Thyme Oil Nanoemulsions Coemulsified by Sodium Caseinate and

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Thyme Oil Nanoemulsions Co-emulsified by Sodium Caseinate and Lecithin Jia Xue, and Qixin Zhong J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/jf5034366 • Publication Date (Web): 18 Sep 2014 Downloaded from http://pubs.acs.org on September 25, 2014

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Journal of Agricultural and Food Chemistry

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Thyme Oil Nanoemulsions Co-emulsified by Sodium Caseinate and Lecithin

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Jia Xue and Qixin Zhong*

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Department of Food Science and Technology, University of Tennessee, Knoxville, TN 37996

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Please send correspondence to

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*Qixin Zhong, Professor

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Department of Food Science and Technology

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The University of Tennessee

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2510 River Drive

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Knoxville, TN 37996

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Phone: (865) 974-6196; Fax: (865) 974-7332

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E-mail: [email protected]

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Abstract Many nanoemulsions are currently formulated with synthetic surfactants. The objective

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of the present work was to study the possibility of blending sodium caseinate (NaCas) and

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lecithin to prepare transparent thyme oil nanoemulsions. Thyme oil was emulsified using NaCas

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and soy lecithin individually or in combination at neutral pH by shear homogenization. The

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surfactant combination improved the oil content in transparent/translucent nanoemulsions, from

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1.0% to 2.5%w/v for 5% NaCas with and without 1% lecithin, respectively. Nanoemulsions

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prepared with the NaCas-lecithin blend had hydrodynamic diameters smaller than 100 nm and

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had significantly smaller and more narrowly-distributed droplets than those prepared with NaCas

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or lecithin alone. Particle dimension and protein surface load data suggested the co-adsorption of

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both surfactants on oil droplets. These characteristics of nanoemulsions minimized

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destabilization mechanisms of creaming, coalescence, and Ostwald ripening, as evidenced by no

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significant changes in appearance and particle dimension after 120-day storage at 21 °C.

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Keywords: Thyme oil, nanoemulsion, sodium caseinate, lecithin, synergistic surface activity

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Journal of Agricultural and Food Chemistry

Introduction Nanoemulsions are frequently studied as delivery systems of functional lipophilic

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compounds such as flavors, 1 vitamins 2 and antimicrobials 3 due to their advantages over other

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oil-containing systems. For example, compared with microemulsions, nanoemulsions can be

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formulated using a large variety of food grade ingredients such as proteins and polysaccharides

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and require relatively lower surfactant concentrations. 4 With small droplets (2 h. The samples

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were scanned using a rectangular cantilever probe (Bruker Nanoprobe, Camarillo, CA) with

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aluminum reflective coating on the backside and a quoted force constant of 2.80 N/m. The

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topography images were collected at the tapping mode.

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Quantification of Protein Surface Load

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The amount of NaCas on thyme oil droplet surface was quantified to investigate the

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effect of lecithin on surface adsorption of NaCas. To facilitate the separation of oil droplets,

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an excess amount (10% w/v) of thyme oil was directly emulsified in the aqueous phase with

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various combinations of NaCas (0, 2.5, and 5% w/v) and lecithin (0, 0.5, and 1.0% w/v).

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Particle sizes were measured right after homogenization and after storage at room

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temperature (21 °C) for 15 days. Emulsions before and after storage were centrifuged at

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12,550g for 60 min using an Eppendorf MiniSpin plus centrifuge (Hamburg, Germany).

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The bottom aqueous phase was filtrated through a 0.22 µm polyvinyl difluoride membrane

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filter. To minimize the interference of thyme oil compounds such as thymol on protein

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assay, 50 µL of the permeate was mixed with 500 µL of an acetone-hexane (1:1, v:v)

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mixture 29 to extract thyme oil and precipitate protein. After vigorous mixing and

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centrifugation at 6,700g for 10 min, the supernatant (organic phase) was discarded, and the

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bottom protein precipitate was re-dissolved in 600 µL of 100 mM NaOH and was quantified

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using the bicinchoninic acid (BCA) method (Thermo Fisher Scientific Inc., Morris Plains,

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NJ). NaCas was used as a reference protein in the BCA assay. The surface load (Γs, mg/m2)

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of protein and the volume-area (d3,2) mean diameters were calculated using eq 1 and 2,

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respectively. Γs =

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Ms d 3 , 2 6Voil

(1)

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where Ms is the mass of NaCas adsorbed on oil droplets, and Voil is the volume of thyme oil.

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The thymol oil density used in calculation was 0.932 g/mL. 30

d 3, 2

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∑n d = ∑n d i

3 i

i

2 i

i =1

(2)

i =1

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where di is the diameter of the ith group of droplets and ni is the corresponding number of

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droplets.

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Statistical Analysis

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Two independent emulsion replicates were studied throughout. Analysis of variance

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(ANOVA) test was conducted using the SPSS 16.0 statistical analysis system (SPSS Inc.,

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Chicago, IL). The least significant difference (LSD) test was used to determine the

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significant difference of mean values at a P level of 0.05.

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Results and Discussion

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Turbidity of emulsions

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Photographs of thyme oil emulsions prepared with various combinations of 5% w/v

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NaCas, 1% w/v lecithin and 10% v/v PG are shown in Figure 1. The treatments with 5% w/v

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NaCas alone and its combination with 10% v/v PG were only capable of emulsifying 1.0% w/v

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thyme oil as transparent or translucent dispersions. In comparison, after adding 1% w/v lecithin,

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emulsions with up to 2.5% w/v thyme oil were translucent when prepared with 5% w/v NaCas,

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and the clarity further improved with 10% v/v PG. The appearance generally agreed with the

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Abs600 (Figure 2). Since PG is fully miscible with water, pre-dissolving thyme oil in PG before

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emulsification likely reduces the oil/water interfacial tension, which is a main mechanism of co-

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surfactants facilitating the formation of nanoemulsions 31. Furthermore, PG had no significant

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impact on emulsion formation by NaCas but facilitated emulsion formation for the NaCas-

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lecithin blend. This is likely due to the impacts on solubility of surfactants: NaCas is water-

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soluble, while lecithin (phosphatidylcholines) is not.

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Subsequently, two concentrations (1.0 and 2.0% w/v) of thyme oil were emulsified using

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various combinations of NaCas (2.5% w/v) and lecithin (0.5 or 1% w/v) concentrations.

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Photographs are shown in Figure 3, while the Abs600 is compiled in Table 1. With 1.0% w/v

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thyme oil, emulsions prepared with combinations of NaCas and lecithin were all transparent,

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while those with 2.5% NaCas or (0.5 or 1.0% w/v) lecithin alone were turbid. As thyme oil

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concentration increased to 2.0% w/v, all samples were turbid. The Abs600 of thyme oil emulsions

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in Table 1 showed that addition of lecithin significantly decreased the turbidity of thyme oil

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emulsions prepared with NaCas (P < 0.05).

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Hydrodynamic diameters of emulsions

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Mean hydrodynamic diameters of thyme oil emulsions are compiled in Table 2. Emulsions prepared with NaCas-lecithin blend had significantly smaller particles than those

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prepared with NaCas or lecithin alone (P < 0.05). For example, compared to treatments with

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1.0% w/v thyme oil emulsified by 1.0% w/v lecithin (mean diameter = 179.7 nm) or 5.0% w/v

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NaCas alone (mean diameter = 105.5 nm), the corresponding nanoemulsion prepared with the

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NaCas-lecithin blend had much smaller droplets with a mean diameter of 66.6 nm (P < 0.05).

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These results were consistent with the visual appearance (Figure 3) and Abs600 (Table 1). Similar

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results have been reported for emulsions made with blends of NaCas and sucrose esters (with

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lipids being mono, di-, and tristearate or palmitate) 35. Small molecular weight surfactants may

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co-adsorb with NaCas or displace NaCas on droplet surfaces and therefore alter the composition

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and properties of interfaces, and the reduction of interfacial tension may facilitate the formation

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of smaller droplets. 32

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Emulsion structures studied by AFM

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Emulsions containing 1.0% w/v thyme oil prepared with 2.5% w/v NaCas, 0.5% w/v

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lecithin, or both were imaged using AFM (Figure 4). Relatively bigger particles were observed

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for the emulsions prepared with NaCas or lecithin alone (Figure 4A and 4B) when compared to

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the treatment prepared with the surfactant blend (Figure 4C). The average particle dimension

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estimated in AFM was 134.3, 147.3, and 76.9 nm for emulsions prepared with NaCas only,

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lecithin only, and both, respectively. These results were generally in agreement with those

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obtained using dynamic light scattering (Table 2).

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Zeta-potential of emulsions

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Zeta-potentials of emulsions prepared with 1.0% w/v thyme oil emulsified by NaCas

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alone, lecithin alone, and their blend were measured at pH 7 (Table 3). The emulsion

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prepared with 1% w/v lecithin only had a highly negative zeta-potential (-58.2 ± 1.2 mV),

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which is attributed to the phosphate group of lecithin. 33 In comparison, the zeta-potential of

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the emulsion prepared with 2.5% w/v NaCas only had a significantly smaller magnitude (-

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25.8 ± 6.8 mV) than that with lecithin only (P < 0.05). When 5% w/v NaCas was used in

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homogenization, the zeta-potential magnitude (-39.7±1.2 mV) was higher than that prepared

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with 2.5% NaCas and was close to the zeta-potential of NaCas solution, 34 which may

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suggest a significant amount of free NaCas in the aqueous phase. For the nanoemulsion

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prepared with 2.5% w/v NaCas and 1% w/v lecithin, the magnitude of zeta-potential (-44.6

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± 2.6mV) was between those prepared with lecithin and NaCas alone. Since free NaCas was

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not removed, the zeta-potential data in Table 3 did not provide straightforward information

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about interfacial structures. It however should be noted that the electrostatic attraction

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between negatively charged phosphate group of lecithin and positively charged amine

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groups of NaCas is still possible at neutral acidity despite both are overall negatively

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charged, as previously demonstrated for pectin and NaCas. 14

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Effect of lecithin on surface adsorption of NaCas

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The protein content on unit surface area of emulsion droplets (Γs, mg/m2) is commonly

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determined to study the surface activity of proteins and the impacts by competing or co-

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adsorbing surfactants. For 10% thyme oil emulsified by 2.5% w/v NaCas and 0-1% w/v lecithin,

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an increase in lecithin content decreased the droplet dimension but not the amount of adsorbed

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NaCas (P > 0.05), resulting in the reduced Γs (Table 4). Because a larger surface area (smaller

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droplets) requires the coverage by a greater amount of surfactants, the data suggest the co-

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adsorption of NaCas and lecithin. The Γs did not change significantly after 15-day storage at 21

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°C, suggesting there was no detachment of NaCas. With the gradual increase in lecithin content,

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the droplet dimension decreased to near those prepared with lecithin only. Therefore, lecithin is

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more surface-active than NaCas in emulsifying thyme oil. For emulsions prepared with 5% w/v

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NaCas, the droplet size (P < 0.05) and the percentage of adsorbed NaCas (P > 0.05) were smaller

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than those prepared with 2.5% NaCas, corresponding to similar Γs (P > 0.05). The Γs of

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treatments prepared with 5% w/v NaCas and 0 and 0.5% lecithin decreased (P < 0.05) after

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storage for 15 days. Because the droplet dimension of these two emulsions did not change after

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storage, the results indicated the detachment of NaCas. Conversely, the treatment prepared with

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5% NaCas and 1% lecithin showed insignificant changes in both droplet dimension and Γs (P >

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0.05).

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The competitive surface adsorption and possible displacement of NaCas by more surface-

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active lecithin are dependent on their overall concentrations and molar ratios. 22, 35, 36 In a study

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co-emulsifying 20% w/w soybean oil by 0.2-2% w/w NaCas and lecithin at lecithin: casein

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molar ratios of 0.7:1 - 49:1, 22 the gradual reduction of Γs of NaCas with increases in lecithin

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concentration was similar to the present study (Table 4), but their Γs increased with increases in

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NaCas concentration and was all below 3.5 mg/m2. The Γs in the present study was much higher

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than the reference 22 and was not significantly different at two (2.5 and 5% w/v) NaCas

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concentrations (Table 4) although the lecithin:casein molar ratios (2.8-11.4:1) in this work were

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within their range. The differences in their and the present studies can result from differences in

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the droplet dimension (300-800 nm in the reference 22), emulsification conditions, polarity of oil,

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and overall NaCas and lecithin concentrations. As for the interfacial structure, Fang and

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Dalgleigh 22 proposed that the thickness of adsorbed casein layer could increase when lecithin

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concentration increases gradually and, when there is a sufficient amount of lecithin, the oil

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droplets are directly covered mostly by lecithin that can be adsorbed by caseins protruding to the

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continuous aqueous phase. At their studied conditions, Fang and Dalgleigh 22 did not observe

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surface displacement of NaCas by lecithin, which is mostly in agreement with the present study

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(Table 4). However, in our case, Γs decreased for nanoemulsions prepared with 5% w/v NaCas

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and 0 and 0.5% w/v lecithin that also showed a decrease in droplet dimension after storage

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(Table 4). Since the thickness of NaCas layer increases with its bulk concentration, 22 the

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observations from these two emulsions can result from the detachment of caseins rather than the

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displacement by lecithin. The speculation however requires experimental verifications.

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Emulsion stability One common concern about essential oil nanoemulsions is their stability against Ostwald

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ripening because of the water solubility of essential oil components being higher than lipids

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composed of medium- or long-chain fatty acids. 31 Physically, compounds in smaller particles

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have a higher solubility, which results in the continuous dissolving and eventually disappearance

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of smaller particles, and the dissolved compounds join bigger particles that grow during storage.

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37

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preparation to serve as inhibitors of Ostwald ripening. 31 Ripening inhibitors however lower the

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loading level and antimicrobial activity of essential oils.

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Nonpolar substances such as corn oil 38 can be blended with essential oils in emulsion

Emulsions with 1 and 2% thyme oil were studied for storage stability at 21 °C for 120

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days. Creaming was observed for emulsions prepared with NaCas alone after 2- or 3-day storage

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at room temperature and became more significant after longer storage. Creaming can be

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contributed by increases in overall particle dimension due to depletion flocculation (by

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unadsorbed NaCas) or particle growth due to coalescence and/or Ostwald ripening. 4 In contrast,

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nanoemulsions prepared with 1 and 2% thyme oil and NaCas-lecithin blend appeared transparent

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or translucent throughout storage.

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When particle size distributions of emulsions prepared with lecithin only or NaCaslecithin blend were compared before and after 4-month storage at room temperature (Figure 5),

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several trends were observed. Emulsions prepared with NaCas-lecithin blend exhibited smaller

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particles with narrower distributions than that prepared with lecithin only, indicating the better

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emulsifying activity of the blend. For these emulsions, the interfacial layer next to thyme oil is

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likely composed of both lecithin and NaCas, different from the model of sequential layers of

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lecithin and NaCas as proposed by Fang and Dalgleigh 122 that would otherwise result in bigger

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droplets for emulsions prepared with both surfactants. The growth of particle size was observed

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for all emulsions, and the growth was much smaller for emulsions prepared with the blend than

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those with lecithin alone, suggesting the better stabilizing ability of the blend. The growth of

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average hydrodynamic diameter (Table 2) however was overall not statistically significant (P >

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0.05).

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In addition to Ostwald ripening discussed above, coalescence can also cause the growth

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of particles during storage, particularly for small molecular surfactants such as lecithin with a

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small head group. 39 Coalescence is initiated by the aggregation of two oil droplets controlled by

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colloidal interactions. In the present study, emulsions prepared with lecithin only had a higher

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magnitude of zeta-potential (Table 3) than those with the NaCas-lecithin blend. Since emulsions

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prepared with lecithin only and the NaCas-lecithin blend had insignificant increase in mean

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particle diameter (Table 2), it may suggest the electrostatic repulsion is effective in preventing

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particle aggregation. The protrusion of NaCas in the continuous phase of emulsions prepared

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with the surfactant blend may have provided additional steric repulsion that resulted in smaller

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net growth of droplets after storage than emulsions prepared with lecithin only (Table 2). Similar

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phenomena were reported for orange oil emulsions prepared with lysolecithin and sucrose

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monopalmitate. 29 Therefore, it is likely Ostwald ripening is the major mechanism responsible

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for particle growth of emulsions in the present study, and the narrower particle size distribution

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and thicker interface of emulsions prepared with the NaCas-lecithin blend both resulted in less

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significant particle size changes than those prepared with NaCas or lecithin only.

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The stability of emulsions prepared with a mixture of proteins and small molecular

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surfactants has been widely studied. In some cases, the interaction or displacement between

288

emulsifiers resulted in the significantly decreased stability. For example, combinations of

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caseinate and Tween® 20 at certain ratios led to severe flocculation and creaming, which

290

was attributed to the depletion flocculation by unabsorbed protein. 40 Combinations of

291

lecithin with other small molecular surfactants also have been shown to improve the

292

stability of emulsions. Lecithin added in emulsions stabilized by sucrose monopalmitate

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strengthened the electrostatic repulsion at acid conditions and resulted in the excellent

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stability of emulsions against Ostwald ripening, flocculation, and coalescence. 41

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Emulsifying soybean oil by combinations of lecithin and non-ionic steric surfactants such as

296

polyethylene glycol hexadecyl ether (Brij®) increased the stability of emulsions at increased

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ionic strengths when compared to those prepared with lecithin only. 42 This is because,

298

although the surfactant blend reduced the zeta-potential magnitude of droplets when

299

compared to those stabilized by lecithin, Brij® provided steric repulsion to stabilize

300

emulsions. 42

301 302

In summary, the technological advancement has been shown in the present work for

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stable and transparent thyme oil nanoemulsions prepared using combinations of GRAS

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emulsifiers NaCas and lecithin. These transparent nanoemulsions had mean diameters smaller

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than ~100 nm at neutral pH. The clearer and smaller droplets of nanoemulsions prepared with the

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NaCas-lecithin blend than those with individual surfactants suggested that NaCas and lecithin

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synergistically emulsified thyme oil rather than the preferential adsorption and displacement of

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NaCas by more surface-active lecithin. The interface composed of both NaCas and lecithin

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provided repulsive electrostatic and also likely steric interactions against destabilization

310

mechanisms of creaming, flocculation, and coalescence and, together with narrow particle size

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distributions, minimized Ostwald ripening. These transparent nanoemulsions prepared from

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GRAS ingredients have great potential to incorporate lipophilic antimicrobials such as thyme oil

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in transparent beverages to enhance the microbiological safety.

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Acknowledgements This work was supported by the University of Tennessee and the USDA National Institute

316 317

of Food and Agriculture.

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emulsions: influence of composition and preparation method. J. Agric. Food Chem. 2011, 59,

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5026-5035.

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maltodextrin conjugates: The enhanced emulsifying capacity and anti-listerial properties in milk

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by propylene glycol. J. Agric. Food Chem. 2013, 61, 12720–12726.

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oil-in-water emulsions stabilized by sucrose monopalmitate and lysolecithin. J. Agric. Food

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Chem. 2014, 62, 3257-3261.

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emulsified with soluble soybean polysaccharide. Food Hydrocolloids. 2014, 39, 144-150.

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properties, performance, biological fate, and potential toxicity. Crit. Rev. Food Sci. Nutr. 2011,

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51, 285-330.

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of surfactant sucrose ester on physical properties of dairy whipped emulsions in relation to those

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of O/W interfacial layers. J. Colloid Interface Sci. 2006, 295, 495-503.

El Maghraby, G. M., Transdermal delivery of hydrocortisone from eucalyptus oil

Kale, N. J.; Allen Jr, L. V., Studies on microemulsions using Brij 96 as surfactant and

Rao, J.; McClements, D. J., Formation of flavor oil microemulsions, nanoemulsions and

Xue, J.; Davidson, P. M.; Zhong, Q., Thymol nanoemulsified by whey protein-

McClements, D. J.; Decker, E. A.; Choi, S. J., Impact of environmental stresses on orange

Wu, J.-E.; Lin, J.; Zhong, Q., Physical and antimicrobial characteristics of thyme oil

McClements, D. J.; Rao, J., Food-grade nanoemulsions: formulation, fabrication,

Tual, A.; Bourles, E.; Barey, P.; Houdoux, A.; Desprairies, M.; Courthaudon, J.-L., Effect

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Chuah, A. M.; Kuroiwa, T.; Kobayashi, I.; Nakajima, M., Effect of chitosan on the

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stability and properties of modified lecithin stabilized oil-in-water monodisperse emulsion

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prepared by microchannel emulsification. Food Hydrocolloids. 2009, 23, 600-610.

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nanoparticles using sodium caseinate. Food Hydrocolloids. 2014, 35, 358-366.

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and. beta.-casein in oil-in-water emulsions. J. Agric. Food Chem. 1991, 39, 1365-1368.

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and sodium caseinate on oil-water interfaces. J. Agric. Food Chem. 1996, 44, 59-64.

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Taylor, P., Ostwald ripening in emulsions. Adv. Colloid Interface Sci. 1998, 75, 107-163.

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Ziani, K.; Chang, Y.; McLandsborough, L.; McClements, D. J., Influence of surfactant

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charge on antimicrobial efficacy of surfactant-stabilized thyme oil nanoemulsions. J. Agric. Food

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Chem. 2011, 59, 6247-6255.

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oil and oil-in-water emulsions. J. Surfactants Deterg. 2002, 5, 135-143.

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caseinate and Tween 20. J. Colloid Interface Sci. 1999, 212, 466-473.

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Formulation and properties of model beverage emulsions stabilized by sucrose monopalmitate:

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Influence of pH and lyso-lecithin addition. Food Res Int. 2011, 44, 3006-3012.

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properties of mixed phospholipid–non-ionic surfactant stabilised oil-in-water emulsions.

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Colloids Surf., A 1999, 152, 59-66.

Chen, H.; Zhong, Q., Processes improving the dispersibility of spray-dried zein

Courthaudon, J. L.; Dickinson, E.; Christie, W. W., Competitive adsorption of lecithin

Fang, Y.; Dalgleish, D. G., Competitive adsorption between dioleoylphosphatidylcholine

Pan, L.; Tomás, M.; Añón, M., Effect of sunflower lecithins on the stability of water-in-

Dickinson, E.; Ritzoulis, C.; Povey, M. J., Stability of emulsions containing both sodium

Choi, S. J.; Decker, E. A.; Henson, L.; Popplewell, L. M.; Xiao, H.; McClements, D. J.,

De Vleeschauwer, D.; Van der Meeren, P., Colloid chemical stability and interfacial

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Figure captions

424 425

Figure 1. Appearance of thyme oil nanoemulsions prepared with various combinations of 5%

426

w/v NaCas, 10% v/v PG, and 1% w/v lecithin. Thyme oil concentration in each image is 0.5, 1.0,

427

1.5, 2.0, and 2.5% w/v from left to right.

428 429

Figure 2. Absorbance at 600 nm of nanoemulsions with 0.5-2.5% w/v thyme oil prepared with

430

various combinations of 5% w/v NaCas, 10% v/v PG, and 1% w/v lecithin.

431 432

Figure 3. Appearance of nanoemulsions with 1.0% w/v (top) or 2.0% w/v (bottom) thyme oil

433

emulsified by 2.5%w/v NaCas, 0.5 or 1%w/v lecithin, or both. All samples contained 10% v/v

434

PG. Labels on vial caps: S - NaCas; L - lecithin; numbers – surfactant concentrations.

435 436

Figure 4. AFM images of thyme oil (1.0% w/v) nanoemulsions prepared with 2.5% w/v NaCas

437

(A), 0.5% w/v lecithin (B), or both (C). All samples contained 10%v/v PG.

438 439

Figure 5. Particle size distributions of nanoemulsions with 1.0% w/v (A and C) or 2% w/v (B

440

and D) thyme oil emulsified by lecithin and NaCas-lecithin blend before (solid curves) and after

441

(dashed curves) storage at room temperature (21 °C) for 4 months.

442

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Table 1. Absorbance at 600 nm of 1 or 2% w/v thyme oil emulsified by 2.5% w/v NaCas and 0-

444

1.0% w/v lecithin.* Thyme oil

Lecithin

Absorbance

(% w/v)

(% w/v)

at 600 nm

1.0

0

1.48±0.14c

1.0

0.5

0.30±0.01d

1.0

1.0

0.27±0.01d

2.0

0

2.44±0.10a

2.0

0.5

2.21±0.16b

2.0

1.0

1.35±0.01c

445

*All samples contained 10% v/v PG. Numbers are mean ± standard deviation from duplicates. Different

446

superscript letters represent significant differences in the mean.

447

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448

Table 2. Mean hydrodynamic diameters (nm) of 1% and 2% w/v thyme oil emulsified by NaCas, lecithin or both, before and after storage at

449

room temperature for 120 days.* Thyme oil

Lecithin

(% w/v)

(% w/v)

1.0

2.0

Hydrodynamic diameter (nm) 0% NaCas

2.5% w/v NaCas

5.0% w/v NaCas

Day 0

Day 120

Day 0

Day 120

Day 0

Day 120

0

N/A

N/A

150.2±6.6c

N/A

105.5±3.5d

N/A

0.5

177.5±3.0bc

188.5±2.4abc

77.1±5.4fg

80.7±0.7efg

74.7±0.4fg

75.4±1.0fg

1.0

179.7±2.2bc

203.6±5.9a

67.5±0.8g

83.9±13.7efg

66.6±2.1g

71.8±4.5g

0

N/A

N/A

206.5±10.5a

N/A

180.7±12.6bc

N/A

0.5

170.3±2.9c

184.3±6.0abc

115.9±10.1d

113.0±0.8d

79.1±1.8efg

86.1±10.6efg

1.0

177.7±4.6bc

196.3±11.5ab

95.2±2.4def

101.6±4.9de

68.4±2.3g

72.7±1.7fg

450

*All samples contained 10% v/v PG. Numbers are mean ± standard deviation from duplicates. Different superscript letters represent significant differences

451

in the mean.

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Table 3. Zeta-potential (mV) of thyme oil (1.0% w/v) nanoemulsions prepared with NaCas

453

with and without lecithin at pH 7.0.* Lecithin (% w/v)

Zeta-potential (mV) 0% NaCas

2.5% w/v NaCas

5.0% w/v NaCas

0

X

-25.8±6.8c

-39.7±1.2b

1.0

-58.2±1.2a

-44.6±2.6b

-41.7±2.4b

454

*All emulsions contained 10% v/v PG. Numbers are mean ± standard deviation from duplicates.

455

Different superscript letters represent significant differences in the mean.

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456

Table 4. Volume-area mean diameter d3, 2 (nm), polydispersity index, percentage of adsorbed NaCas, and surface load of NaCas in emulsions

457

with 10% w/v thyme oil prepared with NaCas, lecithin, or both, before and after storage at 21 °C for 15 days.* NaCas

Lecithin

(% w/v)

(% w/v)

0

2.5

5.0

458

d3,2 (nm)

Polydispersity index

Adsorbed NaCas (%)

Protein surface load (Γs, mg/m2)

Day 0

Day 15

Day 0

Day 15

Day 0

Day 15

Day 0

Day 15

0.5

175.28±6.97c

182.37±7.32c

0.28±0.02ab

0.27±0.02bc

N/A

N/A

N/A

N/A

1.0

163.14±15.22c

161.38±27.09c

0.23±0.00c

0.22±0.02c

N/A

N/A

N/A

N/A

0

307.96±10.54ab

350.80±12.12a

0.31±0.02ab

0.30±0.01ab

69.82±3.36a

69.27±0.33a

8.35±0.40ab

9.43±0.04a

0.5

282.66±12.89b

350.48±8.65a

0.32±0.01a

0.30±0.01ab

68.56±2.91a

64.50±2.14ab

7.53±0.32abc

8.78±0.29a

1.0

182.42±8.52c

181.18±19.96c

0.28±0.01ab

0.29±0.01ab

67.84±1.23a

61.23±0.22abc

4.81±0.09e

4.31±0.02e

0

172.93±11.04c

170.64±11.12c

0.28±0.01ab

0.26±0.01bc

64.15±1.93abc

52.22±2.13cd

8.62±0.26a

6.92±0.28bcd

0.5

159.78±9.82c

143.11±13.98c

0.26±0.02bc

0.26±0.02bc

62.51±1.32abc

48.68±4.12d

7.75±0.16ab

5.41±0.46de

1.0

144.02±0.29c

143.53±7.30c

0.27±0.01bc

0.28±0.02ab

54.64±7.31bcd

46.67±1.43d

6.11±0.82cde

5.20±0.16e

* Numbers are mean ± standard deviation from duplicates. Different superscript letters represent significant differences in the mean.

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Figure 1.

461

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Absorbance at 600nm

2.5 NaCas NaCas+PG NaCas+Lecithin NaCas+Lecithin+PG

2.0

1.5

1.0

0.5

0.0 0.5

1.0

1.5

2.0

Thyme oil concentration(%) 462 463

Figure 2.

464

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465 466

Figure 3.

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467 468

Figure 4.

469

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Journal of Agricultural and Food Chemistry

Differential Intensity (%)

30

(A)

0.5% L

0.5% L+2.5% NaCas 25

0.5% L+5% NaCas 0.5% L

20

0.5% L+2.5% NaCas 0.5% L+5% NaCas

15 10 5 0 0

100

200

300

400

Diameter (nm) 470

Differential Intensity (%)

30

(B) 0.5% L 0.5% L+2.5% NaCas 0.5% L+5% NaCas 0.5% L 0.5% L+2.5% NaCas 0.5% L+5% NaCas

25 20 15 10 5 0 0

100

200

Diameter (nm) 471 472

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Differential Intensity (%)

30 (C) 1% L 1% L+2.5% NaCas 1% L+5% NaCas 1% L 1% L+2.5% NaCas 1% L+5% NaCas

25 20 15 10 5 0 0

100

200

300

400

Diameter (nm) 473

(D) 1% L 1% L+2.5% NaCas 1% L+5% NaCas 1% L 1% L+2.5% NaCas 1% L+5% NaCas

Differential Intensity (%)

25 20 15 10 5 0 0

200

Diameter (nm)

474 475

100

Figure 5.

476 477

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400

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Journal of Agricultural and Food Chemistry

Table-of–content graphic only

479 480

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