions with different

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molecular weight distributions were prepared with ethanol concentrations of < 40%, 40–60% for the natural wheat bran (termed NI and NII), < 35%, and 35–65% for the fermented wheat bran

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(termed FI and FII). According to the chemical composition analysis, the molecular weight

1

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determination, monosaccharide composition and substitution pattern analysis from HPLC, GC and H NMR profiles (Supplementary Materials), their composition and physicochemical properties

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are reported. Further, the water solubility (WS, %, expressed as the fivefold weight of dry SDF fractions in the supernatant to the original weight of water, ∼5 w/w% of water) were performed as previously described with minor modification (Supplementary Materials) (Chen, Ye, Yin, & Zhang, 2014). And all the aqueous solutions of SDF samples were prepared following the dissolution procedure of polysaccharides in the previous literatures (Guo et al., 2013; Welch, Barker, & Banfield, 1999), to ensure dissolved state in the solutions. Briefly, the weighted

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ACCEPTED MANUSCRIPT lyophilized SDF powder was dissolved in water under incubation on an orbital shaker table at 100 rpm for 1 h and constant stirring for 12 h with a magnetic stir bar, and then stored at 25 °C for 24 h before analysis. It is worth noting that the prepared samples were centrifuged at 10000 rpm for 5 min at 4 °C, and no precipitation appeared after centrifugation, indicating the dissolution of

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samples. 2.2. DLS and SLS analysis

For the DLS and SLS analysis, a stock solution of 1.0 mg mL–1 was prepared by dissolving 10 mg lyophilized SDF powder into 10 mM phosphate buffer at pH 7.0 (10 mL) at 25 °C under

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incubation on an orbital shaker table at 100 rpm for 1 h and constant stirring for 12 h with a magnetic stir bar, and then stored at 25 °C for 24 h before analysis. Then various concentrations of

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samples solutions varying from 0.01 mg mL−1 to 1.0 mg mL−1 were obtained by diluting the stock

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solution accordingly and used in the following experiments. Toluene was used as a reference in the SLS measurements. Both the solvent and the sample were filtered through a 0.22-μm filter

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(Whatman International Ltd., England) into glass cells of 10 mm in diameter and 50 mm in height

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and measured at a temperature of 25 ± 0.02 °C in triplicate. Both static and dynamic measurements were undertaken at 532 nm using a BI-200SM multi-angle

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laser light scattering instrument (Brookhaven Instruments Co., Holtsville, New York, USA) including a precision Goniometer (version 2.0), a photomultiplier, a TurboCorr BI-900AT digital autocorrelator (version 1.2), and a 100 mW He-Ne linearly polarized laser. Values of the average diameter (Φ), size polydispersity index (PDI), and hydrodynamic radius (Rh) of SDF fractions was estimated in their aqueous solutions by Brookhaven DLS software (Roger, Cottet, & Cipelletti, 2016). The time correlation function of the scattering intensity was measured

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ACCEPTED MANUSCRIPT at 90° with vertically polarized light (532 nm). Cumulant analysis and a constrained regularization algorithm (CONTIN) or non-negatively constrained least squares (NNLS) were used to fit the data. The averaged values of the hydrodynamic radius Rh were estimated from the dependence on the translational diffusion coefficient (D), following the Stokes–Einstein relationship (Eq. (1)): (1)

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D = KBT/(6πηRh)

where η is the viscosity of a pure solvent, KB is Boltzmann‟s constant, and T is the absolute temperature.

In the SLS measurements, the angular and concentration dependences of the scattered intensities

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were measured at 20 different angles (30°–130°) to determine the radius of gyration (Rg), structure-sensitive parameter (ρ), and the second virial coefficient (A2). Pure toluene with a known

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Rayleigh ratio was used to calibrate the instrument. In all calculations, a refractive index

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increment of 0.135 mL g–1 and calibration constant of 1.548 × 10–10 were used. The basic light scattering equation (Eq. (2)) is as follows (Debye, 1947): (2)

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Kc/Rθ = 1/Mw+1/3(R2g/Mw)q2+2A2c

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where K is an optical contrast factor, c is the polymer concentration, Rθ is the Rayleigh ratio

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(normalized scattering intensity), and the scattering vector q is defined as (Eq. (3)): q = 4πn0sin(θ/2)/λ0

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where n0 is the refractive index and λ0 is the wavelength in a vacuum. The SLS data was analyzed by the Zimm plot approach (Zimm, 1948), which is constructed by plotting Kc/Rθ versus q2 + Kc; the Rg and A2 can then be extracted. 2.3. Small amplitude rheological measurement The dynamic viscoelastic properties of SDF dispersions at 1%, 3%, and 5% (w/w) were

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ACCEPTED MANUSCRIPT determined from small amplitude oscillatory shear measurements using a HAAKE MARS-III rheometer (Thermo Fisher Scientific Inc., Germany) with a measuring geometry of 20 mm in diameter and gap of 1 mm at a constant temperature of 25 °C. The measurements were performed in the linear viscoelastic regime at a frequency of 0.1–10 Hz indicated by a preliminary sweep test,

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with a strain of 0.1%. All measurements were performed in a nitrogen atmosphere to avoid degradation of the samples. The storage modulus G' and loss modulus G'' were recorded. Although steady shear viscosity was measured in the range of 1–100 s−1 due to sensitivity of the rheometer used, the Newtonian plateau value was estimated from the data obtained as the curves

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were close to linear. 2.4. DWS measurement

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The stability of dispersions prepared at 1%, 3%, and 5% (w/w) SDF was assessed by monitoring

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the optical properties according to the precipitation height at room temperature (25 °C) for 24 h. The solution stability was analyzed using a vertical scan analyzer (Turbiscan AGS, Formulaction,

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l'Union, France) equipped with a detection head that could be move up and down along a

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fiat-bottomed cylindrical cell, which is composed of a pulsed near-IR light source (λ = 880 nm) and two synchronous detectors. The synchronous detectors include transmission and

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backscattering detectors, where the transmission detector receives the light going through the sample (0°), while the backscattering detector receives the light backscattered by the sample (135°). Thus, the transmitted and backscattered light intensity as a function of sample height and time was recorded. A repeating scan program from the bottom to the top along a flat-bottomed cylindrical glass tube (140 mm, height; 16 mm, diameter) at 20 s intervals was used to calculate the stability index of sample dispersions in detail.

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ACCEPTED MANUSCRIPT The Turbiscan stability index (TSI) is a statistical parameter used to estimate the suspension stability (Wisniewska, 2010). The TSI was obtained as the sum of all processes occurring in the studied probe. The TSI values were calculated using (Eq. (4)) with a specific computer program: ∑𝑛 𝑖=1 𝑥𝑖 −𝑥𝐵𝑆

𝑇𝑆𝐼 = √

(4)

𝑛−1

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where xi is the backscattering profile for each minute of measurement, xBS is the mean xi, and n is the number of scans.

Then, the most unstable samples, as determined by the results in stability analysis, were transferred directly to the cuvettes of the DWS equipment Rheolaser Master (Formulaction,

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1'Union, France) and held at 25 °C until micro-rheological measurements were performed (between 30 and 50 min later), then heated to 80 °C at a temperature gradient of 5 °C/min and

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held for 25 min at every 20 °C increase, finally being kept at 80 °C for at least 1 h.

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When a laser beam illuminates a fluid sample, the photons penetrating into the sample are backscattered by particles, droplets, and fibers suspended in the fluid. A video camera was used to

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record the dynamic interference patterns of the backscattered waves, often known as „the speckle

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image.‟ Standard numerical algorithms were used to deduce the statistical parameters of the sample from dynamic speckle images, including the mean-squared displacement as a function of

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time (Chen et al., 2012), which, for these tracer particles, is a direct and non-invasive probe of medium properties.

2.5. AFM characterization Samples were dissolved in deionized water at a concentration of 10–3 mg mL–1. The solution (5 µL) was dropped onto a freshly cleaved mica surface and allowed to dry at room temperature for more than 12 h. The AFM was operated in the tapping-mode using a JSPM-5200 instrument

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ACCEPTED MANUSCRIPT (JEOL Co., Kyoto, Japan) equipped with silicon Nanoprobes SPM tips (NSC-11, MikroMasch). The tapping mode was used to scan the sample, and the topography images were generated with a preset scan area of 5.0 × 5.0 μm at a scanning speed of 333.33 m s–1 in air. Height and phase images were obtained simultaneously in tapping mode at a quoted force constant of 48 N m–1.

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2.6. Physicochemical determination The WHC and SC were performed as previously described with minor modification (Betoret, Betoret, Vidal, & Fito, 2011). Briefly, for WHC, 80 mg of the SDF fraction were added to 5 mL of distilled water to prepare a suspension and stirred for 1 h, left at room temperature for 24 h, and

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centrifuged at 3000 rpm for 10 min. After draining of the supernatant, the residual polysaccharide was weighed. WHC was calculated as follows (Eq. (5)) :

𝑤𝑤𝑒𝑡 𝑆𝐷𝐹 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 −𝑤𝑑𝑟𝑦 𝑆𝐷𝐹 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛

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𝑊𝐻𝐶 =

𝑤𝑑𝑟𝑦 𝑆𝐷𝐹 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛

(5)

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For the SC, 500 mg of dry SDF fractions were added to 5 mL of water in a 10-mL measuring cylinder at 25 °C for 24 h. The volume occupied by the wet SDF fraction was measured and the

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2.7. Statistical analysis

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result was expressed as milliliter of swelling volume per gram of initial dry SDF fraction.

Analyses were performed using Statistical Product and Service Solutions (SPSS, version

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17.0.0). The experiments were conducted in triplicate with data reported as mean or mean ± standard deviation. The results were evaluated by one-way ANOVA, followed by a Tukey post hoc test for statistical analysis. The differences were considered statistically significant at P < 0.05. The correlation analysis was performed with Pearson Correlation Coefficient method, followed by a two-tailed test, and differences were considered significant at P < 0.05, with the significance level indicated as * P < 0.05 and ** P < 0.01.

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ACCEPTED MANUSCRIPT 3. Results and discussion 3.1. Composition analysis and molecular characterization These SDF fractions from natural and fermented wheat bran were used for comparisons of the molecular structure and aggregation behavior. The weight-average (MW) and number-average (Mn)

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molecular weights and polydispersity (Pd) of the SDF fractions are listed in Table 1. Fractions NI, FI, NII, and FII displayed a decrease in weight-average molecular weight of 1850, 1780, 592, and 154 kDa.

According to the chemical composition analysis results (Table 1), fractions NI and NII had large of

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total pentosan contents (92.9% and 94.5%). Similar results were observed in the FI and FII fractions (94.9% and 96.6%) obtained from the fermented wheat bran, indicating that the most

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abundant SDF components in NI, NII, FI, and FII were the non-starch polysaccharide arabinoxylans

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(AXs). All fractions contained small amounts of proteins (1.36%, 0.28%, 1.11%, and 0.16%, respectively) and ferulic acid (95.8, 114, 101, and 154 µg/g, respectively), and therefore the

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impact of proteins and ferulic acid on the structure of SDF fractions was subsequently ignored.

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The monosaccharide composition analysis derived from GC profiles showed that fractions NI, NII, FI and FII were mainly composed of arabinose (26.4–31.5%) and xylose (43.8–64.9%), with

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arabinose/xylose ratio of fractions FI (0.54) and FII (0.72) were higher than those of fractions NI (0.41) and NII (0.60), which could be due to un-substituted xylan being susceptible to attack during fermentation. Additionally, the arabinose/xylose ratios of the fractions NII and FII were found to be higher than those of fractions NI and FI, suggesting a higher degree of substitution. The substituents in the polysaccharide chains may increase the steric hindrance of internal rotation and prevent the

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ACCEPTED MANUSCRIPT physical entanglement between molecular chains (Zhang et al., 2011). Aside from the molecular weight and arabinose/xylose ratio, the substituted pattern was also an important indicator of not only the association behavior of polysaccharides in the SDF fraction but also the physicochemical properties of the SDF fraction, for instance, water binding capacity,

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solution stability and swelling capacity (Sun, Cui, Gu, & Zhang, 2011). Fractions NI, FI, NII, and FII displayed a decrease in the un-substituted xylan chain (U-Xylp) ratio of 67.6%, 66.5%, 61.9%, and 58.7%, respectively, but an increase in the di-substituted xylan (2, 3-Xylp) ratio of 16.8%, 19.0%, 23.3%, 28.2%, respectively. According to the results in Table 1, the WS values of fractions

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NI, FI, NII, and FII were 6.74%, 9.13%, 7.12% and 10.3% (w/w). 3.2. Light scattering behavior

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Table 2 shows the analysis results derived from DLS and SLS scattering curves for dilute (0.01 to

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1.0 mg mL-1) aqueous dispersions of SDF fractions. The intensity autocorrelation functions provided information on the populations and dynamics of the scattering elements (Fig. 1). NI and

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FI fractions (0.2 mg mL-1) with a higher molecular weight and lower substitution degree displayed

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lower attenuation velocity (-148.9 and -200.7 for fitting in slope), which is an indication of the presence of a higher fraction of scattered light coming from scattering particles (larger particles)

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unable to relax over the applied experimental time scale (Raghavendra et al., 2006). The autocorrelation function of NII and FII showed an increased attenuation velocity (-276.3 and -321.4 for fitting in slope) compared to the NI and FI fractions, accompanied by a better correlation and baseline tail. As expected, particle mobility was found to decrease (indicated by prolonged attenuation velocity) with increasing molecular weight for all samples. Moreover, the FII aqueous solution exhibited the highest particle mobility at the experimental conditions, while

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ACCEPTED MANUSCRIPT fraction NI displayed the lowest. The slow motions may have arisen from clusters or heterogeneities of SDF molecular aggregates, which are more obvious in higher molecular weight fractions. Considering the molecular characteristics, the degree of substitution or di-substitution ratio may also be an important indicator describing the association behavior of polysaccharides in

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SDF fractions (Bosmans et al., 2014). These results suggest that there is varying particle mobility among the SDF microspheres due to either dynamic or distribution (in)homogeneity (Wang, Raddatz, & Chen, 2013).

The f (diameter) curves (Fig. 1) for the NI and FI in solution show larger particles (indicated by

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higher Φ) and relatively broad distributions of particles (indicated by higher PDI), whereas those of NII and FII show reduced size and narrower distributions. Normally, the column diagram and the

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curve represent the relative and cumulative scattering intensities of polymers, affected by the

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molecular weight and ratio of components (individuals or aggregates) (Warrand et al., 2005). A scattering intensity of particles with a diameter of 50–500 nm was observed in NI and FI rather

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than in NII and FII, indicating that larger particles are present in NI and FI solutions, even at very

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dilute concentrations (Adams, Kroon, Williamson, & Morris, 2003). This was confirmed by the higher average diameter value of NI and FI (154 nm and 136 nm) compared to NII and FII (95.4 nm

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and 76.5 nm). Interestingly, the particle size distribution became narrower, accompanied by a decrease in molecular weight and an increase in branching degree. This was consistent with the observation in the other reports (Graessley, 1983). Small change was observed in the analysis results between 1 and 4 days, and all the samples were tested within 1 day with three parallel experiments to prevent any solvent induced changes in polymer conformation and reduce the experimental error.

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ACCEPTED MANUSCRIPT In order to discuss the changes of the apparent hydrodynamic radius in the SDF system, the Rh values were calculated from translational diffusion coefficients (D) at different concentrations of samples and a scattering angle of θ = 90°. The results are given in Fig. S4 in Supplementary Materials. The concentration dependence can be described by the following equation (5): 𝑅ℎ𝑎 = 𝑅ℎ0 + 𝐾𝑐

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(5)

where Rha is apparent hydrodynamic radius, Rh0 refers to the translational, self-hydrodynamic radius. The good linear regressions (R2 > 0.984) were observed after fitting the linear regression equation of the Rh (the interception value Rh0 labeled as Rh in Table 2) vs concentration (c) of SDF

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solutions. The Rh values of NI, NII, FI and FII were obtained as 74.5 nm, 35.7 nm, 20.3 nm and 12.3 nm. These data displayed the similar trend with Φ, which were increased with the reduced

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molecular weight and increased steric hindrance due to the presence of side chains.

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To avoid aggregation, dilute solutions of SDF fractions were prepared to be used for DLS and SLS measurements. Fig. S4 shows the Rh distributions of SDF fractions in phosphate buffer

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solution with concentrations from 0.01 to 1.0 mg mL-1 at 25 °C (scattering angle θ = 90°). Only

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one peak appeared in the dilute solution with concentration lower than 1.0 mg mL−1 for all the SDF samples. The Rh curves at concentrations equal to and lower than 0.1 mg mL−1 were

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symmetrical and almost completely overlapped with each other, especially for FII solutions, indicating that only isolated molecules chains (individuals of SDF samples) existed in the solution (Yan Fang et al., 2015). Subsequently, the cleanliness of the extremely dilute solution with concentration lower than or equal to 0.1 mg mL−1, was tested by the time-dependent of Rh distribution at the angle of 90° for 30 min. The results showed that no difference was observed. Therefore, the extremely dilute solutions (with concentration of 0.09, 0.07, 0.05, 0.03, and 0.01

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ACCEPTED MANUSCRIPT mg mL−1) were prepared to yield a Zimm plot with SLS analysis, as shown in Fig. S5 in Supplementary Materials. Then, the parameters of Mw, Rg, A2, critical overlap concentration (c*) and structure-sensitive parameter (ρ) of the SDF samples were obtained and summarized in Table 2.

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The parameter ρ is defined as the ratio of the radius of gyration Rg obtained from SLS to the hydrodynamic radius Rh obtained from DLS (Kajiwara & Burchard, 1984). The ρ values for some molecular architecture could be a good test as to whether the system conformation matches the expected experimental behavior. The ρ values for the individuals of SDF samples were estimated

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to be 1.1-1.8, indicating the random coil conformation of SDF fractions in phosphate buffer solution at 25 °C (Andrewartha, Phillips, & Stone, 1979; Morris, Adams, & Harding, 2014). The

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lower ρ value of NI and FI (1.12 and 1.30) compared to NII and FII (1.57 and 1.73) indicated that the conformations of SDFs with higher molecular weight (indicated by substitution degree) seem

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to be more compact. From the Mw and Rg, we calculated the c* (c*=3Mw/(4π𝑅g3 NA )) (Ganesan et

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al., 2013) to be more than 0.95×10-3 g mL−1. And the positive A2 values indicate good solvent

CE

quality for SDF samples, indicating that no aggregates were detected in these the extremely dilute solutions (Guo et al., 2013). These results supported that it was proper to use the extremely dilute

AC

solutions with the concentration less than 0.1 mg mL−1 (less than the minimum of c*) in the SLS analysis, which could yield relative trustable data for obtaining characterization of these SDF fractions. Compared with the values of A2 for NII and FII, the reduced A2 value also indicated a relatively compact conformation in NI and FI, as has been suggested in a previous study, which could blunt the interaction between polysaccharide molecules and other molecules (Cyran, Izydorczyk, & MacGregor, 2002; Xu, Xue, Chang, Chen, & Wang, 2016). Simultaneously, the

17

ACCEPTED MANUSCRIPT excessive compact conformation due to the insufficient structural stretch of the SDF molecular chains could lead to incomplete hydration of SDF fractions and thus result in reduced stability and adverse rheological properties during processing. 3.3. Stability and rheological properties

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The values of the storage (G') and loss modulus (G'') increased with frequency for 1%, 3%, and 5% (w/w) polymer concentration (Fig. 2). The micro-scale differences of interaction between the molecular chains were evidenced by a shift to higher G'' of fractions NI and FI compared to fractions NII and FII at higher frequency, but no such shift in G' in the small amplitude dynamic

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rheology profile was observed. The angular frequency at the shift point decreased to lower values (4.64, 2.15, and 1.47 Hz) with increasing polymer concentration since an increase in concentration

MA

decreases the kinetic motion of the molecule chains and thus promotes entanglement of the chains,

ED

leading to an increase in G' (Ali, Rihouey, Larreta-Garde, Le, & Picton, 2013). The mechanical spectra clearly show the different small amplitude dynamic viscoelastic properties of these

PT

SDF-aqueous solution systems. For a more in-depth understanding, the viscoelastic properties

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were supposed to correlate with aggregation behavior between molecular chains of SDF. Compared with fractions NII and FII, fractions NI and FI, which have relatively long chains and

AC

low branching degrees, had stronger chain flexibility and longer collision times, and tended to form disordered tangles, potentially blunting the interaction between the SDF fractions and water molecules; this was confirmed by their light scattering behavior. Taking the structure chain flexibility and collision times into consideration, the higher G'' but lower G' of fractions NI and FI induced by the higher frequency could be understandable (Wang, Bai, Zhang, Fang, & Wang, 2016). Generally, the disordered tangles led to a more significant variation in modulus with

18

ACCEPTED MANUSCRIPT increasing concentration and frequency. However, dynamic viscosity (η*) and steady state viscosity (η) were closely related or almost overlapped for fractions NI and FI within the testing region, when the sample concentrations reached 5%. Unlikely, the NII and FII fractions still exhibited a significantly distinct high-shear Newtonian plateau value. According to a previous

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report (Shelat, Vilaplana, Nicholson, Gidley, & Gilbert, 2011), a η* and η overlap indicates a greater physical entanglement in the water-soluble polysaccharides in aqueous solutions. Thus, this also confirms the different interpenetrating behavior in NII and FII aqueous solutions from the disordered tangles present in the NI and FI aqueous solutions.

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A useful flow model, the Cross model (Eq. (6)) (Rincón, Muñoz, Ramírez, Galán, & Alfaro, 2014), was used to obtain the flow characteristics of SDF solutions in this case, adequately describing the

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flow properties of biopolymer solutions in semi-dilute concentrations. 𝜂 −𝜂

0 ∞ Cross model: 𝜂 = 𝜂∞ + 1+(𝜏× 𝛾)𝑚

(6)

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Where η, η0, and η∞ are the shear, zero shear, and infinite shear viscosity (Pa s), respectively; τ is

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Cross relaxation time (s), γ is the shear rate (1/s), and m is the Cross rate index (dimensionless).

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The steady apparent viscosity exhibited both concentration and molecular weight dependence in the SDF fractions. η0 and τ increased from 0.01 to 16.57 Pa·s and from 0.74 to 20.63 s for all SDF

AC

fractions as concentration increased from 1% (w/w) to 5% (w/w), especially for high molecular weight fractions NI and FI (Table 3). The increased values of η0 indicate increases in the zero shear viscosity. The increased values of τ indicate the corresponding increase in the time required to relax the stresses imposed on the systems as SDF concentration or molecular weight increased. The rate index m, is a measure of the dependence degree of viscosity on shear rate in the shear thinning region (Nwokocha & Williams, 2014), were in the range of 0.03-0.93. The values of m

19

ACCEPTED MANUSCRIPT for NI and FI solutions were less than 0.20, but those of NII and FII solutions were higher than 0.60, notably 0.93 for FII solutions at 1% (w/w). The decreased values of m indicate the reduced dependence degree of viscosity on shear rate with the increasing concentration and molecular weight. To our best known, the results shown by Table 3 could be explained in terms of the degree

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of chain entanglements; at high concentration or molecular weight, there is more restriction of movement of the individual chains as a result of the corresponding increase in entanglement, which results in an increase in time to replace the entanglements disrupted by the imposed deformation (Graessley, 1974). As mentioned above, the reduced substitution could also limit

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particle mobility among the SDF microsphere, therefore increasing entanglement in the molecular chain.

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The TSI curves of all SDF solutions at 25 °C showed a significantly increasing trend in a time,

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concentration (1%, 3%, and 5%, w/w), and molecular weight dependent manner (Fig. 3). High TSI values usually indicate a low stability, which can be attributed to an increasing amount of particles

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sedimenting in the vial (Lv et al., 2016). Higher concentrations or a higher molecular weight

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result in increased chain entanglement, which restricts the diffusion of the individual chains and increases the tendency of precipitation; as a result, the stability of the solution is relatively low.

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After prior checking for time stability at 25 °C, a 5% (w/w) SDF solution (a relatively unstable mixture as the most representative one for highlighting key differences among samples) was transferred directly to the DWS cuvette to undergo increasing temperature stability testing (Fig. S1 in Supplementary Materials). Micro-rheology techniques can characterize molecular level responses of the external environment by using passively diffusing or actively driven micro-scale probes (beads) to sense network dynamics (Falzone & Robertson-Anderson, 2015). The

20

ACCEPTED MANUSCRIPT logarithmic plots of mean square displacement (MSD) against the decorrelation time show a decrease in curve slope followed by a shift from linear behavior to non-linear behavior with increasing temperature and preservation time (Fig. S1 in Supplementary Materials). These results can be ascribed to the discrepancies in motion and local deformation of molecular chains, and are

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directly correlated to the viscoelastic properties (Zhang et al., 2015). Slight increases in the macroscopic viscosity index (MVI) and elasticity index (EI), followed by a significant drop, corresponded to a reverse tendency in solid liquid balance (SLB) with increasing temperature from 60 °C to 80 °C and transient thermal insulation at 80 °C (Fig. 3). However, a more obvious

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increasing trend in MVI and EI corresponded to a decrease in SLB during long-term heating. On the basis of these findings, temperature-induced dilation of the molecular chain is likely

MA

responsible for the slight increases in MVI and EI and the decrease in SLB at intermediate

ED

temperatures, where extension of the chain will produce a transient network or drag effect on molecular diffusion through an increase in the amount of chain friction (Lopez-Franco,

PT

Cervantes-Montano, Martinez-Robinson, Lizardi-Mendoza, & Robles-Ozuna, 2013). However,

CE

the extended chain will have a faster relaxation as the temperature rises due to the reinforced Brownian motion induced by temperature. Furthermore, during thermal insulation at relatively

AC

higher temperatures, chains that are still partly entangled are redistributed and begin to self-aggregate. These more confined entanglements of chains at a larger scale cannot relax as quickly, resulting in an enhancement of MVI and EI and a decrease in SLB. These results may be ascribed to the distinct diffusion coefficient of molecular chains during the various thermally induced coupling stages in polysaccharide aqueous solutions (Razavi, Cui, Guo, & Ding, 2014). Indeed, thermally induced differences in chain motion corresponding to the coupling of gelation

21

ACCEPTED MANUSCRIPT and phase separation of water-soluble polysaccharides in aqueous solutions has been previously observed (Fairclough et al., 2012). The different MVI, EI, and SLB features in the temperature program were observed in SDF fractions with various structures. The higher molecular weight and lower chain branching level

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(substitution or di-substitution degree) of NI and FI can explain why these solutions exhibit more liquid dynamics (indicated by a higher SLB) at intermediate temperatures and more solid dynamics at higher temperatures (indicated by a lower SLB) (Meissner & Einfeldt, 2004; Monteiro, Rebelo, Silva, & Lopes-da-Silva, 2013). The more compact intrinsic network formed

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by NI and FI molecule chains are not easily forced apart (limiting dilation) and hardly relax at intermediate temperatures, which was attributed to lower chain motions and lower steric

MA

hindrance (Fishman et al., 2015). Furthermore, at higher temperatures, the molecular chain rearrangement may lead to disordered tangles between the larger particles, based on a far longer

ED

collision time than that of the interpenetrating behavior (τc >> τp) between adjacent molecular

PT

chains (Ledvinkova & Kosek, 2013). However, as the molecular chains become shorter and steric

CE

hindrance increases due to the decreased molecular weight and increased branching level (represented by NII and FII), the effect of the intermediate temperature on entanglement is

AC

sufficient to lead to more extended molecular chains and a narrower molecular chain size distribution. These segments display a dominant tendency of interpenetrating behavior between adjacent molecular chains, resulting from the reduced τc close to or slightly less than τp. 3.4. Correlation of the physicochemical parameters of SDF fractions with the solution behaviors The correlation is one of the most common and most useful statistics to describe the strength and

22

ACCEPTED MANUSCRIPT direction of linear relationships between pairs of variables (Eckhardt, 1984). Here the correlation analyses were analyzed by taking into account the physicochemical properties of the SDF molecules in order to evaluate the effects of intermolecular aggregation to their solution behaviors. The first intention was to determine how these parameters correlate with each other upon the

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different molecular weight, substitution degree and extensibility of molecular chain. The coefficients of correlation (|r| ≥ 0.60) of all the parameters are shown in Table 4. The ρ was linearly correlated with both the Mw, and Ara/xyl of the SDF fractions, as supported by the respective correlation coefficients of -0.981 and 0.943. This result confirmed that the reduced Mw

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(molecular weight) and increased Ara/xyl (substitution degree) of the SDF molecules offered a more extended molecular chains of the SDF fractions (represented by N II and FII fractions), as

MA

mentioned above.

The η0 and τ of the 5% (w/w) SDF fractions among the shear rheology parameters significantly

ED

correlated linearly with Mw, Ara/xyl and ρ of the SDFs molecules. These results emphasized that

PT

both the molecular weight, substitution and conformational compactness (self-aggregation), which

CE

has been reported to be related to molecular steric hindrance and chain flexibility, influenced the rheological behaviors of the SDF fractions (Egorov, Milchev, Virnau, & Binder, 2016; Price,

AC

Harirchian-Saei, & Moffitt, 2011). Moreover, both parameters showed a significant negative correlation with the Ara/xyl and ρ of the SDF fractions. Therefore, a lower steric hindrance and less extended molecular chains could increase the steady apparent viscosity, which may be detrimental for the high scale processing of SDF products. The diffusing wave spectroscopy parameters TSI of the 5% (w/w) SDF at 25 °C and 24 h, EI, MVI and SLB fractions of the 5% (w/w) SDF at 80 °C and 3600 s showed significant linear correlations

23

ACCEPTED MANUSCRIPT with the Mw, Ara/xyl and ρ of the SDFs. This result indicated that the rheological stability of the SDF may depend on the self-aggregation, which was promoted by the increased molecular weight, reduced substitution and limited by the restricted extensibility of molecular chain (Egorov et al., 2016; Wei et al., 2016). In addition, the TSI, MVI and SLB presented significant correlations with

SC RI PT

most of the SDF's properties or measurements of the shear rheology. However, the EI value only displayed significant correlations with the structural parameters and chain extensibility. The results corroborated with the higher G' value observed by small amplitude dynamic rheology but lower EI value observed by DWS measurement for the NII and FII fractions. To the best of our

NU

knowledge, on the basis of the model of tangled molecular chains, the different molecular morphology and dynamics (indicated by different EI) could be explained by their collision and

MA

interpenetrating behavior of the molecules (Ledvinkova et al., 2013).

ED

These analyses validated that the self-aggregation of the SDF's network played a key role in the rheological behaviors of the SDF solutions. However, higher molecular size and a limited steric

PT

hindrance in the SDF network resulted in large-size SDF aggregates that displayed less mobility

network.

CE

of the molecules and required high energy for processing owing to the absence of hydrated SDF

AC

3.5. AFM characterization

The AFM profiles presented here (Fig. 4, measuring the mean diameter and heights of the particles) provide evidence of the existence of the distinct aggregation (or entanglement) behavior of SDF fractions in extremely dilute aqueous solutions (1 µg mL–1). As determined from the analysis of AFM images, NI and FI particles showed a distribution of elongated shapes and irregular spherical clusters, with a mean diameter and height of approximately 28.5 nm and 130

24

ACCEPTED MANUSCRIPT nm, respectively, for NI, and 16.8 nm and 89.9 nm, respectively, for FI. NII and FII particles were more homogeneous and well disassociated, with a mean diameter of 4.77 nm and 2.18 nm, respectively, and a mean height of 55.4 nm and 24.8 nm, respectively. However, the height of a single polysaccharide chain is approximately 0.1–1 nm (Shahbuddin, Bullock, MacNeil, &

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Rimmer, 2014), and there have been suggestions that arabinoxylans are worm-like chains in solution (Nawrocka, Szymanska-Chargot, Mis, Wilczewska, & Markiewicz, 2016). The data in this study suggest that these SDF fractions should be considered as high molecular weight entangled chains folded into globular clusters due to their strong intermolecular or intramolecular

NU

interactions. These SDF fractions showed a reduction in total chain length with decreasing molecular weight as observed by AFM. Such result is consistent with a progressive reduction in

MA

the size of the average chain length with a decrease in molecular weight after xylanase treatment

ED

(Nawrocka et al., 2016). The observation of this aggregation behavior of SDF fractions has important implications for the understanding of the molecular interaction mechanisms between

PT

SDFs, where variability in internal molecular structural features such as molecular weight,

CE

branching degree, and substitution pattern should be considered (Franz et al., 2016). An overall decrease in the aggregation (or entanglement) of these SDFs with a decrease in

AC

molecular weight and an increase in the degree of substitution (lower proportion of un-substituted xylose residues and higher proportion of doubly substituted xylose) were observed, as indicated by the relatively disassociated distribution of particles in NII and FII (Fig. 4). It is possible that the aggregation (or entanglement) of these SDFs are related to the stiffness of the arabinoxylans molecules. Previous studies have shown that hemicelluloses of low molecular weight and with high steric hindrance due to an increased number of side chains were more stiff and sufficient to

25

ACCEPTED MANUSCRIPT prevent intermolecular aggregation of xylose residues (Kohnke et al., 2008; Lazaridou, Serafeimidou, Biliaderis, Moschakis, & Tzanetakis, 2014). 3.6. Properties of hydration interaction The different aggregation behaviors (disordered or interpenetrating) exert an influence in the

SC RI PT

stability and rheological properties of SDF in solution, as well as on the physicochemical properties. The WHC and SC of the SDF fractions were considered as the important physicochemical features investigated herein (Fig. S2 and S3 in the Supplementary materials). The measurement of WHC or SC elucidates the interaction between SDF and water, which is

NU

related to the SDF cross-linked networks (Lopez Rubio et al., 2016). A decrease in the WHC for SDF fractions was observed in fractions with a lower molecular weight (1.279 and 2.549 g/g for

MA

FII and NII, compared to 3.831 and 4.989 g/g of FI and NI), and this was more obvious in

ED

fermented fractions with a less bulky matrix structure. The WHC of dietary fiber has been previously shown to decrease with a decreasing particle size (Sangnark & Noomhorm, 2003). A

PT

higher SC was observed in FII and NII compared to FI and NI, in agreement with previously

CE

published results, which indicated that the SC of carrot fiber increased with a decreasing particle size (Idrovo Encalada, Basanta, Fissore, De'Nobili, & Rojas, 2016). The WHC significantly

AC

increased with molecular weight or structural compactness. Of note, a higher molecular weight leads to a decrease in SC. Generally speaking, the WHC is the ability of a moist material to retain water when subjected to an external centrifugal gravity force or compression; it consists of the sum of bound water, hydrodynamic water and, mainly, physically trapped water (Vazquez-Ovando, Rosado-Rubio, Chel-Guerrero, & Betancur-Ancona, 2009). Therefore, it was hypothesized that the narrow space in larger sized SDF particles caused by the strong self-aggregation at higher

26

ACCEPTED MANUSCRIPT molecular weights was sufficient to trap moisture (Torres, Tarrega, & Costell, 2010). However, according to basic thermodynamic principles, swelling stretches the polymer strands and the maximum SC of the crosslinking network in contact with the pure solvent is related to the crosslinking density (Flory & Rehner, 1943). The excessively narrow space within the molecule

SC RI PT

due to the higher crosslinking (or entanglement) density could limit the aforementioned stretching effect. On the other hand, the excessively narrow space negatively affected the exposure of the surface area and the water-binding sites for the surrounding water, further reducing the SC (Yan, Ye, & Chen, 2015). Such deviations in the initial sizes for those polymers due to their different

rheological hardening of SDF aggregates.

NU

swelling behavior can explain the function of SDF components and retard the progress in

MA

Based on the above analysis, the aggregation behavior of SDF fractions could affect their

ED

interaction with water molecules, and thus may exert an effect in SDF-food system quality. Additionally, this interaction may become unfavorable due to the complex inhomogeneous media

PT

by large-size SDF aggregates rely on molecular characteristics such as higher molecular weight

CE

and lower branching, affect the consistency of the SDF-food system. In order to prevent the formation of large-size SDF aggregates due to their strongly disordered tangles, the aggregation

AC

behavior of a high SDF content fraction produced by flour processing was evaluated under the influence of intrinsic (molecular characteristic) and extrinsic factors (temperature and shear). The molecular relaxation and rearrangement process induced by the extrinsic factors are shown in Fig. 5. For the entangled macromolecules, the reduced molecular size and increased steric hindrance could reverse the aggregation behavior from disordered tangles to an interpenetrating network. Induced by external factors, the molecular chain with high molecular weight and low branching

27

ACCEPTED MANUSCRIPT level provide a much larger value of τc than τp (τc >> τp), which could lead to a strong aggregation cluster by disordered tangles coupled with a more solid-like behavior and greater apparent instability of the mixture system; with lower molecular weight and higher branching level, the reduced intermolecular collision time τc contributes significantly to the interpenetrating network of

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the molecular chains. This interpenetrating network caused by extrinsic factors gives rise to a dynamic equilibrium, preventing the formation of a strong aggregation cluster. Conclusions

To the best of our knowledge, the molecular weight and branching level of SDF fractions from

NU

wheat bran may vary depending on their molecular features. SDF fractions with high molecular weight and low branching level tend to form disordered tangles, which could limit their stability

MA

and compatibility with other coexisting components; while SDF fractions with low molecular

ED

weight and high branching level tend to display more extended molecular chains and prevent from disordered tangles. The present work shows that among the SDF fractions obtained from wheat

PT

bran, NII and especially FII, are the most compatible with each other, characterized by a reduced

CE

molecular weight and increased branching level leading to stability and rheological benefits. The results supported that the high molecular weight or/and low-branched SDF fractions tended to a

AC

strong aggregation cluster by disordered tangles coupled with a more solid-like behavior. These results are significant for the preparation a more stable or compatible systems containing SDF and the development of SDF ingredients, as they provide a deeper understanding of the regulation and control of their aggregation behavior in food processing. Simultaneously, we presented the promising application of fermentation technology, which may be helpful to develop SDF resources as low molecular weight and high-branched products for future scope and industrial

28

ACCEPTED MANUSCRIPT applicability. Acknowledgements This work was supported by the National Key Research and Development Program of China [2017YFD0400106]; the Special Fund for Agroscientific Research in the Public Interest [No.

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201303071]; the National Natural Science Foundation of China [No. 31501531]; the Tianjin Science and Technology Commission [No. 15JCQNJC14900]; the Tianjin Education Commission [No. 20140610]; and the Ph.D. Training Foundation of the Tianjin University of Science and Technology [No. 2016002].

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Agricultural and Food Chemistry, 64, 2094-2104. Nwokocha, L. M., & Williams, P. A. (2014). Isolation and characterization of a novel polysaccharide from seeds of Peltophorum pterocarpum. Food Hydrocolloids, 41, 319-324. Phillips, G. O., & Cui, S. W. (2011). An introduction: Evolution and finalisation of the regulatory definition of dietary fibre. Food Hydrocolloids, 25, 139-143.

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Reisinger, M., Tirpanalan, Ö., Prückler, M., Huber, F., Kneifel, W., & Novalin, S. (2013). Wheat bran biorefinery – A detailed investigation on hydrothermal and enzymatic treatment.

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Zimm, B. H. (1948). Apparatus and Methods for Measurement and Interpretation of the Angular

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Variation of Light Scattering; Preliminary Results on Polystyrene Solutions. The Journal

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of Chemical Physics, 16, 1099-1116.

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ACCEPTED MANUSCRIPT Figure Captions Fig. 1. The profile of dynamic light scattering for different soluble dietary fiber fractions from wheat bran. (a) Fluctuation graph of scattering intensity autocorrelation curve; (b) The particle size distribution curve (concentration, 0.2 mg/mL; temperature, 25 °C).

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Fig. 2. Small amplitude rheological profile of soluble dietary fiber fractions from wheat bran. Fig. 3. Turbiscan stability index, elasticity index, macroscopic viscosity index, solid liquid balance

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Fig. 4. The atomic force microscopy profile of soluble dietary fiber fractions from wheat bran. Fig. 5. The diagram of molecular relaxation and rearrangement. HMW, Higher molecular weight

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fractions; LMW, Lower molecular weight fractions.

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ACCEPTED MANUSCRIPT Table 1. Molecular features of soluble dietary fiber from natural and fermented wheat brana Sampleb NII

FI

FII

Mw/10 Da Mn/104 Da

185 161

59.2 45.0

178 139

15.4 12.9

Pd

1.14

1.31

1.28

1.19

GC

xylose

64.9

49.9

56.9

43.8

arabinose arabinose/xylose

26.4 0.41

29.9 0.60

30.2 0.54

31.5 0.72

total pentosanc

92.9

94.5

94.9

96.6

protein (%) ferulic acid (µg/g)

1.23 95.8

0.18 114

0.67 101

0.10 154

U-Xylp (%) 2,3-Xylp (%)

67.6 16.8

61.9 23.3

1H NMR

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66.5 19.0

58.7 28.2

WS % 6.74 9.13 7.12 10.3 b Data are presented as the mean (n = 3); NI and NII are natural SDF fractions precipitated with < 40% and 40-60% ethanol. FI and FII are fermented SDF fractions precipitated with < 35% and 35-65% ethanol; U-Xylp and 2,3-Xylp refer to un-substituted and 2,3-disubstituted xylan chains, respectively. c Expressed as % of sample dry matter. WS (water solubility, %) expressed as the fivefold weight of dry SDF fractions in the supernatant to the original weight of solvent.

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ACCEPTED MANUSCRIPT Table 2. The average diameter (Φ), size polydispersity index (PDI), hydrodynamic radius (Rh), weight average molecular weight (MW), radius of gyration (Rg), structure-sensitive parameter (ρ), critical overlap concentration (c*), and the second virial coefficient (A2) for soluble dietary fiber fractions in phosphate buffer Φ ρ c* Rh MW Rg A2 PDI 5 -1 –3 -1 nm nm 10 g moL nm Rg/Rh 10 g mL 10–4 154a

0.357a

74.5a

14.2a

84.0a

1.12d

0.95d

1.40d

NII

95.4c

0.254d

20.3c

6.90c

32.0c

1.57b

8.35b

5.20b

FI

136b

0.292b

35.7b

10.1b

46.7b

1.30c

3.51c

2.90c

FII

76.5d

0.194c

12.3d

2.40d

21.3d

1.73a

9.76a

7.20a

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Data are presented as the mean (n = 6). Different letters at the end of figure on the same line indicate significant differences (P < 0.05). The parameters Φ, PDI, Rh were determined by DLS analysis and MW, Rg, A2 by SLS analysis. All deviations are less than 1%.

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η0 (Pa·s)

τ (s)

m

R2

NI

1.62

4.82

0.09

1.000

NII

0.21

0.84

0.72

1.000

FI

0.39

2.33

0.17

0.999

FII

0.01

0.74

0.93

0.999

NI

6.97

10.08

0.05

NII

0.77

1.42

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1.000

0.70

0.999

FI

3.46

5.57

0.13

0.993

FII

0.18

1.07

0.87

1.000

NI

16.57

20.63

0.03

0.999

NII

5.62

1.56

0.64

0.999

FI

10.91

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10.19

0.10

0.992

FII

0.80

1.17

0.85

1.000

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ρ

Ara/xyl

η0

τ

TSI

-0.903 0.097

ρ

-0.972*

0.943*

0.028

0.013

*

0.946 0.036 0.884*

-0.991** 0.009 -0.931**

-0.965* 0.040 -0.968*

0.955*

0.016

0.007

0.031

0.045

**

**

*

0.990**

0.947*

η0 τ TSI

0.892

-0.998

-0.923

0.080

0.002

0.034

0.010

0.032

*

*

*

0.761

0.735

0.845

0.265 0.978*

0.155 0.963*

0.685

0.814

-0.832

MVI

0.048 0.960*

0.016 -0.959*

0.030 -0.993*

0.239 0.987*

0.040

0.041

0.010

0.013

0.022

0.037

0.315

*

**

*

*

*

*

-0.982* 0.018

0.895 0.012

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0.949 0.007

-0.948 0.021

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-0.935 0.042

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EI

SLB

-0.876

MVI

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Ara/xyl

EI

-0.812 0.019

-0.930 0.032

-0.903* 0.023

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Fig. 4

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Fig. 5

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Graphical Abstract

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ACCEPTED MANUSCRIPT Highlights

The effect of SDF aggregation on their rheological behaviors is analyzed.



The aggregation of SDF is correlated to its molecular weight and branching level.



DWS was employed to investigate the stability and rheological properties.



The rheological behaviors based on tangle and interpenetration are discussed.

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

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