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Physicochemical characteristics of stored gels from starch blends
Accepted Manuscript Physicochemical characteristics of stored gels from starch blends H.A. Fonseca Florido, G. Méndez Montealvo, G. Velazquez, M.E. Rodríguez-García, L.A. Bello-Pérez, E. Hernández-Hernández, C.A. Gómez-Aldapa PII:
S0023-6438(19)30750-9
DOI:
https://doi.org/10.1016/j.lwt.2019.108408
Article Number: 108408 Reference:
YFSTL 108408
To appear in:
LWT - Food Science and Technology
Received Date: 12 April 2019 Revised Date:
27 June 2019
Accepted Date: 16 July 2019
Please cite this article as: Fonseca Florido, H.A., Méndez Montealvo, G., Velazquez, G., RodríguezGarcía, M.E., Bello-Pérez, L.A., Hernández-Hernández, E., Gómez-Aldapa, C.A., Physicochemical characteristics of stored gels from starch blends, LWT - Food Science and Technology (2019), doi: https://doi.org/10.1016/j.lwt.2019.108408. 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.
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Physicochemical characteristics of stored gels from starch blends
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Fonseca Florido, H. A. a, Méndez Montealvo, G.b*, Velazquez, G.b, Rodríguez-
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García, M. E.c, Bello-Pérez, L. A.d, Hernández-Hernández, E.a and Gómez-Aldapa,
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C. Ae*
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a
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Aplicada (CIQA), Saltillo, Coahuila, México. +CONACYT Research Fellow.
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b
Instituto Politécnico Nacional, CICATA unidad Querétaro, Querétaro, México.
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c
Universidad Nacional Autónoma de México, Departamento de Nanotecnología,
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Centro de Física Aplicada y Tecnología Avanzada, Campus Juriquilla, Querétaro,
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México.
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d
Instituto Politécnico Nacional, CEPROBI, Yautepec, Morelos, México.
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e
Universidad Autónoma del Estado de Hidalgo, Instituto de Ciencias Básicas e
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Ingeniería, Mineral de la Reforma, Hidalgo, México.
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*Corresponding author: [email protected], [email protected]
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Departamento de Materiales Avanzados, Centro de Investigación en Química
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Abstract
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Starch blends are widely used in food industry for several purposes, e.g. to reduce
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the retrogradation, to maintain the soft texture of some product and to develop
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different materials like microcapsules or biodegradable films. The aim of this work
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was to study the reorganization of the amylopectin in gels from amaranth (AmS)
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and achira (AS) starch blends stored at 4 °C during 21 days. The hardness,
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thermal properties, crystallinity and morphology of the gels were assessed. During
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the first 14 storage days, the structural rearrangement in the gels was mainly due
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to the long chains of amylopectin in AS, limiting the recrystallization and modifying
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the retrogradation process of the starches. The starch structure formed after the
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gelatinization along with the amylopectin fine structure resulted in a lower
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retrogradation extent of the blends when compared to the native starches. These
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starch blends could be used in systems where a decrease in the retrogradation
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process is crucial to maintain the textural and quality properties.
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Keywords: starch blends, retrogradation degree, amylopectin structure, remaining
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structure, crystallinity
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1. Introduction
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Starch is used in several food products to improve specific properties, for example,
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water holding capacity or rheological properties. Also, it is used to prepare
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microcapsules, films and foams due to its biodegradability. In order to understand
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and eventually to predict the effect of the starch on the properties and behavior of
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different systems, the gelatinization and retrogradation processes of starch have
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been the main topic of several studies (Fu, Wang, Li, Zhou, & Adhikari, 2013;
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Nguyen Vu & Lumdubwong, 2016). During the retrogradation, the reordering of
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amylopectin chains begins with the formation of double helices followed by an
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improvement of the crystalline structure (Fu et al., 2013; Wang & Copeland, 2015).
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The rearrangement process is influenced by several factors including storage
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temperature, time, water content, extent of gelatinization, presence of other
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solutes, botanical source, amylose/amylopectin ratio and chain-length distribution
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of amylopectin (Ambigaipalan, Hoover, Donner, & Liu, 2013; Fu et al., 2013; Wang,
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Li, Copeland, Niu, & Wang, 2015). The retrogradation of starch during storage is
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considered as the major reason for the deterioration of several functional
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properties in starch-based products (Ji et al., 2017).
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Native starch blends are been increasingly applied in industry, e.g. to prepare food
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with a desired rheological property, texture, storage stability or to replace chemical
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and physical modified starch (Gupta, Bawa, & Semwal, 2009; Nguyen Vu &
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Lumdubwong, 2016). However, for several applications the effect of the
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retrogradation process on the performance of starch blends still has not been fully
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studied. The understanding of the retrogradation process could be useful to
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develop new products, control processing parameters and formulate starch blends
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from unmodified starches possessing some of the desired characteristics of
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modified starches.
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Some authors have studied retrogradation of starch blends through pulsed nuclear
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magnetic resonance (Yao, Zhang, & Ding, 2003), gel hardness analysis (Gupta et
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al., 2009; Karam, Grossmann, Silva, Ferrero, & Zaritzky, 2005; Puncha-arnon,
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Pathipanawat, Puttanlek, Rungsardthong, & Uttapap, 2008), differential scanning
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calorimetry (Gunaratne & Corke, 2007; Obanni & Bemiller, 1997; Ortega-Ojeda &
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Eliasson, 2001; Zhu, Wang, & Wang, 2013) or syneresis (Yadav, Kumar, & Yadav,
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2016). In general, it has been reported that blending different starches may retard
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the retrogradation process. However, to our knowledge, in the literature there are
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no studies about the relationship between the structure reached after gelatinization
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and the amylopectin reorganization of starch blends as well as the effect of these
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parameters on the gel hardness, thermal properties and the crystallinity during
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storage.
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Achira and amaranth are considered as novel and alternative botanical sources for
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starch isolation. Achira starch has an average granule size of 45.4 µm, B-type
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diffraction pattern and amylose content of 30.75%, meanwhile amaranth starch has
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an average granule size of 0.9 µm, A-type diffraction pattern and amylose content
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of 12.35% (Fonseca-Florido, Méndez-Montealvo, Velazquez, & Gómez-Aldapa,
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2016).
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To understand the effect of the amylose content, granule size, diffraction pattern
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and fine structure on the reorganization of amylopectin during the storage of gels
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from the blend of the two starches, the aim of this work was to study the molecular
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reorganization level during the retrogradation of amaranth and achira starch blends
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at 40% solids stored for 21 days. The structural properties were evaluated by
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measuring crystallinity percentage, thermal properties and gel hardness.
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2. Materials and methods
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2.1 Materials and formulation of blends
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The producer Hernando Diaz Burbano provided the achira starch (Popayan,
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Colombia). Amaranth was obtained from a local market in Queretaro, Mexico. The
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amaranth starch was isolated following the method reported by Fonseca-Florido et
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al. (2016). Native amaranth (AmS) and achira (AS) starches and their blends in
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proportions of 75% AmS/25% AS (AmS75AS25, w/w), 50% AmS/50% AS
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(AmS50AS50, w/w) and 25% AmS/75% AS (AmS25AS75, w/w) were studied
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under limited water conditions (40% solids).
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2.2 Fine structure of debranched amylopectin
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The amaranth and achira starches were debranched using the method reported by
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Chávez‐Murillo, Wang, and Bello‐Pérez, (2008). Debranched starch was analyzed
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by HPAEC-PAD using a Dionex ICS 5000 instrument equipped with a Dionex AS-
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AP auto-sampler (Thermo Scientific, Waltham, United States), CarboPac PA200 (3
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× 250 mm) column and CarboPac PA200 guard column (3 × 50 mm). The potential
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and time periods for the pulsed amperometric detection were: E1, +0.10 V for 0.4 s;
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E2, -2.0 V for 0.02 s; E3, +0.60 V for 0.01 s; E4, -0.10 V for 0.07 s. Two eluents
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were used as the mobile phase: eluent A, 150 mM sodium hydroxide; and eluent B,
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150 mM sodium hydroxide containing 500 mM sodium acetate. The flow was 0.5
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mL min−1 and an eluent gradient was used as follow: 95% of eluent A for 5 min,
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60% to 18 min, 15% to 55 min and 95% to 75 min. The data was processed using
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the Chromeleon v. 6.80 SR11 software (Thermo Scientific, Waltham, United
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States). The degree of polymerization (DP) was reported as the percentage of
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area. Maltotriose and maltopentose were used as references to determine the
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elution time of respective DP polymer chains. DP for total chain distribution was
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calculated using the Equation 1 (Koch, Andersson, & Åman, 1998). ∑ ∑
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(Eq. 1)
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Where n is the number of peaks, Ai is the peak area and Ni is the degree of
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polymerization of the i-th peak.
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2.3 Thermal properties
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Thermal properties were determined using a differential scanning calorimeter
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(DSC-1, Mettler-Toledo, United States). Samples were gelatinized following the
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methodology reported by Fonseca-Florido et al. (2016), then the pans were stored
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at 4 °C for 1, 7, 14 and 21 days. After this period, the pans were equilibrated at
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room temperature for 1 h, and then rescanned under the same previous conditions
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(Heating at 5 °C/min from 25 to 95 °C). Onset (To), peak (Tp) and end (Te)
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temperatures were determined. Gelatinization enthalpy (∆HG) and retrogradation
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enthalpy on reheating (∆HR) of starch gels were calculated. All measurements
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were performed in triplicate. The degree of retrogradation (DR) was calculated
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using the Equation 2 at 1, 7, 14 and 21 days of storage.
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(%) = (∆H ⁄∆H )×100
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2.4 X-ray diffraction analysis
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To evaluate the crystallinity, gels were prepared under the same conditions
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described for thermal properties and stored at 4 °C for 1, 7, 14 and 21 days, then
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the samples were lyophilized (Freezone 4.5 Freeze Dry System, Labconco Corp.,
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United States). Later, X-ray diffraction (XRD) patterns were obtained using a
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diffractometer (Rigaku, Ultima IV, Japan), with a potential difference of 40 kV and
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30 mA, with monochromatic copper radiation, CuKα with λ=1.54 Å and filter of Ni.
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The Bragg-Brentano technique was used and the data were collected in the 2θ
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angle from 5 to 40° at 10°/min and angular step of 0.02 using a detector DTeX of
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high speed. In diffractograms, the areas corresponding to the crystalline and
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amorphous regions were determined using the Fytik software (Version 0.9.8).
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Crystallinity was determined following the method described by Hermans and
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Weidinger, (1948).
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2.5 Scanning electron microscopy
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Starch gels at 40% solids were stored for 1, 7, 14 and 21 days and then lyophilized
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(Freezone 4.5 Freeze Dry System, Labconco Corp., United States). Subsequently,
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the starch gels were observed using a scanning electron microscope (JEOL, JSM-
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6060LV, Japan). Samples were deposited on a sample holder with electrically
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conductive double-sided carbon tape, coated with gold and observed at 12-20 Pa
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of pressure and 20 KV of electron acceleration. The images were obtained by a
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secondary electron signal.
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2.6 Gel hardness 7
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Native starches and their blends at 40% solids, were heated at 90 °C using test
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tubes in a water bath for 30 min and stored at 4 °C for 21 days to allow
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retrogradation. For texture profile analysis, gel samples were cut into cylinders (2.5
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cm diameter x 1 cm height), placed in a texturometer (TA-XT plus, Stable Micro
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Systems, United Kingdom) and compressed at 30% deformation using a 2 mm/s
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crosshead speed. Three replicates were analyzed per sample. The hardness,
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calculated as the maximum force during compression at 30%, was used as an
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indicator for strength of the gel structure.
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2.7 Statistical analysis
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Results were analyzed using one-way and two-way analysis of variance (ANOVA)
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using Origin software (Version 9.0), with a 95% confidence level. Tukey's test was
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used to compare means (p ≤ .05). A second-order polynomial model was used
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(Equation 3) to describe the effect of the proportion of each starch and the storage
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time on the reorganization level of amylopectin molecules using the parameters of
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Tp, ∆HR, DR and crystallinity.
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yi = b0i + b1i x1 + b2i x2 + b3i x1 x2 + b4i x12+ b5i x22
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where x1 and x2 are the code variables for amaranth content and storage time,
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respectively, meanwhile b0i, b1i...b5i are regression coefficients. R2 and critical F-
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value parameters were estimated to determine if the model was adequate for
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describing the experimental data.
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(Eq. 3)
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3. Results and discussion
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As mentioned by Yao et al. (2003), the moisture content of each swollen granule is
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determined by the gelatinization temperature and the swelling power and it may not
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be necessarily distributed evenly in the starch gel system due to the heterogeneity
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of the granules. The authors also mentioned that at a high starch concentration
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(50%), a competition for water molecules took place and a non-additive behavior
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was observed. Considering that the retrogradation of starch can be greatly affected
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by the moisture content, our study is focus in describing evaluating the effect of the
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difference in granule size, amylose content and amylopectin chain length
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distribution on the retrogradation of gels from starch blends at 40% solids during
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the storage. The parameters that allowed obtaining the lowest retrogradation
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extent were identified.
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The effect of the amylose content and the granule size of amaranth and achira
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starches on the gelatinization process was reported in a previous work (Fonseca-
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Florido et al. 2016). The effect of the fine structure of debranched amylopectin is
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discussed in the present study. Chain distribution of native starches are
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summarized in Table 1. Amylopectin branch chains were grouped into four chain
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types, namely A, B1, B2, and B3+ corresponding to the 6-12, 13-24, 25-36, and
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>36 DP, respectively (Hanashiro, Abe, & Hizukuri, 1996). AmS showed higher
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proportions of A chain and smaller proportions in B1, B2 and B3+ chains than
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those in AS; consequently, AmS presented a slightly lower average chain length
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(16.8) when compared to AS (18.8). These differences in the structure between
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starches could affect their behavior during retrogradation.
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3.1 Thermal properties: changes of Tp, ∆HR and degree of retrogradation
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It is generally accepted that the transition endotherms observed in retrograded
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starch gels at temperatures below 100 °C are attributed to the rearrangement of
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the amylopectin (Vamadevan & Bertoft, 2018). The differences in To, Tp and Te
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reflect changes in the crystalline structure stability of the reorganized amylopectin,
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which is influenced by the chain-length distribution and the level of disorganization
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reached during the gelatinization of each starch (see supplementary information).
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In gels at 40% solids, Tp values of recrystallized amylopectin were lower than the
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temperatures of gelatinization reported in Fonseca-Florido et al. (2016), probably
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due to the type of crystalline structure developed during retrogradation. The
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interval of Te-To for the retrogradation ranged from 16.6 to 29.9 °C and it was
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broader than that reported for the gelatinization of the same samples (Fonseca-
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Florido et al., 2016). This behavior could be explained by the heterogeneity in the
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crystalline structure including differences in size, stability and perfection of the
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crystals formed during retrogradation.
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A polynomial model was used to describe the behavior of Tp, ∆HR and degree of
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retrogradation in the gels from starch blends (Figures 1). The critical F values
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ranged from 0.0000074 to 0.00010, and the R2 values ranged from 0.8358 to
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0.8916.
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AmS, AmS75AS25 and AmS50AS50 had similar Tp values (Figure 1A) of the
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studied samples ranged from 44.3 to 61.7 °C. In general, the storage time did not
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affect the Tp, but this value increased when the proportion of AS increased in the
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blend. This behavior could be associated with a high proportion of long chains
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(Table 1) and the presence of remaining structure of gelatinization which were
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reported by Fonseca-Florido et al. (2016). All the samples showed an increase in
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enthalpy of retrogradation (Figure 1B) associated with the formation of double
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helices of the amylopectin as a consequence of the recrystallization taking place
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during storage. AmS50AS50 had the lowest ∆H value, the lower values in ∆H of
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the blends than those from pure starches suggest a lower tendency to
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retrogradation.
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The degree of the retrogradation of AS, AmS and their blends is shown in Figure
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1C. In general, higher percentages of retrogradation were observed as the storage
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time increased. Samples of AS (0 % amaranth) showed the highest values at 1, 7
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and 14 days, while AmS (100% amaranth) reached the maximum value at day 21.
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Long chains of AS contribute to a greater increase of the retrogradation kinetics,
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allowing a faster reorganization in a shorter time than that of AmS. Silverio,
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Fredriksson, Andersson, Eliasson and Åman (2000), found that the long chain in
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amylopectin enhanced the retrogradation as shown by the high ∆H values
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measured by DSC. On the other hand, blends presented a non-additive effect with
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lower values.
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Differences in the thermal properties between starch blends when compared to
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pure starches during storage are related to the content of amylopectin, the
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remaining structure and the distribution of moisture.
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According to Vamadevan and Bertoft (2018), the high ∆H values, high transition
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temperatures and broad melting range observed in type 4 amylopectin starches
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(potato and achira starch) agreed with previous studies that have shown that amylopectin in cereals is less prone to retrogradation, which explains the difference
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between AmS and AS found in this study. Also, competition for water during
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gelatinization and the remaining crystalline structure in starch blends affected its
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retrogradation process. The restriction in molecular interactions (molecular
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mobility) between chains of the same starch as well as between starches, modified
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the retrogradation process.
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3.2 X-ray diffraction (XRD)
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Figure 2 shows the X-ray diffraction patterns for gels from AmS and AS at 40% of
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solids through the storage time, similar trend in the diffraction patterns was
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observed for all the studied blends (data not shown). The molecular rearrangement
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during retrogradation is characterized by the formation of crystalline structures that
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determine the signal intensity. The intensity and type of signal depend on the
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storage temperature, water content and amylose/amylopectin ratio (Ambigaipalan
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et al., 2013).
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Under limiting water conditions (40% solids), the percentage of crystallinity and the
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intensity of peaks in the diffractograms increase a little during 21 days of storage,
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probably because the high proportion of remaining ordered structure limited the
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interactions among amylopectin chains. Also, the amylopectin fine structure could
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have prevented the formation of an ordered structure (Bertoft et al., 2016; Fu et al.,
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2013). This behavior is reflected in low values of ∆HR (Figure 1B) and in the
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percentage of retrogradation (Figure 1C).
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The percentage of crystallinity for AmS, AS and their blends is shown in Figure 3.
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The crystallinity of AmS75AS25 blend increased from 9.9 to 12.53 % at day 1 and
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day 21, respectively. The low values of crystallinity obtained in this blend may be
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related to the higher degree of disorganization during gelatinization (Fonseca-
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Florido et al., 2016). A higher disorganization could cause a change in orientation
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of the two chains that constitute the double helices, retarding the reorganization
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during retrogradation (Fisher & Thompson, 1997).
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For AmS50AS50 blend, the percentage of crystallinity was 12.85 and 13.65% at 1
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and 21 days, respectively. AmS25AS75 blend had the same behavior than
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AmS50AS50 blend. These values increased up to 13.71 and 15.77% for the same
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storage times. The chain-length distribution of amylopectin in AS could explain the
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highest increase in the percentage of crystallinity as Vamadevan and Bertoft,
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(2018) indicated that retrogradation is strongly influenced by the interactions
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between the long amylopectin chains.
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The differences in the crystallinity observed in the AmS and AS blends are
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explained by the structure of amylopectin, the content and competition for water
289
and the ordered structure after gelatinization, which limited the mobility and the
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interactions between adjacent chains. Blending AmS and AS allowed decreasing
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the reorganization of starch crystals. In the starch gels studied, a high crystallinity
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was observed probably due to a high quantity of initial structure remaining and the
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high solids content; however, these parameters did not changed significantly
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during storage probably due to the limitation in molecular mobility.
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3.3 Scanning electron microscopy during the retrogradation process 13
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The morphology of the retrograded gels is shown in Figure 4. All gels showed a
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non-uniform structure with differences in the arrangement (alignment, shape of the
299
cavities and fractures) and tightly interconnected after recrystallization of
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amylopectin.
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The formation of a three-dimensional network with cavities or pores at day 1 was
302
observed in the AmS25AS75 and AmS50AS50 blends (see marking arrows)
303
(Figure 4). At higher magnifications, some non-gelatinized granules were detected
304
with more detail. In AmS50AS50 blend, the structure was heterogeneous and
305
rough with a high amount of entrapped granules (see marking circles) acting as
306
retarding agents, which could have limited the recrystallization of amylopectin.
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A different structure arrangement between day 1 and 21 was found in the blends.
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At day 21, a high quantity of remnant granules with least cavities or pores were
309
observed. This behavior allows correlating the changes in the morphological
310
structure of the blends with the low percentage of retrogradation, ∆HR and the
311
percentage of crystallinity during storage.
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According to SEM micrographs, the formation of a heterogeneous and rough
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structure with non-gelatinized granules embedded in the starch matrix could have
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prevented the rearrangement of the amylopectin molecules in the blends.
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Bertoft et al. (2016) found that low amounts of B2-chains resulted in low ∆H values
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and low iodine binding properties. The results suggest that very few intermolecular
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interactions involving internal chain segments were established, and probably most
319
interconnections took place among external chains of adjacent molecules.
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3.4 Gel hardness
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Gel hardness values of AmS, AS and their blends after 21 days of storage are
323
shown in Table 2. The increasing of gel hardness during storage could be due to
324
intermolecular bridges established simultaneously (Bertoft et al., 2016), although
325
the remaining structure limited the propagation of the crystals.
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The blends showed a behavior similar to that of AmS. The increasing of AmS in the
327
blends resulted in lower values of hardness. Results suggest that the
328
retrogradation process in the studied blends was more influenced by AmS. The
329
high content of highly-branched amylopectin with a low average chain length in
330
AmS, resulted in softer gels during recrystallization. Vamadevan and Bertoft (2018)
331
mentioned that the amylopectin with short chains results in weak gels with short
332
double-helices, poor inter-molecular alignment and short inter-molecular double-
333
helical junctions.
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The increase in hardness during storage of the AS and the AmS25A75 samples is
335
explained by the amylose content and the high proportion of amylopectin long
336
chains which contain more cross-linking zones for the reorganization of the
337
molecules. Saeaurng and Kuakpetoon (2018) mentioned that long amylopectin
338
chains contributed to a high degree of amylopectin retrogradation.
339
On the other side, no significant differences (p<0.05) were found among the blends
340
at 21 days of storage (Table 2) which could also be attributed to the remaining
341
structure of native starch (Fonseca-Florido et al., 2016).
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The hardness values for AS gels at 40% solids changed slightly through 21 days of
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storage. Probably, a decrease in the interaction between external chains of
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amylopectin enforced the gel structure during retrogradation. Also, the lack of
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propagation of crystals promoted by the remaining structure resulted in the low
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hardness values in the blends containing AS.
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The gel hardness could be controlled by the proportion of the long and short chains
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depending on the botanical source of starches in the blend.
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4. Conclusions
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Due to the long amylopectin chains and the high amount of amylose, achira starch
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drove the retrogradation process of the blends up to 14 days of storage.
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Nevertheless, at 21 days, the amaranth starch, because of its high amylopectin
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content, ruled the retrogradation process. In the blends, the achira starch acted as
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a retarding agent limiting the recrystallization and modifying the retrogradation
356
process.
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Amylopectin reorganization during storage of starch blends depended on the
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presence of remaining structure and the differences in chain-length distribution of
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amylopectin. Incomplete gelatinization and high restriction on chain mobility
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significantly affected the rearrangement of amylopectin in retrograded starches
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blends.
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The behavior of the gels obtained from blends of amaranth and achira starches
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could be useful to maintain the texture and quality during storage of food products
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containing starch. Additionally, starch blends might provide the same response that
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starches chemically modified and they can be used when natural products are
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required.
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Acknowledgment 16
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M. Alicia Del Real-López, for the service and loan of the scanning electron
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microscopy equipment of the Centro de Física Aplicada y Tecnología Avanzada,
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Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro. HAFF
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acknowledge the scholarship from CONACyT-Mexico, and the support of the
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Laboratorio Nacional en Innovación y Desarrollo de Materiales Ligeros para la
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Industria Automotriz (LANIAUTO), CONACyT Project 294030. The support of Q.A.
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Martín Adelaido Hernández Landaverde for the X-ray analysis is appreciated.
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amylopectin on retrogradation. Food Hydrocolloids, 80, 88–96.
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Wang, S., & Copeland, L. (2015). Effect of acid hydrolysis on starch structure and
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Wang, S., Li, C., Copeland, L., Niu, Q., & Wang, S. (2015). Starch Retrogradation:
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potato, and rice starch blends for their physicochemical and pasting properties.
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https://doi.org/10.1080/23311932.2015.1127873
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Yao, Y., Zhang, J., & Ding, X. (2003). Retrogradation of starch mixtures containing rice starch. Journal of Food Science, 68(1), 260–265. 20
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https://doi.org/10.1111/j.1365-2621.2003.tb14149.x Zhu, F., Wang, S., & Wang, Y. J. (2013). Physical properties and enzyme susceptibility of rice and high-amylose maize starch mixtures. Journal of the
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Figure caption
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Figure 1. Peak temperature (A), enthalpy of retrogradation (B) and degree of
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retrogradation (C) of gels from AmS and AS and their blends at 40 % solids during
476
storage at 4 °C.
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Figure 2. X-ray diffraction patterns of: A) AmS, B) AS at 40% solids, stored at 4 °C.
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Figure 3. Crystallinity percentage of AmS and AS and their blends at during
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storage at 4 °C
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Figure 4. Microphotograph of blends at 40% solids, stored at 4 °C at 250, 1000
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and 2500 magnifications.
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Table 1. Degree of polymerization of amaranth and achira starches.
AS AmS
% Chain-length distribution
18.8 ± 0.1
A chain (DP 6-12) 31.6± 0.5
B1 chain (DP 13-24) 49.2 ± 0.1
B2 chain (DP 25-36) 9.7 ± 0.3
B3 + chain (DP≥37) 9.4± 0.2
16.8 ± 0.1
43.5 ± 0.2
41.1 ± 0.1
8.1 ± 0.1
7.2 ± 0.1
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Average chain length (DP)
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DP=Degree of polymerization. Values are means of three replicates
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Table 2. Gels hardness for AmS, AS and their blends at 21 days of storage at 4 °C. Blends
Hardness (N)
Increase over time (%) 171
83.89±1.67a
AmS75AS25
118.23±2.43b
30.8
AmS50AS50
124.63±4.18b
11.5
AmS25AS75
115.91±3.72b
3.13
AS
149.48±3.44c
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AmS
1
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Values with different letter indicate significant difference (p<0.05).
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Highlights - Orderly structure remaining affects amylopectin reorganization - Achira starch acts like retardant agent to amaranth starch retrogradation
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- Starch blends presented lower degree of retrogradation and retrogradation enthalpy
- Water competition between starches limits molecular mobility
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- Amylopectin chain length affects the molecular interaction of starches blends
S0023-6438(19)30750-9
DOI:
https://doi.org/10.1016/j.lwt.2019.108408
Article Number: 108408 Reference:
YFSTL 108408
To appear in:
LWT - Food Science and Technology
Received Date: 12 April 2019 Revised Date:
27 June 2019
Accepted Date: 16 July 2019
Please cite this article as: Fonseca Florido, H.A., Méndez Montealvo, G., Velazquez, G., RodríguezGarcía, M.E., Bello-Pérez, L.A., Hernández-Hernández, E., Gómez-Aldapa, C.A., Physicochemical characteristics of stored gels from starch blends, LWT - Food Science and Technology (2019), doi: https://doi.org/10.1016/j.lwt.2019.108408. 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.
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Physicochemical characteristics of stored gels from starch blends
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Fonseca Florido, H. A. a, Méndez Montealvo, G.b*, Velazquez, G.b, Rodríguez-
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García, M. E.c, Bello-Pérez, L. A.d, Hernández-Hernández, E.a and Gómez-Aldapa,
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C. Ae*
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a
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Aplicada (CIQA), Saltillo, Coahuila, México. +CONACYT Research Fellow.
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b
Instituto Politécnico Nacional, CICATA unidad Querétaro, Querétaro, México.
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c
Universidad Nacional Autónoma de México, Departamento de Nanotecnología,
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Centro de Física Aplicada y Tecnología Avanzada, Campus Juriquilla, Querétaro,
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México.
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d
Instituto Politécnico Nacional, CEPROBI, Yautepec, Morelos, México.
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e
Universidad Autónoma del Estado de Hidalgo, Instituto de Ciencias Básicas e
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Ingeniería, Mineral de la Reforma, Hidalgo, México.
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*Corresponding author: [email protected], [email protected]
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Departamento de Materiales Avanzados, Centro de Investigación en Química
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Abstract
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Starch blends are widely used in food industry for several purposes, e.g. to reduce
21
the retrogradation, to maintain the soft texture of some product and to develop
22
different materials like microcapsules or biodegradable films. The aim of this work
23
was to study the reorganization of the amylopectin in gels from amaranth (AmS)
24
and achira (AS) starch blends stored at 4 °C during 21 days. The hardness,
25
thermal properties, crystallinity and morphology of the gels were assessed. During
26
the first 14 storage days, the structural rearrangement in the gels was mainly due
27
to the long chains of amylopectin in AS, limiting the recrystallization and modifying
28
the retrogradation process of the starches. The starch structure formed after the
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gelatinization along with the amylopectin fine structure resulted in a lower
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retrogradation extent of the blends when compared to the native starches. These
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starch blends could be used in systems where a decrease in the retrogradation
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process is crucial to maintain the textural and quality properties.
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Keywords: starch blends, retrogradation degree, amylopectin structure, remaining
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structure, crystallinity
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1. Introduction
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Starch is used in several food products to improve specific properties, for example,
38
water holding capacity or rheological properties. Also, it is used to prepare
39
microcapsules, films and foams due to its biodegradability. In order to understand
40
and eventually to predict the effect of the starch on the properties and behavior of
41
different systems, the gelatinization and retrogradation processes of starch have
42
been the main topic of several studies (Fu, Wang, Li, Zhou, & Adhikari, 2013;
43
Nguyen Vu & Lumdubwong, 2016). During the retrogradation, the reordering of
44
amylopectin chains begins with the formation of double helices followed by an
45
improvement of the crystalline structure (Fu et al., 2013; Wang & Copeland, 2015).
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The rearrangement process is influenced by several factors including storage
47
temperature, time, water content, extent of gelatinization, presence of other
48
solutes, botanical source, amylose/amylopectin ratio and chain-length distribution
49
of amylopectin (Ambigaipalan, Hoover, Donner, & Liu, 2013; Fu et al., 2013; Wang,
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Li, Copeland, Niu, & Wang, 2015). The retrogradation of starch during storage is
51
considered as the major reason for the deterioration of several functional
52
properties in starch-based products (Ji et al., 2017).
53
Native starch blends are been increasingly applied in industry, e.g. to prepare food
54
with a desired rheological property, texture, storage stability or to replace chemical
55
and physical modified starch (Gupta, Bawa, & Semwal, 2009; Nguyen Vu &
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Lumdubwong, 2016). However, for several applications the effect of the
57
retrogradation process on the performance of starch blends still has not been fully
58
studied. The understanding of the retrogradation process could be useful to
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develop new products, control processing parameters and formulate starch blends
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from unmodified starches possessing some of the desired characteristics of
61
modified starches.
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Some authors have studied retrogradation of starch blends through pulsed nuclear
63
magnetic resonance (Yao, Zhang, & Ding, 2003), gel hardness analysis (Gupta et
64
al., 2009; Karam, Grossmann, Silva, Ferrero, & Zaritzky, 2005; Puncha-arnon,
65
Pathipanawat, Puttanlek, Rungsardthong, & Uttapap, 2008), differential scanning
66
calorimetry (Gunaratne & Corke, 2007; Obanni & Bemiller, 1997; Ortega-Ojeda &
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Eliasson, 2001; Zhu, Wang, & Wang, 2013) or syneresis (Yadav, Kumar, & Yadav,
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2016). In general, it has been reported that blending different starches may retard
69
the retrogradation process. However, to our knowledge, in the literature there are
70
no studies about the relationship between the structure reached after gelatinization
71
and the amylopectin reorganization of starch blends as well as the effect of these
72
parameters on the gel hardness, thermal properties and the crystallinity during
73
storage.
74
Achira and amaranth are considered as novel and alternative botanical sources for
75
starch isolation. Achira starch has an average granule size of 45.4 µm, B-type
76
diffraction pattern and amylose content of 30.75%, meanwhile amaranth starch has
77
an average granule size of 0.9 µm, A-type diffraction pattern and amylose content
78
of 12.35% (Fonseca-Florido, Méndez-Montealvo, Velazquez, & Gómez-Aldapa,
79
2016).
80
To understand the effect of the amylose content, granule size, diffraction pattern
81
and fine structure on the reorganization of amylopectin during the storage of gels
82
from the blend of the two starches, the aim of this work was to study the molecular
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reorganization level during the retrogradation of amaranth and achira starch blends
84
at 40% solids stored for 21 days. The structural properties were evaluated by
85
measuring crystallinity percentage, thermal properties and gel hardness.
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2. Materials and methods
88
2.1 Materials and formulation of blends
89
The producer Hernando Diaz Burbano provided the achira starch (Popayan,
90
Colombia). Amaranth was obtained from a local market in Queretaro, Mexico. The
91
amaranth starch was isolated following the method reported by Fonseca-Florido et
92
al. (2016). Native amaranth (AmS) and achira (AS) starches and their blends in
93
proportions of 75% AmS/25% AS (AmS75AS25, w/w), 50% AmS/50% AS
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(AmS50AS50, w/w) and 25% AmS/75% AS (AmS25AS75, w/w) were studied
95
under limited water conditions (40% solids).
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2.2 Fine structure of debranched amylopectin
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The amaranth and achira starches were debranched using the method reported by
99
Chávez‐Murillo, Wang, and Bello‐Pérez, (2008). Debranched starch was analyzed
100
by HPAEC-PAD using a Dionex ICS 5000 instrument equipped with a Dionex AS-
101
AP auto-sampler (Thermo Scientific, Waltham, United States), CarboPac PA200 (3
102
× 250 mm) column and CarboPac PA200 guard column (3 × 50 mm). The potential
103
and time periods for the pulsed amperometric detection were: E1, +0.10 V for 0.4 s;
104
E2, -2.0 V for 0.02 s; E3, +0.60 V for 0.01 s; E4, -0.10 V for 0.07 s. Two eluents
105
were used as the mobile phase: eluent A, 150 mM sodium hydroxide; and eluent B,
106
150 mM sodium hydroxide containing 500 mM sodium acetate. The flow was 0.5
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mL min−1 and an eluent gradient was used as follow: 95% of eluent A for 5 min,
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60% to 18 min, 15% to 55 min and 95% to 75 min. The data was processed using
109
the Chromeleon v. 6.80 SR11 software (Thermo Scientific, Waltham, United
110
States). The degree of polymerization (DP) was reported as the percentage of
111
area. Maltotriose and maltopentose were used as references to determine the
112
elution time of respective DP polymer chains. DP for total chain distribution was
113
calculated using the Equation 1 (Koch, Andersson, & Åman, 1998). ∑ ∑
⋀ ⋀
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(Eq. 1)
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Where n is the number of peaks, Ai is the peak area and Ni is the degree of
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polymerization of the i-th peak.
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2.3 Thermal properties
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Thermal properties were determined using a differential scanning calorimeter
120
(DSC-1, Mettler-Toledo, United States). Samples were gelatinized following the
121
methodology reported by Fonseca-Florido et al. (2016), then the pans were stored
122
at 4 °C for 1, 7, 14 and 21 days. After this period, the pans were equilibrated at
123
room temperature for 1 h, and then rescanned under the same previous conditions
124
(Heating at 5 °C/min from 25 to 95 °C). Onset (To), peak (Tp) and end (Te)
125
temperatures were determined. Gelatinization enthalpy (∆HG) and retrogradation
126
enthalpy on reheating (∆HR) of starch gels were calculated. All measurements
127
were performed in triplicate. The degree of retrogradation (DR) was calculated
128
using the Equation 2 at 1, 7, 14 and 21 days of storage.
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(%) = (∆H ⁄∆H )×100
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2.4 X-ray diffraction analysis
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To evaluate the crystallinity, gels were prepared under the same conditions
132
described for thermal properties and stored at 4 °C for 1, 7, 14 and 21 days, then
133
the samples were lyophilized (Freezone 4.5 Freeze Dry System, Labconco Corp.,
134
United States). Later, X-ray diffraction (XRD) patterns were obtained using a
135
diffractometer (Rigaku, Ultima IV, Japan), with a potential difference of 40 kV and
136
30 mA, with monochromatic copper radiation, CuKα with λ=1.54 Å and filter of Ni.
137
The Bragg-Brentano technique was used and the data were collected in the 2θ
138
angle from 5 to 40° at 10°/min and angular step of 0.02 using a detector DTeX of
139
high speed. In diffractograms, the areas corresponding to the crystalline and
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amorphous regions were determined using the Fytik software (Version 0.9.8).
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Crystallinity was determined following the method described by Hermans and
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Weidinger, (1948).
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2.5 Scanning electron microscopy
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Starch gels at 40% solids were stored for 1, 7, 14 and 21 days and then lyophilized
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(Freezone 4.5 Freeze Dry System, Labconco Corp., United States). Subsequently,
147
the starch gels were observed using a scanning electron microscope (JEOL, JSM-
148
6060LV, Japan). Samples were deposited on a sample holder with electrically
149
conductive double-sided carbon tape, coated with gold and observed at 12-20 Pa
150
of pressure and 20 KV of electron acceleration. The images were obtained by a
151
secondary electron signal.
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2.6 Gel hardness 7
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Native starches and their blends at 40% solids, were heated at 90 °C using test
155
tubes in a water bath for 30 min and stored at 4 °C for 21 days to allow
156
retrogradation. For texture profile analysis, gel samples were cut into cylinders (2.5
157
cm diameter x 1 cm height), placed in a texturometer (TA-XT plus, Stable Micro
158
Systems, United Kingdom) and compressed at 30% deformation using a 2 mm/s
159
crosshead speed. Three replicates were analyzed per sample. The hardness,
160
calculated as the maximum force during compression at 30%, was used as an
161
indicator for strength of the gel structure.
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2.7 Statistical analysis
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Results were analyzed using one-way and two-way analysis of variance (ANOVA)
165
using Origin software (Version 9.0), with a 95% confidence level. Tukey's test was
166
used to compare means (p ≤ .05). A second-order polynomial model was used
167
(Equation 3) to describe the effect of the proportion of each starch and the storage
168
time on the reorganization level of amylopectin molecules using the parameters of
169
Tp, ∆HR, DR and crystallinity.
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yi = b0i + b1i x1 + b2i x2 + b3i x1 x2 + b4i x12+ b5i x22
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where x1 and x2 are the code variables for amaranth content and storage time,
172
respectively, meanwhile b0i, b1i...b5i are regression coefficients. R2 and critical F-
173
value parameters were estimated to determine if the model was adequate for
174
describing the experimental data.
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3. Results and discussion
179
As mentioned by Yao et al. (2003), the moisture content of each swollen granule is
180
determined by the gelatinization temperature and the swelling power and it may not
181
be necessarily distributed evenly in the starch gel system due to the heterogeneity
182
of the granules. The authors also mentioned that at a high starch concentration
183
(50%), a competition for water molecules took place and a non-additive behavior
184
was observed. Considering that the retrogradation of starch can be greatly affected
185
by the moisture content, our study is focus in describing evaluating the effect of the
186
difference in granule size, amylose content and amylopectin chain length
187
distribution on the retrogradation of gels from starch blends at 40% solids during
188
the storage. The parameters that allowed obtaining the lowest retrogradation
189
extent were identified.
190
The effect of the amylose content and the granule size of amaranth and achira
191
starches on the gelatinization process was reported in a previous work (Fonseca-
192
Florido et al. 2016). The effect of the fine structure of debranched amylopectin is
193
discussed in the present study. Chain distribution of native starches are
194
summarized in Table 1. Amylopectin branch chains were grouped into four chain
195
types, namely A, B1, B2, and B3+ corresponding to the 6-12, 13-24, 25-36, and
196
>36 DP, respectively (Hanashiro, Abe, & Hizukuri, 1996). AmS showed higher
197
proportions of A chain and smaller proportions in B1, B2 and B3+ chains than
198
those in AS; consequently, AmS presented a slightly lower average chain length
199
(16.8) when compared to AS (18.8). These differences in the structure between
200
starches could affect their behavior during retrogradation.
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3.1 Thermal properties: changes of Tp, ∆HR and degree of retrogradation
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It is generally accepted that the transition endotherms observed in retrograded
205
starch gels at temperatures below 100 °C are attributed to the rearrangement of
206
the amylopectin (Vamadevan & Bertoft, 2018). The differences in To, Tp and Te
207
reflect changes in the crystalline structure stability of the reorganized amylopectin,
208
which is influenced by the chain-length distribution and the level of disorganization
209
reached during the gelatinization of each starch (see supplementary information).
210
In gels at 40% solids, Tp values of recrystallized amylopectin were lower than the
211
temperatures of gelatinization reported in Fonseca-Florido et al. (2016), probably
212
due to the type of crystalline structure developed during retrogradation. The
213
interval of Te-To for the retrogradation ranged from 16.6 to 29.9 °C and it was
214
broader than that reported for the gelatinization of the same samples (Fonseca-
215
Florido et al., 2016). This behavior could be explained by the heterogeneity in the
216
crystalline structure including differences in size, stability and perfection of the
217
crystals formed during retrogradation.
218
A polynomial model was used to describe the behavior of Tp, ∆HR and degree of
219
retrogradation in the gels from starch blends (Figures 1). The critical F values
220
ranged from 0.0000074 to 0.00010, and the R2 values ranged from 0.8358 to
221
0.8916.
222
AmS, AmS75AS25 and AmS50AS50 had similar Tp values (Figure 1A) of the
223
studied samples ranged from 44.3 to 61.7 °C. In general, the storage time did not
224
affect the Tp, but this value increased when the proportion of AS increased in the
225
blend. This behavior could be associated with a high proportion of long chains
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(Table 1) and the presence of remaining structure of gelatinization which were
227
reported by Fonseca-Florido et al. (2016). All the samples showed an increase in
228
enthalpy of retrogradation (Figure 1B) associated with the formation of double
229
helices of the amylopectin as a consequence of the recrystallization taking place
230
during storage. AmS50AS50 had the lowest ∆H value, the lower values in ∆H of
231
the blends than those from pure starches suggest a lower tendency to
232
retrogradation.
233
The degree of the retrogradation of AS, AmS and their blends is shown in Figure
234
1C. In general, higher percentages of retrogradation were observed as the storage
235
time increased. Samples of AS (0 % amaranth) showed the highest values at 1, 7
236
and 14 days, while AmS (100% amaranth) reached the maximum value at day 21.
237
Long chains of AS contribute to a greater increase of the retrogradation kinetics,
238
allowing a faster reorganization in a shorter time than that of AmS. Silverio,
239
Fredriksson, Andersson, Eliasson and Åman (2000), found that the long chain in
240
amylopectin enhanced the retrogradation as shown by the high ∆H values
241
measured by DSC. On the other hand, blends presented a non-additive effect with
242
lower values.
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Differences in the thermal properties between starch blends when compared to
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pure starches during storage are related to the content of amylopectin, the
246
remaining structure and the distribution of moisture.
247
According to Vamadevan and Bertoft (2018), the high ∆H values, high transition
248
temperatures and broad melting range observed in type 4 amylopectin starches
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(potato and achira starch) agreed with previous studies that have shown that amylopectin in cereals is less prone to retrogradation, which explains the difference
251
between AmS and AS found in this study. Also, competition for water during
252
gelatinization and the remaining crystalline structure in starch blends affected its
253
retrogradation process. The restriction in molecular interactions (molecular
254
mobility) between chains of the same starch as well as between starches, modified
255
the retrogradation process.
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3.2 X-ray diffraction (XRD)
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Figure 2 shows the X-ray diffraction patterns for gels from AmS and AS at 40% of
259
solids through the storage time, similar trend in the diffraction patterns was
260
observed for all the studied blends (data not shown). The molecular rearrangement
261
during retrogradation is characterized by the formation of crystalline structures that
262
determine the signal intensity. The intensity and type of signal depend on the
263
storage temperature, water content and amylose/amylopectin ratio (Ambigaipalan
264
et al., 2013).
265
Under limiting water conditions (40% solids), the percentage of crystallinity and the
266
intensity of peaks in the diffractograms increase a little during 21 days of storage,
267
probably because the high proportion of remaining ordered structure limited the
268
interactions among amylopectin chains. Also, the amylopectin fine structure could
269
have prevented the formation of an ordered structure (Bertoft et al., 2016; Fu et al.,
270
2013). This behavior is reflected in low values of ∆HR (Figure 1B) and in the
271
percentage of retrogradation (Figure 1C).
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The percentage of crystallinity for AmS, AS and their blends is shown in Figure 3.
274
The crystallinity of AmS75AS25 blend increased from 9.9 to 12.53 % at day 1 and
275
day 21, respectively. The low values of crystallinity obtained in this blend may be
276
related to the higher degree of disorganization during gelatinization (Fonseca-
277
Florido et al., 2016). A higher disorganization could cause a change in orientation
278
of the two chains that constitute the double helices, retarding the reorganization
279
during retrogradation (Fisher & Thompson, 1997).
280
For AmS50AS50 blend, the percentage of crystallinity was 12.85 and 13.65% at 1
281
and 21 days, respectively. AmS25AS75 blend had the same behavior than
282
AmS50AS50 blend. These values increased up to 13.71 and 15.77% for the same
283
storage times. The chain-length distribution of amylopectin in AS could explain the
284
highest increase in the percentage of crystallinity as Vamadevan and Bertoft,
285
(2018) indicated that retrogradation is strongly influenced by the interactions
286
between the long amylopectin chains.
287
The differences in the crystallinity observed in the AmS and AS blends are
288
explained by the structure of amylopectin, the content and competition for water
289
and the ordered structure after gelatinization, which limited the mobility and the
290
interactions between adjacent chains. Blending AmS and AS allowed decreasing
291
the reorganization of starch crystals. In the starch gels studied, a high crystallinity
292
was observed probably due to a high quantity of initial structure remaining and the
293
high solids content; however, these parameters did not changed significantly
294
during storage probably due to the limitation in molecular mobility.
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3.3 Scanning electron microscopy during the retrogradation process 13
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The morphology of the retrograded gels is shown in Figure 4. All gels showed a
298
non-uniform structure with differences in the arrangement (alignment, shape of the
299
cavities and fractures) and tightly interconnected after recrystallization of
300
amylopectin.
301
The formation of a three-dimensional network with cavities or pores at day 1 was
302
observed in the AmS25AS75 and AmS50AS50 blends (see marking arrows)
303
(Figure 4). At higher magnifications, some non-gelatinized granules were detected
304
with more detail. In AmS50AS50 blend, the structure was heterogeneous and
305
rough with a high amount of entrapped granules (see marking circles) acting as
306
retarding agents, which could have limited the recrystallization of amylopectin.
307
A different structure arrangement between day 1 and 21 was found in the blends.
308
At day 21, a high quantity of remnant granules with least cavities or pores were
309
observed. This behavior allows correlating the changes in the morphological
310
structure of the blends with the low percentage of retrogradation, ∆HR and the
311
percentage of crystallinity during storage.
312
According to SEM micrographs, the formation of a heterogeneous and rough
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structure with non-gelatinized granules embedded in the starch matrix could have
314
prevented the rearrangement of the amylopectin molecules in the blends.
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Bertoft et al. (2016) found that low amounts of B2-chains resulted in low ∆H values
317
and low iodine binding properties. The results suggest that very few intermolecular
318
interactions involving internal chain segments were established, and probably most
319
interconnections took place among external chains of adjacent molecules.
320 14
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3.4 Gel hardness
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Gel hardness values of AmS, AS and their blends after 21 days of storage are
323
shown in Table 2. The increasing of gel hardness during storage could be due to
324
intermolecular bridges established simultaneously (Bertoft et al., 2016), although
325
the remaining structure limited the propagation of the crystals.
326
The blends showed a behavior similar to that of AmS. The increasing of AmS in the
327
blends resulted in lower values of hardness. Results suggest that the
328
retrogradation process in the studied blends was more influenced by AmS. The
329
high content of highly-branched amylopectin with a low average chain length in
330
AmS, resulted in softer gels during recrystallization. Vamadevan and Bertoft (2018)
331
mentioned that the amylopectin with short chains results in weak gels with short
332
double-helices, poor inter-molecular alignment and short inter-molecular double-
333
helical junctions.
334
The increase in hardness during storage of the AS and the AmS25A75 samples is
335
explained by the amylose content and the high proportion of amylopectin long
336
chains which contain more cross-linking zones for the reorganization of the
337
molecules. Saeaurng and Kuakpetoon (2018) mentioned that long amylopectin
338
chains contributed to a high degree of amylopectin retrogradation.
339
On the other side, no significant differences (p<0.05) were found among the blends
340
at 21 days of storage (Table 2) which could also be attributed to the remaining
341
structure of native starch (Fonseca-Florido et al., 2016).
342
The hardness values for AS gels at 40% solids changed slightly through 21 days of
343
storage. Probably, a decrease in the interaction between external chains of
344
amylopectin enforced the gel structure during retrogradation. Also, the lack of
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propagation of crystals promoted by the remaining structure resulted in the low
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hardness values in the blends containing AS.
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The gel hardness could be controlled by the proportion of the long and short chains
348
depending on the botanical source of starches in the blend.
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4. Conclusions
351
Due to the long amylopectin chains and the high amount of amylose, achira starch
352
drove the retrogradation process of the blends up to 14 days of storage.
353
Nevertheless, at 21 days, the amaranth starch, because of its high amylopectin
354
content, ruled the retrogradation process. In the blends, the achira starch acted as
355
a retarding agent limiting the recrystallization and modifying the retrogradation
356
process.
357
Amylopectin reorganization during storage of starch blends depended on the
358
presence of remaining structure and the differences in chain-length distribution of
359
amylopectin. Incomplete gelatinization and high restriction on chain mobility
360
significantly affected the rearrangement of amylopectin in retrograded starches
361
blends.
362
The behavior of the gels obtained from blends of amaranth and achira starches
363
could be useful to maintain the texture and quality during storage of food products
364
containing starch. Additionally, starch blends might provide the same response that
365
starches chemically modified and they can be used when natural products are
366
required.
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Acknowledgment 16
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M. Alicia Del Real-López, for the service and loan of the scanning electron
370
microscopy equipment of the Centro de Física Aplicada y Tecnología Avanzada,
371
Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro. HAFF
372
acknowledge the scholarship from CONACyT-Mexico, and the support of the
373
Laboratorio Nacional en Innovación y Desarrollo de Materiales Ligeros para la
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Industria Automotriz (LANIAUTO), CONACyT Project 294030. The support of Q.A.
375
Martín Adelaido Hernández Landaverde for the X-ray analysis is appreciated.
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Figure caption
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Figure 1. Peak temperature (A), enthalpy of retrogradation (B) and degree of
475
retrogradation (C) of gels from AmS and AS and their blends at 40 % solids during
476
storage at 4 °C.
477
Figure 2. X-ray diffraction patterns of: A) AmS, B) AS at 40% solids, stored at 4 °C.
478
Figure 3. Crystallinity percentage of AmS and AS and their blends at during
479
storage at 4 °C
480
Figure 4. Microphotograph of blends at 40% solids, stored at 4 °C at 250, 1000
481
and 2500 magnifications.
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Table 1. Degree of polymerization of amaranth and achira starches.
AS AmS
% Chain-length distribution
18.8 ± 0.1
A chain (DP 6-12) 31.6± 0.5
B1 chain (DP 13-24) 49.2 ± 0.1
B2 chain (DP 25-36) 9.7 ± 0.3
B3 + chain (DP≥37) 9.4± 0.2
16.8 ± 0.1
43.5 ± 0.2
41.1 ± 0.1
8.1 ± 0.1
7.2 ± 0.1
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Average chain length (DP)
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Table 2. Gels hardness for AmS, AS and their blends at 21 days of storage at 4 °C. Blends
Hardness (N)
Increase over time (%) 171
83.89±1.67a
AmS75AS25
118.23±2.43b
30.8
AmS50AS50
124.63±4.18b
11.5
AmS25AS75
115.91±3.72b
3.13
AS
149.48±3.44c
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Highlights - Orderly structure remaining affects amylopectin reorganization - Achira starch acts like retardant agent to amaranth starch retrogradation
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- Starch blends presented lower degree of retrogradation and retrogradation enthalpy
- Water competition between starches limits molecular mobility
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- Amylopectin chain length affects the molecular interaction of starches blends