Soy Protein Films Research Articles

Robust soy protein films obtained by slight chemical modification of polypeptide chains

Soy protein based materials are of great interest because of the merits of biocompatibility, biodegradability, renewability, etc. However, the poor mechanical properties and high water sensitivity limit their further application in many fields. In this paper, we tried to overcome these shortcomings through a slight chemical modification of the polypeptide chains of soy protein. 31P NMR and solid state 13C CP/MAS NMR spectroscopy confirmed that the diethoxy phosphoryl groups were successfully grafted onto soy protein chains with a molar grafting ratio of 0.15–1.18%, which almost did not change the nature of soy protein. The isoelectric point and rheological behavior of the modified soy protein sample varied with the grafting ratio, indicating that the tertiary structure of the protein was changed after phosphoryl modification. The FTIR spectra of the modified soy protein suggested that the increase of β-sheet conformation from the slight chemical modification could be the reason for the change of the globular structure of soy protein. Finally, we obtained a robust soy protein film as expected, and we did not use any crosslinking agent and plasticizer that were almost unavoidable in the previous studies reported in the literature. The tensile strength and the elongation at break of our soy protein films were 35 ± 5 MPa, 2.5 ± 0.5% in the dry state, and 3.8 ± 1.5 MPa, 125 ± 5% in the wet state, respectively. We believe that the method we developed in this communication provides a practical approach to improve the mechanical properties and broaden the applications of natural soy protein based materials.

Protein–protein resistance investigated by quartz crystal microbalance

By use of quartz crystal microbalance with dissipation (QCM-D), we have investigated the adsorption of proteins such as fibrinogen, bovine serum albumin or lysozyme on the surface of soy protein film in PBS buffer solution in real time. Our studies demonstrate that the proteins can be adsorbed on soy protein film at a pH between the isoelectric point (pIsp) of soy protein film and that (pIfp) of the foreign protein, where the adsorption decreases with the concentration of added salt. Beyond the pH range, soy protein generally resists the adsorption of the foreign protein due to electrostatic repulsion, which is slightly affected by the concentration of the added salt in the range we investigated. At a pH close to pIsp or pIfp, the proteins can also be adsorbed on soy protein film due to hydrophobic interactions. The present study reveals that the protein resistance of soy protein film is determined by electrostatic interactions, hydrophobic interactions and hydrogen bonding between the foreign protein and soy protein.

Soy protein films for wound-healing applications: antibiotic release, bacterial inhibition and cellular response

Use of naturally derived materials is becoming widespread in the biomedical field. Soy protein has advantages over the various types of natural proteins employed for biomedical applications, due to its low price, non-animal origin and relatively long storage time and stability. In the current study, soy protein isolate (SPI) was investigated as a matrix for wound-dressing applications. The antibiotic drug gentamicin was incorporated into the matrix for local controlled release and thus continuous bactericidal effect. Homogeneous high-quality films were cast from aqueous solutions and tested for the effects of gentamicin release on bacterial inhibition. The cytotoxicity and in vitro biocompatibility of these films were also examined. The gentamicin release profiles exhibited a moderate burst effect followed by a decreasing release rate, which was maintained for at least 4 weeks, thus enabling a suitable bacterial inhibition effect. The materials released from the films during an indirect cytotoxicity test were found to be safe, except for a slight inhibitory effect in the presence of high concentrations of glycerol. The biocompatibility test showed confluent cell cultures in close proximity to the SPI films. It is clear that these new antibiotic-eluting SPI films exhibit a high potential for use as wound dressings.

An Ultraelastic Poly(ethylene oxide)/Soy Protein Film with Fully Amorphous Structure

An Ultraelastic Poly(ethylene oxide)/Soy Protein Film with Fully Amorphous Structure

Thermal properties of polyfurfuryl alcohol absorbed/adsorbed on arylated soy protein films

Abstract In this study, polyfurfuryl alcohol was absorbed/adsorbed on soy protein isolate films by immersing the SPI films in acid-catalysed furfuryl alcohol solution for 60 h followed by complete curing at 145–150 °C for 2 h. PFA absorbed/adsorbed soy protein films designated as SPI-PFA were then arylated in the presence of 0.5% (w/v) 2,2-diphenyl-2-hydroxyethanoic acid for 4 h to fabricate arylated soy protein films designated as SPI-PFA-Ar. The incorporation of PFA and introduction of aromatic backbone through arylation is revealed from Fourier transform infrared study. Thermal studies of SPI, SPI-PFA and SPI-PFA-Ar were carried out by thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical thermal analysis. In addition, mechanical properties, surface morphology and water uptake of all the three different types of the films were evaluated. Results indicated that PFA absorbed/adsorbed arylated soy protein films showed higher thermal stability than native SPI films.

Investigation on thermally‐induced conformation transition of soy protein film with variable‐temperature FTIR spectroscopy

AbstractSoy proteins are important and versatile foodstuffs, and are potentially very valuable natural materials as replacements for synthetic polymers if mechanical properties and water sensitivity could be improved by changing its conformational structure during processing. As part of such investigations, the thermally‐induced conformation transitions of soy protein films were studied in detail with variable‐temperature FTIR spectroscopy and two‐dimensional correlation analysis. The results show that during the heating process, relatively mobile random coil segments in the soy protein chains reconfigure to a relatively stable β‐turn conformation as part of major structural changes. The observations in heated‐cooled‐heated experiments reveal that a fraction of such a conformation transition is reversible. As part of this analysis, we identify for the first time that the peak at 1500 cm−1 in the FTIR spectra can be assigned to the characteristic absorption of β‐turn, which is also associated with the peak at 1700 cm−1 and is seen in other important structural proteins such as silk fibroin. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effect of Ultrasound Treatment on Properties of Soy Proteins Film

Soy protein isolate(SPI) based edible film as matrix materials have been prepared using the casting techniques. Ultrasound treatment (UT) could represent an interesting strategy for improving Soy protein film appearance. Different UT exposure times were applied to film-forming dispersion. The aim of this work was to investigate the effect of ultrasound treatment on Soy protein films at molecular structure and mechanical properties. The results showed that the structure of SPI film became more homogeneous and the properties has been improved largely after treated by ultrasonic, with the output power 1000 w for 16 s the tensile strength was the best; for 12 s, elongation reach the peak.

Bioavailability of Soy Protein and Corn Zein Films

The in vivo bioavailability of soy protein isolates and corn zein film material before and after film formation by heat/ pressure was determined. The In vitro digestibility of corn zein before and after film formation was also measured. Films were produced from anhydrous protein with 30% glycerol added using a heat-press method with no use of casting solvents or cross-linking agents. Corn zein raw and film material were ground under liquid nitrogen then digested in two enzyme-acid cocktails with free amino acid analysis before and after digestion. The protein efficiency ratio and net protein ratio were determined for both zein and soy protein using a weanling Sprague-Dawley descended rat feeding study. The In vitro digestibility study indicated that the non-heat pressed corn zein was more digestible than the heat pressed zein. However, the in vivo results indicated that corn and soy protein were equally bioavailable whether they were derived from film mixture prior to or after film formation. Both corn zein and soy protein material had lower protein efficiency ratio than the control diet. Furthermore, soy protein films materials had a higher protein efficiency ratio than corn zein.

Nanoemulsions Prepared by a Low-Energy Emulsification Method Applied to Edible Films

Catastrophic phase inversion (CPI) was used as a low-energy emulsification method to prepare oil-in-water (O/W) nanoemulsions in a lipid (Acetem)/water/nonionic surfactant (Tween 60) system. CPIs in which water-in-oil emulsions (W/O) are transformed into oil-in-water emulsions (O/W) were induced by changes in the phase ratio. Dynamic phase inversion emulsification was achieved by slowly increasing the water volume fraction (fw) to obtain O/W emulsions from water in oil emulsions. Composition and processing variables were optimized to minimize droplet size and polydispersity index (PdI). It was found that addition of the continuous phase to the dispersed phase following the standard CPI procedure resulted in the formation of oil droplets with diameters of 100-200 nm. Droplet size distribution during CPI and emulsification time depended on stirring speed and surfactant concentration. Droplet sizes in the inverted emulsions were compared to those obtained by direct emulsification: The process time to reach droplet sizes of around 100 nm was reduced by 12 times by using CPI emulsification. The Acetem/water nanoemulsion was also used as a carrier to incorporate oregano and cinnamon essential oils into soy protein edible films. The resulting composite films containing oregano oil showed better moisture barrier and mechanical properties compared to soy protein films.

Effect of Salicylic Acid on the Mechanical Properties and Water Resistance of Soy Protein Isolate Films

Soy protein composites films (SF) have been prepared using soy protein isolate (SPI), salicylic acid (SA) and glycerol as a plasticizer. To prepare water resistant soy protein composites films (SF-B), 2, 2-diphenyl-2-hydroxyethanoic acid (DPHEAc) was used. Different amounts of SA were added in both SF and SF-B films. The results showed that the SF-B films with 0.5% (wt) of SA had higher tensile strength and modulus with low water uptake than that of SF films at same amount of SA. Contact angle analysis also indicated that the SF-B films showed hydrophobic surface. Thus both lower levels of water uptake and hydrophobic surface indicated high water resistance of the materials. Higher transmittance value and increased intermolecular hydrogen bonding showed higher compatibility between SPI and SA. This work provided a new approach in the use of SA in water resistant soy protein films for enhancing the processing window.

Thermal and mechanical properties of soy protein films processed at different pH by compression

Glycerol-plasticized soy protein isolate (SPI) based films were prepared by compression with the aim to obtain environmentally friendly materials for packaging applications. Previously to the hot-pressed step, the protein was dispersed in water, the pH was fixed to values higher, lower and at the isoelectric point of SPI (pH = 4.6), and the dispersion was freeze-dried. The effect of pH on physico-chemical properties has been explained using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and thermo-gravimetric analysis (TGA). The changes observed by FTIR in the intensity of the bands corresponding to the amide group showed that pH affected protein–glycerol interactions. Apart from pH effect, heat and pressure also affected the grade of denaturation of SPI shown by the disappearance of the DSC peak corresponding to 7S globulin. Mechanical properties were also evaluated and related to pH and storage time. Both tensile strength and elongation at break are higher at basic pHs, when the unfolding of protein seems to be optimum in order to interact with the plasticizer. Mechanical properties remained invariable after having been stored under specific conditions for two months. Preparation of SPI-based biofilms processed at different pHs by compression is an innovative study in this field, in which the most employed technique to prepare films has been casting.

Mechanical and thermal properties of soy protein films processed by casting and compression

Soy protein isolate (SPI) based films are environmentally friendly because they are biodegradable and come from renewable sources but they are brittle. Different ratios of plasticizer were incorporated into SPI-based films to improve mechanical properties. Glycerol has a plasticizing effect on the films in the range of 30–40%. Apart from the plasticizer, the processing method employed to prepare films also influenced on the mechanical properties. Films processed by compression showed much better mechanical properties, higher tensile strength and elongation at break, than the ones processed by casting. Analysis of the thermal properties revealed that denaturation temperatures of the two main globulin fractions present in SPI were influenced by the moisture content of the sample but not by the processing method employed.

Effect of Water-Mediated Arylation Time on the Properties of Soy Protein Films

In situ and dip coating methods were used to prepare arylated soy protein films designated as ISP and DSP, respectively. ISP and DSP protein films were arylated with 2,2-diphenyl-2-hydroxyethanoic acid, in the presence of water, at different time intervals to impart the hydrophobicity in the protein films. DSP and ISP series films suffered a dramatic loss of mechanical properties with the increase in arylation time. Morphological characterization of the soy protein films arylated at different time intervals was done by scanning electron microscopy. It was observed that the increase in arylation time leads to the clustering of the hydrophobic units, through hydrophobic interactions, resulting in the hydrophobic collapse. Hydrophobic collapse in the arylated protein films showed significant decrease in the mechanical properties of the protein films. However, the water uptake of these protein films was independent of the arylation time. The immediate implications of these experimental results are related to the promising use of water-mediated arylated soy proteins as films and composites.

Soy protein films with the hydrophobic surface created through non-covalent interactions

Different plasticizers (P) such as glycerol, 1,2 propanediol, trimethylol propane, thiodiglycol, and formamide (30% by weight w.r.t. soy protein) were used to prepare soy protein films (coded as SP) by compression molding at 140 °C and 20 MPa. The SP films were immersed in 0.5% (w/v) benzilic acid solution for 26 h to get arylated soy protein films (SP-B) with the evolution of CO 2, leading to the formation of diphenylhydroxymethane (DPHM) on the surface. Lotus leaf like structure, on the surface of SP-B film, with high hydrophobicity has been created, supported by the existence of nano/micro spheres. The SP-B and SP films were characterized by Fourier transformed infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, tensile testing, optical transmittance, contact angle, and biodegradation experiments. The mechanical properties, transmittance, and contact angle of SP-B films increased significantly, compared with SP. The SP-B films exhibited high water resistance in the range of 67–82%. These results indicated attractive interactions (often termed as π-interactions) of DPHM aromatic groups took place in the SP-B films resulting in the formation of nanospheres or microspheres. This work provided a good way for increasing the surface hydrophobicity and the mechanical properties of the protein materials through non-covalent interactions.

Structure and properties of soy protein films plasticized with hydroxyamine

AbstractTwo kinds of transparent films of soy protein were successfully prepared by plasticizing with diethanolamine (DEA) and triethanolamin (TEA). The films were hot pressed at 140°C and 20 MPa, and characterized with Fourier transform infrared spectroscopy, scanning electron microscope, ultraviolet–visible spectrometer, differential scanning calorimetry (DSC), thermogravimetric analysis, and tensile testing. The results indicated that films with triethanolamine plasticizers possessed better optical transmittance (more than 80% at 800 nm) than those with diethanolamine and glycerol. All of the sheets exhibited only one Tg in DSC curves. Moreover, the soy protein plastics with TEA had higher thermal stability and mechanical properties, as well as lower water uptake than those with DEA and glycerol, as a result of the strong interaction between TEA and protein molecules. The soy protein materials will be promising for the application in the fields of package and container, substituting for the nongreen polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Effects of drying conditions on some physical properties of soy protein films

The influence of drying conditions (air temperature and relative humidity) on mechanical properties, solubility in water, and color of two kinds of soy protein isolate film: a commercial one (CSPI) and other obtained under laboratory conditions (LSPI) were evaluated using the response surface methodology (RSM). Soy protein films were prepared by casting using glycerol as plasticizer. The films were dried in a chamber with air circulation under controlled conditions of relative humidity (24%, 30%, 45%, 60%, 66%) and air temperature (34, 40, 55, 70, 76 °C). It was verified that mechanical properties of films made from LSPI and CSPI are influenced in a very different way by the drying conditions due to a diverse initial protein conformation in both materials, as was revealed by DSC and SDS–Page studies. The solubility of the LSPI film was affected by temperature and relative humidity, being lowest (∼50%) for films obtained at high RH and temperatures ranging from 45 to 76 °C. For CSPI films, in contrast, solubility did not depend on the drying process and it remained relatively constant (∼40%). The optimal drying conditions determined by RSM were: 70 °C and 30% RH for CSPI films and 60 °C and 60% RH for LSPI films. Dried under these conditions, CSPI films presented a higher tensile strength, lower elongation at break, lower solubility and better water and oxygen permeability than LSPI ones.

Kinetics of the breakdown of cross-linked soy protein films for drug delivery

The aim of the present work was to investigate the potential of soy protein isolate (SPI) films as controlled release systems for active compounds. Mechanical properties, dissolution and compound release kinetics of SPI films prepared with different concentrations of formaldehyde were measured over time in the absence or presence of digestive enzymes at gastric or intestinal pH. The effect of formaldehyde on tensile strength, elastic modulus, % elongation and swelling suggested that increasing its concentration increased film cross-linking density. Film bulk erosion in the presence of digestive enzymes followed first-order kinetics. Methylene blue or rifampicin release followed variable kinetics depending on compound solubility during a 1–2 h initial phase, followed by zero-order release. Cross-linking density appears to provide effective means of regulating the erosion and release rate of SPI films. SPI film networks displayed excellent compound binding capacity, especially for hydrophobic molecules, and hence potential for use in controlled release systems based on matrix erosion.

Banana fiber-reinforced biodegradable soy protein composites

Banana fiber, a waste product of banana cultivation, has been used to prepare banana fiber reinforced soy protein composites. Alkali modified banana fibers were characterized in terms of density, denier and crystallinity index. Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were also performed on the fibers. Soy protein composites were prepared by incorporating different volume fractions of alkali-treated and untreated fibers into soy protein isolate (SPI) with different amounts of glycerol (25%–50%) as plasticizer. Composites thus prepared were characterized in terms of mechanical properties, SEM and water resistance. The results indicate that at 0.3 volume fraction, tensile strength and modulus of alkali treated fiber reinforced soy protein composites increased to 82% and 963%, respectively, compared to soy protein film without fibers. Water resistance of the composites increased significantly with the addition of glutaraldehyde which acts as cross-linking agent. Biodegradability of the composites has also been tested in the contaminated environment and the composites were found to be 100% biodegradable.

Soy protein–polysaccharides interactions at the air–water interface

This work studies the interfacial behavior of mixed soy protein (SP) + polysaccharide (PS) systems to gain knowledge on the interactions between these biopolymers at the air–water interface under dynamic conditions at neutral pH where a limited incompatibility between macromolecules can occur. The PSs used were: hydroxypropylmethylcellulose (HPMC) as surface-active PS; lambda carrageenan ( λ C ) and locust bean (LB) gum as non-surface-active PSs. Protein and PS concentration in the mixed systems were 2% and 0.25%, respectively. The dynamic surface pressure and rheological properties of films were evaluated with a drop tensiometer at 20 ∘ C , pH 7 and ionic strength 0.05 M. The presence of HPMC and λ C greatly increased the surface pressure, surface dilatational elasticity and relative viscoelasticity on the basis of different mechanisms. HPMC competed for the interface with SP, but due to its unusual strong surface activity it could dominate the surface pressure and improve film viscoelasticity. The modification of surface pressure and rheological properties of adsorbed SP films in the presence of λ C necessarily suggests the participation of λ C + contaminants at the interface. Pure λ C could influence the interface by a complexation mechanism, or indirectly by a depletion mechanism in the vicinity of the interface. In addition surface-active contaminant of λ C if strongly bound to the PS could bring some PS molecules at the interface. LB little affected the surface pressure and rheological properties of SP films even if surface-active contaminants were present in the commercial preparation. Differences in the interaction of λ C and LB gum with the protein should be mainly ascribed to different degrees of incompatibility and to the fact that LB is not charged.

Effect of Malic and Lactic Acid Incorporated Soy Protein Coatings on the Sensory Attributes of Whole Apple and Fresh-Cut Cantaloupe

ABSTRACT: Whole apples and fresh-cut cantaloupe cubes were coated with soy protein + glycerol (SP) films and 2 other films that were demonstrated to have antimicrobial activity in model system, SP + malic acid (MSP), and SP + lactic acid (LSP). Treated apples and cantaloupe cubes were stored at 5°C, and the sensory properties were evaluated with a trained descriptive analysis panelists. Texture and color were also measured with instruments. The sourness of SP-coated apples was lower than non-coated, MSP-coated, and LSP-coated apples after 28 d of storage. The sweetness of the LSP-coated cantaloupe cubes was higher than the non-coated and the MSP-coated samples at 7 d. The sensory evaluation of the MSP and LSP coatings on the apples and the cantaloupe cubes showed no significant difference in the other attributes of taste and appearance. Although instrumental measurements showed that hardness of the coated apples was higher than that of the non-coated ones, the panelists did not detect the differences. Instrumental measurements also showed that the hardness of the SP-coated cantaloupe cubes was lower than the non-coated, LSP-coated, and MSP-coated cantaloupe cubes, and the panelists did not detect the differences. The color of the apples evaluated by panelists was correlated with instrumental color measurements. Organic acid incorporated films (MSP and LSP) did not adversely impact the sensory properties of the tested products. Malic and lactic acids incorporated soy protein film that can be used to coat the whole apple and the fresh-cut cantaloupes without affecting the sensory properties.