Mechanical, rheological and structural properties of fiber-containing microgels based on whey protein and alginate

Accepted Manuscript Title: Mechanical, rheological and structural properties of fiber-containing microgels based on whey protein and alginate Authors: Alicia Magaly Leon, Jos´e M. Aguilera, Dong J. Park PII: DOI: Reference:

S0144-8617(18)31427-9 https://doi.org/10.1016/j.carbpol.2018.11.094 CARP 14347

To appear in: Received date: Revised date: Accepted date:

30 September 2018 25 November 2018 29 November 2018

Please cite this article as: Leon AM, Aguilera JM, Park DJ, Mechanical, rheological and structural properties of fiber-containing microgels based on whey protein and alginate, Carbohydrate Polymers (2018), https://doi.org/10.1016/j.carbpol.2018.11.094 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Mechanical, rheological and structural properties of fiber-containing microgels based on whey protein and alginate

Author Alicia Magaly Leon

Affiliation Pontificia Universidad Católica de Chile, Ingeniería Química y Bioprocesos, Av. Vicuña Mackenna

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4860, CL, Chile Phone number +56999153277

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Email [email protected]

HIGHLIGHTS

Gelled microparticles (GMP) were fabricated from whey protein and alginate

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Incorporation of fiber to GMP was demonstrated by light and electron microscopy

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Texture profile analysis revealed good adhesiveness and cohesiveness of GMP

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GMP showed the behavior of a structured liquid with tan () less than one

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GMP-DF could be used as soft fluid gels or mixed into purees or pastes

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ABSTRACT

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Dietary fiber (DF) - inulin (IN), bacterial cellulose nanofibers (BC), crystalline cellulose (CC) and oat fiber (OF) – were added at a concentration of 5% (2.5% for OF) to a whey protein isolate (WPI)/sodium

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alginate (NaAlg) dispersion. Gel microparticles (GMP) were formed by cold gelation followed by mechanical shearing. Compression stress-strain curves of bulk gels were similar for GMP-CC and GMPOF but different from GMP-IN and GMP-BC. The soluble fiber IN did not change the aggregated matrix of the parent WPI/NaAlg gel, while other sources of DF became incorporated into the microgel matrix.

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Rheological tests (20°C) revealed that GMP with added DF had a predominantly elastic behavior. Texture profile analysis suggested that GMP and GMP-IN had advantages over a commercial thickener in terms of adhesiveness and cohesiveness. GMP with added DF may find applications in foods for the elderly as texturizer and/or a carrier of fiber.

Keywords: Microgels, elderly foods, rheology, texture, whey protein isolate, dietary fiber, microstructure

1.

Introduction Aging of the world’s population occurs at a rapid pace. The elderly are now the fastest growing

demographic segment and by 2050 there will be approximately 400 million people aged 80 or more (United Nations, 2015). This situation imposes the urgent challenge of providing appropriate foods that satisfy their particular needs, among them, easy mastication, safe swallowing and key nutrients (Aguilera & Park, 2016). Only in Japan, the market for foods aimed at the elderly with swallowing

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problems and in need of nutrition supplements is expected to rise to over $350 million per year by 2020 (MAFF, 2017). Thus, the development of soft, texture-modified (TM) foods intended for the frail elderly has become an area of active research in food technology (Painter, Le Couteur, & Waite, 2017; Cichero,

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2016; Funami, 2016). For example, alternatives that moderate the flow rate of thin liquids during swallowing and avoid choking and aspiration into the lungs are being investigated (Moret-Tatay, Rodríguez-García, Martí-Bonmatí, Hernando, & Hernández, 2015; Quinchia et al., 2011). In Japan, over

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80% of the pneumonia patients diagnosed with aspiration pneumonia were elderly aged 70 years and

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older (Teramoto, 2014).

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Some old people tend to avoid foods with a high content of fiber (e.g., fruits or vegetables) due to

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mastication and swallowing problems, precluding their modulatory effect on the bowel function and making constipation a common disorder (Chen & Huang, 2003; Donini, Savina, & Cannella, 2009; Schuster, Kosar, & Kamrul, 2015). Thus, soft foods with added fiber supplements have been

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recommended for elderly patients with constipation (Gallegos-Orozco, Foxx-Orenstein, Sterler, & Stoa, 2012). Dietary fiber (DF) is that part of edible plant material which is resistant to enzymatic digestion by

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humans. DF components include cellulose, non-cellulosic polysaccharides such as hemicellulose, pectic substances, gums, mucilages, and the non-carbohydrate component lignin (DeVries et al., 2001; Dror,

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2003; Prosky, 2000). DF sources are usually classified into soluble in water (pectins, inulin, gums and mucilages) and insoluble ones (e.g., cellulose, hemicellulose, lignin) (Dhingra, Michael, Rajput, & Patil, 2012). Major physiological functions of DF are to increase the fecal weight by retaining water and the promotion of bacterial growth in the intestine (prebiotic action) (Spiller, 2001). Additionally, DF may

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have a protective effect against cardiovascular diseases, diabetes, obesity and intestinal disorders (Anderson et al., 2009; Nsor-Atindana, Chen, Goff, & Zhong, 2017). Technologically, DF imparts hydrocolloidal properties as a food ingredient and it is used as a fat and sugar replacer, bulking agent and texture modifier (Dhingra et al., 2012). Cell wall material in fruits, vegetables, cereals and nuts as well as gums are the main sources of DF in human diets (Dhingra et al., 2012). Inulin and other fructooligosaccharides are water soluble sources of DF which can induce a range of health benefits as well as functional properties to several foods (Shoaib et al., 2016). Bacterial cellulose is naturally present in

several fermented foods as well as produced from agricultural wastes (Castro et al., 2011; Iguchi, Yamanaka, & Budhiono, 2000). However, the direct addition of DF in the form of powders can adversely affect the textural and sensorial quality of many manufactured foods, such as baked goods, pasta, and dairy products (Grigor, Brennan, Hutchings, & Rowlands, 2016; Li & Komarek, 2017; Yang, Ma, Wang, & Zheng, 2017). Microgels are small, soft particles (usually under 100 m in size) that exhibit a fluid-like behavior

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at low concentrations of the gelling polymer and are being increasingly utilized for rheology control and encapsulation in several trades, including the food industry (Shewan & Stokes, 2013; Norton, Frith, & Ablett, 2006). Gel microparticles can be used as such, incorporated to finished products or added as

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texture modifiers to liquid foods such as juices, beverages and milk (Ellis & Jacquier, 2009). Due to its mechanical and viscoelastic properties, an artificial bolus based on an alginate gel has been proposed to evaluate the swallowing of patients with dysphagia, and the design of optimal menus (Hosotsubo, Magota, Egusa, Miyawaki, & Matsumoto, 2016). Soft and moist cold-gelled microparticles have been

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obtained from whey protein isolate (WPI) and sodium alginate (NaAlg), and proposed to modify the

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rheological behavior of foods for the elderly (Leon, Medina, Park, & Aguilera, 2016). Aguilera and Park

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(2016) have suggested that beyond their texture-imparting properties, these microgels may also be used as carriers for flavors and nutrients, in this case a fast-digesting protein source (whey protein), which is

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key for muscle health in elderly adults (Nowson & O’Connell, 2015). Currently, elderly that experience swallowing difficulties are given liquids thickened with starch and/or gums that may impair the release

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of medication, have a poor flavor and increase the feelings of thirst (Cichero, 2013). Fluid gels in the form of pourable suspensions of small gel particles have already been proposed to safely deliver drugs

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to older adults who have difficulties in swallowing (Mahdi, Conway, & Smith, 2014).

The use of fillers in gel matrices (e.g., addition of a small proportion of particulate inclusions)

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usually results in properties different than those of the parent material (Banerjee & Bhattacharya, 2012). Physical properties of texture-modified foods for the elderly are usually assessed by mechanical compression or penetration testing, and small amplitude oscillatory shear rheometry (Wendin et al.,

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2010). Shi, Zhang, Phillips, and Yang (2014) reported that fiber particles obtained from sugar cane contributed to a firmer gel structure in foods. Alakhrash, Anyanwu, and Tahergorabi (2016) suggested that surimi gels filled with oat bran (up to 8 g/100 g) exhibited enhanced gel texture (measured as Kramer shear force and by texture profile analysis), and provided a higher water retention after cooking. Recently, insoluble DF particles (i.e., microcrystalline cellulose, oat fiber and walnut shell flour) have been used as potential fillers and texture modifiers of myofibrillar gel systems (Gravelle, Barbut, & Marangoni, 2017).

The objective of the present study was to assess the microstructural characteristics as well as the mechanical and rheological properties of gelled microparticles (GMP) of whey protein and alginate, and containing soluble and insoluble (or partly soluble) sources of DF. The hypothesis of this work was that if the mechanical and rheological properties of fiber-laden GMP met the requirements of soft foods aimed at the frail elderly, they may become a new line of food matrices and carriers of dietary fiber.

Materials and methods

2.1.

Materials

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2.

Whey protein isolate (WPI) with a moisture content of 4.7% ± 0.3 and protein content of 97.7% ± 0.7 (dry basis) was purchased from Davisco (BiPRO, Davisco Foods Intl., MN, USA). Sodium alginate

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(NaAlg) was obtained from Gelymar Natural Extracts (Chile) with a composition of 38% mannuronic acid, 16% guluronic acid and 46% alternate units. Added dietary fiber (DF) sources were: a commercial inulin (IN) soluble fiber (Fibruline® Instant; Cosucra Groupe Warcoing S.A., Belgium); a refined product derived

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from microcrystalline cellulose (CC) (Avicel® cellulose gel, FMC Corporation Health and Nutrition, PA, USA) having an average particle size of around 75 µm; a commercial delignified, bleached oat fiber

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having a DF content over 90% by weight (OF) (Canadian Harvest® oat fiber 780, SunOpta Grains and

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Foods Inc., MN, USA) with particle sizes between 75 µm and 100 µm; and, a bacterial cellulose (BC)

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supplied by the School of Engineering, Universidad Pontificia Bolivariana, Medellin, Colombia, and produced by fermentation (Castro et al., 2011). Since fluid microgel suspensions may be an alternative or partial replacement to liquids thickened with pre-gelatinized starch, a commercial maize starch-based

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thickener (TH) (Thick & Easy, Hormel Health Labs, Austin, MN), specially designed for the management of dysphagia was used as control (Moret-Tatay et al., 2015). The artificial VISCOFAN corrugated cellulose

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casings (used for meat products) 20 mm in diameter and 30-60 µm in thickness, were purchased from Filter Print Ltda. (Santiago, Chile), and calcium chloride obtained from Sigma Chemical Co. (St. Louis,

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MO, USA).

2.2.

Preparation of gelled microparticles with dietary fiber The general procedure to prepare gelled microparticles (GMP) is described in Leon et al. (2016).

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A solution of 6% WPI in distilled water was heated in a temperature controlled water bath at 80 °C for 30 min to denature and aggregate the whey proteins. Subsequently, NaAlg and the individual DF were incorporated to the WPI solution at a 5% level, except the oat fiber that due to its high water holding capacity and resulting increase in viscosity could only be added at a concentration of 2.5%. Cold gelation of the mixed solutions of WPI, NaAlg and DF took place inside the cellulosic casings sealed on both sides and immersed in a 150 mM calcium chloride bath for 12 h at 5 °C, as previously reported by Leon et al. (2016). Cylindrical gels obtained after removal of the artificial membranes are referred to as bulk gels.

The GMP with or without DF of different sources (referred to as GMP-DF, see Table 1) were obtained by mechanical size reduction of the respective bulk gels, first by triturating for one minute using a handheld blender, and then homogenized into a paste with a high-speed blender (Ultra Turrax digital T25, IKA-Werke, Germany) for 5 min at 8000 rpm (Leon et al., 2016). The starch-based commercial thickener used as control was dissolved in distilled water at 0.08 g/mL, to a pudding-like consistency. Selection of TH as control emphasizes the comparison of different GMP with a commercial product already used to feed the frail elderly, while GMP (no fiber added) is often used a reference to compare properties of

2.3.

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GMP-DF .

Microstructural features of GMP with DF

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Microstructural characteristics of the BC dispersion, GMP, GMP-IN and GMP-BC were evaluated with a scanning microscope (model TM 3000, SEM Hitachi, Tokyo, Japan). Samples were critical point dried, coated with gold/palladium and observed under a voltage of 15 kV. Micrographs were taken at

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7000 × and selected images from at least three specimens per sample are reported. Additionally, small aliquots of GMP and GMP-DF samples were placed on glass slides, gently dispersed with one drop of

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distilled water, covered with a coverslip and observed in an optical microscope (model SMZ-2T 2B,

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Nikon Corp., Tokyo, Japan), attached to a digital camera Toup Tek, Photonics (model UCMOS 08000,

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Zhejiang, China) with a resolution of 2540 × 1744 pixels.

Mechanical properties of gelled bulk gels

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Cylindrical samples cut from bulk gels (20 mm diameter × 10 mm height) were subjected to uniaxial compression up to 80% strain (i.e., 8 mm total displacement of the probe divided by original

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height of sample, 10 mm) in a texture analyzer (model TA.XT2 Plus, Stable Micro System Ltd., Godalming, UK) using a round plate 75 mm in diameter and a constant crosshead speed of 1 mm s-1. All

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measurements were done in triplicate.

2.5.

Rheological properties of GMP and GMP-DF suspensions GMP and GMP-DF had the consistency of a suspension or slurry, i.e., they behaved as a thick and

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cohesive mass of moist particulates that could be poured and spread. All types of GMP and the starch thickener were subjected to small amplitude dynamic oscillatory measurements at 20°C using a Discovery hybrid rheometer (model RH-2, TA Instruments, New Castle, DE) with a 40 mm diameter parallel plate geometry and a 1 mm gap. To determine the linear viscoelastic region, stress sweeps were performed at 1 Hz. Then, frequency sweeps were performed over the range between 0.1 to 100 rad s-1 and the values of the storage or elastic modulus (G’), loss or viscous modulus (G’’) and loss tangent (tan δ = G”/G’) were calculated using the equipment software. All measurements were done at least in

triplicate using fresh samples. Data were expressed as a power law model using a linear least squares fitting method: G’ = G’1×ωm

(1)

where G’1 is defined as an effective coefficient (Pa × sm), m is effective flow behavior index, and ω is the angular velocity (rad s-1) (Quinchia et al., 2011; Steffe, 1996).

2.6.

Two-cycle back extrusion test (TCBET)

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Samples (around 20 g) of GMP, GMP-DF and the starch thickener were subjected to two consecutive back extrusion cycles using a TA.XTplus Texture Analyzer (Stable Micro System Ltd, Goodling, Surrey, UK). The sample holder (22 mm diameter and 60 mm height) and compression probe

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(15 mm diameter) were made in acrylic (Fig. 1). Testing was done at a speed of 1 mm s-1 and a down stroke to 20 mm from the bottom of the cell (approximately 50% of the initial height of GMP) (James et

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al., 2011).

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Fig. 1. Scheme of the back extrusion cell used in the two-cycle compression test (TCBET) of suspensions of GMP.

Results of the TCBET were interpreted as in the texture profile analysis (TPA), and they provided

a proxy of the mechanical properties and textural attributes during oral processing of foods (Bourne, 2002; Liu, Deng, Gong, Han, & Wang, 2017; Wilkinson, Dijksterhuis, & Minekus, 2000). Parameters derived from the TPA (e.g., hardness, resilience, adhesiveness and cohesiveness) of semi-solid food gels have been used to evaluate foods for dysphagic patients (Devezeaux de Lavergne, van de Velde, van Boekel, & Stieger, 2015; Momosaki, Abo, & Kobayashi, 2013). Fig. 2 shows a scheme of a typical TCBET curve and the parameters derived. Hardness is the force corresponding to the maximum height of the

first curve. Resilience is the ratio of the upstroke and downstroke work of the first cycle (A2/A1). Adhesiveness is the area of the negative force curve (A3) and represents the adhesion of the sample to the plunger after the first cycle. Cohesiveness is the total area under the curve for the second cycle divided by the total area during the first cycle [(A4 + A5)/(A1 + A2)] and represents the degree of structure breakdown after the first cycle (Devezeaux de Lavergne et al., 2015; Liu et al., 2017; Marfil,

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Anhe, & Telis, 2012; Texture Technologies Corp. and Stable Micro Systems, 2018).

A4 + A5

Cohesiveness =

A1 + A2

Hardness

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A2 Resilience =

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A1

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Adhesiveness

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Resting time

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First compression cycle

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A3

A4

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Force (N)

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Second compression cycle

Time (s)

Experimental design and statistical analysis

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2.7.

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Fig. 2. Scheme of two cycle penetration test (TCPT) to GMP and GMP-DF suspensions and the starch thickener.

Experiments were carried out following a complete randomized design with five treatments and

three repetitions (Table 1). Statistical significance was determined using Statgraphics Plus software

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(Statistical Graphics Corporation, version 5.1, Rockville, USA) at a probability level of 0.05 (P <0.05).

Table 1 Complete randomized design of experiments and nomenclature TREATMENT

Sample name

T0

WPI/NaAlg

T1

WPI/NaAlg + soluble fiber

SYMBOL GMP GMP-IN

T3 T4 T5

WPI/NaAlg + insoluble/partly soluble fiber

Results and discussion

3.1.

Microstructural features of GMP

GMP-CC GMP-OF

Commercial thickener

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GMP-BC

TH

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T2

Light microscopy images obtained for the four types of GMP-DF are shown in Fig. 3. The gel matrix

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of all GMP-DF consisted of irregularly shaped clusters of agglomerates, most of them under 100 m in size. These structures are typical of the process of aggregation during cold gelation of denatured whey proteins (Donato, Kolodzieccyk, & Rouvet, 2011; Leon et al., 2016). GMP containing inulin were similar

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in size and structure to the GMP of pure WPI/NaAlg (Leon et al., 2016) as expected since inulin is

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dispersed at the molecular level in the gel matrix (Fig. 3A). The addition of bacterial cellulose was not appreciated at this scale of resolution, but it apparently brought clusters closer together as shown by

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some dark areas within the clusters (Fig. 3B). Insoluble cellulose fibrils with elongated shapes seemed

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to adhere to the surface of the GMP matrix in GMP-CC (Fig. 3C). A few large fibrils of cellulose from the oat fiber source protruded into the gel matrix in GMP-OF (Fig. 3D), probably due to their good water

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holding capacity (Steenblock, Sebranek, Olson, & Love, 2001; Yamazaki, Murakami, & Kurita, 2005).

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D

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Fig. 3. Light photomicrographs of GMP-DF suspended in water. (A) GMP with 5% of IN, (B) GMP with 5% BC, (C)

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GMP with 5% of CC and (D) GMP with 2.5% OF. Marker = 50 m (all figures).

Scanning electron microscoscopy (SEM) permited a more detailed view of the microstructure of gel matrices, although they had undergone water removal by critical point drying, a process that

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usually induces changes compared to the fully hydrated state (Fig. 4). Figures 4A and 4B, confirmed the microstructural similarity between GMP and GMP-IN matrices, and the predominant presence of

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aggregates as reported for mixed whey protein-polysaccharide cold-set gels (de Jong, Klok, & van de Velde, 2009). Fig. 4C displays the microstructure of an entaglement of thin BC nanofibers formed by 20 to 70 nm-wide ribbons (Castro et al., 2011). Fig. 4D shows how cellulose nanofibers penetrated into the GMP matrix segregating it into fragments “glued” together by a separated network of nanofibers.

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Similar microstructures were observed in synthetic gels to which BC had been added (Numata, Sakata, Furukawa, & Tajima, 2015).

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Fig. 4. Scanning electron micrographs of GMP and DF. (A) WPI/NaAlg GMP; (B) WPI/NaAlg GMP with added inulin;

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(C) Bacterial cellulose fibers, and; (D) WPI/NaAlg GMP with added bacterial cellulose. Marker = 10 m (all figures).

Mechanical properties of bulk gels

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Stress-deformation curves of cylindrical bulk gels during uniaxial compression are shown in Fig. 5. All treatments exhibited a similar behavior up to a strain of around 45%. Young’s moduli (i.e., stress

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divided by deformation in the initial portion of the curve) of around 40 kPa were in the middle of the range of those reported by Hosotsubo et al. (2016) for their alginate bolus used to evaluate swallowing in patients with dysphagia. Addition of insoluble fiber in the form of CC and OF did not produce a notorious change in the mechanical behavior during compression with respect to the fiber-less sample

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GMP in the entire range of deformation. On the other hand, addition of inulin reduced the gel stress beyond a strain of about 45%. Balanč et al. (2015) reported that the addition of inulin to gelled alginate microbeads led to a softer texture. Evageliou, Tseliou, Mandala, and Komaitis (2010) found that the strength of gellan gels also decreased in the presence of inulin and attributed this result to the interference of inulin with the aggregation of the gellan helices. This mechanism is unlikely to explain the weakening of the WPI/NaAlg gel since gelation of alginate occurs by Ca binding between G-blocks in the polymer. Addition of bacterial cellulose fibers increased the strength of the bulk gel up to about

60% strain, in fact, even reinforced the structure, as was also observed by Numata et al. (2015). Beyond this strain value, a series of fracture events started to occur that weakened the gel. Based on the microstructure of GMP-BC in Fig. 4D, it can be surmised that beyond the 60% strain, the network of cellulose nanofibers gluing together the gel aggregates started to collapse and the assembly of

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fragments was not as strong as the homogeneous (unbroken) matrix of the other bulk gels.

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Fig. 5. Stress-strain curves for uniaxial compression of cylindrical bulk gels.

3.3.

Rheological properties of GMP, GMP-DF and commercial thickener As shown in Fig. 3, high-speed shearing of WPI/NaAlg bulk gels produced polydispersed

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microparticles, mostly less than 100 m in size (Leon et al., 2018). These microgel suspensions exhibit a fluid-like behavior and they can be poured or spread depending on the shear rate, quite differently from the fracture experienced by the quiescent bulk gels (Norton, Frith & Ablett, 2006). Mechanical spectra representing storage modulus (G’) and loss modulus (G’’) as a function of frequency (ω) for GMP, GMPDF and the commercial thickener are shown in Fig. 6. G' (Fig. 6A) was higher than G'' (Fig. 6B) throughout the frequency range, indicating that there was a predominance of the elastic over the viscous behavior in all samples, as is typically observed for gelled structures (Nazir, Asghar, & Aslam Maan, 2017). Also,

there was only a slight dependence of both moduli with frequency as it is often reported for structured liquids. Values of the viscoelastic moduli G' and G'' for GMP-OF, GMP-CC and GMP-CB were higher than those of the control GMP and GMP-IN, suggesting that the presence of insoluble DF in the GMP matrix provided a reinforcement effect (Le Goff, Gaillard, Helbert, Garnier, & Aubry, 2015; Wang & Chen, 2017). The presence of inulin, however, did not weaken the gel matrix. Glibowski (2009) indicated that a firm gel is formed between whey proteins and inulin due to their synergistic interactions. In

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summary, all GMP suspensions can be described as weak gel-like systems, because G′ and G″ were almost parallel, G′ > G″ and both moduli varied with frequency (Ikeda & Nishinari, 2001; Picout & RossMurphy, 2003; Seo & Yoo, 2013). These characteristics suggest that GMP-DF suspensions could

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contribute to form a bolus with a weak gel consistency, easy to masticate and swallow (Ishihara, Nakauma, Funami, Odake, & Nishinari, 2011). Dynamic moduli for TH were in the range reported for commercial starch-based thickeners designed for the management of dysphagia when dispersed to give

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a pudding-like consistency (Moret-Tatay, Rodríguez-García, Martí-Bonmatí, Hernando, & Hernández,

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2015).

Fig. 6. Mechanical spectra as a function of angular frequency of GMP with different DF and the commercial thickener. A. Storage modulus, G’ (Pa); and, B. Loss modulus, G’’(Pa). () GMP, () GMP-IN, () GMP-BC, ()

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GMP-CC, () GMP-OF, and () TH.

Mechanical spectra curves of GMP, GMP-DF and the commercial thickener were modelled

according to a power law equation to describe the variation of the storage modulus G’ with frequency (Quinchia et al., 2011). Parameters of the resulting equations are shown in Table 2. RMSE (root mean square error) values were low for all G’ data and adjusted R2 were superior and equal to 0.96.

Table 2

Parameters of the power law model for GMP, GMP-DF and commercial thickener Power law parameters of storage modulus (G’) Treatments GMP GMP-IN

G’1 (Pa × sm) 3831c ± 772

m

R2-Adj

0.12a ± 0.009

0.99

RMSE (Pa × sm) 161

3515c ± 606

0.12a ± 0.007

0.96

293

GMP-BC

bc

7759 ± 584

0.12 ± 0.005

0.98

354

GMP-CC

10008b ± 1741

0.12a ± 0.002

GMP-OF

23550 ± 7283 c

TH

629 ± 58

Pudding1

0.98

521

a

0.98

996

b

0.98

0.13 ± 0.004 0.07 ± 0.008 0.15-0.16

1

12

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(Quinchia et al. 2011)

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a

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The effective flow behavior index (m) was similar for all GMP (around 0.12) and significantly different (P<0.05) from that of TH (0.07), in accordance with the more complex microstructure of the

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GMP. Quinchia et al. (2011) reported m values for a pudding between 0.15 and 0.16 at 25°C, slightly

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larger than those of GMP samples. The effective coefficient G’1 of GMP-OF was much higher than those of other GMP, in accordance with the large experimental value of G’ of this sample. The low G’1 of TH is

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in the order of magnitude of the G’1 of puddings (200-400 Pa x sm) studied by Quinchia et al. (2011),

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suggesting this type of consistency for the starch suspension at the concentration used in the study. The commercial oat fiber used is a delignified, defibrillated and ground product known for its very high

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water holding capacity (Bodner & Sieg, 2009; Ramaswamy, 1987). OF bound a large amount of water and imparted a high viscosity to the parent WPI/NaAlg solution that precluded its incorporation at levels

BC (Fig. 3C).

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beyond 2.5%. Cellulose fibrils in OF can be appreciated in Fig. 3D and were thicker than nanofibers from

Tan δ values for all samples were < 1 in the studied frequency range (Fig. 7), suggesting that they

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exhibited predominantly elastic properties (Funami, 2016). Tan  values were similar for GMP and GMP-DF (values between 0.17 and 0.28) and different from that of TH. The distinctive low value of tan  for TH (mainly due to the low G”) may reflect its different structure (i.e., polymeric dispersion) as

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compared to GMP and GMP-DF samples (i.e., dispersions of gel microparticles).

0.35 T0 T1 T2 T3 T4 T5

0.30

(GMP) (GMP-IN) (GMP-BC) (GMP-CC) (GMP-OF) (TH)

Tan

0.25

0.20

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0.15

0.05 0.1

1

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0.10

10

(rad s-1)

100

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Fig. 7. Loss tangent as a function of angular frequency for GMP suspensions and the commercial thickener.

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Values of tan (δ) in the range of 0.1–1 have been suggested as rheological criterion for safe-

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swallow foods destined for dysphagia patients (Ishihara et al., 2011). Leon et al. (2018) subjected WPI/NaAlg GMP containing a small amount of emulsified oil to frequency sweeps lasting 12 min at 40

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and 60°C and observed a rise in tan (δ) only at the higher temperature but values remained below 0.75, so they should be quite stable in warm foods. The case of cooking for prolonged times needs to be

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studied but warm GMP could be added and mixed into hot dishes after cooking. Funami (2011), suggested that gels could be a good material for dysphagia diets due their viscoelastic character. Thus, GMP and GMP-DF not only may be used to modify the viscosity of liquid foods, as proposed by

Two-cycle back extrusion test (TCBET)

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3.4.

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Ellis and Jacquier (2009), but also to be consumed directly as food carriers.

Main textural parameters determined for TM- foods are hardness (hard to soft), adhesiveness

(i.e., tendency of particles to adhere to surfaces) and cohesiveness (ability to form a swallow-safe bolus

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in the mouth) (Aguilera & Park, 2016). Determination of mechanical properties of wet particulate materials had been resolved using a back extrusion cell (Brusewitz & Yu, 1996; Reyes & Jindal, 1990). A two-cycle compresion test similar to the texture profile analysis (TPA) has been performed in a back extrusion cell to evaluate soft gels such as yogurt (James et al., 2011; Sandoval-Castilla, Lobato-Calleros, Aguirre-Mandujano, & Vernon-Carter, 2004). Results of the TCBET are shown in Fig. 8.

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Fig. 8. Two cycle back-extrusion test (TCBET) parameters for GMP, GMP-DF and the starch thickener. (A) Hardness;

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(B) Resilience; (C) Adhesiveness, and; (D) Cohesiveness.

Fig. 8A shows that incorporation of the soluble DF inulin reduced significantly (P<0.05) the hardness of GMP from 0.87 to 0.72 N, a value similar to that of the commercial thickener TH (around

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0.69 N). These results coincide with those obtained by Delgado and Bañón (2018) who reported that inulin decreased the gel strength of jellies when used unheated and at a low concentration.

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Conversely, addition of insoluble or partly soluble DF (CC and OF) increased significantly the hardness of the GMP matrix to values of ~1.57 N. Gravelle et al. (2017), found that microcrystalline cellulose and oat fiber increased the hardness of myofibrillar gels when they were used as filler particles due to their crowding properties. GMP-BC exhibited an intermediate value of hardness between that of GMP

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and the GMP-CC and GMP-OF samples. Resilience or the capacity of suspensions to spring back to their initial state and shape after the first cycle of compression (Fig. 8B), was highest for GMP-CC and GMPOF (~0.015), coincidental with their high hardness values (Fig. 8A). GMP, GMP-IN, GMP-BC and TH had lower (~0.009) and similar values (P>0.05). Structural recovery is a determinant factor among rheological properties of the bolus in texture-modified foods for the elderly (Zargaraan, Rastmanesh, Fadavi, Zayeri, & Mohammadifar, 2013). Addition of DF to GMP resulted in a wide range of adhesiveness values, from -5.53 to -11.45 N × s (Fig. 8C). Adhesion between gel microparticles is probably due to the

formation of a thin liquid bridge between their surfaces (Adhikari, Howes, Bhandari, & Truong, 2001). Adhesiveness of GMP and GMP-IN were similar to that of the commercial thickener TH (~ -6.1 N × s). Cohesiveness is an important characteristic of foods for the elderly, and in this case reflects the internal and interfacial forces of a particulate material that holds it together as a piece (Adhikari et al., 2001). Cohesive TM-foods will not break easily into pieces in the mouth, thus avoiding the scatter of small particles in the pharyngeal phase of swallowing (Ishihara et al., 2011). Average cohesiveness values of all samples studied varied between 0.69 and 0.87 (Fig. 8D), however, values of treatments containing

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insoluble or partly soluble fiber particles were significantly lower than those of GMP, GMP-IN and TH. Yet, these cohesiveness values (0.69-0.73) are higher than those reported for pureed therapeutic cakes (0.48 and 0.57) by Houjaij, Dufresne, Lachance, and Ramaswamy (2009). In particular, the low

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adhesiveness and high cohesiveness of GMP containing soluble DF as inulin are quite promising for the design of food matrices for the elderly (Ishihara et al., 2011; Momosaki et al., 2013). In summary, hardness, resilience, cohesiveness and adhesiveness of GMP and GMP-IN were quite similar or superior

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to those of the commercial thickener.

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Mechanical and rheological properties of GMP may be tuned to potential applications by

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adjusting the concentration of the biopolymers, the fiber source and calcium, as well as the particle size,

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among others. One possible advantage of GMP-DF that needs to be demonstrated by sensorial studies, is an improved mouthfeel of gritty fiber particles when they are dispersed in the soft microgels (Burey, Bhandari, Howes, & Gidley, 2008). There are several foreseeable applications for the GMP suspensions.

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After flavoring, they could be consumed as such and act as fiber carriers. Kim & Joo (2015) reported that foods prepared by spherification techniques (formation of small alginate gel droplets) have had an

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auspicious reception among the elderly in Korea, while Brennan and Sorensen (2015) praise the creativity of modern chefs to exploit the properties of gels, including their use as thick fluids. Flavored

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GMP could be used as partial replacement of starch thickeners in liquids thus, offsetting some of their disadvantages (Cichero, 2013). Furthermore, they may be mixed with purees, pastes and creams, as an added source of fiber and protein. In fact, a wide range of prepared commercial dishes aimed at the elderly with difficulties in oral processing is already available in Japan (MAFF, 2017). GMP should

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withstand heating without disintegration since WPI will undergo a secondary thermal gelation above 80°C making GMP harder, and alginate gels are known to withstand boiling without losing structural integrity (Ching, Bansal, & Bhandari 2017; Hongsprabhas & Barbut, 1997). Another alternative would be to add the GMP to hot foods at their temperature of serving or consumption (60-80°C). The search for novel formats of soft foods for the ailing elderly using gelation will demand several complementary studies but it cannot be overlooked.

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Conclusions Given the urgent need to feed the frail elderly combining good nutrition with adequate textural

functionalities, gelled microparticles (GMP) appear to be effective carriers for nutrients like fiber and protein. Soluble and insoluble (or partly soluble) sources of dietary fiber (DF) of different origins were incorporated into the matrix of whey protein isolate/sodium alginate GMP. Formulated GMP-DF had mechanical and rheological properties in the range of soft foods recommended for the elderly with swallowing problems. Adhesiveness and cohesiveness derived from the texture profile analysis of fiber-

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less GMP and GMP containing inulin, were similar to those of the commercial thickener (TH) used as control. This proof of concept highlights the potential application of GMP-DF in the formulation of foods for the elderly, either directly as thick fluid gels or mixed into purees or pastes. Reported results should

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be further assessed by sensory evaluation and culinary performance in real foods and beverages, as well as validated by studies of their clinical efficacy against constipation.

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Acknowledgements

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Work reported is part of the doctoral thesis of Alicia Leon Tacca under support of CONICYT (The National

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Commission for Science and Technology, Chile). Financial support from the Korea Food Research Institute (KFRI) through a contract with the Pontificia Universidad Católica de Chile is appreciated. We

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also thank to Robin Octavio Zuluaga Gallego for supplying the sample of bacterial cellulose. References

A

CC E

PT

ED

Adhikari, B., Howes, T., Bhandari, B. R., & Truong, V. (2001). Stickiness in foods: a review of mechanisms and test methods. International Journal of Food Properties, 4(1), 1-33. Aguilera, J. M., & Park, D. J. (2016). Texture-modified foods for the elderly: Status, technology and opportunities. Trends in Food Science & Technology, 57, 156-164. Alakhrash, F., Anyanwu, U., & Tahergorabi, R. (2016). Physicochemical properties of Alaska pollock (Theragra chalcograma) surimi gels with oat bran. LWT - Food Science and Technology, 66(Supplement C), 41-47. Anderson, J. W., Baird, P., Davis Jr, R. H., Ferreri, S., Knudtson, M., Koraym, A., . . . Williams, C. L. (2009). Health benefits of dietary fiber. Nutrition Reviews, 67(4), 188-205. Balanč, B., Kalušević, A., Drvenica, I., Coelho, M. T., Djordjević, V., Alves, V. D., … Bugarski, B. (2015). Calcium-alginate-inulin microbeads as carriers for aqueous carqueja extract. Journal of Food Science, 81(1), E65–E75. Banerjee, S., & Bhattacharya, S. ( 2012). Food gels: gelling process and new applications. Critical Review of Food Science Nutrition, 52(4), 334-346. Bodner, J. M., & Sieg, J. (2009). Fiber. In: R. Tarté (Ed.), Ingredients in Meat Products (pp. 83-109). New York, NY: Springer Bourne, M. (2002). Food Texture and Viscosity: Concept and Measurement (2nd ed.). London, Unit Kingdom: Academic Press. Brenner, M. P., & Sorensen, P. M. (2015). Biophysics of molecular gastronomy. Cell, 161, 5–8. Burey, P., Bhandari, B. R., Howes, T., & Gidley, M. J. (2008). Hydrocolloid gel particles: formation, characterization, and application. Critical Reviews in Food Science and Nutrition, 48(5), 361-377. Brusewitz, G. H., & Yu, H. (1996). Back extrusion method for determining properties of mustard slurry. Journal of Food Engineering, 27(3), 259-265.

A

CC E

PT

ED

M

A

N

U

SC R

IP T

Castro, C., Zuluaga, R., Putaux, J.-L., Caro, G., Mondragon, I., & Gañán, P. (2011). Structural characterization of bacterial cellulose produced by Gluconacetobacter swingsii sp. from Colombian agroindustrial wastes. Carbohydrate Polymers, 84(1), 96-102. Chen, H.-L., & Huang, Y. I.-C. (2003). Fiber intake and food selection of the elderly in Taiwan. Nutrition, 19(4), 332-336. Ching, S. H., Bansal, N., & Bhandari, B. (2017). Alginate gel particles - A review of production techniques and physical properties. Critical Reviews in Food Science and Nutrition, 57(6), 1133-1152. Cichero, J. A. Y. (2016). Adjustment of food textural properties for elderly patients. Journal of Texture Studies, 47(4), 277-283. Cichero, J. A. Y. (2013). Thickening agents used for dysphagia management: Effect on bioavailability of water, medication and feelings of satiety. Nutrition Journal, 12(1), 54. de Jong, S., Klok, H. J., & van de Velde, F. (2009). The mechanism behind microstructure formation in mixed whey protein–polysaccharide cold-set gels. Food Hydrocolloids, 23(755-764). Delgado, P., & Bañón, S. (2018). Effects of replacing starch by inulin on the physicochemical, texture and sensory characteristics of gummy jellies. CyTA - Journal of Food, 16(1), 1-10. Devezeaux de Lavergne, M., van de Velde, F., van Boekel, M. A. J. S., & Stieger, M. (2015). Dynamic texture perception and oral processing of semi-solid food gels: Part 2: Impact of breakdown behaviour on bolus properties and dynamic texture perception. Food Hydrocolloids, 49, 61-72. DeVries, J. W., Camire, M. E., Cho, S., Craig, S., Gordon, D., Jones, J. M., . . . Tungland, B. C. (2001). The definition of dietary fiber. Cereal Foods World, 46, 112-129. Dhingra, D., Michael, M., Rajput, H., & Patil, R. T. (2012). Dietary fibre in foods: A review. Journal of Food Science and Technology, 49(3), 255-266. Donato, L., Kolodzieccyk, E., & Rouvet, M. (2011). Mixtures of whey protein microgels and soluble aggregates as building blocks to control rheology and structure of acid induced cold-set gels. Food Hydrocolloids, 25, 734-742. Donini, L. M., Savina, C., & Cannella, C. (2009). Nutrition in the elderly: Role of fiber. Archives of Gerontology and Geriatrics, 49, 61-69. Dror, Y. (2003). Dietary fiber intake for the elderly. Nutrition, 19(4), 388-389. Ellis, A., & Jacquier, J. S. (2009). Manufacture and characterisation of agarose microparticles. Journal of Food Engineering, 90(2), 141-145. Evageliou, V., Tseliou, G., Mandala, I., & Komaitis, M. (2010). Effect of inulin on texture and clarity of gellan gels. Journal of Food Engineering, 101(4), 381-385. Funami, T. (2011). Next target for food hydrocolloid studies: Texture design of foods using hydrocolloid technology. Food Hydrocolloids, 25(8), 1904-1914. Funami, T. (2016). The formulation design of elderly special diets. Journal of Texture Studies, 47(4), 313322. Gallegos-Orozco, J. F., Foxx-Orenstein, A. E., Sterler, S. M., & Stoa, J. M. (2012). Chronic constipation in the elderly. The American Journal of Gastroenterology, 107, 18-25. Glibowski, P. (2009). Rheological properties and structure of inulin–whey protein gels. International Dairy Journal, 19(8), 443-449. Gravelle, A. J., Barbut, S., & Marangoni, G. A. (2017). Food-grade filler particles as an alternative method to modify the texture and stability of myofibrillar gels. Scientificreports, 1-16. Grigor, J.M., Brennan, C. S., Hutchings, S. C., & Rowlands, D. S. (2016). The sensory acceptance of fibreenriched cereal foods: a meta-analysis. International Journal of Food Science &Technology, 51(1), 3-13. Hongsprabhas, P., & Barbut, S. (1997). Ca2+-Induced cold gelation of whey protein isolate: effect of twostage gelation. Food Research International, 30(7), 523-527. Hosotsubo, M., Magota, T., Egusa, M., Miyawaki, T., & Matsumoto, T. (2016). Fabrication of artificial food bolus for evaluation of swallowing. PLoS ONE, 11(12), e0168378. http://doi.org/10.1371/journal.pone.0168378 Houjaij, N., Dufresne, T., Lachance, N., & Ramaswamy, H. S. (2009). Textural characterization of pureed cakes prepared for the therapeutic treatment of dysphagic patients. International Journal of Food Properties, 12, 45-54.

A

CC E

PT

ED

M

A

N

U

SC R

IP T

Iguchi, M., Yamanaka, S., & Budhiono, A. (2000). Bacterial cellulose: a masterpiece of nature's arts. Journal of Materials Science, 35, 261-270. Ikeda, S., & Nishinari, K. (2001). “Weak gel” - type rheological properties of aqueous dispersions of nonaggregated kappa-carrageenan helices. Journal of Agricultural and Food Chemistry, 44364441. Ishihara, S., Nakauma, M., Funami, T., Odake, S., & Nishinari, K. (2011). Swallowing profiles of food polysaccharide gels in relation to bolus rheology. Food Hydrocolloids, 25(5), 1016-1024. James, B., Young, A., Smith, B., Kim, E., Wilson, A., & Morgenstern, M. P. (2011). Texture changes in bolus to the “point of swallow” - fracture toughness and back extrusion to test start and end points. Procedia Food Science, 1(Supplement C), 632-639. Kim, S.-G., Yoo, W., & Yoo, B. (2014). Effect of thickener type on the rheological properties of hot thickened soups suitable for elderly people with swallowing difficulty. Preventive Nutrition and Food Science, 19(4), 358–362. Le Goff, K. J., Gaillard, C., Helbert, W., Garnier, C., & Aubry, T. (2015). Rheological study of reinforcement of agarose hydrogels by cellulose nanowhiskers. Carbohydrate Polymers, 116, 117-123. Leon, A. M., Medina, W. T., Park, D. J., & Aguilera, J. M. (2018). Properties of microparticles from a whey protein isolate/alginate emulsion gel. Food Science and Technology International, 24(5), 414423. Leon, A. M., Medina, W. T., Park, D. J., & Aguilera, J. M. (2016). Mechanical properties of whey protein/Na alginate gel microparticles. Journal of Food Engineering, 188, 1-7. Li, Y. O., & Komarek, A. R. (2017). Dietary fibre basics: Health, nutrition, analysis, and applications. Food Quality and Safety, 1(1), 47-59. Liu, D., Deng, Y., Gong, A., Han, Y., & Wang, H.-m. D. (2017). Impact of the breakdown behavior on chinese traditional stewed pork with brown sauce: Physical properties using microstructural analysis. Journal of Food Quality, 2017, 1-10. MAFF (2017). Efforts relating to "Smile Care Food". Ministry of Agriculture, Forestry and Fisheries, Japan. http://www.maff.go.jp/e/policies/food_ind/attach/pdf/index-9.pdf. Mahdi, M. H., Conway, B. R., & Smith, A. M. (2014). Evaluation of gellan gum fluid gels as modified release oral liquids. International Journal of Pharmaceutics, 475(1-2), 335-343. Marfil, P. H. M., Anhe, A. C. B. M., & Telis, V. R. N. (2012). Texture and microstructure of gelatin/corn starch-based gummy confections. Food Biophysics, 7, 236-243. Momosaki, R., Abo, M., & Kobayashi, K. (2013). Swallowing analysis for semisolid food texture in poststroke dysphagic patients. Journal of Stroke & Cerebrovascular Diseases, 22(3), 267-270. Moret-Tatay, A., Rodríguez-García, J., Martí-Bonmatí, E., Hernando, I., & Hernández, M. J. (2015). Commercial thickeners used by patients with dysphagia: Rheological and structural behaviour in different food matrices. Food Hydrocolloids, 51, 318-326. Nazir, A., Asghar, A., & Aslam Maan, A. (2017). Food gels: gelling process and new applications. In A. J., P. Ptaszek & S. Basu (Eds.), Advances in Food Rheology and its application (pp. 335-353). Cambridge, MA: Woodhead Publishing. Norton, I. T., Frith, W. J., & Ablett, S. (2006). Fluid gels, mixed fluid gels and satiety. Food Hydrocolloids, 20, 229-239. Nowson, C., & O’Connell, S. (2015). Protein requirements and recommendations for older people: A Review. Nutrients, 7(8), 6874–6899. Nsor-Atindana, J., Chen, M., Goff, H. D., & Zhong, F. (2017). Functionality and nutritional aspects of microcrystalline cellulose in food. Carbohydrate Polymers, 172, 159-174. Numata, Y., Sakata, T., Furukawa, H., & Tajima, K. (2015). Bacterial cellulose gels with high mechanical strength. Materials Science and Engineering: C, 47(Supplement C), 57-62. Painter, V., Le Couteur, D. G., & Waite, L. M. (2017). Texture-modified food and fluids in dementia and residential aged care facilities. Clinical Interventions in Aging, 12, 1193–1203. Picout, R. D., & Ross-Murphy, S. B. (2003). Rheology of bioplymers solutions and gels. The Scientific World, 3, 105-121. Prosky, L. (2000). When is dietary fiber considered a functional food? BioFactors, 12(1-4), 289-297.

A

CC E

PT

ED

M

A

N

U

SC R

IP T

Quinchia, L. A., Valencia, C., Partal, P., Franco, J. M., Brito-de la Fuente, E., & Gallegos, C. (2011). Linear and non-linear viscoelasticity of puddings for nutritional management of dysphagia. Food Hydrocolloids, 25(4), 586-593. Ramaswamy, S. R. (1987). Fiber and method of making. U. S. Patent No. 5,023,103. Washington, D. C.: Patent and Trademark Office. Reyes, V., & Jindal, V. (1990). A small sample back extrusion test for measuring texture of cooked‐rice. Journal of Food Quality, 13(2), 109-118. Sandoval-Castilla, O., Lobato-Calleros, C., Aguirre-Mandujano, E., & Vernon-Carter, E. J. (2004). Microstructure and texture of yogurt as influenced by fat replacers. International Dairy Journal, 14, 151-159. Schuster, B. G., Kosar, L., & Kamrul, R. (2015). Constipation in older adults: Stepwise approach to keep things moving. Can Fam Physician, 61(2), 152-158. Seo, C. W., & Yoo, B. (2013). Steady and dynamic shear rheological properties of gum-based food thickeners used for diet modification of patients with dysphagia: Effect of concentration. Dysphagia, 28, 205-211. Shewan, H. M., & Stokes, J. R. (2013). Review of techniques to manufacture micro-hydrogel particles for the food industry and their applications. Journal of Food Engineering, 119(4), 781-792. Shi, Z., Zhang, Y., Phillips, G. O., & Yang, G. (2014). Utilization of bacterial cellulose in food. Food Hydrocolloids, 35, 539-545. Shoaib, M., Shehzad, A., Omar, M., Rakha, A., Raza, H., Sharif, H. R., . . . Niazi, S. (2016). Inulin: Properties, health benefits and food applications. Carbohydrate Polymers, 147(Supplement C), 444-454. Spiller, G. A. (2001). Definition of dietary fiber. In G. A. Spiller (Ed.), Dietary Fiber in Human Nutrition (3rd ed., pp. 9-10). California: CRC Press LLC. Steenblock, R. L., Sebranek, J. G., Olson, D. G., & Love, J. A. (2001). The effects of oat fiber on the properties of light bologna and fat-free frankfurters. Journal of Food Science, 66, 1409-1415. Steffe, J. F. (1996). Rheological methods in food process engineering. Agricultural Engineering, 23, 249250. Teramoto, S. (2014). Clinical significance of aspiration pneumonia and diffuse aspiration bronchiolitis in the elderly. Journal of Gerontology and Geriatric Research, 3, 142. Doi: 10.4172/21677182.1000142. Texture Technologies Corp. and Stable Micro Systems, L. (2018). Overview of Texture Profile Analysis. from http://texturetechnologies.com/resources/texture-profile-analysis#resources. United Nations. (2015). World Population Prospects: The 2015 Revision, Key Findings and Advance Tables. Department of Economic and Social Affairs, Population Division. Working Paper No. ESA/P/WP.241. Wang, X., & Chen, J. (2017). Food oral processing: Recent developments and challenges. Current Opinion in Colloid & Interface Science, 28(Supplement C), 22-30. Wendin, K., Ekman, S., Bülow, M., Ekberg, O., Johansson, D., Rothenberg, E., & Stading, M. (2010). Objective and quantitative definitions of modified food textures based on sensory and rheological methodology. Food and Nutrition Research, 54, 1-12. Wilkinson, C., Dijksterhuis, G. B., & Minekus, M. (2000). From food structure to texture. Trends in Food Science & Technology, 11(12), 442-450. Yamazaki, E., Murakami, K., & Kurita, O. (2005). Easy preparation of dietary fiber with the high waterholding capacity from food sources. Plant Foods for Human Nutrition, 60, 17-23. Yang, Y. Y., Ma, S., Wang, X., & Zheng, X. 2017. Modification and application of dietary fiber in foods. Journal of Chemistry, vol. 2017, Article ID 9340427, 8 pages. Zargaraan, A., Rastmanesh, R., Fadavi, G., Zayeri, F., & Mohammadifar, M. A. (2013). Rheological aspects of dysphagia-oriented food products: A mini review. Food Science and Human Wellness, 2(3), 173-178.