Article pubs.acs.org/JAFC
Adsorption and Distribution of Edible Gliadin Nanoparticles at the Air/Water Interface Dengfeng Peng,† Weiping Jin,†,∥ Jing Li,† Wenfei Xiong,† Yaqiong Pei,† Yuntao Wang,† Yan Li,†,‡ and Bin Li*,†,‡,§ †
College of Food Science and Technology, Huazhong Agricultural University, Wuhan, Hubei 430070, People’s Republic of China Key Laboratory of Environment Correlative Dietology, Ministry of Education, Huazhong Agricultural University, Wuhan, Hubei 430070, People’s Republic of China § Functional Food Enginnering & Technology Research Center of Hubei Province, Wuhan, Hubei 430070, People’s Republic of China ∥ College of Food Science and Engineering, Wuhan Polytechnic University, Wuhan, Hubei 430023, People’s Republic of China ‡
ABSTRACT: Edible gliadin nanoparticles (GNPs) were fabricated using the anti-solvent method. They possessed unique high foamability and foam stability. An increasing concentration of GNPs accelerated their initial adsorption speed from the bulk phase to the interface and raised the viscoelastic modulus of interfacial films. High foamability (174.2 ± 6.4%) was achieved at the very low concentration of GNPs (1 mg/mL), which was much better than that of ovalbumin and sodium caseinate. Three stages of adsorption kinetics at the air/water interface were characterized. First, they quickly diffused and adsorbed at the interface, resulting in a fast increase of the surface pressure. Then, nanoparticles started to fuse into a film, and finally, the smooth film became a firm and rigid layer to protect bubbles against coalescence and disproportionation. These results explained that GNPs had good foamability and high foam stability simultaneously. That provides GNPs as a potential candidate for new foaming agents applied in edible and biodegradable products. KEYWORDS: gliadin nanoparticles, air/water interface, foam, interfacial properties, stability
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stabilize foam.16 Thewissen et al. found that gliadin has good foaming properties, which were similar to those of egg white protein.17,18 Uthayakumaran et al. investigated that γ-gliadinstabilized foams have higher stability than those of α- and ωgliadins.19 However, poor solubility and dispersity in the aqueous solution limit its application. To solve this problem, gliadin was made into well-dispersed and narrow-sizedistributed edible colloidal particles via the anti-solvent method.20 The key problem is to build the relationship between foaming characteristics [foamability (FA) and foam stability (FS)] of particles and interfacial properties. Besides, to the best of our knowledge, no report about changes of interfacial morphology of foams stabilized by protein particles has been found. Thus, in the present work, we fabricated gliadin nanoparticle (GNP) dispersion and investigated the influence of the particle concentration on foaming properties and interfacial behaviors. Subsequently, changes of morphology at the air/water interface with the extension of time were determined to better understand the stabilization mechanism of protein-particle-stabilized foams.
INTRODUCTION Foam is a subject of much research in colloid science, owning to its wide application in food, cosmetic, and pharmaceutical industries.1 Synthetic small-molecular-weight surfactants or amphiphilic polymers are traditionally used to stabilize foams through either reducing interfacial tension or forming a viscoelastic film. However, they have some disadvantages of requiring a high concentration or existing toxicity.2 Recently, partially hydrophobic colloidal particles are found to stabilize foam effectively as a result of their abilities to quickly adsorb at the air/water interface and provide a physical barrier to slow liquid drainage.3−5 However, most particles belong to inorganic particles or synthetic particles, such as polystyrene particles,6 poly[2-(dimethylamino)ethyl methacrylate] (PDMA)−polystyrene particles,7 and SiO2 particles.8 These particles have limitations in edible and biodegradable products. Therefore, studies of biological origin materials as edible particle stabilizers are of scientific significance. Ethyl cellulose,9 hydrophobic cellulose,10 and soy protein isolate11 have been developed to stabilize foams, but the variety is still a problem. Therfore, it is necessary to fabricate novel kinds of edible colloidal particles to act as foaming agents. Gliadin plays a predominant role in the foaming properties of gluten, which is the co-product of industrial wheat starch isolation.12,13 Gliadin is classified into α, γ, and ω types according to the biochemical and genetic data.14,15 The central area of the gliadin molecule is rich in glutamine and proline, and the terminal area is generally rich in hydrophobic amino acids. The amphiphilic parts in the gliadin molecule indicate that it may have surface-active properties and the potential to © XXXX American Chemical Society
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MATERIALS AND METHODS
Materials. Commercial wheat gluten (crude protein content of ≥80%), ovalbumin (protein content of ≥90%), and sodium caseinate Received: Revised: Accepted: Published: A
December 24, 2016 February 21, 2017 February 27, 2017 February 27, 2017 DOI: 10.1021/acs.jafc.6b05757 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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Journal of Agricultural and Food Chemistry (protein content of ≥85%) were purchased from Sigma-Aldrich Company (St. Louis, MO, U.S.A.). Other chemicals with analytical grade were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) and used without further purification. Gliadin Extraction. Gliadin was extracted according to the procedure described by Joye et al.21 and Wang et al.,22 with slight modification. Gluten was defatted using dichloromethane (the ratio of gluten/extract solution was 1:10, w/v) for 2 h at room temperature and then filtered through a filtered paper. The above procedures were repeated 3 times, and finally, the gluten fraction was dried at room temperature. Subsequently, the defatted gluten was extracted at room temperature with 70% (v/v) ethanol (the ratio of raw material/extract solution was 1:10, w/v). The solution after stirring for 2 h was centrifuged (10000g for 10 min). Next, the supernatant was collected and, after a night’s rest at 4 °C, centrifuged for a second time (10000g for 10 min) to remove any precipitates. Then, the remaining ethanol was removed using a rotary evaporator at 40 °C. Finally, gliadin powders were obtained after freeze-drying, and the protein content (85.0%) was analyzed by a nitrogen analyzer (FP-428, Leco Corp., St. Joseph, MI, U.S.A.) (a factor of 5.7 was used to convert the nitrogen to protein). Preparation of Edible GNPs. Edible GNPs were prepared using an anti-solvent method.23,24 Gliadin (2.5%, w/v) stock solution was obtained by dissolving powder in ethanol solution (70%, v/v) under stirring at room temperature (25 °C). Then, 1.2 mL of gliadin stock solution was trickled into 28.8 mL of deionized (DI) water. After that, the particle suspension was stirred vigorously for an additional 2 min. The final concentration of GNPs was 1 mg/mL. GNP solutions with different particle concentrations (0.05, 0.1, and 0.5 mg/mL) were obtained by diluting the dispersion of 1 mg/mL using aqueous ethanol binary solvent to ensure the same final alcohol content. Particle Size and ζ Potential Measurements. The particle size distributions and ζ potential of GNPs in freshly prepared suspensions were determined using a ZS Zetasizer Nano (Malvern Instrument, Ltd., U.K.). All measurements were carried out at 25 °C and repeated 3 times. Morphology Observations. The surface morphology of GNPs was observed using scanning electron microscopy (SEM, SU8000, Japan). When 50 particles were randomly selected in SEM images, the mean diameters of GNPs were estimated using Nanosize measurer software. Surface Hydrophobicity (H0). H0 of GNPs was measured using 8-anilino-1-naphthalenesulfonic acid ammonium salt (8-ANS), according to the method of Wu et al.20 and Xiong et al.25 ANS was dispersed into 10 mM phosphate-buffered saline (PBS, pH 7.0) to obtain a concentration of 8 mM. ANS (20 μL) was added to 4 mL of sample solution. The sample was excited at 385 nm, and the emission spectrum was measured from 400 to 650 nm using a fluorescence spectrophotometer (Shimadzu RF-5310PC, Japan) under 25 °C. The emission and excitation slits were set to 5 nm. H0 was calculated according to eq 1 H0 = S1 − S2
Foaming Microstructure Observation by Optical Microscopy. Microstructures of foams stabilized by GNPs were visualized using a microscope (SDPTOP, CX40). Foams were observed after foams were stored at 25 °C for 2, 10, 30, and 60 min. Foaming Interfacial Morphology Observation by SEM. Foams stabilized by GNPs was prepared according to the procedure mentioned in the method of foaming properties. After whipping, foams were stored for 2, 10, and 30 min first and then frozen in −86 °C. Before SEM (SU8000, Japan) observation, foams were freezedried. Dynamic Surface Pressure and Surface Dilatational Rheology. The dynamic surface pressure and surface dilatational modulus of samples at the air/water interface, formed with an air bubble submerged into a cuvette filled with GNP dispersions, were determined using an oscillating bubble rheometer (Tracker Teclis/ IT Concept, France). All of the experiments were carried out at 25 °C. GNP dispersions were placed in a rectangular glass cuvette sealed with Parafilm. An axisymmetric bubble of air was formed at the top of the needle of a syringe whose verticality was controlled by a computer. The bubble profile was digitized and analyzed through a chargecoupled device (CCD) camera coupled to a video image profile digitizer board. The dynamic surface tension of all samples was monitored for 120 min at a constant area of 18 mm2 of the bubble. The surface tension (γ) was calculated from the shape analysis of a rising bubble according to the Gauss/Laplace equation. The surface pressure (π) was calculated as γs − γp, where γs is the surface tension of the solvent and γp is the time-dependent surface tension of tested solutions. To obtain surface dilatational parameters, sinusoidal interfacial compression and expansion were performed through changing the bubble area at 10% of deformation amplitude (ΔA/A) and 0.1 Hz of angular frequency (ω). Details of this experiment were described elsewhere.26,27 The bubble was subjected to repeated measurements of 4 sinusoidal oscillation cycles and 4 static oscillation cycles up to 120 min. The surface viscoelastic modulus (E) and its elastic (Ed) and viscous (Ev) components were derived from the change in surface tension (γ) (dilatational stress) resulting from a small change in the surface area (dilatational strain). The viscoelastic modulus indicated two contributions of real and imaginary parts (E = Ed + iEv). Statistical Analysis. All experiments were performed using freshly prepared samples. Values are shown in means ± standard deviations (SDs). One-way analysis of variance (ANOVA) was used for establishing the significance of differences among mean values at p < 0.05.
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RESULTS AND DISCUSSION Characteristics of GNPs. The preparation of edible GNPs was based on the anti-solvent approach. When the stock solution of gliadin was dropped into DI water, a decrease of gliadin solubility led to the self-assembly of gliadin molecules, producing relatively uniform nanoparticles. The inset picture of Figure 1A showed the visual appearance of GNPs with a light blue color. The droplet size distribution of GNPs demonstrated a nearly monomodal distribution, and the particle diameter was around 105.3 ± 0.3 nm (Figure 1A). The value of polydispersity (PDI) was 0.078 ± 0.008, which indicated the uniform distribution of particles. Shapes of particles were close to spherical with a rough surface (Figure 1B). GNPs had a size arithmetic mean diameter of 90.6 ± 16.2 nm calculated using Nanosize measurer software. The value was smaller than that of dynamic light scattering (DLS), which may be attributed to dehydration of GNPs during drying. Surface hydrophobicity (H0) was measured to evaluate the surface wettability of particles or proteins, which could be used to identify the structural changes and reflect the surface activity.20,28 H0 value of GNPs was 1711.2 ± 8.4, which was almost 9-fold higher than that of ovalbumin.25 The ζ potential
(1)
where S1 is the area of solution, S2 is the area of solvent, and S1 − S2 is the H0 of samples. Foaming Properties. The foaming properties were determined by the method of Xiong et al.,25 with a slight modification. GNP fresh solution (15 mL) was placed in a glass cylinder (internal diameter of 30 mm and height of 150 mm). Then, the solution was whipped with a homogenizer (T25, IKA) at 8000 rpm for 1 min at 25 °C. After whipping, the foam was immediately poured into a 50 mL measuring cylinder. FA was measured by comparing the foam volume at 2 min to the initial liquid volume of samples. FS was determined by comparing the foam volume at 60 min to the initial foam volume of samples
FA (%) = V2/15 × 100
(2)
FS (%) = V60/V2 × 100
(3)
where V2 is the foam volume at 2 min and V60 is the foam volume at 60 min. B
DOI: 10.1021/acs.jafc.6b05757 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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GNPs was 27- and 9-fold larger than that of ovalbumin and sodium caseinate, respectively (Figure 2A). This indicated that GNPs had an outstanding FA, even at a very low concentration. Besides, the FA of GNPs was much better than that of most proteins and protein/surfactant mixtures, as reported in the literature, such as β-lactoglobulin31 and the soy glycinin/ stevioside mixture.26 In addition, the FS of GNPs was significantly higher than that of ovalbumin and sodium caseinate (p < 0.05). The size changes of bubbles formed by GNPs, ovalbumin, and sodium caseinate at the concentration of 1 mg/mL with the extension of time were indicated in Figure 3 and Table 1.
Figure 1. (A) Particle size distribution of the GNP suspension (the inset is a visual image of the GNP suspension in DI water) and (B) SEM image of GNPs. Figure 3. Time evolution of air bubbles within foams formed by GNPs, ovalbumin, and sodium caseinate at the concentration of 1 mg/ mL. The solid bars in all images correspond to the length of 100 μm.
of GNPs was relatively low (+16.2 ± 0.5 mV) and could better stabilize the interface because of their partial flocculation.29,30 Foaming Properties of GNPs Comparing to Ovalbumin and Sodium Caseinate. The foaming properties (FA and FS) of GNPs, ovalbumin, and sodium caseinate at the same concentration of 1 mg/mL were showed in Figure 2. The FA of
Foams stabilized by ovalbumin showed a large bubble diameter in the initial 2 min (455.7 ± 95.2 μm). The bubble diameters of foams stabilized by GNPs and sodium caseinate were 62.7 ± 19.3 and 57.4 ± 22.8 μm, respectively. They showed the smaller initial bubble size and more uniform bubbles than ovalbumin, which suggested that the foam properties of them were superior to that of ovalbumin. For three systems, the bubble size gradually increased with the extension of time, which may be due to liquid drainage, coalescence, and disproportionation. In comparison to ovalbumin, GNP-stabilized foams exhibited a smaller bubble size at 10, 30, and 60 min. This illustrated that the ability of GNPs to prevent coalescence of foams was stronger than that of ovalbumin. Effect of the Concentration on Foaming Properties. The influence of the GNP concentration (0.05−1 mg/mL) on FA and FS was investigated (Figure 4). As the GNP concentration increased from 0.05 to 1 mg/mL, an obvious increase of the foam volume at 2 min was found (Figure 4B), indicating that the higher concentration of GNPs promoted FA. This was attributed to a greater amount of particles absorbed onto the air/water interface and a larger or thickener interfacial area created during the whipping. Similar results were obtained using high-aspect-ratio nanosheets10 and hexylamine-modified laponite particles.32 It was noteworthy to mention that, even at the low concentration (1 mg/mL), GNPs still exhibited impressive FA (174.2 ± 6.4%). FS was evaluated by measuring the foam volume after sitting for 60 min (Figure 4). It can be clearly seen that FS increased with raising the GNP concentration from 0.05 to 0.5 mg/mL. Changes of the bubble size at different GNP concentrations (0.05−1 mg/mL) with the extension of time were presented in Figure 5 and Table 1. The diameter of bubbles formed from GNPs at 0.05 mg/mL was 187.2 ± 49.8 μm in the initial 2 min. It gradually decreased with an increasing concentration. When
Figure 2. (A) FA and FS of GNPs, ovalbumin (OVA), and sodium caseinate (SC) at the concentration of 1 mg/mL and (B) visual foam volume image of GNPs, OVA, and SC (1 mg/mL) at 2 and 60 min. C
DOI: 10.1021/acs.jafc.6b05757 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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Table 1. Diameter of Foams Formed by Ovalbumin (1 mg/mL), Sodium Caseinate (1 mg/mL), and GNPs (0.05−1 mg/mL) time (min)
a
emulsifier
2
1 mg/mL OVA 1 mg/mL SC 1 mg/mL GNPs 0.5 mg/mL GNPs 0.1 mg/mL GNPs 0.05 mg/mL GNPs
± ± ± ± ± ±
455.7 57.4 62.7 108.4 133.5 187.2
10 95.2 22.8 19.3 29.0 44.3 49.8
30
a
138.5 116.2 193.1 239.7 371.1
N ± ± ± ± ±
30.7 28.8 64.6 87.5 221.6
181.6 192.6 282.1 327.3
N ± ± ± ± N
60 44.9 66.8 91.8 131.8
218.5 230.6 334.0 369.9
N ± ± ± ± N
41.3 64.2 101.9 174.5
N means no data.
Figure 5. Time evolution of air bubbles within foams formed by GNPs with different concentrations (0.05−1 mg/mL). The solid bars in all images correspond to the length of 100 μm.
Figure 4. (A) FA and FS of GNPs (concentrations of 0.05−1 mg/mL) and (B) visual foam volume image of GNPs (concentrations of 0.05−1 mg/mL) at 2 and 60 min.
the concentration reached 1 mg/mL, the initial bubbles had a smaller size with a more uniform size distribution. In addition, for all concentrations, the bubble size gradually increased with an increasing time. The higher concentration displayed the slower rate of increase, suggesting having a stronger capability to prevent foam coalescence or disproportionation. Interfacial Morphology of Foams. The interfacial morphology of foams stabilized by GNPs was recorded in Figure 6. In the initial 2 min, the bubble surface was compactpackaged by particles, suggesting the anchoring of GNPs onto the air/water interface (Figure 6A). The distribution of particles at the interface was not uniform (Figure 6B). The diameter range of particles on the surface of the bubble was around 60−800 nm, which could be backed up by the bidirectional arrows on Figure 6B. Particles with a diameter of larger than 300 nm confirmed the presence of particle aggregation. For GNPs stored at 25 °C for 10 min, the vast majority of particles were fused into an irregular film at the air/ water interface (Figure 6C). A few discrete spherical dots can be clearly observed on the foam surface (Figure 6D), indicating
Figure 6. SEM images of (A and B) foaming interfacial morphology after being stored at room temperance (25 °C) for 2 min, (C and D) foaming interfacial morphology after being stored at 25 °C for 10 min, and (E and F) foaming interfacial morphology after being stored at 25 °C for 30 min.
that some particles were still not entirely integrated on the foaming interface. A complete relatively smooth film without discrete particles was found after GNPs stored at 25 °C for 30 min (panels E and F of Figure 6). This very interesting phenomenon might be the result from the strong interaction of GNPs at the air/water interface. Films formed by fusion particles were capable of forming thick steric barriers against coalescence and made the low gas diffusion between the air D
DOI: 10.1021/acs.jafc.6b05757 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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GNPs had a faster mass transport rate than most of the proteins, such as soy glycinin,34 β-lactoglobulin,35 and casein.36 From 600 s to 2 h, the surface pressure gradually increased and became relatively constant. The curve of viscoelastic modulus (E) versus π was used to investigate the interaction and interface adsorption capacity of particles.20 When the slope of the E−π curve was larger than 1 (characteristic of the behavior of an ideal gas), it proved that surface-active components existed in the interactions.26 The evolution of E with π in the surface layer for the adsorption of GNPs under different particle concentrations was presented in Figure 8A. For all of the samples at the concentration of 0.05−1 mg/mL, E increased with increasing π. This indicated that GNPs adsorbed from the bulk onto the interface. At the concentrations of 0.05 and 0.1 mg/mL, E increased slowly until the π value reached 15 mN/m, implying that larger amounts of particles at the interface were required to establish intermolecular interactions. When the π value was above 15 mN/m, the slopes (about 5.5) of concentrations from 0.05 to 1 mg/mL were higher than 1, suggesting the presence of high molecular interactions between the adsorbed GNPs. Panels B−D of Figure 8 presented the evolution of the viscoelastic modulus (E), elastic modulus (Ed), and viscous modulus (Ev) of GNPs with time. In all cases, the increase in E, Ed, and Ev with adsorption time should be associated with the adsorption of GNPs at the interface. For the GNP solution with concentrations of 0.5 and 1 mg/mL, E, Ed, and Ev dramatically increased with time from 0 to 600 s, revealing the existence and increase of interactions between the adsorbed GNPs. Interestingly, it is worth noting that the Ev values were evidently larger than most proteins, such as casein micelles,36 suggesting that GNPs were the special colloidal particle with the firm viscoelastic interfacial film during the adsorption period.
bubbles. Therefore, foams stabilized by GNPs would have high FS. It was highlighted that the foaming interfacial structures stabilized by GNPs were unique and obviously different from other particles, such as rod-shaped nanofibrillated cellulose nanoparticles,33 colloidal ethyl cellulose particles,9 and hydrophobic cellulose microparticles.1 Effect of the Concentration on Interfacial Properties. Figure 7 showed the time evolution of surface pressure (π) of
Figure 7. Time evolution of the surface pressure (π) for the adsorption of GNPs (concentrations of 0.05−1 mg/mL) at the air/ water interface.
GNPs in relation to the particle concentration at the air/water interface. The initial adsorption value (the first data recorded by an oscillating bubble rheometer) was obviously increased with raising the concentration from 0.05 to 1 mg/mL. This indicated that increasing the particle concentration increased the amount of GNP adsorption from the bulk onto the interface. For all concentrations, the surface pressure rapidly increased within the first 600 s, which might be associated with fast adsorption of GNPs at the interface. This indicated that
Figure 8. (A) Surface dilatational modulus (E) as a function of surface pressure (π) for GNPs (concentrations of 0.05−1 mg/mL) at the air/water interface and time evolution of the surface dilatational modulus (B), elastic modulus (C), and viscous modulus (D) for the adsorption of GNPs (concentrations of 0.05−1 mg/mL) at the air/water interface. E
DOI: 10.1021/acs.jafc.6b05757 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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(2) Chassaing, B.; Koren, O.; Goodrich, J. K.; Poole, A. C.; Srinivasan, S.; Ley, R. E.; Gewirtz, A. T. Dietary emulsifiers impact the mouse gut microbiota promoting colitis and metabolic syndrome. Nature 2015, 519, 92−96. (3) Matsumiya, K.; Murray, B. S. Soybean protein isolate gel particles as foaming and emulsifying agents. Food Hydrocolloids 2016, 60, 206− 215. (4) Lam, S.; Velikov, K. P.; Velev, O. D. Pickering stabilization of foams and emulsions with particles of biological origin. Curr. Opin. Colloid Interface Sci. 2014, 19, 490−500. (5) Binks, B. P.; Johnston, S. K.; Sekine, T.; Tyowua, A. T. Particles at Oil-Air Surfaces: Powdered Oil, Liquid Oil Marbles, and Oil Foam. ACS Appl. Mater. Interfaces 2015, 7, 14328−14337. (6) Fukuoka, K.; Tomikawa, A.; Nakamura, Y.; Fujii, S. Aqueous Foams Stabilized with Several Tens of Micrometer-sized Polymer Particles: Effects of Surface Hydrophilic−Hydrophobic Balance on Foamability and Foam Stability. Chem. Lett. 2016, 45, 667−669. (7) Fujii, S.; Akiyama, K.; Nakayama, S.; Hamasaki, S.; Yusa, S.; Nakamura, Y. pH- and temperature-responsive aqueous foams stabilized by hairy latex particles. Soft Matter 2015, 11, 572−579. (8) Carl, A.; Bannuscher, A.; von Klitzing, R. Particle stabilized aqueous foams at different length scales: Synergy between silica particles and alkylamines. Langmuir 2015, 31, 1615−1622. (9) Jin, H.; Zhou, W.; Cao, J.; Stoyanov, S. D.; Blijdenstein, T. B. J.; de Groot, P. W. N.; Arnaudov, L. N.; Pelan, E. G. Super stable foams stabilized by colloidal ethyl cellulose particles. Soft Matter 2012, 8, 2194−2205. (10) Guevara, J. S.; Mejia, A. F.; Shuai, M.; Chang, Y.-W.; Mannan, M. S.; Cheng, Z. Stabilization of Pickering foams by high-aspect-ratio nano-sheets. Soft Matter 2013, 9, 1327−1336. (11) Morales, R.; Martinez, K. D.; Pizones Ruiz-Henestrosa, V. M.; Pilosof, A. M. Modification of foaming properties of soy protein isolate by high ultrasound intensity: Particle size effect. Ultrason. Sonochem. 2015, 26, 48−55. (12) Blomfeldt, T. O.; Kuktaite, R.; Johansson, E.; Hedenqvist, M. S. Mechanical properties and network structure of wheat gluten foams. Biomacromolecules 2011, 12, 1707−1715. (13) Diao, C.; Xia, H.; Parnas, R. S. Wheat Gluten Blends with Maleic Anhydride-Functionalized Polyacrylate Cross-Linkers for Improved Properties. ACS Appl. Mater. Interfaces 2015, 7, 22601− 22609. (14) Wang, P.; Tao, H.; Wu, F.; Yang, N.; Chen, F.; Jin, Z.; Xu, X. Effect of frozen storage on the foaming properties of wheat gliadin. Food Chem. 2014, 164, 44−49. (15) Staiano, M.; Matveeva, E. G.; Rossi, M.; Crescenzo, R.; Gryczynski, Z.; Gryczynski, I.; Iozzino, L.; Akopova, I.; D’Auria, S. Nanostructured silver-based surfaces: New emergent methodologies for an easy detection of analytes. ACS Appl. Mater. Interfaces 2009, 1, 2909−2916. (16) Banc, A.; Desbat, B.; Renard, D.; Popineau, Y.; Mangavel, C.; Navailles, L. Structure and orientation changes of ω-and γ-gliadins at the air-water interface: A PM-IRRAS spectroscopy and Brewster angle microscopy study. Langmuir 2007, 23, 13066−13075. (17) Thewissen, B. G.; Celus, I.; Brijs, K.; Delcour, J. A. Foaming properties of wheat gliadin. J. Agric. Food Chem. 2011, 59, 1370−1375. (18) Thewissen, B. G.; Celus, I.; Brijs, K.; Delcour, J. A. Foaming properties of tryptic gliadin hydrolysate peptide fractions. Food Chem. 2011, 128, 606−612. (19) Uthayakumaran, S.; Tömösközi, S.; Tatham, A.; Savage, A.; Gianibelli, M.; Stoddard, F.; Bekes, F. Effects of gliadin fractions on functional properties of wheat dough depending on molecular size and hydrophobicity. Cereal Chem. 2001, 78, 138−141. (20) Wu, N. N.; Zhang, J. B.; Tan, B.; He, X. T.; Yang, J.; Guo, J.; Yang, X. Q. Characterization and interfacial behavior of nanoparticles prepared from amphiphilic hydrolysates of beta-conglycinin-dextran conjugates. J. Agric. Food Chem. 2014, 62, 12678−12685. (21) Joye, I. J.; Nelis, V. A.; McClements, D. J. Gliadin-based nanoparticles: Fabrication and stability of food-grade colloidal delivery systems. Food Hydrocolloids 2015, 44, 86−93.
From these results and analysis, to better understanding the mechanism of FA and FS of GNPs, we proposed a conjecture. To use the anti-solvent method, we prepared edible GNPs with smaller size, uniform distribution, suitable H0, lower ζ potential, and spherical shape. All of the physical properties gave GNPs the ability to quickly diffuse and adsorb to the air/water interface. Then, through relating interfacial properties of GNPs to the macroscopic foaming properties (FA and FS), we found that there existed a strong correlation between the FA of GNPs and initial adsorption speed onto the air/water interface. With the increase of the concentration, the initial adsorption speed of GNPs became fast, causing the increase of FA. In addition, after GNPs adsorbed on the interface, they began to interact and gradually fused into viscoelastic interfacial films, which played an important role in FS.37,38 With increasing the concentration, the increase of E of interfacial films contributed to the enhanced FS of GNPs. We employed the anti-solvent method to prepare edible GNPs, in which the water dispersibility of gliadin was significantly improved. In addition, those edible GNPs exhibited extraordinary FA and high FS, even at a low concentration (1 mg/mL). From the view of foaming surface morphology and interfacial properties, we were able to shed light on four major observations. First, the absorbed particle layer at the interface gradually fuses into films, which was different from other particles. Second, at all concentrations, the surface pressure rapidly increased with the adsorption time from 0 to 600 s, indicating that GNPs had a faster mass transport rate. Third, with increasing the concentration of GNPs from 0.05 to 1 mg/mL, the initial adsorption values were obviously increased. Fourth, during the test period (7200 s), E, Ed, and Ev were raised with increasing the concentration. Not only were the surface properties of GNPs influenced by particle concentration, the foaming properties (FA and FS) of GNPs were also dominated by them. In comparison to the low concentration, GNPs had the higher FA and FS at high concentrations, owing to the faster initial adsorption speed and formation of a larger viscoelastic film. Results confirmed that GNPs were appropriate for acting as a new foaming agent and could be widely applied in the food, cosmetic, and pharmaceutical industries.
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AUTHOR INFORMATION
Corresponding Author
*Telephone: +86-27-87283462. Fax: +86-27-87282966. E-mail:
[email protected]. ORCID
Bin Li: 0000-0001-7763-4245 Funding
This work was financially supported by the Ministry of Science and Technology of the People’s Republic of China (2016YFD0400804) and the Hubei Provincial Science− Technology Supporting Plan of China (2015BBA191). Notes
The authors declare no competing financial interest.
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REFERENCES
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DOI: 10.1021/acs.jafc.6b05757 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.jafc.6b05757 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
