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Structural and functional properties of soy protein isolates modified by soy soluble polysaccharides Yan-Teng Xu, and Ling-ling Liu J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b02737 • Publication Date (Web): 08 Sep 2016 Downloaded from http://pubs.acs.org on September 10, 2016
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Journal of Agricultural and Food Chemistry
Structural and functional properties of soy protein isolates modified by soy soluble polysaccharides
Yan-Teng Xu*, Ling-ling Liu School of Food Science and Engineering, South China University of Technology, Guangzhou, Guangdong 510640, People’s Republic of China *Corresponding author. Fax: 086-20-87114263. E-mail:
[email protected] ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
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ABSTRACT
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Aiming to achieve the modification to soy protein isolate (SPI) by soy soluble polysaccharides
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(SSPS), electrically driven complex systems were first established in the environment of pH 3.0,
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and then reconstituted SPI particles with different SPI-SSPS ratios were obtained under freeze-
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drying process. Through these treatment, the structures of SPI particles were partly unfolded and
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adsorbed SSPS mainly via hydrophobic interactions and hydrogen bonding with larger particle sizes.
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The adherent of SSPS decreased the surface hydrophobicity of reconstituted SPI particles, but
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exerted no much influence on the emulsifying and foaming activities and increased the
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corresponding stabilities due to enhancing the unfolded extent of structure and improving the
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conformation flexibility. Reconstituted SPI-SSPS particles might rearrange and link each other due
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to presence of SSPS on the air-water interface to better stabilize these systems. At SPI-SSPS ratio
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of 10:1, lower temperature was required to form gels with lower gel intensity and porous structure.
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The findings provide a further comprehension to the relationship between structures and functional
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properties of SPI modified by SSPS and the feasibility of applying these reconstituted particles to
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needed areas.
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KEYWORDS: soy protein isolates, soy soluble polysaccharides, structure, interface, gelation
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INTRODUCTION
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Soy proteins are a kind of common but significant proteins in food industry, which are extracted
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from soybean with favorable functional properties, high nutritional value and some beneficial
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healthy influence (e.g. cholesterol-reducing ability).1, 2 Soy protein isolates (SPI) are the major soy
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protein product, generally prepared from defatted soybean meal applying the conventional method
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of alkali-solution and acid-isolation.3-5 Owing to the amphipathic (hydrophilic and hydrophobic)
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Journal of Agricultural and Food Chemistry
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nature of soy proteins, SPI possess a favorable capacity to being adsorbed onto the oil-water or air-
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water interface and maintaining the structure of corresponding system as stabilizers, i.e., SPI have
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good foaming and emulsifying abilities. In regard to forming SPI-based gels, common gelation
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methods such as thermal treatment, acid inducement, divalent salt inducement and enzyme
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treatment can be used to achieve the formation of gels.2 Polysaccharides play vital roles as
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thickening, stabilizing, and gelling agents in many foods. Soy soluble polysaccharides (SSPS) are a
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family of pectin-like acidic biopolymers extracted from the residual carbohydrate byproduct of SPI
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production (okara).6 These polysaccharides are composed of a main rhamnogalacturonan backbone
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branched with β-1,4-galactan and α-1,3 or α-1,5-arabinan chains, and homogalacturonan covalently
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bound to a hydrophobic protein part that is essential for the surficial activity of SSPS.7,8 SSPS is a
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flexible random coil in solution, and due to special structure (short main chain and long branch
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chains, the shape in solution is similar to spherical structure.9, 10 Many previous researches indicated
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that SSPS have high water solubility, low pH and high temperature stability, low bulk viscosity, and
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are able to form strong interfacial films with thick of 17 ~ 30 nm capable of stabilizing emulsions
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via steric repulsion.7-12
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Protein-polysaccharide complex systems have received increasing interest in recent years. And
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there has been abundant scientific literature focusing on the electrostatic attractions between
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oppositely charged proteins and polysaccharides owing to the convenience and simplicity for
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complex formation.6, 13-16 The complexation process is basically governed by pH, ionic strength,
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polymer ratio, polymer concentration, and charge quantity. Given the molecular characteristics of
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applied protein or polysaccharide and processing parameters, electrically driven complex systems
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with various compositions and structures can be established, e.g., soluble and insoluble complexes,
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coacervates, and gels. These systems can be used to encapsulate and protect sensitive materials, to
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purify macromolecules and to delivery bioactive substance or as colloidal entities as, thus exhibiting
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a wide-range application in food industry, cosmetic and medicine fields.16-21
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However, there are scarcely any reports about the formation and properties of proteins modified
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by polysaccharide through freeze-drying treatment based on electrically driven complex systems.
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Therefore, this study first formed the SPI-SSPS complex systems under condition of pH 3.0, then
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freeze-drying/reconstituted SPI-SSPS particles were obtained. With the aim to further
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understanding of the relationship between the structures and functional properties of this SPI
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modified by SSPS and provide helpful scientific references to apply these reconstituted SPI-SSPS
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particles at neutral conditions as materials in the areas of food, cosmetic and medicine, these related
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determinations was conducted at pH 7.0 from zeta-potential, particle size, intrinsic fluorescence,
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surface hydrophobicity, atomic force microscopy, emulsifying properties, foaming properties,
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interfacial tension and thermal induced gelation.
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METERIALS AND METHODS
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Materials. Defatted soy flour with low protein denaturation was obtained from Shandong
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Yuwang Industrial and Commercial Co. Ltd. (Yucheng, Shandong Province, China). Commercial-
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grade SSPS (CA200: moisture: 6.2%, crude protein/dry basis: 6.4%, crude ash/dry basis: 7.7%,
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crude fat/dry basis:
