j ourna l ho me pa g e: www.elsev ier .com/ locate /carbpol
ncapsulation of vitamin E: Effect of physicochemical properties ofall material on retention and stability
oseph Hategekimanaa, Kingsley George Masambaa,b, Jianguo Maa, Fang Zhonga,∗
Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School of Food Science and Technology, Jiangnan University, Wuxi 214122,R ChinaLilongwe University of Agriculture and Nature Resources, Bunda College, Department of Food Science and Technology, P.O. Box 219, Lilongwe, Malawi
r t i c l e i n f o
rticle history:eceived 21 September 2014eceived in revised form9 December 2014ccepted 15 January 2015vailable online 10 February 2015
eywords:
a b s t r a c t
Spray drying technique was used to fabricate Vitamin E loaded nanocapsules using Octenyl SuccinicAnhydride (OSA) modified starches as emulsifiers and wall materials. Several physicochemical propertiesof modified starches that are expected to influence emulsification capacity, retention and storage stabilityof Vitamin E in nanocapsules were investigated. High Degree of Substitution (DS), low Molecular Weight(Mw) and low interfacial tension improved emulsification properties while Oxygen Permeability (OP)and Water Vapor Permeability (WVP) affected the film forming properties. The degradation profile ofVitamin E fitted well with the Weibull model. Nanocapsules from OSA modified starches MS-A and MS-B
retained around 50% of Vitamin E after a period of 60 days at 4–35 C. Reduced retention and short half-life (35 days) in nanocapsules fabricated using MS-C at 35 ◦C were attributed to autoxidation reactionoccurred due to poor film forming capacity. These results indicated that low molecular weights OSAmodified starches were effective at forming stable Vitamin E nanocapsules that could be used in drugand beverage applications.
Vitamin E (VE) has been widely used in functional food additives,osmetics and drugs. However, utilization of its beneficial effects isimited due to its instability to heat and oxygen, where it is con-erted to quinone via epoxide formation (Yoo, Song, Chang, & Lee,006). Additionally, VE is hydrophobically active, which makes itifficult to be directly dispersed into an aqueous phase (Piorkowski
McClements, 2013).To obtain sufficient chemical and/or physical stability and high
ioaccessibility, VE is first made into colloidal O/W suspensionsnown as microemulsions, nanoemulsions or conventional emul-ion systems with respect to their droplets diameter d, with
< 100 nm, d < 200 nm and d > 200 nm, respectively (McClements,012). The colloidal O/W suspensions containing small particleiameter (<100 nm) are transparent and they have been reported torovide an extended physical and chemical stability and improved
ioaccessibility due to the small size of their particles (Liang,hoemaker, Yang, Zhong, & Huang, 2013). However, the fact thaticroemulsions systems often require high emulsifier content or
the use of organic co-solvents food and beverage industries are nowfocusing on formulation of nanoemulsions rather than microemul-sions (Huang, Yu, & Ru, 2010). Nanoemulsions provide high opticalclarity, high kinetic stability and enhanced bioaccessibility (Huanget al., 2010; Rao & McClements, 2012).
Contrary to microemulsions which are thermodynamicallystable under a particular range of conditions, nanoemulsionsare thermodynamically unstable (McClements, 2012), therefore,through a variety of physicochemical mechanisms that occurover time, nanoemulsions may undergo deteriorations: crea-ming, sedimentation, flocculation, coalescence or Ostwald ripening(Piorkowski & McClements, 2013).
The reported challenges to VE nanoemulsions stabilitydeservedly calls for remedies. The application of microencapsula-tion technology to aqueous VE based delivery systems has beenreported to either partially or totally overcome those instabilityproblems by protecting nanoemulsions from various deteriorationscaused by intrinsic and/or extrinsic physicochemical changes dur-ing storage (Krishnan, Kshirsagar, & Singhal, 2005; Yoo et al., 2006).
Although many techniques of encapsulation have been devel-
oped, Spray drying is the most popular due to the low cost andavailability of equipment. However, the choice of wall material maybe critical because it affects the encapsulation efficiency and stabil-ity of the resultant nanocapsules (Rosenberg, Kopelman, & Talmon,
990). A good choice for a wall material should be based on itshysicochemical properties such as solubility in water, molecu-
ar weight, glass or melting transition, crystallinity, diffusibility,lm forming and emulsifying properties (Gharsallaoui, Roudaut,hambin, Voilley, & Saurel, 2007). Biopolymers being approved
or food use and perceived as “label friendly”, have been used inood and pharmaceutical industries for this purpose (Piorkowski &
cClements, 2013).In the group of biopolymers, Octenyl Succinic Anhydride (OSA)
odified starches are one of the most preferred wall materials dueo their good emulsifying and film forming properties, low vis-osities, high oil loading capacities, oxygen barrier properties andow molecular weight (Frascareli, Silva, Tonon, & Hubinger, 2012;usoff & Murray, 2011). Additionally, the unique advantages of OSAodified starches are that they work as stabilizers of nanoemul-
ions and then serve as wall materials.The main objective of this study was to fabricate stable VE
nriched nanocapsules and to identify the physicochemical prop-rties necessary for OSA modified starches to serve as goodmulsifiers as well as good wall materials in VE nanoencapsulationsing spray-drying technique. This study was considered usefulo the food and pharmaceutical industries interested in deliveringE in form of nanocapsules by helping them in deciding appro-riate wall materials while bearing in mind a better stability andissolubility of nanocapsules.
. Material and methods
OSA-modified starches CAPSUL (MS-A), CAPSUL TA (MS-B) andICAP100 (MS-C) were obtained from Ingredion (New Jersey,SA). MS-A and MS-C are modified food starches derived fromaxy maize while MS-B was derived from Tapioca starch. Vita-in E ((+)−�−tocopherol from vegetable oil) (VE) was purchased
rom Sigma–Aldrich, Shanghai Trading Co. Ltd. (Shanghai, China).eobee 1053 (medium-chain triacylglycerol, MCT oil) with 44% C-0 and 56% C-8 was from Stepan Company (Maywood, New Jersey).ll other chemicals were of analytical grade and used without fur-
her purification.
.1. OSA modified starches characterization
.1.1. Degree of substitutionDegree of substitution (DS) was determined using hydrolysis
ethod as reported by Elomaa et al. (2004). Acetyl content (%A)as calculated according to the following Equation:
A = [(V0 − Vn) × N × 0.043 × 100]/M (1)
here V0 = ml of 0.5 N HCl used to titrate blank, Vn = ml of 0.5 N HClsed to titrate sample, N = Normality of HCl, M = sample amount asry substance, g and 43 = weight of acetyl group. Acetyl content%A) was used to calculate the degree of substitution, DS, using theollowing equation:
S = 162 × %A/[4300 − (42 × %A)] (2)
.1.2. Molecular weight distributionsMolecular weight distributions of OSA modified starches were
etermined as reported by Liang, Shoemaker, et al. (2013) withlight modification. Modified starch was dispersed in 50% DMSOissolved in 0.1 M NaNO3 at a concentration of 1% (w/w) andhen filtered through 0.22 �m nylon syringe filters. The filtratesere collected in 2 ml HPLC vessels and then injected into
he high-performance size-exclusion chromatography-multiangleaser light scattering refractive-index (HPSEC–MALLS–RI) system.he HPSEC–MALLS–RI system consisted of Wyatt DAWN HELLOSI multi-angle LS detector and Wyatt Technology Optilab T-rEX RI
Polymers 124 (2015) 172–179 173
detector. A size-exclusion chromatography column (ShodexOHpakSB-806 HQ, Showa Denko Japan) was used to determine the molec-ular weight distributions of modified starches. Temperature wasmaintained at 40 ◦C. 50% DMSO in 0.1 M NaNO3 with 0.02% NaN3was selected as the mobile phase with a flow rate of 0.35 ml/min.Astra V software (version 5.3, Wyatt technology Corp, USA) wasused to analyze the molecular weight distributions.
2.1.3. ViscosityThe shear viscosity of the dispersed phase and nanoemulsions
was studied using controlled stress/strain/rate Rheometer (ModelAR-G2, TA Instruments, Crawley, England) using cone-and-plategeometry with 40 mm cone diameter, 2 cone angle, 108 �m gapand temperature was maintained to 25 ◦C. Samples were loadedbetween the cone-and-plate fixtures. The dispersions were charac-terized regarding their steady shear viscosity, using a unidirectionalsteady shear flow, at shear rates ranging from 1.0 to 1000/s.
2.1.4. Interfacial tensionThe interfacial tension versus surfactant concentration was
measured at oil–water interfaces with a Dynamic Contact AngleMeter and Tensiometer (Data Physics, DCAT 21, Data Physics Instru-ments GmbH, Filderstadt, Germany) using Wilhelmy plate PT 11made of platinum–iridium at room temperature. The oil phaseswere a mixture of VE and MCT. The aqueous phases were preparedby mixing appropriate amounts of distilled water and modifiedstarch. The oil phase was injected into the aqueous phase and theinterfacial tension was determined by drop shape analysis after thesystem had time (5 min) to reach the equilibrium.
2.2. Preparation of VE nanoemulsions
Aqueous solutions were prepared by dissolving OSA modifiedstarches (32%, w/w) in distilled water at 70 ◦C under gentle stirringfor 30 min to enhance hydration then cooled to room tempera-ture. The lipid phase was prepared by dispersing VE in MCT (1:1,w/w). Coarse emulsions were produced by blending lipid phase andaqueous phase in the ratio of 3:7 (w/w) using a rotor-stator homog-enizer (Ultra-turrax IKA T18 Basic, Wilmington, NC, USA) operatedat 14,000 rpm for 5 min at room temperature. Fine emulsions wereproduced by use of high-pressure homogenizer (IKA HPH 2000/4-SH5, Staufen, Germany) operated at 120 MPa for 5 passes.
2.3. Spray-drying process
Homogenized nanoemulsions were spray-dried in a MobileMinorTM spray dryer (GEA Niro, Soeborg, Denmark) equippedwith a co-current nozzle atomizer. Inlet and outlet temperatureswere 150 ◦C and 85 ◦C respectively, with a feed rate of 10 ml/min.Obtained nanocapsules were sealed into plastic bag and kept intoa desiccator at room temperature for further analysis.
2.4. Nanocapsules characterization
2.4.1. Quantification of VE in nanocapsules by HPLCNanocapsules (5 mg) containing VE was dispersed in 5 ml of
Methanol/Acetonitrile (97:3). The mixture was sonicated 3 timesfor 20 min at 2 min intervals. After sonication, the solution wascentrifuged at 8000 rpm for 20 min. The supernatant was collectedand the concentration of VE was quantified by a HPLC system (Shi-
madzu, Kyoto, Japan) equipped with a PDA Detector (Waters 2996Photodiode Array Detector) at 295 nm. 20 �l was injected into aC18 column (InertsilODS-SP, 5 �m 4.6 × 150 mm, GL science, Tokyo,Japan) at 40 ◦C. An isocratic elution was used with a mobile phase
1 drate Polymers 124 (2015) 172–179
cs
2
F2
2
2
odmmb
2
smStutC
3
3
3m
ir4lweGtoits
Md0iitordt
(ttnsi
Table 1Power Law indices (n), consistency coefficients (�) and regression coefficients of oilphases made up by MCT and VE at ratio 1:1 (w/w), nanoemulsions ready for spraydrying and OSA modified starches.
onsisting of Methanol (97%) and Acetonitrile (3%). Flow rate waset to 1 ml/min.
.4.2. Field emission scanning electron microscopy (FeSEM)Nanocapsules morphology was studied using the Hitachi S4800
ESEM (Tokyo, Japan). Acceleration voltage was kept constant at.0 kV.
.5. Original and reconstituted nanoemulsions characterization
.5.1. Particle size characterization, PDI and �-potentialSize distributions, the average particle size, PDI and �-Potential
f initial and reconstituted nanoemulsions were measured usingynamic light scattering (ZetasizerNano-ZS90, Malvern Instru-ents, Worcestershire, UK). Reconstituted nanoemulsions wereade by dispersing 5 g of nanocapsules into 100 ml distilled water
y magnetic stirring.
.6. Experimental design and statistical analysis
The experiment was conducted in duplicate, and all analy-es were carried out at least in triplicate and expressed as theean ± standard deviation (±SD). Errors bars were reported as
tandard Errors. One-way ANOVA was used to compare means andhen, correlations between the studied parameters were evaluatedsing the Tukey’s LSD method at P < 0.05 significance level. All sta-istical analysis was performed using SPSS, version 19 (SPSS Inc.,hicago, USA).
. Results and discussion
.1. Properties of modified starches
.1.1. Degree of substitution (DS) and interfacial tension ofodified starches
The DS determines the surface load of modified starches dur-ng stabilization of emulsions (Zhu, Li, Chen, & Li, 2013). The DSesults were in the order MC-B < MS-C < MS-A with values: 2.7%,.3% and 5.1%, respectively. In principal, modified starches stabi-
ize an O/W emulsion by adsorbing to the interface of water/oil,here both emulsifying capacity and colloidal stability of resulting
mulsion increase directly with DS (Sweedman, Tizzotti, Schäfer, &ilbert, 2013). However, adsorption of modified starch molecules
o the interface of water/oil may vary following the nature ofils (Sweedman et al., 2013; Zhu et al., 2013). Therefore, it wasmportant to evaluate the relationship between DS and interfacialension of modified starches during stabilization of VE nanoemul-ions using MCT as carrier oil.
Similar interfacial properties were observed in MS-A, MS-B andS-C and furthermore each modified starch showed considerable
ecreases in interfacial tension as concentration increased from.5% to 3%. The initial addition of 0.5% surfactant dropped the
nterfacial tension to 35 mN/m and further increases decreased thenterfacial tension to as low as 5 mN/m. Further addition of surfac-ant showed no decrease in interfacial tension indicating saturationf the interface with surfactant (Yang & McClements, 2013). Theseesults therefore showed that the increase in surfactant would notecrease nanoemulsion droplets size but might lead to the forma-ion of micelles (Yang, Leser, Sher, & McClements, 2013).
Since OSA modified starches used in this study have low DS2.7–5.1%), they could be considered as weakly charged polyelec-rolytes and therefore their stabilizing capacity would be related
o their interaction with oppositely oil/water interface and thick-ess of formed layer (Nilsson & Bergenståhl, 2007). Our resultshowed no clear relationship between DS and interfacial tensionn all starches though it was generally expected that DS would
Different letters in superscript for � values (sub columns) indicate significant dif-ferences at P < 0.05.
relate strongly to the interfacial tension of modified starch in VE-MCT environment. These results are in agreement with Nilsson andBergenståhl, (2007) who reported an absence of any correlationbetween surface load and DS while using modified starches (DSvalues ranging from 0.76 to 2.24%) and oil phases containing MCT.Similar observations were also reported by other authors (Shogren& Biresaw, 2007) who found no effect of DS on surface or interfacialtension in the DS range of 0.3–0.8.
3.1.2. Viscosity of OSA modified starchesAn effective wall material should include low viscosity at higher
concentrations in spray drying process (Loksuwan, 2007). The highviscosity OSA modified starches have been reported to producesolutions that are difficult to homogenize, nanoemulsions withincreased amount of dissolved oxygen and droplet size, resultinginto nanocapsules with low oxidative stability and low oil retention(Sweedman et al., 2013).
Results for the apparent viscosity versus shear rate for MS-A,MS-B and MS-C prepared at 4 different concentrations (10%, 20%,30% and 40% w/w) are presented in Fig. 1. Table 1 presents thevalues of the consistency index (�) and flow behavior index (n)obtained from the Power law model. The Power law model’s rela-tionship between shear stress and shear rate is given by: ı = � �n
(Campanella, Dorward, & Singh, 1995) where ı is the shear stress(in Pa), � is the flow consistency index (in Pa sn), � is the shearstrain rate (in s−1), and the exponent n is the dimensionless Powerlaw index.
All OSA modified starches showed a shear thinning behav-ior with constant viscosity at high shear rates. As concentrationincreased from 10% to 30%, there were no significant differencesin � values in all starches, however, the � increased remark-ably when concentration reached 40%. Nevertheless, at 40%, theviscosities of MS-A (� = 1.89 Pa s), MS-B (� = 1.98 Pa s) and MS-C(� = 1.86 Pa s) were lower than that of VE alone (� = 2.91 Pa s). Theseresults showed that OSA modified starches MS-A, MS-B and MS-C were able to create coarse emulsions that were easy to passthrough high-pressure homogenizer even at high concentration(40%). The viscosities of nanoemulsions fabricated using 32% mod-ified starches were around 1.29 ± 0.3, 1.04 ± 0.6 and 1.33 ± 0.8 Pa sfor MS-A, MS-B and MS-C, respectively. Values of � showed that theready to spray dry nanoemulsions formed from MS-C was moreviscous compared to MS-A and MS-B, which was assumed to beclosely related to its molecular weigh distribution, � and the Rzvalue.
3.1.3. Molecular weights and molecular structure of modified
starches
Results summarized in Table 2 showed that MS-A and MS-B presented monomodal molecular weight distributions withavMw 7.07 × 104 g/mol and 4.28 × 104 g/mol, respectively, while
J. Hategekimana et al. / Carbohydrate Polymers 124 (2015) 172–179 175
Fig. 1. The dependence of viscosity on shear rate for OSA Modified starches MS-A, MS-B and MS-C as a function of percent concentration. Samples were prepared by dissolvingappropriate percentage of OSA starches in distilled water.
Table 2Physicochemical properties and molecular characteristics of OSA-modified starches selected for this study.
From (Liang, Huang, et al., 2013) with OP (cm3 �m/m2 day kPa) and WVP (g mm/mifferent letters in superscript for OP and WVP within a column indicate significant
S-C presented a bimodal molecular weight distribution with larger pick (avMw = 166.60 × 104 g/mol) and a smaller peakavMw = 0.76 × 104 g/mol) (Fig. 2). The lowest dispersed molecu-ar density (defined as � = Mw/Rz3, g/mol nm3) was found in MS-B15.20 ± 0.3 g/mol nm3) while MS-C presented the highest value20.10 ± 0.2 g/mol nm3).
Results have also shown that the Radius of Gyration (Rz)as high and significantly different from the others in MS-C
34.60 ± 0.2 nm). The highest values of � and the Rz suggestedhat MS-C had more compact conformation than MS-A and MS-Bince starches having large � are suspected to have more branchedhains, which result in more densely, packed molecules whileolecules of modified starches having large Rz are believed to have
ccupied a larger volume in the solution, which is then relatedo the branch chain length and the pattern of molecules (Liang,hoemaker, et al., 2013; Yoo & Jane, 2002). As avMw measure-ent emphasizes the mass of molecules, it is possible that MS-B
ossessed shorter molecules than MS-A and MS-C (Kowittaya &umdubwong, 2014).
In our previous publication, we have shown that during nanoen-apsulation, � and DS are the determinants of the film formingapacity of OSA modified starch, whereas other factors such as oxy-en permeability (OP) and water vapor permeability (WVP) definehe water barrier properties of the films which affect the storagetability of their nanocapsules (Liang, Huang, Ma, Shoemaker, &hong, 2013).
.2. Nanoemulsions characterization
.2.1. Viscosity of fresh nanoemulsions stabilized by modifiedtarches
Results on viscosity showed that both MCT and VE possessedhear-thinning behaviors given that their n values were less than. It was observed that VE was difficult to be homogenized withoutixing it with low viscous oil due to its high viscosity (� = 2.91 Pa s).
or example, coarse emulsion formed by oil phase consistingnly by VE and MS-A at ratio 3:7 (w/w) resulted in a coarsemulsion with � = 2.31 Pa s making it difficult to pass through high-ressure homogenizer (120 MPa). Therefore, MCT, a low viscosity
ences at P < 0.05.
(� = 0.04 Pa s) vegetable oil was used to reduce the overall viscos-ity of the disperse phase. As it can be seen in Table 1, the additionof MCT dropped � value of disperse phase to 0.12 Pa s. The addi-tion of higher amounts of MCT would have reduced the viscosityto even lower levels, but this would have also reduced the overallpercentage of VE in formulated nanoemulsions and consequentlyin the resultant nanocapsules. Increasing the amount of VE in thesystem tended to increase the viscosity of the emulsion, therefore,the encapsulation efficiency was reduced when higher amount ofVE was used (data not shown). The 1:1 ratio (VE:MCT) was found tobe the suitable to produce nanoemulsions and nanocapsules withdesirable properties.
3.2.2. Particle size of initial and re-dispersed nanoemulsionsParticle size plays an important role in the stability of nanoemul-
sion systems and also the decrease in particle diameter has beenreported to increase bioavailability of encapsulated compounds(Ozturk, Argin, Ozilgen, & McClements, 2014). The Results for par-ticle size measurement are presented in Fig. 3. The average particlediameters ranged between 208 and 235 nm with MS-B having thesmallest mean particle diameter. Although average particle diam-eters were significantly different, PDI and �-potential were similar.As can be observed in Fig. 3, the reconstituted nanoemulsions main-tained their original narrow monomodal distribution with slightincrease in average particle diameters.
The highest increase in average particles diameter was 16.37 nmin nanoemulsions made from MS-C, which was not significantlydifferent. In general, the overall droplet size, PDI and �-potentialwere similar in initial and reconstituted nanoemulsions for allmodified starches. The fact that reconstituted emulsions retainedtheir polydispersity values (PDI < 0.250) and particle diameter(<250 nm) suggested that the spray drying process did not affectthe nanoemulsions characteristics. Results showed that the parti-cle sizes of fresh and reconstituted emulsions were directly relatedto DS, avMw and the viscosity of dispersed phase. The parti-
cle sizes were in order MS-B < MS-A < MS-C, with low molecularweight and low DS modified starches having smaller particle sizes.These results are in agreement with findings of Liang, Shoemaker,et al. (2013) who reported that the droplet size and particle size
176 J. Hategekimana et al. / Carbohydrate Polymers 124 (2015) 172–179
FtH
dwtplStho
Fig. 3. Particle size distributions of freshly made and reconstituted nanoemulsions.Initial nanoemulsions were produced by blending lipid phase (VE-MCT, 1:1, w/w)and aqueous phase (32%, w/w) in the ratio of 3:7 (w/w) using a high-pressure
ig. 2. Weight-average molecular weight and concentration signals versus elutionime profiles of OSA modified starches (MS-A, MS-B and MS-C) determined by anPSEC–MALLS–RI system. Molar mass in g/mol (a); Differential refractive index (b).
istributions of fresh and reconstituted �-carotene nanoemulsionsere affected by the difference in molecular weight distributions of
he modified starches. Some authors have also reported increasedarticle size with increasing molecular weight when encapsu-
ated with fish oil using spray-drying technique (Serfert, Drusch,
chmidt-Hansberg, Kind, & Schwarz, 2009). This could be attributedo the fact that modified starches with higher avMw possess alsoigh � and high Rz, which form micelles with larger dimension,ccupying a larger volume with more densely, packed interior
homogenizer operated at 120 MPa for five passes. Reconstituted nanoemulsionswere made by dispersing 5 g of the spray-dried nanocapsules into 100 ml distilledwater by magnetic stirring. F: initial nanoemulsions, R: reconstituted nanoemul-sions.
structure (Zhu et al., 2013). However, Viswanathan, (1999) foundthat among three modified starches with different DS values (3%, 7%and 11%), sample with DS 7% formed the best emulsions. This wasattributed to the combination of hydrophobic chains, which nor-mally act better than a single kind chain (Sweedman et al., 2013).On the other hand, Sweedman et al. (2013) explained this as theresult of octenyl succinate groups being predominantly located atthe midsections of starch chains at high DS, thus becoming unavail-able for interaction with the hydrophobic phase.
3.3. VE retention and its degradation kinetics in nanocapsules
The order of VE retained in the nanocapsules relative to theoriginal values after spray drying was MS-B > MS-A > MS-C with79.16%, 73.15%, 71.46%, respectively. VE retention was higherin nanocapsules formed from emulsions with the lowest avMw(4.28 × 104 g/mol), and lowest DS (2.7%).
3.3.1. The degradation kineticsThe degradation mechanism of encapsulated VE during storage
over time (60 days) at different temperatures (4 ◦C, 20 ◦C and 35 ◦C)and constant relative humidity (73%) was studied using the Weibullmodel with following equation:
Vt = V0 exp−(kt)ˇ(3)
Where Vt is the VE concentration at a time t, V0 is the initialVE concentration, k is the degradation rate constant (days−1) and
is the shape factor determining the shape of degradation curve.The reaction half-time (t1/2) was calculated assuming the first orderkinetic using the following equation:
t1/2 = − ln(0.5)k
(4)
Where t1/2 is the time (days) required for VE to drop by 50%.The time-courses degradation curves of VE fitted to the Weibullmodel for nanocapsules produced by MS-A, MS-B and MS-C underdifferent temperatures are shown in Fig. 4, with the fitted kinetic
J. Hategekimana et al. / Carbohydrate Polymers 124 (2015) 172–179 177
Table 3Kinetic parameters and correlation coefficients of the degradation of VE in nanocapsules encapsulated by different modified starches stored at different temperatures and73% RH.
Wall materials Storage temperature (◦C) Weibull parameters
Different letters in superscript for k values (columns) for each MS indicate significant diff
Fig. 4. Retention of VE in nanocapsules encapsulated by different OSA modifiedstarches over time at different storage temperature: (�) 4 ◦C; (�) 20 ◦C and (•) 35 ◦C.The solid lines denoted the fitting data by Weibull model.
b 1.15 ± 0.002 0.98 35.85
erences at P < 0.05.
parameters presented in Table 3. According to the results, highregression coefficient (R2 > 0.98) was observed in all samples, whichshowed that Weibull model was suitable to model the degradationof VE by yielding a good fit of the experimental data.
Typically the stability of tested compounds in Weibull modelis determined by a rate constant k. If the value of k is high, thestability is low. If < 1, the degradation rate decreases with time,if > 1, the rate of degradation increases over time. In the firstorder degradation, the shape factor is equal to 1 with a con-stant rate of degradation over time (Syamaladevi, Sablani, Tang,Powers, & Swanson, 2011). Our results have shown that most of thesamples at tested temperatures had convex degradation rate withincreasing pattern ( > 1). These findings are in line with previouspublished results using the same modified starches to encapsulate�-carotene (Liang, Shoemaker, et al., 2013). It can be noted thatas VE retention increased, the reaction rate constant k decreased,which is in line with previous reports on anthocyanin (Syamaladeviet al., 2011) and �-carotene (Liang, Huang, et al., 2013) degrada-tion studies. The overall results of k and half-life (Table 3) showedthat samples stored at 35 ◦C might be more susceptible to degrada-tion, which would be attributed to the instability of VE at elevatedtemperatures.
The stability of VE in spray-dried nanocapsules have beenextensively studied and different approaches have been elucidated(Partanen, Hakala, Sjövall, Kallio, & Forssell, 2005; Soottitantawatet al., 2005). Previously published results associated the degrada-tion of VE in spray-dried nanocapsules to the oxidation reactionby oxygen diffusion through the wall materials (Partanen et al.,2005). Another approach to the loss of VE during storage shouldbe associated to the physicochemical properties of wall materi-als. As stated earlier in this study, avMw, � and DS of modifiedstarch define its film forming capacity while OP and WVP deter-mine the stability of core material in nanocapsules. The lowerthe OP, the better the stability of the core material. The values ofWVP, OP, DS and Mw presented in Table 2, are in direct agree-ment with k values shown in the Table 3. Comparison betweenmodified starches showed that high VE retention after a period of60 days in MS-B with WVP (3.82 ± 0.09 g mm/m2 h kPa) and low-est OP (1.20 cm3 �m/m2 day kPa) might have resulted to its greaterpossibility to offer a good toughness to the wall of nanocapsules,forming a barrier to environmental factors and preventing oxida-tion and caking, hence increasing stability. Moreau and Rosenberg(1998) reported that the stability of encapsulated material dependsstrongly on the permeability of the wall matrix by oxygen. Nunesand Mercadante (2007) indicated that the drying process yieldstrongly depends on the equipment configuration, whilst the
microencapsulation efficiency and percent retention of core arerelated to the physicochemical characteristics of both the coreand wall material. Results showed that the nanocapsules madefrom lowest molecular weight modified starches (MS-B and MS-A)
178 J. Hategekimana et al. / Carbohydrate
Fsa
wrswdtse
o
tion reaction occurred due to its high avMw, � and DS. This study
ig. 5. Field Emission Scanning Electron Micrographs of the spray dried nanocap-ules encapsulated by MS-A (a), MS-B (b) and MS-C (c) obtained after 10 days storaget room temperatures and 73% relative humidity.
ere more powdery, which was explained in virtue of previouslyeported finding affirming that the rate of moisture uptake ofpray dried nanocapsules depends on the molecular weight of theall material (Niazi, Zijlstra, & Broekhuis, 2013). Therefore, it isesirable that modified starches used in encapsulation of bioac-ive ingredients should possess low molecular weight and high DSince high molecular weight negatively affects the encapsulation
fficiency (Rosenberg et al., 1990).
The effect of high molecular weight of the OSA modified starchesn encapsulation efficiency during spray drying process may be
Polymers 124 (2015) 172–179
attributed to the fact that they create solutions that are difficult toprocess due to their high viscosity. Sweedman et al. (2013) reportedthat increasing the viscosity of the emulsion before spray dryingincreases the amount of dissolved oxygen and the droplet size,resulting into nanocapsules with low oxidative stability and low oilretention. The lower molecular weight modified starches have beenreported to provide good toughness and good rheological proper-ties resulting in homogeneous and powdery samples (Li, Anton,Arpagaus, Belleteix, & Vandamme, 2010).
Our results suggested that MS-B was able to form the best bar-rier to environmental factors and prevented oxidation and cakingof nanocapsules. However, other factors may be essential to therate of degradations of VE by autoxidation during storage such asmatrix porosity, trace minerals levels, relative humidity and wateractivities (Liang, Huang, et al., 2013).
3.4. Nanocapsules morphology
Micrographs of the nanocapsules produced from MS-A, MS-Band MS-C are presented in Fig. 5. It is evident that the nanocap-sules morphology is almost similar with various sizes (an averagediameter of 6.44 ± 1.1, 4.49 ± 1.82 and 5.65 ± 2.34 �m for MS-A,MS-B and MS-C, respectively) and mostly dominated by roundedsurface. All modified starches produced capsules with smooth anddepressed surface where smaller particles tended to agglomer-ate among themselves. Previously, other authors have reported adirect relationship between interfacial tension of emulsifiers andtheir nanocapsules morphology (Yeom, Oh, Rhim, & Lee, 2000). Asoutlined earlier, all our modified starches had similar interfacialproperties and therefore it is justifiable that their nanocapsules alsopresented similar morphology. The surface depressions observedwere due to the particle shrinkage or collapse of droplets duringinitial stages of drying and cooling (Frascareli et al., 2012).
Despite the irregularities of the nanocapsules surface, therewere few or no wall cracks or porosity on the surface in MS-A andMS-B, indicating a complete coverage of modified starches overthe core (VE). However, in addition to some rough surfaces, MS-Cpresented also few wall cracks (Fig. 5c). This morphology might beassociated to its high avMw, � and DS, which negatively affected itsfilm forming capacity. The same morphology might also explain itspoor VE retention (Fig. 4) and short half-life either at low or hightemperatures (i.e., 35.84 days at 35 ◦C, see Table 3) compared toMS-A and MS-B.
4. Conclusions
This study has shown that VE can be successfully encapsu-lated using MS-A, MS-B and MS-C as emulsifiers and wall materialsby spray drying technique. The physicochemical properties of themodified starches ideal for good emulsification were found to behigh DS, low avMw and low interfacial tension whereas OP, WVPwere found to enhance the film forming properties. However, mostof the physicochemical properties may play multiple functions, i.e.,avMw enhancing emulsification while helping in creating solid andtough wall matrix. Overall results showed that MS-A and MS-B wereable to fabricate nanocapsules with VE retention of around 50% ofits initial value after 60 days storage at 4–35 ◦C and good suspen-sion in water. Reduced VE retention and short half-life (35 days)in nanocapsules fabricated using MS-C in nanocapsules stored athigh temperature (35 ◦C) was attributed to an increased autoxida-
might be useful to service providers interested in delivering VE inform of nanocapsules in identifying appropriate modified starch toact as emulsifier and wall material.
drate
A
2P
R
C
E
F
G
H
K
K
L
L
L
L
M
M
N
N
N
J. Hategekimana et al. / Carbohy
cknowledgments
This work was financially supported by National 863 Program011BAD23B02, 2013AA102207, NSFC 31171686, 30901000, 111roject-B07029 and PCSIRT0627
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