Research Article Received: 11 August 2013

Revised: 14 November 2013

Accepted article published: 26 November 2013

Published online in Wiley Online Library: 27 December 2013

(wileyonlinelibrary.com) DOI 10.1002/jsfa.6495

Starch nanocrystals as particle stabilisers of oil-in-water emulsions Chen Li, Yunxing Li, Peidong Sun and Cheng Yang∗ Abstract BACKGROUND: As an environmentally benign particle emulsifier, starch nanocrystal (SNC) has attracted considerable attention. By submitting waxy maize starch to acid below the gelatinisation temperature of starch, nanoscale crystalline residues, which are SNCs, were separated from starch granules by hydrolysing amorphous regions. The SNC could be used as a particle emulsifier to stabilise emulsions. RESULTS: The SNC could adsorb at the oil–water interface to stabilise oil-in-water emulsions with high stability to coalescence. The creaming of emulsions occurred after homogenisation but decreased with increasing SNC content, which was mainly due to the formation of an inter-particle network in the emulsions. Because of the amount of sulfuric groups at the surface, the SNC was negatively charged. Therefore, at low pH values or high salt content the electrostatic repulsion of the SNC was reduced, which further caused droplet aggregation and an increase in size of the particles in the emulsions stabilised by the SNC. CONCLUSION: The SNC was an efficient particle emulsifier for preparing Pickering emulsions. The size of emulsions stabilised by the SNC could be tailored by changing the pH value or salt concentration. c 2013 Society of Chemical Industry  Keywords: Pickering emulsion; starch nanocrystals; food-grade; electrostatic repulsion

INTRODUCTION

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An emulsion is a system consisting of dispersed droplets of one immiscible liquid in another immiscible liquid. Emulsions are extensively used in food, cosmetics and pharmaceutics. Particle-stabilised emulsions, usually referred to as Pickering emulsions, have attracted considerable research interest in the past decade due to their unique properties.1,2 The essentially irreversible anchoring and specific inter-particle interactions at the interface are the physical basis of the peculiar properties of the particle-stabilised emulsions. Some of the most interesting properties of these systems involve the possibilities for completely blocking the process of Ostwald ripening, and forming an emulsion with long-term stability. A number of particles have been used to stabilise emulsions, such as hydrophobic silica,3 – 5 clays,6,7 carbon nanotubes,8 latex9,10 and microgels.11,12 Recently, environmentally benign particle emulsifiers have received reasonable attention due to their high biocompatibility and novel applications. It has been found that emulsions could be stabilised by cellulose microparticles,13,14 cellulose nanoparticles,15 chitin nanocrystals,16 hydrophobic modified starch microparticles17 – 19 and starch nanoparticles. 20 However, compared to the amount of research into synthesised organic particles and inorganic particles, there is much less relating to the environmentally benign particle emulsifiers. Furthermore, the emulsifying mechanism of environmentally benign particle emulsifiers has been still unclear. Starch nanocrystal (SNC) is a valuable particle emulsifier because it is inexpensive, abundant, biocompatible, biodegradable and non-toxic.21 Our previous work showed that oil-in-water emulsions could be stabilised by SNC.22 In this paper, the rheological behaviour and the effect of pH value and salt concentration on J Sci Food Agric 2014; 94: 1802–1807

the properties of emulsions stabilised by SNC were investigated to gain more useful information for SNC as a potential particle emulsifier in the food, cosmetics and pharmaceutical industries.

MATERIALS AND METHODS Materials Waxy maize starch was purchased from Tokyo Kasei Kogyo Co., Ltd., Japan. Sulfuric acid (AR), hydrochloric acid (AR), sodium hydroxide(AR), sodium chloride(AR), paraffin liquid (CR) and sodium azide were purchased from Guoyao Co. Ltd. (Shanghai, China). Methyl vinyl polysioxane (viscosity of 200 mPa s composed of 4% by moles of methyl vinyl siloxane units), methyl hydrogen polysiloxane (viscosity of 28 mPa s composed of 95% by moles of methyl hydrogen siloxane units) and chloroplatinic acid were purchased from Wuxi Quanli Chemical Company (Wuxi, China). Preparation of starch nanocrystals The preparation of starch nanocrystals was carried out in the same manner as described in previous studies23 with minor modification. A quantity of 10 g of waxy maize starch was dispersed in 100 mL



Correspondenceto: Cheng Yang, The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China. E-mail: cyang@ jiangnan.edu.cn The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China

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Starch nanocrystals as emulsion stabilisers

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3.16 mol L−1 H2 SO4 solution with stirring (100 rpm) at 40◦ C for 6 days. Then the suspensions were subjected to continual wash by centrifugation in water until the pH value reached around 7.0. The final precipitate was freeze dried (FD-1A-50 Freeze dryer; Beijing Boyikang Technology Co., Ltd, Beijing, China) to 2.61 g powder. Preparation of emulsions The volume ratio of water to paraffin liquid was kept at a constant 1:1. A certain mass of starch nanocrystals was initially ultrasonically dispersed in 7 mL water containing 0.2 mg mL−1 sodium azide, followed by adding 7 mL of paraffin liquid, and the mixture was homogenised at 10 000 rpm for 4 min using an XHF-D homogeniser (Ningbo Xinzhi, Ningbo, China) fitted with a dispersing tool with the outer diameter equal to 1.4 cm. The particle concentrations are expressed as weight content relative to the water phase. A series of emulsions were prepared by adjusting them to different pH before homogenisation using HCl (1 mol L−1 ) or NaOH (1 mol L−1 ) solution. The series of emulsions with different ionic strength were prepared by adding the NaCl solution. The emulsion type was identified by the drop test. After homogenisation, a drop of the emulsion was added to a small volume of the oil and aqueous phase separately. An emulsion which dispersed in the aqueous phase but not in the oil phase was assessed as water continuous (O/W); conversely, an emulsion dispersing singularly in the oil phase was assessed as oil continuous (W/O). Scanning electron microscopy An environmental scanning electron microscope (S-4800; Hitachi, Tokyo, Japan) was used at a high voltage (1.0 kV) to access the structure of SNC-stabilised emulsion. Because of the volatility of liquid paraffin, the formed emulsions could not be introduced into chamber of the scanning electron microscope. Although cryo-scanning electron microscopy (SEM) would allow direct observation of oil-in-water Pickering emulsions, polymerisable resins offered convenient alternatives for oil-in-water emulsion using the classical SEM approach.15 It was found that the SNC could stabilise the silicone oil droplets, therefore the silicone oil-in-water emulsion stabilised by SNC was prepared and then solid particles for SEM observation were obtained by cross-linking of silicone oil. Methyl vinyl polysioxane (2 mL), methyl hydrogen polysiloxane (3 mL) and 10 ppm chloroplatinic acid by weight of polysiloxane was mixed and then added in 7 mL water containing 5.0 mg mL−1 SNC and then homogenised. The emulsion was kept at 50◦ C for 10 h to cross-link the polysiloxane. The SNC-covered solid particles were obtained by depositing the cross-linked droplets onto a glass plate and then dried at room temperature. Rheology of the emulsions For valuation of the visco-elastic properties of emulsions stabilised by SNC, small deformation oscillatory measurements were performed by a HAAKE RS 600 rheometer (Thermo Fisher Scientific, Waltham, USA). The storage modulus (G ), loss modulus (G ) and G /G (tan δ) were performed over the frequency range of 0.1–10 Hz at 25◦ C. All the rheological measurements were completed before any visual phase separation shown for the emulsions.

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Measurement of the zeta potential SNC was dispersed in water (0.2 mg mL−1 ) with homogenisation. A series of SNC dispersions were prepared by adjusting them to different pH before homogenisation using HCl (1 mol L−1 ) or NaOH (1 mol L−1 ) solutions. The zeta potentials were measured using a commercial Zetasizer (ZetaPALS) at 25◦ C. All the measurements were performed in triplicates. Optical microscopy The optical micrographs of the emulsions were captured by a VHX-1000 digital microscope (Keyence Int. Trading Co. Ltd., Osaka, Japan). The emulsion samples were placed directly on a microscope slide. The droplet size and distribution were obtained by measuring over two hundred droplets from the digital microscopy image. The surface mean diameter (d32 ) and the volume mean diameter (d43 ) of droplets were calculated from Eqns (1) and (2):  d32 =   d43 = 

di3 di2 di4 di3

(1)

(2)

where di is the diameter of a droplet. d43 is sensitive to the presence of large droplets. The polydispersity index of droplet sizes (PDI) could be characterised by: d43 PDI =  di /N

(3)

where N is the total number of droplets.

RESULTS AND DISCUSSION Preparation of the emulsions The preparation and properties of SNC have been reported in our previous work.22 SNC were prepared by means of sulfuric acid hydrolysis of waxy maize starch. The SNC were polygonal in structure and their sizes ranged from 40 to 100 nm, but nanocrystals were generally observed in aggregates larger than 100 nm. Figure 1 shows the emulsions stabilised by SNC. These emulsions were typical O/W emulsions. When the concentration of SNC was above 0.2 mg mL−1 , emulsion could be formed. Table 1 shows the droplet size of emulsions stabilised by SNC. With the increasing of SNC, the average droplet size was decreased which was due to more SNC being available to stabilise smaller oil droplets. No coalescence and no significant variation in droplet size were found during long-term storage (above 1 year). This indicates that the emulsions were very stable to coalescence. The creaming

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Dynamic light scattering Particle size measurements were performed at 25◦ C with a commercial Zetasizer (ZetaPALS; Brookhaven, NY, USA). A series of 0.2 mg mL−1 SNC dispersions were prepared by adjusting

them to different pH before homogenisation using HCl (1 mol L−1 ) or NaOH (1 mol L−1 ) solution. The series of 0.2 g mL−1 SNC dispersions with different ionic strength were prepared by adding the NaCl solution. For each measurement, a given volume of the dispersion was rapidly injected in the Zetasizer cell immediately after 2 min homogenisation at 10 000 rpm (XHF-D homogeniser; Ningbo Xinzhi. Measurements were performed after stable values were reached. All the measurements were performed in triplicates.

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Figure 1. Vessels containing emulsions stabilised by starch nanocrystal (SNC) of different concentrations (2 months after preparation). From left to right: 0.2 mg mL−1 , 0.5 mg mL−1 , 1.0 mg mL−1 , 10.0 mg mL−1 , 30.0 mg mL−1 and 60.0 mg mL−1 .

Table 1. The size and size distribution of droplets stabilised by different concentrations of starch nanocrystals (SNC) (after 5 months and 1 year of storage)

SNC concentration (mg mL−1 ) 0.2 0.5 1 10 30 60 a

Surface mean diameter, d32 (µm) 5 months 30 28 27 18 16 12

1 year 38 33 31 20 18 13

Volume mean diameter, d43 (µm) 5 months 33 (1.36)a 30 (1.34) 29 (1.36) 19 (1.27) 18 (1.58) 13 (1.39)

1 year 46 (1.56) 38 (1.44) 33 (1.36) 21 (1.33) 19 (1.27) 14 (1.21)

Polydispersity index of droplet sizes (PDI) [see Equation (3)]. Figure 2. Scanning electron microscopy image for cross-linked silicone oil emulsion stabilised by starch nanocrystal (SNC). The concentration of SNC was 1.0 mg mL−1 relative to water.

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was observed after homogenisation but it decreased with the increasing of SNC concentration. To prove the emulsions were indeed stabilised by SNC, the structure of emulsions was observed by SEM. It was found that the SNC could stabilise the silicone oil droplets, therefore the silicone oil-in-water emulsion stabilised by SNC was prepared and then solid particles for SEM observation were obtained by cross-linking of silicone oil. Figure 2 shows the structure of silicone particles covered by SNC. It was evidence that oil droplets were stabilised by SNC. Figure 2 also revealed that the SNC tended to aggregate at the interface of oil and water.

the average droplet size was reduced.22 Owing to the decreased size, more interaction surface in emulsion was shown which further increased the G values. On the other hand, the aggregation of excess SNC in the continuous phase might enhance the interdroplet network formed in the emulsion. From these results, it was reasonable to deduce that the creaming stability might be mainly achieved through the formation of a gel structure due to the aggregation between droplets.

Rheology of the emulsions Figure 3 shows the mechanical behaviour of the emulsions. When the SNC concentration was 1.0 mg mL−1 , the storage modulus (G ) was slightly higher than the loss modulus (G ) and the latter increased slightly with an increase in frequency, which showed G > G at high frequency. These results show that the emulsions exhibit typical weak gel behaviour of a weak gel. However, when the SNC concentration was higher than 60.0 mg mL−1 , the G was much higher than G and both of them was independent with the frequency in the range of this experiment explored. This suggested that the emulsions containing a high SNC content had a strong gel behaviour. Figure 4 shows that G increased but tan δ decreased with the SNC concentration (frequency 1 Hz). Two main reasons can explain the visco-elastic behaviour of emulsions stabilised by SNC. According to the previous work, with the increasing of SNC

Effect of pH value on the emulsions Figure 5 shows the zeta potential of SNC at different pH value. SNC was negatively charged in the range of measured pH values and the zeta potential decreased with the increasing of pH value. Because SNC was prepared by concentrated sulfuric acid hydrolysis of native starch, many sulfate groups were created at the surface of SNC, which caused SNC to be negatively charged.24 The ionisation of the sulfate group was inhibited at low pH values but was enhanced at high pH values so that increasing the pH resulted in an increase of the zeta potential of SNC. Figure 6 shows that the apparent sizes of SNC shifted to larger side while decreasing the pH value. The average apparent sizes of SNC are 453 ± 36 nm, 418 ± 35 nm, 334 ± 25 nm, 327 ± 22 nm, 296 ± 15 nm, 251 ± 15 nm for pH value 3.4, 4.4, 6.5, 8.4, 10.6, 12.6, respectively. The negative charges on the surface of SNC played an important

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104 G′ 1.0 mg mL

-1

-15

-1

G′′ 1.0 mg mL -1 G′ 60 mg mL G′′ 60 mg mL

-20

-1

Zeta potential (mV)

G′, G′′ (Pa)

103

102

10

1

-25 -30 -35 -40 -45 -50

10-1

100

101

102

-55

Frequency (Hz)

-60

2

Figure 3. The mechanical behaviour of emulsions stabilised by starch nanocrystal.

4

6

8

10

12

pH value

Figure 5. The zeta potential of starch nanocrystal (SNC) at different pH values. 0.40

1800 G′

tan δ

0.35

G ′ (Pa)

0.25 600

tan δ

0.30

1200

0.20 0.15

0

0.10 0

10

20

30

40

50

60

70

SNC concentration (mg mL-1)

Figure 4. The dependence of the storage modulus (G ) and loss angle (tan δ) of starch nanocrystal (SNC)-stabilised emulsions upon the SNC content.

role in the SNC aqueous dispersion. High charge density on the surface would make SNC disperse well in water due to the strong electrostatic repulsion between the SNC, whereas SNC with a low charge density on the surface readily aggregated in water. Figure 7 shows that the SNC-stabilised emulsion can be formed over a wide range of pH values. Table 2 shows that the size of emulsion droplets increased with decreased pH values. As discussed above, the SNC aggregated to larger particles at low pH values, therefore it was reasonable to infer that larger SNC aggregates stabilised larger oil droplets. By using the maximum surface coverage concept, the required particle mass per volume of oil to generate a SNC stabilised emulsion of a given drop size could be roughly estimated from Eqn 4:18,19 d32,s Cso = 4ρsg ϕ (4) d32,d

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Figure 7. Vessels containing emulsions stabilised by starch nanocrystal (SNC) at different pH values. From left to right: 4.4, 5.5, 6.5, 7.4, 8.4 and 9.5. Upper row: 2 months after homogenisation; lower row: 5 months after homogenisation. SNC concentration was 1.0 mg mL−1 relative to water.

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where C so is the SNC-to-oil ratio (mg mL−1 ), ρ sg is the SNC density, ϕ the packing density, d32,s the surface mean diameter of SNC and d32,d the surface mean diameter of the oil droplets to be stabilised. According to Eqn 4, the C so could be scaled to d32,s as C so ∼ d32,s . The larger aggregation of SNC, the higher mass was required to cover an equal interfacial area. Therefore, when the mass of SNC was equal, larger SNC aggregates stabilised larger oil droplets. This is the reason why the size of the oil droplets increased with decreasing pH. The previous studies found that the overall stability of particle-stabilised emulsion was inversely proportional

Figure 6. The size distribution of starch nanocrystal (SNC) in aqueous dispersion at different pH values.

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Table 2. The size and size distribution of droplets stabilised by starch nanocrystals at different pH values (24 h after homogenisation and 5 months storage)

Surface mean diameter, d32 (µm) pH 5.47 6.45 7.24 8.38 9.51 a

24 h 20 15 13 12 10

5 months 30 27 23 16 16

Table 3. The size and size distribution of droplets stabilised by starch nanocrystals (SNC) at different concentrations of sodium chloride (24 h after homogenisation and 5 months storage)

Surface mean diameter, d32 (µm).

Volume mean diameter, d43 (µm) 24 h 22 (1.41)a 16 (1.36) 13 (1.31) 13 (1.34) 11 (1.38)

5 months

NaCl (mmol L−1 )

35 (1.57) 29 (1.36) 25 (1.31) 18 (1.36) 17 (1.28)

50 100 150 200 250 300 500

Polydispersity index of droplet sizes (PDI) [see Equation (3)].

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a

24 h

5 months

72 96 275 437 566 675 930

83 141 336 503 661 828 1004

Volume mean diameter, d43 (µm) 24 h 77 (1.34)a 106 (1.36) 286 (1.27) 446 (1.58) 583 (1.27) 695 (1.58) 940 (1.07)

5 months 88 (1.30) 153 (1.35) 344 (1.20) 511 (1.14) 671 (1.17) 842 (1.18) 1011 (1.05)

Polydispersity index of droplet sizes (PDI) [see Equation 3].

significantly, and the emulsion was only stable to coalescence for 2 months. The emulsion was broken faster when the pH was adjusted to lower values. Dyab26 also found that the negatively charged silica-stabilised emulsion was unstable at low pH values. The poor emulsifying ability of SNC at low pH was partially due to the formation of large SNC aggregates at low pH and partially due to a change in the wettability of SNC at low pH values.

Figure 8. The size distribution of starch nanocrystal (SNC) in aqueous dispersion at different concentrations of sodium chloride.

to particle size, with smaller particles giving a higher packing efficiency, and producing a more homogenous layer.2,3,10,25 The creaming of emulsion occurred in the 24 h after homogenisation and the pH values had no significant effect on the creaming ability. When the pH value was in the range of 5–10, during long-term storage, Table 2 also shows the droplets size and size distribution of these emulsions had slightly increase indicating that they were very stable against coalescence. However, as shown in Fig. 7, when the pH value was as low as 5, the stability of the emulsion decreased

Effect of salt content on the emulsions Salt exhibited a stronger effect on the aggregation of SNC in water than did the pH value. Figure 8 shows that the apparent size of SNC increased sharply with the increasing of NaCl concentration. The number average apparent size of SNC is 352 ± 25 nm, 414 ± 37 nm, 434 ± 37 nm, 465 ± 38 nm, 496 ± 40 nm, 505 ± 40 nm, 602 ± 46 nm for NaCl concentrations of 50 mmol L−1 , 100 mmol L−1 , 150 mmol L−1 , 200 mmol L−1 , 250 mmol L−1 , 300 mmol L−1 , 500 mmol L−1 , respectively. This was because the salt could strongly inhibit the ionisation of the sulfate group at the SNC surface so that electrostatic repulsion between the SNC was greatly reduced. Figure 9 shows that the SNC-stabilised emulsion formed even at high ionic strength. However, the droplets were large enough to be seen by eye. Surprisingly, Table 3 shows that these emulsions were stable to coalescence for several months.This was a typical characteristic of particle-stabilised emulsions. Such quite large droplets stabilised by small molecular surfactant or polymer are unstable. Table 3 shows the droplet size increased with salt concentration, because the SNC formed large aggregates

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Figure 9. Vessels containing emulsions stabilised by starch nanocrystal (SNC) at different concentrations of sodium chloride. From left to right: 0 mmol L−1 , 50 mmol L−1 ,100 mmol L−1 , 150 mmol L−1 , 200 mmol L−1 , 250 mmol L−1 , 300 mmol L−1 , 500 mmol L−1 . The figure shows results at 5 months after homogenisation. SNC concentration was 1.0 mg mL−1 related to water.

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Figure 10. Optical micrography of starch nanocrystal (SNC)-stabilised emulsion. The figure shows results at 5 months after homogenisation. SNC concentration was 10.0 mg mL−1 relative to water. The NaCl concentration was 200 mmol L−1 .

at high ionic strength. This was similar to the effect of pH upon the emulsions. Figure 10 shows that large SNC aggregates indeed adsorb oil droplets at high salt concentration. This was evidence that emulsions stabilised by both single SNC and SNC aggregates and larger particles stabilised larger droplets. It was known that good emulsion stabilisation was achieved when the particles were weakly flocculated by adding salt or surfactant, and that a less stable emulsion formed when particles were completely flocculated.27 Even under neutral conditions and without addition of salt, after homogenisation, SNC readily flocculated within several hours to days depending on the concentration of SNC. The addition of salt or decreasing of pH value produced stronger flocculation of SNC so that SNC quickly formed larger aggregates, whose adsorption reduced and could only stabilise larger oil droplets. Therefore, addition of salt or decreasing of the pH value would reduce the stability of SNC-stabilised emulsions.

CONCLUSION The SNC could stabilise emulsions with high stability against coalescence. The strong inter-droplet network in the emulsions could form with the increased SNC content. This could inhibit the creaming of emulsions stabilised by SNC. The SNC were negatively charged in the aqueous dispersion due to ionisation of the sulfate groups at their surface. The electronic repulsion between the charged SNC played an important role in the aggregation of SNC in aqueous dispersion and, consequently, affected the emulsifying ability of SNC on the account of the particle-stabilised larger oil droplets. Because SNC is environmentally benign and available in abundance, this novel particle emulsifier has much potential for use in the food, cosmetics and pharmaceutical industries.

ACKNOWLEDGEMENT The financial support of the Qing Lan Project is gratefully acknowledged.

2 Hunter TN, Pugh RJ, Franks GV and Jameson GJ, The role of particles in stabilising foams and emulsions. Adv Colloid Interface Sci 137:57–81 (2008). 3 Binks BP and Lumsdon SO, Influence of particle wettability on the type and stability of surfactant-free emulsions. Langmuir 16:8622–8631 (2000). 4 Binks BP and Whitby CP, Silica partical-stabilized emulsions of silicone oil and water: Aspects of emulsification. Langmuir 20:1130–1137 (2004). 5 Midmore BR, Preparation of a novel silica-stabilized oil/water emulsion. Colloids Surf A 132:257–265 (1998). 6 Ashby NP and Binks BP, Pickering emulsions stabilised by laponite clay particles. Phys Chem Chem Phys 24:5640–5646 (2000). 7 Nonomura Y and Kobayashi N, Phase inversion of the Pickering emulsions stabilized by plate-shaped clay particles. JColloidInterface Sci 330:463–466 (2009). 8 Shen M and Resasco DE, Emulsions stabilized by carbon nanotube–silica nanohybrids. Langmuir 25:10843–10851 (2009). 9 Ashby NP, Binks BP and Paunov VN, Bridging interaction between a water drop stabilised by solid particles and a planar oil/water interface. Chem Commun 4:436–437 (2004). 10 Binks BP and Lumsdon SO, Pickering emulsion stabilized by mono-disperse latex particles: Effects of particle size. Langmuir 17:4540–4547 (2001). 11 Li Z, Ming T, Wang J and Ngai T, High internal phase emulsion stabilized solely by microgel particles. Angew Chem Int Ed. 48:8490–8493 (2009). 12 Brugger B, Rosen BA and Richtering W, Microgels as stimuli-responsive stabilizers for emulsions. Langmuir 24:12202–12208 (2008). 13 Andresen M and Stenius P, Water-in-oil emulsions stabilized by hydrophobized microfibrillated cellulose. J Dispers Sci Technol 28:837–844 (2007). 14 Wege H, Kim S, Paunov VN, Zhong Q and Velev OD, Long-term stabilization of foams and emulsions with in-situ formed microparticles from hydrophobic cellulose. Langmuir 24:9245–9253 (2008). 15 Kalashnikova I, Bizot H, Cathala B and Capron I, New Pickering emulsions stabilized by bacterial cellulose nanocrystals. Langmuir 27:7471–7479 (2011). 16 Tzoumaki MV, Moschakis T, Kiosseoglou V and Biliaderis CG, Oil-inwater emulsions stabilized by chitin nanocrystal particles, Food hydrocolloids 25:1521–1529 (2011). 17 Yusoff A and Murray BS, Modified starch granules as particle-stabilizers of oil-in-water emulsions. Food hydrocolloids 25:42–55 (2011). 18 Rayner M, Timgren A, Sjo¨ o¨ M and Dejmek P, Quinoa starch granules: A candidate for stabilising food-grade Pickering emulsions. J Sci Food Agric 92:1841–1847 (2012). 19 Rayner M, Sjo¨ o¨ M, Timgren A and Dejmek P, Quinoa starch granules as stabilizing particles for production of Pickering emulsions, Faraday Discuss 158:139–155 (2012). 20 Tan Y, Xu K, Liu C, Li Y, Lu C and Wang P, Fabrication of starchbased nanospheres to stabilize Pickering emulsion. CarbohydrPolym 88:1358–1363 (2012). 21 Le Corre D, Bras J and Dufrense A, Starch nanoparticles: A review. Biomacromolecules 11:1139–1153 (2010). 22 Li C, Sun P and Yang C, Emulsion stabilized by starch nanocrystals., Starch/St¨arke 64:497–502 (2012). 23 Putaux J, Molina-Boisseau S, Momaur T and Dufresne A, Platelet nanocrystals resulting from the disruption of waxy maize starch granules by acid hydrolysis. Biomacromolecules 4:1198–1202 (2003). 24 Le Corre D, Bras J, Choisnard L and Dufresne A, Optimization of the batch preparation of starch nanocrystals to reach daily time-scale, Starch/St¨arke 64:489–496 (2012). 25 Binks BP and Whitby CP, Nanoparticle silica-stabilised oil-inwater emulsions: Improving emulsion stability. Colloids Surf A 253:105–115 (2005). 26 Dyab AKF, Destabilisation of Pickering emulsions using pH. Colloids Surf A 402:2–12 (2012). 27 Aveyard R, Binks BP and Clint JH, Emulsions stabilised solely by colloidal particles. Adv Colloid Interface Sci 100–102:503–546 (2003).

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1 Leal-Calderon F and Schmitt V, Solid-stabilized emulsion. Curr Opin Colloid Interface Sci 13:217–227 (2008).

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Starch nanocrystals as particle stabilisers of oil-in-water emulsions.

As an environmentally benign particle emulsifier, starch nanocrystal (SNC) has attracted considerable attention. By submitting waxy maize starch to ac...
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