Soy Protein-Based Blends, Composites and Nanocomposites E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
This unique book will enable engineers and natural-based polymer scientists to achieve multi-functionality in products using soy protein and various nano- and micro-sized biobased materials and reinforcements. Many of the recent research accomplishments in the area of soy-based blends, composites and bionanocomposites are presented in this book. In addition to introducing soy protein and its structure and relationship properties, the book covers many other relevant topics such as the state-of-the-art, new challenges, advances and opportunities in the field such as: biomedical applications of soy protein; electrospinning of soy protein nanofibers, their synthesis and applications; soy protein-based materials rheology; soy proteins as a potential source of active peptides of nutraceutical significance; soy protein isolate-based films; and use of soy protein-based carriers for encapsu??lating bioactive ingredients.
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Veröffentlichungsjahr: 2017
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Contents
Cover
Title page
Copyright page
Preface
Chapter 1: Soy Protein: State-of-the-Art, New Challenges and Opportunities
1.1 Soy Protein: Introduction, Structure and Properties Relationship
1.2 Advances in Soy Protein-Based Nanocomposites
1.3 Applications of Soy Protein-Based Blends, Composites, and Nanocomposites
1.4 Biomedical Applications of Soy Protein
1.5 Electrospinning of Soy Protein Nanofibers: Synthesis and Applications
1.6 Soy Proteins as Potential Source of Active Peptides of Nutraceutical Significance
1.7 Soy Protein Isolate-Based Films
1.8 Use of Soy Protein-Based Carriers for Encapsulating Bioactive Ingredients
References
Chapter 2: Soy Protein: Introduction, Structure and Properties Relationship
2.1 Introduction
2.2 Structure of Soy Proteins
2.3 Source of Soy Proteins
2.4 Properties of Soy Proteins
2.5 Chemical Modification of Soy Proteins
2.6 Characterization of Soy Proteins
2.7 Conclusion
References
Chapter 3: Advances in Soy Protein-Based Nanocomposites
3.1 Introduction
3.2 Preparation Methods of Soy Protein Nanocomposites
3.3 Properties of Thermoplastic Soy Protein Nanocomposites
3.4 Protein-Based Nanocomposites
3.5 Conclusion
Acknowledgements
References
Chapter 4: Applications of Soy Protein-Based Blends, Composites, and Nanocomposites
4.1 Introduction
4.2 Applications of Soy Protein Particulars
4.3 Applications of Soy Protein-Based Blends
4.4 Applications of Soy Protein-Based Composites
4.5 Applications of Soy Protein-Based Nanocomposites
4.6 Conclusion
References
Chapter 5: Biomedical Applications of Soy Protein
5.1 Introduction
5.2 The Forms of SP
5.3 Wound-Dressing Materials
5.4 Potential Applications of SP in Regenerative Medicine and Tissue Engineering
5.5 Application of SP Product for Regeneration of Bone
5.6 Application of SP in Drug Delivery Systems
5.7 Conclusion
Acknowledgement
References
Chapter 6: Electrospinning of Soy Protein Nanofibers: Synthesis and Applications
6.1 Introduction
6.2 Properties of Soybean Proteins That Affect Electrospinning
6.3 Applications
6.4 Conclusion and Outlook
References
Chapter 7: Soy Proteins as Potential Source of Active Peptides of Nutraceutical Significance
7.1 Introduction
7.2 Soy Proteins as Source of Bioactive Peptides
7.3 Identification of Potential Bioactive Peptides from Soy Proteins
7.4 Production of Bioactive Peptides from Soy Proteins
7.5 Potential Applications of Bioactive Peptides from Soy Proteins
7.6 Conclusion
References
Chapter 8: Soy Protein Isolate-Based Films
8.1 Introduction
8.2 Soy Protein Film Preparation
8.3 Characterization of Soy Protein Films
8.4 Modifications
8.5 Applications
References
Chapter 9: Use of Soy Protein-Based Carriers for Encapsulating Bioactive Ingredients
9.1 Introduction
9.2 Encapsulation Methods
9.3 Soy Protein-Based Encapsulation Carriers
9.4 Conclusion
References
Index
End User License Agreement
Guide
Cover
Copyright
Contents
Begin Reading
List of Tables
Chapter 4
Table 4.1.: Applications of soy protein-based blends and composites in the biomedical field.
Table 4.2.: Production of packaging based on soy protein raw material.
Chapter 6
Table 6.1.: Summary of solvents and main conditions used in different soy protein electrospinning studies.
Chapter 7
Table 7.1.: Amino acid composition of soybean proteins*.
Table 7.2.: Identified bioactive peptides derived from soybean storage proteins through
in silico
hydrolysis with gastrointestinal enzymes and some commercial enzymes*,a,b.
Table 7.3.: Predicted bioactive peptides derived from soybean storage proteins through
in silico
hydrolysis with gastrointestinal enzymes and some commercial enzymes*,a,b.
Table 7.4.: Bioactive peptides derived from soybean proteins by different digestion procedures.
Chapter 8
Table 8.1.: Optimum extrusion conditions for protein/glycerol mixtures.
Table 8.2.: TS, strain at break (
ε
),
E
, and puncture tests of films at pH 2, 8, and 11 [78].
Table 8.3.: Structural parameters of native and heat-treated SPI derived from SAXS and DLS data.
Table 8.4.: Spacing values of zein-based materials tested by WAXS and SAXS [97].
Chapter 9
Table 9.1.: Encapsulation with SPI-based wall material.
List of Illustrations
Chapter 3
Figure 3.1: Synthetic route for
N
-phthaloyl soy protein.
Figure 3.2: SEM images of the surfaces of SA-0 (a1, b1, and c1), SA-4 (a2, b2, and c2), SA-8 (a3, b3, and c3) and SA-20 (a4, b4, and c4) after seven-day exposure to three funguses at 37 °C. The number after SA means the content of AlCl
3
. The character “a” in the labels means the plastic sheets were degraded by Chaetomium olivaceum, “b” means Trichoderma viride, and “c” means Aspergillus oryzae. The scale bar inside represents 30 μm.
Figure 3.3: Illustration of the cross-linking reactions for SPI/GPTMS/POSS (d) from SPI (c), GPTMS (b) and POSS (a).
Figure 3.4: Citric acid-modified starch nanoparticles (left) and unmodifiedstarch (right) (5%, w/v in water) after heating a 100 °C.
Figure 3.5: Reaction among SPI, MCNC, and EGDE (a) SPI, (b) EGDE, (c) MCNC, and (d) SPI-based films cross-linking networks.
Figure 3.6: Upper section SP-NFC composite aerogels of a few selected compositions: 100% NFC, 50:50 SP-NFC and 100% SP. Lower section tomography images of cubic sections of the respective aerogel.
Figure 3.7: TEM micrographs of soy protein/polystyrene nanoblends with (a) 5%, (b) 10%, (c) 20%, and (d) 50% styrene contents.
Figure 3.8: Reaction of arylated soy protein in water.
Figure 3.9: Photographs of the arylated soy protein films (a): left, middle, and right show SB, SB in water for 26 h, and SBWM just removed from water, respectively. SEM images of SB (b,c) and SBWM (d,e) films. Surface morphology (left) and cross-section (right).
Chapter 5
Figure 5.1: Structures of phytosterols found in SP.
Figure 5.2: Structures of selected carbohydrates found in SP.
Figure 5.3: Structures of main compounds in SP responsible for enhanced wound healing.
Figure 5.4: Different forms of wound dressings prepared from SP.
Figure 5.5: Different forms of SP-based drug delivery formulations.
Chapter 6
Figure 6.1: Electrospun soy protein/poly(ethylene oxide) from solutions with total polymer concentration of (a) 9 wt%, (b) 11 wt%, and (c) 13 wt%. The scale bar represents 10 μm. Figure reproduced from Cho
et al
. [18] with permission. Copyright © 2010 John Wiley & Sons, Inc.
Figure 6.2: FE-SEM images of soy protein/lignin with 10 wt% (based on dry fibers) of poly(ethylene oxide) as coadjutant polymer. Top row: glycinin (G)-lignin (L) fibers with different protein/lignin content (G1, G2, G3, G4). Bottom row: soy isolate (I)-lignin (L) fibers I2, I3, I4). Fiber diameter increase with lignin content (from left to right).The scale bar shown is 5 μm [21].Reprinted from
Reactive and Functional Polymers
, Vol. 85, Carlos Salas, Mariko Ago, Lucian A. Lucia, Orlando J. Rojas, Synthesis of soy protein-lignin nanofibers by solution electrospinning, Pages 221–227., Copyright © 2014 with permission from Elsevier.
Figure 6.3: Growing of human dermal fibroblasts after eight days of culture on electrospunscaffolds prepared form (a) 5% SPI, 0.05% PEO, (b) 8% SPI, 0.05% PEO (c) 40% zein, (d) gelatin, (e) poly(lactic-co-glycolic acid), PLGA, and (f) glass. (Nuclei, blue; F-actin cytoskeleton, red. Magnification: 200x). Figure reproduced from Lin et al. [10] with permission. Copyright © 2013 John Wiley & Sons, Inc. [10].
Figure 6.4: Micrograph of tissue from porcine model after 4 weeks injury, stained with Masson’s trichrome (MTS). (a) Healthy skin taken close to the untreated control. (b) Wound area of an untreated control. (c) Wound area of soy protein scaffold treated wound. Purple stained areas correspond to collagen [11]. Reprinted from Wound Medicine, Vol. 5, Yah-el Har-el, Jonathan A. Gerstenhaber, Ross Brodsky, Richard B. Huneke, Peter I. Lelkes. Electrospun soy protein scaffolds as wound dressings: Enhanced re-epithelialization in a porcine model of wound healing. Pages 9–15., Copyright © 2014 with permission from Elsevier.
Chapter 7
Figure 7.1: Example of identification of bioactive peptides from glycinin G1 protein. Angiotensin I converting enzyme (ACE)-inhibitory peptides (ACEIPs; green), antioxidative peptides (AOPs; red), DPP-IV inhibitors (DPP-IVPs; blue), peptides that function as both ACEIP and AOP (pink), peptides that function as both ACEIPs and DPP-IVPs (purple) and peptides that function as both AOPs and DPP-IVPs (yellow). Different peptides having the same functionality in the adjacent rows are underlined.
Figure 7.2: Example of
in silico
hydrolysis with Asp-N in combination with GI enzymes (pepsin, trypsin, and chymotrypsin) and identification of bioactive peptides from glycinin G1 protein. Angiotensin I converting enzyme (ACE)-inhibitory peptides (ACEIPs; green), antioxidative peptides (AOPs; red), DPP-IV inhibitors (DPP-IVPs; blue), peptides that function as both ACEIPs and AOPs (pink), peptides that function as both ACEIPs and DPP-IVPs (purple) and peptides that function as both AOPs and DPP-IVPs (yellow). Predicted ACEIPs are in bold, predicted AOPs are italic and predicted DPP-IVPs are underlined. Peptide sequences in yellow are not assigned; separation from other adjacent peptide is by means of underlining.
Chapter 8
Scheme 8.1: Reaction of acetic and succinic anhydride with soy protein [32].
Figure 8.1: Structure of rutin and epicatechin (a) and TS and tensile elongation of SPI films with or without rutin and epicatechin (b) [8].
Figure 8.2: DMA of E’ (a) and loss modulus (b) on temperatures for SPI plastics. Note: BUT12, BUT13, GLY, PRO, and CON represent SPI plastics with 1,2-butanediol, 1,3-butanediol, glycerol, propylene glycol, and unplasticized SPI plastics, respectively [84].
Figure 8.3: TGA (a) and DTG (b) curves of SPI/PBAT blends in N
2
atmosphere [85].
Figure 8.4: DSC of SPI solutions (a) SPI films (b) at pH 2, 8, and 11 [31].
Figure 8.5: SEM images of cross-sections of the SPI-based films [10].
Figure 8.6: TEM images of SPI and modified SPI samples [41].
Figure 8.7: Surface morphology of SPI materials (a) unmodified (b) modified SPI films [89].
Figure 8.8: Surface dilatational modulus (
E
) as a function of surface pressure (π) for native and heat-treated SPI (SPI-90 and SPI-120) at the oil-water interface [91].
Figure 8.9:
G
′(a) and
G
″(b) curves of SPI and SPI-CNF to oscillatory shear frequency [92].
Figure 8.10: SAXS of SPI-based samples [91].
Figure 8.11: Proposed structure models of zein-oleic acid resin films, side view (a) and top view (b), aggregated longitudinally to form platelets [97].
Figure 8.12: Schematic diagram of possible interactions in cross-linked protein films (a) [119,120]; cross-linking reaction mechanisms of SPI and ESO (b) [10]; oxidized sucrose and soy protein (c) [121]; and Maillard reaction between amino acids and CMC (d) [122].
Figure 8.13: Scheme of LBL modification on mats [139].
Chapter 9
Figure 9.1: pH stability of free and encapsulated
E. faecalis
HZNU P2 in simulated gastric fluid (SGF) pH 2.5 and 2.0. (a) The stability of free and encapsulated
E. faecalis
HZNU P2 (SPI-alginate) in SGF pH 2.5. (b) The stability of free and encapsulated
E. faecalis
HZNU P2 (SPI-alginate) in SGF pH 2.0. (c) The stability of free and encapsulated
E. faecalis
HZNU P2 (soy milk-alginate) in SGF pH 2.5. (d) The stability of free and encapsulated
E. faecalis
HZNU P2 (soy milk-alginate) in SGF pH 2.0.
Figure 9.2: Release of encapsulated
E. faecalis
HZNU P2 in simulated intestine fluid (SIF). (a) SPI-Alginate microspheres. (b) Soy milk-Alginate microspheres.
Figure 9.3: Storage stability of free and encapsulated
E. faecalis
HZNU P2 at 4, 25 °C and 37 °C. (a) Storage stability of free and encapsulated
E. faecalis
HZNU P2 at 4 °C (SPI-alginate).
(b)
Storage stability of encapsulated
E. faecalis
HZNU P2 at 25 and 37 °C (SPI-alginate). (c) Storage stability of free and encapsulated
E. faecalis
HZNU P2 at 4 °C (soy milk-alginate). (d) Storage stability of free and encapsulated
E. faecalis
HZNU P2 at 4 °C (soy milk-alginate).
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Scrivener Publishing100 Cummings Center, Suite 541JBeverly, MA 01915-6106
Publishers at ScrivenerMartin Scrivener ([email protected])Phillip Carmical ([email protected])
Soy Protein-Based Blends, Composites and Nanocomposites
Edited by
Visakh P. M
Olga Nazarenko
This edition first published 2017 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA© 2017 Scrivener Publishing LLCFor more information about Scrivener publications please visit www.scrivenerpublishing.com.
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Library of Congress Cataloging-in-Publication DataISBN 978-1-119-41830-6
Preface
Many of the recent research accomplishments in the area of soy-based blends, composites and bionanocomposites are presented in this book. In addition to introducing soy protein and its structure and relationship properties, an attempt has been made to cover many other relevant topics such as the state-of-the-art, new challenges, advances and opportunities in the field; biomedical applications of soy protein; electrospinning of soy protein nanofibers, their synthesis and applications; soy proteins as a potential source of active peptides of nutraceutical significance; soy protein isolate-based films; and use of soy protein-based carriers for encapsulating bioactive ingredients.
This book is intended to serve as a one-stop reference resource for important research accomplishments in the area of soy protein-based biocomposites and bionanocomposites. It will be a very valuable reference source for university and college faculties, professionals, post-doctoral research fellows, senior graduate students, and researchers from R&D laboratories working in the area of soy protein and its biocomposites and bionanocomposites. Since the various chapters in this book have been contributed by prominent researchers from industry, academia and government/private research laboratories across the globe, it is an up-to-date record of the major findings and observations in the field. The first chapter acts as an introduction to soy protein-based blends, composites and nanocomposites, including their scope, state of the art, preparation methods, environmental concerns regarding nanoparticles and related challenges and opportunities.
Included in the second chapter introducing general aspects of soy proteins, is a discussion of their source, structure and relationship properties. Chemical modification and characterization of soy proteins are also included in this chapter along with a description of the applications of soy protein-based nanocomposites and blends. Advances in soy protein-based nanocomposites are addressed in the third chapter, in which the authors discuss how the incorporation of nanoparticles proves to be an effective way to improve physical properties, especially the mechanical properties and water resistance which limit their extensive use. The properties of the resulting nanocomposites are highly dependent on the processing methods, nature of nanofillers, as well as the dispersion effect of the filler in the matrix. Therefore, the fabrication methods, property-structure relationship, and application of soy protein nanocomposites are also reviewed in this chapter.
The following chapter on applications of soy protein-based blends, composites and nanocomposites discusses many topics, including the particulars of soy protein applications, soy protein-based blends, and those of soy protein-based nanocomposites. The fifth chapter based on biomedical applications of soy protein summarizes many of the recent accomplishments in the area of biomedical research. In this chapter, the authors discuss various topics such as forms and properties of soy proteins, application of plant protein in biomedical applications, application of soy proteins in wound dressings, and the potential use of soy proteins in products and applications in regenerative medicine, tissue engineering, and drug delivery systems.
The following chapter is a good structural basis for the understanding of electrospinning of soy protein nanofibers. Discussed in the chapter are the production of nanofibers from different synthetic and natural polymers, the physical properties of soy proteins that affect their electrospinning, followed by a summary of relevant work that has been done in the area. The chapter closes with a discussion on possible applications of electrospun nanofibers from soy proteins. The use of soy proteins as a potential source of active peptides of nutraceutical significance is the subject of the seventh chapter, which introduces the main concepts along with examples to help readers understand them. This chapter is devoted to reviewing the literature to identify and describe the available methodologies for the identification and production of bioactive peptides from soybean proteins. In addition, potential applications of these peptides as functional foods and therapeutic agents are also highlighted.
The authors of the eighth chapter present a brief account of the topic of soy protein isolate-based films, including soy protein film preparation, characterization of soy protein films, modifications and applications. The last chapter of the book reviews recent progress in the preparation of soy protein-based carriers for bioactive ingredients encapsulation.
In conclusion, the editors would like to express their sincere gratitude to all of the contributors to this book for their excellent support in the successful completion of this venture. We are grateful to them for the commitment and sincerity they have shown towards their contributions. Without their enthusiasm and support, this book would not have been possible. We would also like to thank all the reviewers who have taken their valuable time to make critical comments on each chapter. We also thank the publisher John Wiley and Sons Ltd. and Scrivener Publishing for recognizing the demand for such a book, realizing the increasing importance of the area of soy protein-based blends, composites and nanocomposites, and for starting such a new project, which not many other publishers have handled.
Visakh. P. MOlga NazarenkoTomsk, RussiaJune 2017
Chapter 1Soy Protein: State-of-the-Art, New Challenges and Opportunities
Visakh P. M
Department of Ecology and Basic Safety, Tomsk Polytechnic University, Tomsk, Russia
Corresponding author:[email protected]
Abstract
This chapter deals with a brief account on various topics in rubber-based bionanocomposites: Preparation and state-of-the-art. It also discusses different topics such as soy protein: Introduction, structure and properties relationship, thermoplastic-based soy protein nanocomposites, applications of soy protein-based blends, composites, and nanocomposites, biomedical application of soy protein, preparation of soy protein nanofibers by electrospinning, physiologically active peptides derived from soy protein, soy protein polymer-based (film) membranes and encapsulation of bio actives using soy protein-based material.
Keywords: Rubber-based bionanocomposites, soy protein, soy protein nanocomposites, soy protein nanofibers
1.1 Soy Protein: Introduction, Structure and Properties Relationship
Soy proteins are one of the most abundant and most widely utilized plant proteins on this planet. With high content of essential amino acid and desirable functional properties, soy proteins have attracted persisting interest in food and pharmaceutical industry. The 11S and 7S globulins represent approximately 60% of the storage protein in soybeans. They are the most important contributors to the physicochemical and functional properties of soy protein products. It exhibits a high content of negatively charged amino acids such as glutamic acid and aspartic acid, whereas the percentage of hydrophobic amino acids such as leucine is relatively low [1]. β-conglycinin is relatively flexible, as evidenced by its high contents of α-helix, and random coils [2]. It comprises six major isomers, each of which is composed of three major subunits and two minor ones (γ and δ) [3].
As can be seen, the whole soybean seed is cleaned, cracked, dehulled, and flaked to produce soy powder. The powder is then subjected to oil extraction with organic solvents such as hexane. The particle sizes range from grits (or flakes) of varying sieve specification to fine powders. The soy meal could be further ground into soy flour (SF), a product that contains less than 1% oil and a protein content ranging from 40–60%. Soy proteins with higher purity may also be produced with smaller particles, because the protein can be more effectively extracted from finer flours, making the separation of protein from insoluble carbohydrate more efficient and complete.
There exist three major types of soy protein-rich products, SPC (soy protein concentrate, and fractionated 11S/7S globulins (protein content >90%, fraction purity >85%). Quite a few methods have been developed to produce these products with desirable features, and several typical approaches with respect to their principles, major procedures, advantages, and drawbacks. The majority of the protein is precipitated and recovered by a second centrifugation. The curd-like precipitate is neutralized with alkali, washed with water to remove excessive alkali and salt, and finally spray dried or lyophilized to yield the final product. The typical protein of yield (weight ratio between the product and the raw material) is around 30%, though a yield of as high as 44% has been reported [4]. The product loses part of its original solubility as a result, but it gains some desirable properties such as good texture and water holding capacity [5].
In pilot scale production, the solvent such as alcohol and hot water can be recovered through evaporation and condensation, thus achieving higher extraction efficiency. In addition to the traditional methods, membrane-based techniques including micro- and ultrafiltration have also been widely studied for the preparation of SPC. Teng et al. further investigated the effect of divalent cations on the fractionation process. They suggested that using Mg2+ instead of Ca2+ as a precipitant improved the purities of both fractions without affecting their yields significantly. Soy proteins tend to adopt a compactly folded structure, with their hydrophilic and charged amino acid residues maximally exposed to the solvent and hydrophobic moieties buried in the globular core. The surface charge of colloidal particles is usually gauged by the electrical potential at the interfacial double layer at the location of the slipping plane relative to a point in the bulk fluid away from the interface. Proteins as amphiphilic molecules bear both hydrophilic and hydrophobic groups which endow their ability to interact with both the polar and nonpolar solvents and serve as an emulsifier [6].
Two parameters are commonly referred to when describing the emulsifying properties of a molecule. As many other proteins, soy proteins show viscoelasticity when dispersed in water. Under room temperature without the addition of cross-linkers (such as transglutaminase or calcium salts), the dispersion exhibits viscous property (G″) as the predominant characteristic [7]. Since viscosity is indicative for the friction between the molecule and the solvent, it is highly dependent on the interaction between them. Heated soy protein films exhibit decreased water vapor permeability, and increased percentage of elongation at break (%E) when compared to unheated ones [8].
While thermal denaturation is conventionally considered as a detrimental factor for protein solubility, combination of thermal treatment with a suitable pressure may make the protein more soluble. Glycerol is by now the most widely utilized plasticizer for soy protein-based plastics, owing to its relatively short and flexible chain as well as its strong hydrophilicity. The former character facilitates the insertion of glycerol into the peptide chains in the soy proteins, and the latter one promotes its interaction with the protein via extensive hydrogen bonding. Soy proteins are rich in both amine and carboxyl groups; therefore, they can readily react with additional carboxyl or amine groups. The reaction between the positively charged amine groups on the soy proteins and an external carboxylic acid is comparable to phosphorylation.
1.2 Advances in Soy Protein-Based Nanocomposites
Residual soy proteins, a by-product of the soy oil industry, are currently utilized in applications such as animal feed and food supplement. Soy proteins are composed of a mixture of albumins and globulins, 90% of which are storage proteins with globular structure, consisting mainly 7S (conglycinin) and 11S (glycinin) globulins. Soy protein contains 18 amino acids including those containing polar functional groups, such as carboxyl, amine, and hydroxyl groups that are capable of chemically reacting and making soy protein easily modification [9]. Biopolymer films are usually plasticized by hydroxyl compounds [10]. Glycerol has a high boiling point and good stability, and is regarded as one of the most efficient plasticizers for soy protein plastics [11]. Glycerol-plasticized soy protein possesses good processing properties and mechanical performance [12]. The bio-nanocomposites consist of a biopolymer matrix reinforced with particles having at least one dimension in the nanometer range (1–100 nm) and exhibit much improved properties due to high aspect ratio and high surface area of the nanoparticles.
Soy protein films reinforced with starch nanocrystals (SNC) could be prepared by casting method [13]. The SNC synthesis was developed by acid hydrolysis of native cornstarch. Soy protein is one of the few natural polymers that can be thermoplastically processed under the plasticization of small molecules [14]. Soy protein plastics without any additive have a brittle behavior, which makes processing difficult. Addition of plasticizers is an effective way to improve the flowability of soy protein melts and obtain flexible soy protein-based films. Phthalic anhydride modified soy protein (PAS)/glycerol plasticized soy protein (GPS) composite films were fabricated by using extrusion and compression-moulding [15]. Soy/BN nanocomposites were prepared by low-cost green technique with water as the solvent. The thermal properties of the nanocomposites were studied by thermogravimetric analysis (TGA). The biodegradation behaviors of maleated PCL/ isolated soy protein (SPI) composites reinforced with organoclay were evaluated by soil burial test [16]. Composites containing higher percentage of soy protein degraded rapidly in the initial 8 weeks and a gradual decrease of weight occurred during the next 8 weeks.
Soy protein films are effective barriers to the passage of lipid, oxygen, and carbon dioxide. However, the inherent hydrophilicity of proteins and the substantial amount of plasticizer added in the film perform poorly in moisture barrier and mechanical properties as packaging material. In addition of in situ synthesis, soy protein/silica nanocomposites could be fabricated through compounding nano-SiO2 particles into soy protein isolate matrix [17]. Zheng et al. reported the nanocomposite sheets by compounding MWNTs of various sizes into SPI matrix through solution mixing and then compression-molding method [18]. Blending SPI with other biodegradable polymers such as polycaprolactone, poly(lactic acid), poly(vinyl alcohol), natural rubber, etc., thus becomes a way to enlarge its applications. The properties of the blend materials could further improved by nanoreinforcing. Sasmal et al. prepared a kind of bio-based, eco-friendly nanocomposites from maleated polycaprolactone/soy protein isolate blend (50/50 wt/wt) reinforced with organo-modified clay by melt compounding [19]. Soy protein plastics possess good mechanical strength and water resistance by compositing PS nanoparticles into soy protein matrix. The water uptakes of the nanoblends ranged from 11% to 19%, which is much lower than that of pure SPI (32%) at 75% RH.
1.3 Applications of Soy Protein-Based Blends, Composites, and Nanocomposites
Soybean is an important raw material for food industry, because is one of the most consumed grains in the world. Special applications of soy protein for development of biomaterials, composites, nanocomposites, and blends have been reported as potential use of this grain in several areas, such as biomedical, optoelectronic, optical coating, and packaging [20–24]. The soy protein nanocomposites can be used as adhesives, asphalt, resins, cleaning products, paper coatings, plastics, polyesters, and textile fibers that allow its use over a large area, such as packaging, medical, aerospace, and automotive fields. Meikle et al. [25] studied soybean-based hydrogels with different physicochemical properties and bioactivity, which were obtained by sequential or simultaneous procedure of SF defatting process and material extraction. SPI the major component of soybean has been used to prepare biodegradable materials, such as adhesives, plastics, and various binders in recent years.
Although the SPI plastics usually possess good biodegradability, their application is limited by poor flexibility and water resistance. Wang et al. [26] in which they incorporate cellulose whiskers to SPI aiming to improve mechanical properties, the authors obtained composites which showed greater water resistance and thermal stability. The improvement in the properties of the SPI/cellulose whisker composites may be ascribed to cross-linking networks caused by intermolecular hydrogen bonds between the cellulose whiskers and the SPI matrix. SPI is a biopolymer that has potential applications in packaging (films or coatings), because it offers interesting film-forming properties, good barrier properties to oxygen, aromas and lipids when in low to intermediate moisture conditions, besides it is a low-cost raw material [27].
The behavior of soy protein packaging systems is the modification of SPI with cross-linking agents. Cross-linking agents can work improving the mechanical and water barrier properties of soy protein films reducing its solubility, ability to swell, and gas/water vapor permeability. The SPI cross-linked with genipin was considered promising natural biodegradable materials for use in food packaging. Soy protein has many unique properties such as low cost, ease of handling, low press temperatures, and the ability to bind wood with relatively high moisture content, representing a very practical and inexpensive material for wood adhesives [28]. Thames et al. [29] developed a water resistant soy protein-based adhesive blend with polyol plasticizer, preferred glycerol, and with a vegetable oil derivative, aleinized methyl ester of tung oil. This adhesive can be useful in the manufacture of particleboard and other composites. SPI films high water vapor permeability is the most important obstacle to its use in food coatings [30], drawback which can be exceeded by blending methodology and thus many works have been developed in this area by blending.
Luo et al. [31] prepared a series of cellulose/SPI membranes, and observed that porous structure and the size of the pores in the surfaces increased with an increase of SPI content, and the incorporation of SPI in cellulose changed the compositions and microstructure, improving the biocompatibility of the membranes. In addition, the application of the PLA layer presented an important effect on the mechanical properties of the films, decreasing the elongation at break and increasing the tensile strength and the Young’s modulus, resulting in a material less elongable and more resistant compared to those of pure SPI films. The resultant film made of soy/MMT is recommended to be used for packing food with high moisture content as fresh fruit and vegetable in order to replace low-density polyethylene (LDPE) and polyvinylidene chloride (PVDC).
1.4 Biomedical Applications of Soy Protein
Soybeans also contain a high amount of phytic acid that is antioxidant and can inhibit the growth of cancer cells, reduces blood sugar level and inflammation [32–34]. They are also a good source of fibre, iron, calcium, zinc, and vitamin B [35]. Soy Protein products can swell when they absorb water or can dissolve in water and this is an important functional property in drug delivery systems. In a research study by Ramnath et al., composite biomaterials prepared from SP and sago starch cross-linked with gluteraldehyde were prepared as temporary wound-dressing materials [36]. Chein et al. studied the biocompatibility of SP scaffolds fabricated by freeze-drying and three-dimensional printing [37].
The content of SP in the scaffolds was varied. It was assessed using a subcutaneous implant model in female BALB/c mice age 6–8 weeks. These results indicated that SP is a potential biocompatible implant for tissue regeneration. The scaffold porosity, soy protein density, and scaffold degradation rate significantly affected the acute and humoral immune response. Chien and Shah prepared porous SP-based scaffolds [38]. Xu et al. reported the preparation of water-stable electrospun SP-based scaffolds [39]. The scaffolds had large volume and ultrafine fibres oriented randomly and evenly in three dimensions. They were used to simulate native extracellular matrices of soft tissues. In another research report, the parameters for electrospinning fibrous scaffolds from SP isolate by the addition of poly(ethylene oxide) dissolved in 1,1,3,3,3-hexafluoro-2-propanal were investigated. Their physicochemical properties were studied and they were found to exhibit mechanical properties that are similar to human skin. Silva et al. reported soy- and casein-based membranes for biomedical applications [40]. The membranes were subjected to cross-linking with glyoxal and tannic acid followed by thermal treatment. The cytotoxicity of both soy- and casein-based protein biomaterials were evaluated and it correlated with the materials degradation behavior. The SP isolate/poly(ethylene oxide) mats were cross-linked using carbodiimide to increase its robustness. SP isolate/poly(ethylene oxide) fiber diameters ranged between 50 nm and 270 nm depending on electrospinning and solution parameters. Soy hydrogels were injected into the subcutaneous pocket of mice and histological staining showed minimal fibrous capsule formation up to 20 days. It was found to be a potential biomaterial for tissue engineering and drug delivery applications [41].
A self-hardening soy/gelatine/hydroxyapatite composite foam was prepared and it was able to retain porosity upon injection. The foamed paste produced a calcium-deficient hydroxyapatite scaffold after setting. Implantation of the soybeans biomaterial over a period of 8 weeks produced bone repair with features distinct from those obtained by healing in a nontreated defect. New and progressively maturing trabeculae appeared in the animal group where soybeans biomaterial granules were implanted whereas; the sham operation produced only a rim of pseudo-cortical bone still featuring a large defect. Chitosan and soybean protein isolate blended membranes were prepared by solvent casting. These membranes exhibited a biphasic structure that originates in situ porous formation, through a two-step degradation mechanism. Vaz et al. reported SP drug delivery matrix systems prepared by melt-processing techniques, namely extrusion and injection moulding [42]. The soy matrix systems were encapsulated with theophylline drug by extrusion and cross-linking with glyoxal. Reddy et al. demonstrated the potential of SP isolate films as a drug release system for naturally occurring antiproliferative agent [43]. The films were prepared by casting method and the percentage of the resorcinol was varied between 10% and 30%.
In a research study by Chien et al., SP hydrogels were developed by varying the weight percentages of water (15 wt.%, 18 wt.%, and 20 wt.%) [44]. Chemical modifiers or cross-linkers were not used to prepare the hydrogels. This method was useful for developing hydrogels for direct injection in vivo. The concentration of SP was varied and it influenced the rheological, swelling, mechanical properties and the release of the model drug, fluorescein from the hydrogels in vitro.
1.5 Electrospinning of Soy Protein Nanofibers: Synthesis and Applications
These protein-rich products have found uses in many non-food industrial applications, including the manufacture of plastics, adhesives, paper coatings, paint coatings, and composites. The advantages of using soy proteins in such systems are not only due to their physicochemical properties but also due to their renewability and sustainable production. Soybean proteins alone or in combination with other natural and synthetic polymers have been used to produce nanofibers by the electrospinning technique. In the solution electrospinning process, a polymer is first dissolved in a given solvent and the solution is pumped through a nozzle that together with a metallic fiber collector serve as the electrodes between which an electric field is applied.
The storage protein in soybeans accounts for a large fraction of the raw bean weight (between 65% and 80%) [45]. Storage proteins are globulins, that is, their solubility in water is enhanced by the presence of electrolytes. They have been classified according to the sedimentation constant as 7S and 11S or β conglycinin and glycinin, respectively. Reducing agents such as 2-mercaptoethanol, cysteine, NaCN, and dithiothreitol (DTT) have been used to break disulfide bonds in soy protein. Glycinin contains 2 free mol of sulfhydryl group/mol protein in its native state and 2–3 mol of sulfhydryl/mol after heating [46].
As soy proteins are globulins, their solubility in water is enhanced by the content of electrolytes. In addition, the pH will affect the solubility. The isoelectric pH of soy proteins has been reported as 4.5. The solubility will be low to zero at pH values near the isoelectric pH and increased at higher pH values. The solvents included water, acetic acid, ethanol, hydrochloric acid, acetone, sodium hydroxide, ammonium hydroxide, and some polar but less water soluble solvents, namely dimethylformamide (DMF), tetrahydrofuran (THF), and 1,1,1,3,3,3 Hexafluoro-2-propanol (HFIP). Pure soy protein globulins are rarely used in practical applications due to the cost involved in purification. Furthermore, the generalization is not straight forward, and the selection of a “suitable” solvent must fulfill the requirements of dissolving the solute within a reasonable time, being good solvent and environmentally friendly as well. The use of pure protein fractions could be also of little practical interest. That is why most reports have focused on the use of commercially available soy protein. Typically isolate has been used because of its high protein content; however, its cost is still high compared with SF which has been used very recently [47, 48] on electrospinning applications.
Additional complications in term of solubility and preparation of solutions for electrospinning arise when soy protein is blended with other polymers. This is because the solvent of choice has to be a good solvent for both the protein and the coadjutant polymer. This implies that the coadjutant polymer should be water soluble. To this end, polyethylene oxide and polyvinyl alcohol have been used. Other biopolymers include corn zein, wheat protein (gluten), and lignin [49]. The fibers were uniform, the blends with zein reduced drastically the content of soy protein on the final fibers, that is, the fibers were zein fibers containing soy protein [50].
A follow-up study of the same system [51] included the effect of changing the pH (9 and 12) on mechanical properties and biodegradability of soy protein isolate-polyvinyl alcohol elctrospun fibers. The nanofiber mats prepared from solutions at pH 9 exhibited a higher load and elongation at break than those prepared at pH 12. This effect was ascribed to the lower denaturation of the proteins at pH 9 compared with pH 12. The nanofiber samples exhibited low contact angles (high wettability), which could limit their practical application [52]. The synergy between soy proteins with other natural polymers to produce electrospun nanofibers has remained essentially unexplored, with only blends of zein-soy protein isolate-SF-gluten and soy protein isolate-lignin being reported.
Because of its high protein content, soy protein isolate has been the product of preference in most electrospinning of soy protein reports; however, the use of SF was reported recently. Soy protein/PVA (9 kDa and 130 kDa) and soy protein/PCL (80 kDa) fibers were electrospun on top of a rayon support membrane. Blends of SPI-PEO (1:4, 2:3, and 3:2) were used to prepare electrospun nanofibers and tested for wound-dressing applications [53]. SPI in dilute NaOH and PEO (300 kDa) in ethanol was prepared separately, then blended at different ratios of SPI: PEO before electrospinning.
The SPI/PEO mats exhibit antibacterial activity against one gram-negative (Pseudomonas aeruginosa) and one gram-positive bacteria (Staphylococcus aureus) as determined by the disk diffusion method. Although the experiments for wound-healing effect were qualitative observations on winstar rats (i.e., no quantification of ephitelial cell growth), the comparison indicates that the wounds covered with SPI/PEO electrospun mats exhibit a slightly better healing ability compared to uncovered wound. The produced soy protein scaffolds (3 cm × 3 cm) were applied to the wounds at different times. The results indicate that the protein scaffolds in contact with the skin get completely hydrated and dissolved in the wound. In addition the bacterial filtration efficiency increased with the load of nanofibers, with 5 g/m2 exhibiting the highest efficiency. It was hypothesized that the adhesion of bacteria to the nanofibers might be as a result of electrostatic interactions, owed to the charge balance of aminoacids on the protein.
1.6 Soy Proteins as Potential Source of Active Peptides of Nutraceutical Significance
Recent developments in food bioactive protein/peptide databases, coupled with improved knowledge of various enzyme specificities can be used in a process known as in silico hydrolysis for the identification of potential bioactive peptides from food/soy proteins. In silico produced peptides with known sequences can then be subjected to quantitative structure–activity relationship (QSAR) studies for a preliminary assessment of their bioactivity potential. Fermentation of soybean has been shown to result in the release of peptides with various functionalities and these aspects have also been reviewed. Solid-phase peptide synthesis is considered as a more established method and has been used to synthesize significant numbers of bioactive peptides [54].
There are several advantages to produce bioactive peptides by chemical synthesis, which include producing peptides of high purity and quantity, desired sequences that are otherwise difficult to obtain from natural sources, and peptides of known activity identified in natural sources but are difficult to ensure their release through hydrolysis. Products such as soy milk, tempeh, and tofu are the examples of soy products consumed as protein sources, whereas soy sauce and miso are examples of soy products used to flavor other food preparations. Major applications of soy protein apart from its use for human consumption are in paper coatings [55] and as animal feed. Currently, however, soybean proteins are used in the preparation of functional peptides such as antioxidative [56–58], antihypertensive [59–61], and anticancer [62] peptides.
Clostripain (EC 3.4.22.8) also known as Arg-C peptidase [63] is a sulfhydryl protease produced by Clostridium histolyticum and prefers arginine over lysine residue. Under controlled hydrolysis conditions it will cleave proteins at peptide bonds limited to arginine P1 sites, including trypsin-resistant arginylprolyl bonds [64], and produce peptides containing arginine residues at C1 positions. Many peptides produced from these hydrolyses have also been produced from other food protein sources and reported extensively in scientific literature to have ACE-inhibitory activity. This type of protein has been reported to possess antinutritive action and hydrolysis of this protein has been reported to degrade protease inhibitor in soybean [65]. This degradation has twofold impact, that is, increase the bioavailability of soybean protein and decreasing anticancer and anti-inflammatory effect of this soybean protein that has been previously reported [66]. Various studies have reported the antihypertensive effects of ACE-inhibitory peptides derived from food proteins [67–70].
It is also indicated that small ACE-inhibitory peptides are less susceptible to gastrointestinal enzyme degradation and can be absorbed intact into the blood circulation [71, 72]. Chen et al. [73] and Saito et al. [74], for example, identified antioxidative peptides from soybean proteins having 5–16 amino acid residues. These peptides consisted of hydrophobic amino acids, valine (V) or leucine (L), at the N-terminal positions, and proline (P), histidine (H) and tyrosine (Y) in any position in the sequences. Many other tripeptides, tetrapeptides and oligopeptides contain sequence of known DPP-IV inhibitors produced by in silico hydrolysis of β-conglycinins.
The sequence/s of the active peptide/s remains unknown, the findings do indicate the presence of antioxidative peptides released from the fermentation process of soybean proteins. Hypocholesterolemic activity of peptides derived from fermented soybean product has also been reported. Shon et al. [75] reported that fermentation of soy bean in the preparation of soy sauce produces bioactive peptides that can function as antithrombotic agents, although the peptide responsible for this activity remains unknown.
The endopeptidases can be further classified based on their catalytic site into serine proteases, cysteine proteases, metalloproteases, and aspartic proteases [76, 77], while a group of threonine peptidases has also been discovered [78]. The serine proteases are well studied having a maximum activity at alkaline pH and –OH group in the catalytic centre. In the study of high molecular weight fractions (>10 kDa) of hydrolysates, proteins have been found to show higher antioxidant activities when compared to the lower molecular weight fractions [79], although the sequences of active peptides have not been determined. Other researchers, however, have reported various antioxidative peptides derived through hydrolysis of soy proteins [80].
This method has been used successfully to synthesize more than 20 residue peptides. However, this method is time-consuming and the intermediate products need to be isolated and purified before proceeding to the next steps [81]. The solid-phase peptide synthesis is considered as a more established method and has been used to synthesize significant numbers of active peptides. There are various reasons to produce bioactive peptides through chemical synthesis. An extended list of therapeutic proteins produced through genetic engineering using Chlamydomonas reinhardtii is available in the literature [82]. The principle of therapeutic protein production in C. reinhardtii chloroplast involves the introduction of gold or tungsten particles coated with gene for the foreign protein into the algae cells placed at an interior of a vacuum chamber [83]. Two important ones are antihypertensive and antimicrobial agents. As an antihypertensive agent, the use of bioactive peptides as a food ingredient is advisable [84]. Therefore, the functional properties of these peptides assume importance.
1.7 Soy Protein Isolate-Based Films
Soy protein isolate (SPI) films are clearer, smoother, and more flexible; they also show better gas barrier properties than films made by lipids or polysaccharides [85–87]. SPI is a highly refined or purified form of soy protein – over 90% of its protein content is obtained from defatted SF. SPI has higher protein content and better film-forming ability than other SP products such as SF which has 54% protein, or SPC which has 65–72% protein [88–90]. SPI shows considerable potential for use in food, agriculture, bioscience, and biotechnology industry applications. That said, several problems limit their application in practice, including relatively poor mechanical properties, and poor water resistance and high moisture sensibility compared to petroleum-based plastics. These limitations occur due to the inherent hydrophilicity of the material as well as the strong molecular interactions of natural proteins. Many previous researchers have proposed methods of enhancing SPI-based film performance, including custom processing methods, cross-linking with chemicals like formaldehyde, glyoxal, and glutaraldehyde (GA), phenolic compounds, and epoxy compounds, polymerizing with functional groups, and blending with PGA, PVA, PCL, PLA, PU, chitin, wheat gluten, gelatin, keratin, milk protein, zein, or silks. Zhang et al., suggested a multistep process was used to form SPI sheets by mixing SPI, water, glycerol, and other additives in a high-speed mixer, then applying a twin-screw extrusion to form pellet-shaped material [91].
In a study by Mo et al., the thermal properties of molded SPI films plasticized by four polyol-based plasticizers were analyzed using DMA methods ranging from –30 °C to 200 °C at a rate of 5 °C/min, under a static force of 660 mN and dynamic force of 600 mN at 1 Hz frequency. The SPI/PBAT blends were all stable below 200 °C, and a two-step weight loss was observed between 200 °C and 400 °C in line with the two DTG curve peaks around 220 °C and 310 °C, owing to the processing additives and SPI degradation, respectively. Native SPI exhibits a typical bell shape confirming its spherical morphology; heat-treated SPI samples show decreased magnitude of maximum peaks, suggesting the presence of globular shapes and partially unfolded structures of rigid glycinin and β-conglycinin. Researchers have proposed physical, chemical, and combination modifications in effort to extend the practical application of SPI films and overcome disadvantages such as poor mechanical properties and moisture sensitivity [92, 93]. Blending SPI with other biodegradable polymers is generally accepted to be successful [94, 95]. Blending methods do show favorable reinforcing effects, and even low nanofiller loads produce better SPI-based bionanocomposites than SPI alone [96, 97]. The specialized bio-films formed by SPI modified by Cu NCs exhibit better mechanical properties, and those modified with Zn NCs show better hydrophobic properties, than SPI alone. Further X-ray diffraction testing of SPI films indicated that metal nanoclusters change the conformation of SPI from compact to unfolded. Modified SPI-based films can also be used in biochemical and biomedical research fields. Luo et al. conducted a study on a nerve guide conduit from cellulose/SPI hollow tube (CSC) combined with Schwann cells and pyrroloquinoline quinone, and found that the blended film has the ability to repair and reconstruct nerve structure and function owing to the comprehensive contributions from the hollow CSC tube [98]. For the sake of comparison, TiO2-SPI composite films were also prepared by hot surface casting with TiO2 nanoparticles as filler [99]. Mechanical and barrier properties (water vapor, and O2 permeability) of these films were evaluated under different relative humidity (RH) conditions, and in general, TS and E decreased and εb increased as RH increased. Fang et al. prepared SPI/PLA composites with or without MDI and found that TS of PLA/SPI material without MDI was very low due to the stress concentration on the dispersed SPI. After MDI was added, conversely, the TS of the composites significantly improved [100]. SPI films create semipermeable barriers to water vapor or oxygen between food and its ambient environment, effectively protecting foods from oxidative damage [101–104].
Guerrero et al. found that fresh beef patties treated with SPI coating stayed fresh for 14 days as a result of SPI coating delaying the oxidation and deterioration of lipids. The surface color stability of the patties was also maintained during chilled storage [105]. In a similar study by Wang et al., bionanocomposites of SPI/TiO2 film caused a sizeable decline in water vapor and oxygen permeability (decreased by 72.12% and 57.64%, respectively) compared to the control [106]. The SPI film networks displayed excellent compound binding capacity, especially for hydrophobic molecules, and as such showed attractive potential for use in controlled release systems based on matrix erosion.
1.8 Use of Soy Protein-Based Carriers for Encapsulating Bioactive Ingredients
Currently, proteins extracted from animal-derived products (whey proteins, gelatin, casein) and from vegetables (soy proteins, pea proteins, cereal proteins) have been widely used for encapsulation of bioactive ingredients. Compared with animal-derived proteins, the use of vegetable proteins as encapsulation materials shows the present “green” conception in food industry. Soy proteins are obtained from soy bean contain a fraction (35–40%) of proteins mainly glycinin and conglycin (50–90% of total proteins) [107]. Molecular weight of glycinin fraction (11S globulin) is about 350 kDa while conglycin (7S globulin fraction) is about 70 kDa. Soy proteins have interesting physicochemical and functional properties, particularly including gel-forming, emulsifying, and surfactant properties [108–110]. Hydrolyzed SPI could produce the emulsions with smaller droplets and lower oil retention efficiency (39%) in the corresponding powder due to the insufficient chain length of wall material to produce a stable matrix during spray drying. On the other hand, SPI with N-acylation resulted in a significantly higher retention efficiency (>87%) compared to the efficiency obtained with native SPI (80%). SPI microparticles can be made using spray-drying, coacervation, and extrusion [111–113].
Chen and Subirade prepared SPI/zein complex microspheres by extrusion method for delivering riboflavin. The obtained particles (about 15–25 μm) had spherical morphology with homogenous distribution throughout the matrix. Microspheres with SPI/zein ratios of 5:5 and 3:7 displayed near-zero-order release kinetics in simulated gastrointestinal fluids. The results indicated that SPI/zein microspheres showed potential as nutraceutical delivery carriers for the development of functional foods, such as yogurt enriched with vitamins. Rascon et al. [114] investigated the performance of SPI for the encapsulation of paprika oleoresin by spray drying. The authors found that carotenoid retention in the microparticles increased as inlet air temperature was increased from 160 °C to 200 °C. Compared to SPI nanoparticles without FA, FA-SPI nanoparticles showed a lower average size, a higher loading efficiency, and a faster release of curcumin in Tween 20-PBS buffer. The results showed that SPI treated by ultrasonics prior to encapsulation could increase their solubility. The optimum conditions for high encapsulation efficiency were followed as: pH 4.0, 1:1 SPI/GA ratio and 10% core material load.
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