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Solid Lipid Dispersions: Potential DeliverySystem for Functional Ingredients in Foods

Aboagyewa Asumadu-Mensah, Kevin W. Smith, and Henelyta S. Ribeiro

Dispersiones slidas lipdicas: Sistema deEntrega Potencial de IngredientesFuncionales de los AlimentosAboagyewa Asumadu-Mensah, Kevin W. Smith y Henelyta S. Ribeiro

Abstract: Structured solid lipid (SL) systems have the advantages of long-term physical stability, low surfactant concen-trations, and may exhibit controlled release of active ingredients. In this research work, the potential use of high-meltinSLs for the production of the above structured SL carrier systems was investigated. Dispersions containing either SL o blend of solid lipid and oil (SL+O) were produced by a hot melt high-pressure homogenization method. Experimentsinvolved the use of 3 different SLs for the disperse phase: stearic acid, candelilla wax and carnauba wax. Sunflower oil wa

incorporated in the disperse phase for the production of the dispersions containing lipid and oil. In order to evaluate th practical aspects of structured particles, analytical techniques were used including: static light scattering to measure particsizes, transmission electron microscopy (TEM) for investigating particle morphology and differential scanning calorimetr(DSC) to investigate the crystallization behavior of lipids in bulk and in dispersions. Results showed different mean particsizes depending on the type of lipid used in the disperse phase. Particle sizes for the 3 lipids were: stearic acid (SL: 195 2.5 nm; SL+O: 138 6.0 nm); candelilla wax (SL: 178 1.7 nm; SL+O: 144 0.6 nm); carnauba wax (SL: 303 1.5 nm;SL+O: 295 5.0 nm). TEM results gave an insight into the practical morphology, showing plate-like and needle-likestructures. DSC investigations also revealed that SL dispersions melted and crystallized at lower temperatures than th bulk. This decrease can be explained by the small particle sizes of the dispersion, the high-specific surface area, and th presence of a surfactant. Keywords: melting profile, morphology, physical stability, structured lipid systems, waxes

Resumen: Los sistemas de lpidos slidos estructurados ( SL) tienen la ventaja de la estabilidad fsica a largo plazo , bajosurfactante concentraciones y pueden presentar liberacin controlada de principios activos. En este trabajo de investigacise investig el uso potencial de SL de alto punto de fusin para la produccin de los sistemas de portadora SL estructuradoms arriba . Las dispersiones que contienen ya sea SL o mezcla de lpidos slidos y aceite ( SL O) fueron producidos por umtodo de homogeneizacin a alta presin de fusin en caliente . Los experimentos incluyeron el uso de 3 SL de diferente para la fase dispersa : cido esterico , cera de candelilla y cera de carnauba . El aceite de girasol fue incorporada en la fasedispersa para la produccin de las dispersiones que contienen lpidos y el aceite . Con el fin de evaluar los aspectos prcticde partculas estructuradas , se utilizaron tcnicas de anlisis como: dispersin de luz esttica para medir el tamao de las partculas , microscopa electrnica de transmisin (TEM ) para la investigacin de la morfologa de las partculas y lacalorimetra diferencial de barrido ( DSC ) para investigar el comportamiento de cristalizacin de lpidos en granel y endispersiones . Los resultados mostraron diferentes tamaos medios de partcula en funcin del tipo de lpido utilizado en lafase dispersa . Los tamaos de partcula para los 3 lpidos fueron: cido esterico (SL : 195 2,5 nm , SL O: 138 6,0 nm cera de candelilla (SL : 178 1,7 nm , SL O: 144 0,6 nm ), cera de carnauba (SL : 303 1,5 nm , SL O: 295 5.0 nm ) .

Resultados TEM dieron una idea de la morfologa prctica , mostrando estructuras de tipo placa y aguja. DSCinvestigaciones tambin revelaron que las dispersiones SL funden y se cristalizaron a temperaturas ms bajas que el gruesoEsta disminucin se puede explicar por los pequeos tamaos de partcula de la dispersin , el rea de superficie especficaalta , y la presencia de un agente tensioactivo .

Palabras clave : perfil de fusin , la morfologa , la estabilidad fsica , los sistemas de lpidos estructurados , ceras


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Introduction

Solid lipid (SL) dispersions have proved to be promising carriersystems for the encapsulation of active compounds for pharmaceu-tical and cosmetic applications (Muller and Lucks1991; Mullerand others1995; Jenning1999; Radtke and Muller2001; Lacerdaand others2011). This has led to an increased interest in theapplica-tion of these carrier systems in foods (Dickinson andMcClements1995; Mellema and others 2006).

It is reported that the use of a SL matrix material as adelivery system helps to overcome several limitations of oil-in-

water (o/w) emulsions, including coalescence, drug leakage,destabilization of the droplets due to crystallization of activesor migration into the emulsifier film and, more importantly,difficulty in sustained or controlled release (Collins-Gold andothers1990; Prakerd and Stella1990).

The SL dispersions provide better physical stability as well asstrongly reduced mobility of incorporated actives, which reducesleakage and avoids migration of active compounds into the emul-sifier, thus maintaining sustained or controlled release (Muller andothers 1995). Controlled release is achieved because the rate ofmass transfer of the active compounds incorporated in the crys-talline or semicrystalline phases is reduced compared with theliquid phase (Sonoda and others2006).

There have been reports of SL particles exhibiting different re-lease mechanisms based on the structure of the particles. Wissingand others (2003) reported that if the incorporated active com-

MS 20120720 Submitted 5/22/2012, Accepted 4/9/2013. Author Asumadu- Mensah is with School of Biosciences, Univ. of Nottingham, U.K. AuthorSmith is with Fat Science Consulting Ltd, U.K. Author Ribeiro is withUnilever R&D Vlaardin-gen, the Netherlands. Direct inquiries to author

Ribeiro (E-mail: henelyta.ribeiro@ basf.com ).

pound is located primarily in the shell of the particles, there will be an initial burst release, followed by fast release. Mehnert andothers (1997) also reported that if the active compound islocated in the core of the particles, it will be released in acontrolled mode governed by Ficks law of diffusion. introduccin

Dispersiones de lpidos slidos ( SL ) han demostrado ser prometedores sistemas de portadora para la encapsulacin decompuestos activos para aplicaciones farmacuticas y cosmticas( Muller y suertes de 1991 ; Muller y otros 1995 ; Jenning 1999 ;Radtke y Muller 2001 ; Lacerda y otros 2011 ). Esto ha llevado aun creciente inters en la aplicacin de estos sistemas de transporteen los alimentos (Dickinson y McClements 1995 ; Mellema y otros2006 ) .

Se ha informado de que el uso de un material de matriz SL como

un sistema de suministro de ayuda para superar varias limitacionesde aceite - en - agua (O / W ) emulsiones, incluyendocoalescencia , las fugas de drogas , la desestabilizacin de las gotas

debido a la cristalizacin de los ingredientes activos o la migracinen la pelcula de emulsionante y, ms importante , dificultad en laliberacin sostenida o controlada ( Collins - oro y otros 1990 ;Prakerd y Stella 1990 ) .

Las dispersiones SL proporcionan mejor estabilidad fsica, ascomo fuertemente reducida movilidad de los principios activosincorporados , lo que reduce las fugas y evita la migracin de loscompuestos activos en el emulsionante , manteniendo as unaliberacin sostenida o controlada ( Muller y otros, 1995 ) . Laliberacin controlada se logra porque la tasa de transferencia demasa de los compuestos activos incorporados en las fases cris -talline o semicristalino se reduce en comparacin con la faselquida ( Sonoda y otros 2006 ) .

Ha habido informes de partculas SL muestran diferentesmecanismos de liberacin basados en la estructura de las partculas.Wissing y otros ( 2003 ) informaron de que si el compuesto activoincorporado se encuentra principalmente en la cscara de las partculas , habr una liberacin de estallido inicial , seguido deliberacin rpida . Mehnert y otros ( 1997 ) tambin informaronque si el compuesto activo se encuentra en el ncleo de las partculas , que se dar a conocer en un modo controlado regulado por ley de difusin de Fick .

Pure triacylglycerols or waxes in dispersion as droplets exhibitfaster transition into thermodynamically stable forms, leading tothe formation of a tightly packed perfect crystalline matrix. Thismay be due to the acceleration of polymorphic transformation andannealing in the colloidal state. The result will be a premature drugexpulsion if the drug load is above the solubility in the stablecrystal modification; hence, there is no controlled release of activeingredients (Westesen and others 1997; Saupe and others2005).The tightly packed perfect crystalline matrix of SLs into submicronsize particles also limits the incorporation of active compounds inthis system. These limitations in drug loading capacity have beenreported by Wissing and others (2003).

In order to overcome the limitations of SL dispersions, inves-tigations were carried out to develop particulate carrier systems of

certain morphologies that allow increase of the loading capac-ityand prevent drug expulsion (Wissing and others2004). Workcarried out by Radtke and Muller (2001) involved a blend of SLsand liquid lipids (oils). This led to the formation of an imperfectsolid matrix, which allowed a higher incorporation rate of activecompounds. It also offered better prospects for controlled release.

Similar studies carried out by Mehnert and others (1997) re-vealed that the use of more complex lipids (a mixture of mono-, di-, triacylglycerols of different chain lengths) had better prospects forhigher drug loading. This is because spatially different lipids leadto larger distance between the fatty acid chains of the glyc-erides aswell as imperfections in the crystal, providing more room forincorporation of active compounds (Wissing and others2004).Examples of such lipids that have been used in studies include a

C _R _ 2013Institute ofFoodTec hnologists

E1000 Journal of Food Science Vol. 78, Nr. 7, 2013 doi: 10.1111/1750-3841.12162 Further reproduction without permission is prohibited


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Solid lipid dispersions . . .

medium chain triglyceride (Miglyol_R ) and a combination ofsolid fatty acids (Compritol_R ) (Jenning and others2000; Saupeand others2005).

Triacilgliceroles puros o ceras en dispersin en forma de gotitasexhiben una transicin ms rpida en las formastermodinmicamente estables , que conduce a la formacin deuna matriz cristalina perfecta envasados hermticamente . Esto puede ser debido a la aceleracin de la transformacin polimrfica y el recocido en el estado coloidal . El resultadoser una expulsin prematura droga si la carga de frmaco est por encima de la solubilidad en la modificacin cristalinaestable , por lo que no hay liberacin controlada de ingredientesactivos ( Westesen y otros 1997 ; Saupe y otros, 2005 ) . Lamatriz cristalina perfecta fuertemente empaquetada de SL en partculas de tamao submicromtrico tambin limita laincorporacin de los compuestos activos en este sistema . Estaslimitaciones en la capacidad de carga del frmaco han sidoreportados por Wissing y otros ( 2003 ) .

Para superar las limitaciones de dispersiones SL , investiga-ciones se llevaron a cabo para desarrollar sistemas de soportede partculas de ciertas morfologas que permiten aumentar lacapaci-dad de carga y evitar la expulsin de drogas ( Wissing yotros 2004 ) . El trabajo llevado a cabo por Radtke y Muller ( 2001 ) implic una mezcla de SL y lpidos lquidos( aceites ) . Esto condujo a la formacin de una matriz slidaimperfecta , lo que permiti una tasa de incorporacin ms altade compuestos activos . Tambin ofreca mejores perspectivasde liberacin controlada.

Estudios similares llevados a cabo por Mehnert y otros ( 1997 )re - revelado que el uso de lpidos ms complejos ( una mezclade mono - , di - , triglicridos de diferentes longitudes decadena ) tenan mejores perspectivas de mayor carga defrmaco . Esto se debe a espacialmente diferentes lpidosconducen a la mayor distancia entre las cadenas de cidosgrasos de los Glyc - ERIDES as como imperfecciones en elcristal , que proporciona ms espacio para la incorporacin delos compuestos activos ( Wissing y otros 2004 ) . Los ejemplosde tales lpidos que se han utilizado en estudios incluyen untriglicrido de cadena media ( Miglyol_R ) y una combinacinde cidos grasos slidos ( Compritol_R ) ( Jennings y otros,2000 ; Saupe y otros, 2005 ) .

Investigations on topical formulations also revealed that keepinglipids in their meta-stable crystalline forms ( , ) during stor -ageand slowing transition to the more stable form prevents prematureexpulsion of the active (Jenning and others2000).

There are reports of various technologies that can be used to produce submicron particles. High-pressure homogenization has been reported to provide a higher efficiency of droplet break-downto submicron sizes (Keck and Muller2006). According toSchuchmann (2007), one of the principles of high-pressure ho-mogenization is the pumping of a preliminary coarse emulsionthrough a narrow orifice under high pressure (up to 1000 bar).

Stang and others (2001), Aguilar and others (2004), and Freudig(2004) reported that the design of the homogenizing nozzle influ-ences the flow pattern of the emulsion in the nozzle and, hence, thedroplet disruption. Various types of nozzle designs for high- pressure homogenizers include opposing jet (Cook1985; 1990), jetdispersers, and a simple orifice valve (Stang and others2001).Droplet disruption in high-pressure homogenizers may be due toinertial forces in turbulent flow, shear forces in laminar flow andcavitation (Walstra1993; Freudig and others2003).

Microfluidization operates by an opposing jet stream

principle that provides high-energy efficiency in the disruptionof micropar-ticles to submicron size by shear forces and impact(Parikh and Selvaraj1999).

The aims of this study were 2-fold. First, to investigate the potential use of long-chain fatty acid waxes and a solid fatty acidfor the production of different types of structured SL carriersystems, namely SL dispersions and solid lipid+oil dispersions(SL+O) of submicron range (d3,2 < 500 nm). Second, tocharacterize the SL and SL+O to determine the feasibility for theencapsulation of active compounds within them.

Las investigaciones sobre las formulaciones tpicas tambinrevelaron que el mantenimiento de los lpidos en sus formascristalinas metaestables ( , ' ) durante el almacenamiento y ladesaceleracin detransicin a la forma ms estable evita laexpulsin prematura del activo ( Jenning y otros, 2000 ) .

Hay informes de diversas tecnologas que pueden ser utilizados para producir partculas submicrnicas . Homogeneizacin dealta presin ha sido reportado para proporcionar una mayoreficiencia de la gotita de romper hacia abajo a los tamaossubmicromtricas ( Keck y Muller 2006 ) . De acuerdo conSchuchmann ( 2007 ) , uno de los principios de alta presinhomogeneizacin es el bombeo de una emulsin gruesa preliminar a travs de un orificio estrecho a alta presin ( hasta1000 bar ) .

Stang y otros ( 2001 ) , Aguilar y otros ( 2004 ) , y Freudig( 2004 ) informaron de que el diseo de la tobera dehomogeneizacin influencias el patrn de flujo de la emulsinen la boquilla y , por lo tanto , la interrupcin de gotas. Variostipos de diseos de boquillas para homogeneizadores de alta presin incluyen chorro de oponerse ( Cook, 1985 ; 1990 ) ,dispersores de chorro , y una vlvula de orificio sencillo ( Stangy otros, 2001 ) . Interrupcin gotita en homogeneizadores dealta presin puede ser debido a las fuerzas de inercia en el flujoturbulento , las fuerzas de corte en el flujo laminar y cavitacin

( Walstra 1993 ; Freudig y otros, 2003 ) .Microfluidizacin funciona por un principio corriente en chorrooposicin que proporciona alta eficiencia energtica en lainterrupcin de micropartculas de tamao submicrnico por lasfuerzas y el impacto ( Parikh y Selvaraj 1999 ) de corte.

Los objetivos de este estudio fueron 2 veces . En primer lugar, para investigar el posible uso de ceras de cidos grasos decadena larga y un cido graso slido para la produccin dediferentes tipos de sistemas estructurados SL portadoras , asaber, SL y dispersiones de lpidos slidos + dispersiones enaceite ( SL + O ) de rango submicrnico ( d3 , 2 < 500 nm ) . En

segundo lugar, para caracterizar el SL y SL + O para determinarla factibilidad para la encapsulacin de los compuestos activosdentro de ellos .


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Materials and Methods Materials

Stearic acid (95%, powder form), candelilla wax (natural, in pastilles form), and carnauba wax (refined No.1 yellow, in flakeform) waxes were bought from Sigma-Aldrich in United King-dom. Sucrose laurate (L-1695) was bought from Mitsubishi-Kagaku Foods Corp., Japan. Sunflower oil (pure) was boughtfrom Leon Frenkel Limited, Belvedere, Kent. Materiales y MtodosMateriales

Ceras de cido esterico (95%, en polvo), cera decandelilla (natural, en forma de pastillas) y cera decarnauba (refinado No.1 amarillo, en forma deescamas) fueron comprados a Sigma-Aldrich en elReino Unido. Laurato de sacarosa (L-1695) fuecomprado a Mitsubishi-Kagaku Foods Corp.,Japn. El aceite de girasol (puro) fue comprado aLeon Frenkel Limited, Belvedere, Kent.

Preparation of the dispersions Emulsions were prepared with demineralized water and 2% su-crose

laurate (L-1695) as the continuous phase and 5% lipid as the disperse phase. For the preparation of SL, each of the SLs was melted to 10 to20 C above their melting point. The continuous phase was also heatedto approximately 80 to 90 C (as appropriate) to match the temperatureof the disperse phase, while ensuring that it was not boiling. Thedisperse phase was added to the continuous phase and homogenized at13000 rpm for 20 min using a rotor stator system (Ultraturrax_R T25 basic, IKA-WERKE GmbH & Co. KG, Staufen, Germany) to form acoarse pre-emulsion. Ho-mogenization of the coarse emulsion via arotor stator system was carried out in a jacketed beaker connected to awater bath to en-sure that the temperature was maintained above themelting points of the SL. After homogenization of the coarse pre-emulsion, it was immediately further homogenized at 1200 bar for

maximal 2 cy-cles using a Microfluidizer _R M-110S (Microfluidics

TM,

Newton, Preparacin de las dispersiones

Las emulsiones se prepararon con agua desmineralizada y 2 %sacarosa laurato ( L - 1695 ) como la fase continua y 5 % delpidos como la fase dispersa . Para la preparacin de SL , cadauna de las SL se fundi a 10 a 20 C por encima de su punto defusin . La fase continua tambin se calent a aproximadamente80 a 90 C ( segn el caso) para que coincida con latemperatura de la fase dispersa , garantizando al mismo tiempoque no era de ebullicin . La fase dispersa se aadi a la fase

continua y se homogeneiz a 13.000 rpm durante 20 minutilizando un sistema de rotor - estator ( Ultraturrax_R T25 bsico , IKA -Werke GmbH & Co. KG , Staufen , Alemania ) para formar una pre - emulsin gruesa . Homogeneizacin de laemulsin gruesa a travs de un sistema de rotor - estator sellev a cabo en un vaso de precipitados con camisa conectado aun bao de agua a en- asegurarse de que la temperatura semantuvo por encima de los puntos de fusin de la SL . Despusde la homogeneizacin de la pre - emulsin gruesa , que erainmediatamente ms homogeneizada a 1200 bar por 2 ciclos deconmutacin mximas utilizando una Microfluidizer_R M -110S ( MicrofluidicsTM , Newton ,Mass., U.S.A.). It was observed that after 3 homogenization cyclesthe particle sizes and their distributions remain constant. Sampleswere collected in sterile containers and immediately cooled in anice bath shaking gently to facilitate the cooling process untilsamples reached room temperature (20 C). Preparation of SL+O

followed the same procedure except for the incorporation of liquidlipid (sunflower oil), which was combined with the other lipids ofthe disperse phase by mixing while molten. In this case, sunfloweroil formed 10% of the disperse phase. Massachusetts, EE.UU.). Se observ que despus de 3 ciclos dehomogeneizacin de los tamaos de partcula y su distribucin semantienen constantes. Las muestras se recogieron en recipientesestriles e inmediatamente se enfriaron en un bao de hieloagitando suavemente para facilitar el proceso de enfriamiento hastaque las muestras alcanzaron la temperatura ambiente (20 C).Preparacin de SL + O sigui el mismo procedimiento, excepto para la incorporacin de lpido lquido (aceite de girasol), que secombin con los otros lpidos de la fase dispersa, mientras quemediante la mezcla de fundido. En este caso, el aceite de girasolform 10% de la fase dispersa.

Particle size measurements Particle sizes and their distribution were analyzed using static

light scattering (Mastersizer SM 2000, Malvern Instruments,Worcestershire, U.K.). Approximately 3 to 4 drops of sample were placed in the dispersion unit of the o/w cell, which was filled withdeionized water, using a stirrer speed of about 1000 rpm. Size dis-tributions were calculated with the instrument specific softwareapplying the Mie scattering model. This yielded the volume dis-

tribution and Sauter mean diameter (d3,2) of the particles. Eachvalue given in the results corresponds to the average of 3 mea-surements. The refractive index of the disperse phase necessary forthe data analysis was obtained by use of a refractometer (RFM 90,Automatic, Bellingham and Stanley Ltd, Tunbridge Wells, U.K.). Mediciones del tamao de partcula

Tamaos de partculas y su distribucin se analizaron mediantedispersin de luz esttica (SM Mastersizer 2000, MalvernInstruments, Worcestershire, Reino Unido). Aproximadamente 3 a4 gotas de muestra se colocaron en la unidad de la clula o / w, quese llen con agua desionizada dispersin, utilizando una velocidadde agitacin de aproximadamente 1000 rpm. Tamao de lasdistribuciones se calcularon con el software especfico de

instrumento que aplique el modelo de dispersin de Mie. Esto produjo el volumen distribucin y dimetro medio Sauter (d3, 2) delas partculas. Cada valor dado en los resultados corresponde a lamedia de 3 mediciones. El ndice de refraccin de la fase dispersanecesaria para el anlisis de los datos se obtuvo mediante el uso deun refractmetro (RFM 90, Automtico, Bellingham y Stanley Ltd,Tunbridge Wells, Reino Unido).


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Differential scanning calorimetry (DSC) DSC measurements were performed using a Diamond DSC

(Perkin Elmer, Cambridge, U.K.). Samples sizes of 20 to 30 mg forlipid samples and 28 to 40 mg for dispersions were accuratelyweighed into standard aluminium pans. An empty pan was used asreference. To reflect the experimental processes, samples wereheated from room temperature to 100 C, held at this temperaturefor 1 min and cooled to room temperature before reheating to 100 C. The effects of cooling on pure lipids and the correspond-ingdispersions were compared. A heating rate of 10 C/min and acooling rate of 12 C /min were used for all measurements. Each

measurement was performed in triplicate. Calorimetra diferencial de barrido (DSC)Las medidas de DSC se realizaron utilizando un diamante DSC(Perkin Elmer, Cambridge, Reino Unido). Ejemplos de tamaos de20 a 30 mg para las muestras de lpidos, y 28 a 40 mg para lasdispersiones se pesaron con precisin en las cacerolas de aluminioestndar. Un recipiente vaco se utiliza como referencia. Parareflejar los procesos experimentales, las muestras se calentarondesde temperatura ambiente hasta 100 C, se mantuvo a estatemperatura durante 1 min y se enfriaron a temperatura ambienteantes de recalentar a 100 C. Los efectos del enfriam iento sobrelos lpidos puros y correspondien-tes las dispersiones eran encomparacin. Una velocidad de calentamiento de 10 C / min y

una velocidad de enfriamiento de 12 C / min se utilizaron paratodas las mediciones. Cada medicin se realiz por triplicado.

Transmission electron microscopy (TEM) Freeze-fracture. A drop of the emulsions was placed in a top

hat and plunged into liquid nitrogen, cooled to approximately 180 C and fractured in a freeze-fracture unit (Cressington, CFE 50)at 180 C and 106 to 107 mbar. The fractured samples wereshadowed at an angle of 45 with approximately 2-nm thick platinum and 15-nm thick carbon and stabilized by deposition of20-nm pure carbon at 90 for replica production. Replicas werefloated off on water and cleaned, when necessary, with methanol.Samples were viewed with a transmission electron microscope(JEM-1200 EX II, Jeol Ltd, Welwyn, U.K.) operated at 100 kV.

Cryo-thin film. Approximately 20 L of diluted emulsion

were placed on a copper grid with holey carbon film across andthe grid blotted using filter paper for a set time to obtain a thinfilm. The samples were cryofixed by rapidly plunging intoliquid ethane cooled to approximately 180 C in a Gatancryoplunger. The sample was transferred with a cryotransferunit (CT 3500, Oxford Instruments, Oxford, U.K.) into the precooled cryoelec-tron microscope (JEOL JEM-1200 EX II)operated at 100 kV. Samples were viewed under low-electrondose conditions at a pri-mary magnification of 30000 times at aconstant temperature of around 180 C.

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Solid lipid dispersions . . . Storage stability

The storage stability of the dispersions was assessed bystoring at room temperature for up to 4 mo. After this time,measurements of particle size and melting profile were performed. In addition, the samples were assessed visually forevidence of creaming or phase separation.

estabilidad durante el almacenamiento

La estabilidad de almacenamiento de lasdispersiones se evalu mediante elalmacenamiento a temperatura ambiente duranteun mximo de 4 meses. Despus de este tiempo,se realizaron mediciones de tamao de partcula y perfil de fusin. Adems, las muestras seevaluaron visualmente para detectar evidencia deformacin de crema o separacin de fases.

Results and Discussion Particle size distribution of dispersions

All the dispersions were obtained after 2 cycles throughMicrofluidiser _R and rapidly cooled to a temperature of approxi-

mately 20

C. Results obtained by laser light scattering for particlesize distribution of the carrier systems (Figures1 to 3) showed thatthose containing stearic acid seemed to have a narrower distribu-tion than those containing candelilla and carnauba waxes. Also,compared to the waxes, the incorporation of liquid lipid in thedisperse phase (for production of SL+O) seemed to have a greaterimpact on the particle size distribution of stearic acid and resultedin better monodispersity as compared to the particle size distribution of SL. This may be attributed to the morphology of the particles. SLs have been described to be of 2 states: crystalline andamorphous (Small and others1986). Stearic acid, candellila, andcarnauba waxes have a crystalline nature and the incorporation ofoil may have resulted in significant structural changes. Sauter mean

diameters (d3,2) of the dispersions were 140 to 300 nm (Figure4).The incorporation of liquid lipid in the disperse phase for SL+O Resultados y Discusin

Distribucin de tamao de partcula de las dispersiones

Todas las dispersiones se obtuvieron despus de 2 ciclos a travsde Microfluidiser_R y rpidamente se enfriaron a una temperaturade aproxi -madamente 20 C. Los resultados obtenidos pordispersin de luz lser para la distribucin de tamao de partculade los sistemas de soporte ( figuras 1 a 3 ) mostr que los cidoesterico que contiene parecan tener una distribucin ms estrechaque las que contienen ceras de carnauba y candelilla . Adems, en

comparacin con las ceras , la incorporacin de lpido lquido en lafase dispersa ( para la produccin de SL + O ) pareca tener unmayor impacto sobre la distribucin del tamao de partculas decido esterico y dio lugar a una mejor monodispersidad encomparacin con la distribucin del tamao de partcula -bucin deSL. Esto se puede atribuir a la morfologa de las partculas . SL dese han descrito a ser de 2 estados : cristalinos y amorfos ( Pequeoy otros 1986 ) . El cido esterico , candelilla , carnauba y cerastienen un carcter cristalino y la incorporacin de aceite puedehaber dado lugar a importantes cambios estructurales . Dimetromedio Sauter (D3 , 2 ) de las dispersiones haba 140 nm a 300 nm( Figura 4 ) . La incorporacin de lpidos lquido en la fase de SL +O dispersar

d e n s i t y

d i s t r i b u

t i o n 8

7 6

( 1 / m )

5 4

SLN Stearic acid 3 s ear c ac 2

NLC Stearic acid

V o l u m e

SL+O stearic acid 1 0 0.01 0.1 1 10 100 1000 10000

Droplet diameter (m)

Figure 1 Particle size distribution of SL and SL+O stearic acid after2 Microfluidizer _R cycles.Figura 1-distribucin del tamao de partcula deSL y SL O + cido esterico despus de 2 ciclosMicrofluidizer_R.

d e n s

i t y

d i s t r i b u t i o n 5

4

( 1 / m )

3

2 SL candelilla wax

SLN Candelilla wax SL+O cande

V o

l u m e NLC Candeli lillawax

1

0 0.01 0.1 1 10 100 1000 10000


Figure 2 Particle size distribution of SL and SL+O stearic acid after2 Microfluidizer _R cycles.Figura 2-distribucin del tamao de partcula deSL y SL O + cido esterico despus de 2 ciclosMicrofluidizer_R.


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formulations had a minor impact on the Sauter mean diameterof the particles. This observation is in line with the results of astudy conducted by Saupe and others (2005), where particlesize of SL and SL+O were compared. The study reported thatthe inclusion of liquid lipid (oil) in SL+O formulation had aminor impact on the mean particle size. Comparing the resultsof the 3 different lipids used in the dispersions revealed thatstearic acid (Figure4) produced the lowest d3,2 for SL+O(incorporation of liquid lipid in the disperse phase) dispersions.Candelilla wax produced the lowest d3,2 for SL dispersionswhereas carnauba wax produced the highest values for both SL

and SL+O dispersions. This may be due to its higher melting point compared to candelilla wax and stearic acid. f ormulaciones tuvieron un impacto menor en el dimetro medioSauter de las partculas. Esta observacin est en consonanciacon los resultados de un estudio realizado por Saupe y otros(2005), donde se compar el tamao de partcula de SL y SL +O. El estudio inform que la inclusin de grasa lquida (aceite)en la formulacin de SL + O tuvo un impacto menor en eltamao medio de las partculas. Comparando los resultados delos 3 diferentes lpidos utilizados en las dispersiones revelaronque el cido esterico (Figura 4) produjo el d3 ms bajo, 2 paraSL + O (incorporacin de lpido lquido en la fase dispersa)dispersiones. La cera de candelilla produjo el d3 ms bajo, 2 para dispersiones SL mientras que la cera de carnauba produjolos valores ms altos para ambos SL + O y dispersiones SL.Esto puede ser debido a su punto de fusin superior encomparacin con la cera de candelilla y cido esterico.

Storage stability All samples remained physically stable for a period of 3 mo with

the exception of SL+O stearic acid which gelled after a period of 1mo. The gelling is likely to be due to bridging between the particlescaused by recrystallization of stearic acid in the sunflower oil, perhaps leading to crystals that protrude from the droplets. estabilidad durante el almacenamiento

Todas las muestras se mantuvieron fsicamenteestables durante un perodo de 3 meses, con laexcepcin de SL + cido esterico O que segelific despus de un perodo de 1 mes. Lagelificacin es probable que sea debido a puenteentre las partculas causadas por recristalizacinde cido esterico en el aceite de girasol, llevandoquizs a los cristales que sobresalen de las gotitas.

d e n s

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( 1 / m

) 1 SL carnauba wax SLN Carnauba wax SL+O carnauba wax

V o l u m e NLC Carnauba wax

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Figure 3 Particle size distribution of SL and SL + O carnauba wax after R

2 Microfluidizer _ cycles. 350

SL SL+O

300

) 250 3 , 2

( d

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t e r

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Figure 4 Sauter diameter of SL and SL+O formulations of stearicacid, candelilla wax, and carnauba wax. The data are given asdiameter SD (in nanometer).

Figura 4-dimetro Sauter de las formulaciones SLy SL + O de cido esterico, cera de candelilla,cera de carnauba y. Los datos se dan comodimetro SD (en nanmetros).

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Waxes may not recrystallize in the same manner, perhaps becausethey have a lower solubility in sunflower oil. A report by Batte andothers (2007) investigating the phase behavior, stability and me-somorphism of monostearin oil water gels revealed that the for-mation of a white gel mostly depended on the water/monostearinratio and the likelihood of a gel forming was when the ratio was between 2 and 20. For the stearic acid samples, the gel behaviorwas only evident in the SL+O formulation. The ratio of water tostearic acid in this formulation was 20.6. This may imply that forstearic acid the presence of oil may have a contributing factor tothis change in phase behavior as there was no gelling seen in theSL samples. Further studies need to be carried out to investigate thefactors leading to this change in phase behavior exhibited by stearicacid.Las ceras pueden no recristalizar de la misma manera, tal vezdebido a que tienen una solubilidad ms baja en aceite de girasol.Un informe de Batte y otros (2007) investiga el comportamiento defase, la estabilidad y la me-somorphism de geles monoestearina-aceite-agua revel que la for-macin de un gel blanco sobre tododependa de la relacin agua / monoestearina y la probabilidad deun gel de formacin era cuando la proporcin era de entre 2 y 20.Para las muestras de cido esterico, el comportamiento de gel slo

fue evidente en la formulacin SL + O. La relacin de agua a cidoesterico en esta formulacin era 20,6. Esto puede implicar que para el cido esterico la presencia de aceite puede tener un factorque contribuye a este cambio en el comportamiento de fase ya queno haba visto gelificante en las muestras SL. Nuevasinvestigaciones deben llevarse a cabo para investigar los factoresque conducen a este cambio en el comportamiento de fase exhibido por el cido esterico.

In order to ascertain the feasibility of the application of thesedispersions as carrier systems, their thermal stabilities wereinves-tigated. The aim was to ascertain if particle size wouldremain the same if a thermal treatment was applied during theuse of these dispersions in products.

After storage for a period of 3 mo, samples were analyzed byDSC using a heating rate of 10 C/min and a cooling rate of 12 C/min and the particle size of the samples was measured.

Results from the thermal stability of dispersions showed thatsamples were stable for a period of 3 mo. Figure5 shows thatthe particle size and particle size distribution of the samplesremained the same after the heating and cooling process. A fin de determinar la viabilidad de la aplicacin de estasdispersiones como sistemas portadores, sus estabilidades trmicaseran investigaron. El objetivo era determinar si el tamao de partcula seguira siendo el mismo si se aplica un tratamientotrmico durante el uso de estas dispersiones en los productos.

Despus de un almacenamiento durante un perodo de 3 meses, las

muestras fueron analizadas por DSC usando una velocidad decalentamiento de 10 C / min y una velocidad de enfriamiento de12 C / min y el tamao de partcula de las muestras se midi. Los resultados de la estabilidad trmica de las dispersionesmostraron que las muestras eran estables durante un perodo de 3meses. La Figura 5 muestra que el tamao de partcula ydistribucin de tamao de partcula de las muestras se mantuvieronla misma despus de que el proceso de calentamiento yenfriamiento.

DSC investigations of bulk SLs and dispersions Results from DSC curves (Figures6 to 8) indicate that peak

melting and crystallization temperatures for all SL dispersions werelower than the bulk SLs. This may be due to the small particle sizesof the colloidal dispersions, and their high-specific area.

Of the SLs, stearic acid produced the highest enthalpy (202J/g). This is probably due to its highly crystalline naturecompared to the waxes (Small and others1986). In Figures6 to8, peak temperature values indicate that SL+O dispersions crys-

tallized at slightly lower temperatures than SL dispersions withthe exception of stearic acid. The inclusion of liquid lipid in thedisperse phase of stearic acid may have had more influence onits morphology due to its solubility in the oil as compared to thewaxes.

Investigaciones DSC de SLS y dispersiones granel

Los resultados de las curvas de DSC (figuras 6 a 8) indicanque la fusin pico y temperaturas de cristalizacin para todaslas dispersiones SL eran ms bajos que los SL de granel. Esto puede ser debido a los pequeos tamaos de partcula de lasdispersiones coloidales, y su rea de alta especfica.

Del SLS, cido esterico producido la entalpa ms alta (202J / g). Esto es probablemente debido a su naturaleza altamentecristalina en comparacin con las ceras (Pequeo y otros 1986).En las figuras 6 a 8, los valores de pico de temperatura indicanque + O dispersiones SL cristaliz a temperaturas ligeramentems bajas que las dispersiones SL con la excepcin del cidoesterico. La inclusin de lpido lquido en la fase dispersa decido esterico puede haber tenido ms influencia en sumorfologa debido a su solubilidad en el aceite, en comparacincon las ceras.

Melting curves for stearic acid, Figure6A, shows a single melt-ing peak (70 C) for SL dispersion while for the SL+O disper-sions, a 1st major peak was observed (70 C) followed by a 2ndminor peak occurring at approximately 81 C. For the crystalliza-

tion curves (Figure6B), both SL and SL+O dispersions showed 1 Las curvas de fusin para el cido esterico, la Figura 6A, semuestra un nico pico de fusin-cin (70 C) para la dispersinSL mientras que para los SL + O disper-siones, se observ un

pico principal primera (70 C) seguido de un segundo menormxima que se presenta en aproximadamente 81 C. Para lascurvas de cristalizacin-cin (Figura 6B), ambas SL y SL + Odispersiones mostr 1

5.00 4.00

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n ( 1 / m

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Droplet diameter (m) Figure 5 Particle size distribution of SL+O candelilla wax showing the ther-malstability of the sample after undergoing heating and cooling processes.Figura 5-distribucin del tamao de partcula de SL + O cera de candelilla, quemuestra el ther-mal la estabilidad de la muestra despus de someterse aprocesos de calentamiento y enfriamiento.


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prominent peak at 58.7 and 57.4 C, respectively. However, both dispersions exhibited minor peaks at lower temperatures,41 C for SL and 40 C for SL+O. The reason may be due todifferent polymorphs crystallizing or heterogeneous comparedwith homo-geneous nucleation. The single melting peak onheating might suggest the latter explanation in this case.

pico importante en el 58,7 y 57,4 C, respectivamente. Sin embargo,ambas dispersiones exhiben picos menores a temperaturas ms bajas,41 C durante SL y 40 C para SL + O. La razn puede ser debido adiferentes polimorfos cristalizantes o heterognea en comparacin conla nucleacin homognea. El pico de fusin nico de calefaccin podrasugerir la ltima explicacin en este caso.

All DSC thermograms show a normalized curve (W/g). FromFigure 7A, the melting curve for SL dispersion of candelillawax showed a single peak (78.3 C) while that for the SL+Odispersion showed a peak at 65.9 C. Crystallization curvesshowed single peaks for both SL and SL+O dispersions at 43.9and 40.5 C respectively. Enthalpy values for the 1st meltingcurve of all samples were within the expected range with theexception of SL candelilla wax (37.3 J/g), SL+O stearic acid(32.2 J/g), and SL carnauba wax (23.9 J/g) which were higherthan expected. However these values reduced on 2nd melting to7.4 J/g for SL candelilla wax, 10.2 J/g for SL+O stearic acid,and 11.9 J/g for SL carnauba wax. The cause of this highenthalpy during the 1st melting is still unclear.Todos los termogramas de DSC muestran una curvanormalizada (W / g). De la figura 7A, la curva de fusin paraSL dispersin de cera de candelilla mostr un solo pico (78,3 C), mientras que para el SL + O dispersin mostr un pico a65,9 C. Las curvas de cristalizacin mostraron picosindividuales para ambas SL y SL + O dispersiones en 43,9 y40,5 C respe ctivamente. Los valores de entalpa para la primera curva de fusin de todas las muestras estaban dentro delrango esperado, con la excepcin de SL cera de candelilla (37,3J / g), cido esterico + S SL (32,2 J / g), y SL cera de carnauba(23,9 J / g ), que fueron mayores de lo esperado. Sin embargo,estos valores reducidos de segunda fusin a 7,4 J / g para SLcera de candelilla, + cido 10,2 J / g para SL O esterico y 11,9J / g para SL cera de carnauba. La causa de esta alta entalpa

durante la primera fusin todava no est claro.As depicted from Figure8, the 1st melting peak occurred at

84.8 C and there seem to be a minor peak occurring at approximately 90 C. At 70 C, there seem to be some amount of particles in the crystalline state and may not have melted com- pletely. Melting curve for SL+O dispersion showed just 1 major peak at 84.8 C. Crystallization curves for both SL and SL+Odispersions showed prominent single peaks occurring at 51.8and 50.1 C respectively. However there seem to be someminor peaks also occurring. For all samples the onset meltingtemperatures were above 50 C.

Como se muestra en la Figura 8, la primera pico de fusin se produjo a 84,8 C y parece que hay un pico menor se produceen aproximadamente 90 C. A 70 C, parece que hay una ciertacantidad de partculas en el estado cristalino y puede que no sehayan derretido por completo. La curva de fusin de SL + Odispersin mostr slo 1 pico principal a 84,8 C. Las curvasde cristalizacin para ambas SL y SL + O dispersionesmostraron picos individuales destacados que ocurren en el 51,8y 50,1 C respectivamente. Sin embargo parece que hayalgunos picos menores que ocurren tambin. Para todas lasmuestras de las temperaturas de fusin inicio estaban porencimade 50 C.

Mehnert and others (1997) reported that the use of more complex lipids (a mixture of mono-, di-, triacylglycerols of differentchain lengths) has better prospects for higher drug loading. Thisis because spatially different lipids lead to larger distance between the fatty acid chains of the glycerides as well as theimperfections in the crystal, providing more room forincorporation of active compounds (Wissing and others2004).Successful use of such lipids includes Miglyol (mixture of

medium carbon chain liquid oils) and Compritol (Jenning andothers2000; Saupe and others2005).

Mehnert y otros (1997) informaron de que el uso de lpidosms complejos (una mezcla de mono-, di-, triglicridos dediferentes longitudes de cadena) tiene mejores perspectivas demayor carga de frmaco. Esto se debe a espacialmentediferentes lpidos conducen a la mayor distancia entre lascadenas de cidos grasos de los glicridos, as como lasimperfecciones en el cristal, que proporciona ms espacio parala incorporacin de los compuestos activos (Wissing y otros,2004). El uso exitoso de tales lpidos incluye Miglyol (mezclade aceites lquidos cadena carbonada media) y Compritol(Jenning y otros, 2000; Saupe y otros, 2005).

Results of particle size and size distributions, as well as DSCanalysis, reveal some interesting phase behavior of these partic-ulate systems. Melting and crystallization properties of these SL particles are of utmost importance from the technological pointof view. According to Bunjes and others (2007), in an emulsionsystem consisting of submicron particles, the properties of thematrix lipids are altered compared to the bulk material. This is because in an emulsion these lipids may have undergonecrystal-lization and thermal treatment as part of theemulsification pro-cess hence there may be issues of polymorphism or polymorphic transitions.

Resultados de tamao de partcula y distribuciones detamao, as como el anlisis DSC, revelan un comportamientode fase interesante de estos sistemas en partculas. Propiedadesde fusin y la cristalizacin de estas partculas SL son de lamayor importancia desde el punto de vista tecnolgico. Deacuerdo con Bunjes y otros (2007), en un sistema de emulsinque consiste en partculas submicromtricas, las propiedades delos lpidos de la matriz se alteran en comparacin con elmaterial a granel. Esto es porque en una emulsin estos lpidos pueden haber sufrido cristalizacin y tratamiento trmico como parte de la emulsificacin pro-ceso por lo tanto, puede haber problemas de polimorfismo o transiciones polimrficas.

There have been several reports suggesting factors that may beresponsible for the melting and crystallization behavior of lipid

submicron particles. According to Unruh and others (1999), dif-ferences in particle size in lipid submicron particles may result inthese dispersions showing different melting peaks. Mehnert andMader (2001) and Schuchmann (2007) also reported that materialsused in the formulation of these systems have an influence on the behavior of the dispersions. The Sauter mean diameter of disper-sions increased as the melting point of the lipids increased. Thisobservation has been reported by Muller and others (1998) and isin agreement to the general theory of high-pressure homog-enization. Siekmann and Westesen (1992) reported that critical parameters for particle formation are different depending on the Ha habido varios informes de factores que pueden ser responsables para el comportamiento de fusin y cristalizacin de partculassubmicrnicas de lpidos que sugieren. Segn Unruh y otros (1999),las diferencias de tamao de partcula de las partculassubmicrnicas lpidos pueden dar lugar a estas dispersiones quemuestran diferentes picos de fusin. Mehnert y Mader (2001) ySchuchmann (2007) tambin inform de que los materialesutilizados en la formulacin de estos sistemas tienen una influenciaen el comportamiento de las dispersiones. El dimetro medio Sauterde disper-siones aument a medida que el punto de fusin de loslpidos se increment. Esta observacin ha sido reportado porMuller y otros (1998) y est de acuerdo con la teora general dealta presin de homogeneizacin. Siekmann y Westesen (1992)informaron de que los parmetros crticos para la formacin de partculas son diferentes dependiendo de la

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lipid used. These parameters include speed of lipid crystallizationand lipid hydrophilicity (self-emulsifying properties). In this study,this was also observed. Stearic acid, the lowest melting of the 3lipids studied, had the fastest crystallization rate and crystallized athigher temperatures (57.4 and 58.7 C for SL and SL+O respec-tively) compared to candelilla wax (SL: 43.9 C; SL+O: 40.5 C)and carnauba wax (SL: 51.8 C; SL+O: 50.2 C).

According to Small and others (1986), lipids can be classifiedinto 2 categories based on their surface interactions with water.These are nonpolar and polar. Waxes are classified as nonpolarlipids. Candellila and carnauba waxes are principally composed oflong-chain fatty acids esterified to long-chain alcohols. Waxeswhen in contact with water will form a lens of oil on the surface ofthe water. This lens of oil is a separate phase and does not spread

U n s u

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Figure 6 DSC thermograph showing 1stmelting (A); crystallization (B); 2nd melting(C) of stearic acid bulk material (bulk), SL (5% stearic acid) and SL+O (4.5 % stearicacid, 0.5 % sunflower oil). Temperature

range from 25 to 100 C, heating rate 10

C/min; cooling rate 12 C/min.

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lpidos utilizado. Estos parmetros incluyen la velocidad decristalizacin de lpidos y la hidrofilia lpidos (propiedades de auto-emulsionantes). En este estudio, esto tambin se observ. cidoesterico, el punto de fusin ms bajo de los 3 lpidos estudiados,tuvo la velocidad de cristalizacin ms rpida y se cristaliza atemperaturas ms altas (57,4 y 58,7 C para SL y SL + O,respectivamente) en comparacin con la cera de candelilla (SL:43,9 C; SL + O: 40,5 C) y cera de carnauba (SL: 51,8 C, SL +O: 50,2 C).

Segn Small y otros (1986), los lpidos se pueden clasificar en 2categoras en funcin de sus interacciones con la superficie delagua. Estos son no polares y polares. Las ceras se clasifican comolos lpidos no polares. Ceras de carnauba y candelilla est ncompuestos principalmente de cidos grasos de cadena largaesterificados de alcoholes de cadena larga. Ceras al entrar encontacto con agua se forma una lente de aceite en la superficie delagua. Esta lente de aceite es una fase separada y no se extiende.

flujo de calor no sustrado (W / g)

Figura 6 DSC-termgrafo mostrando primero de fusin (A);cristalizacin (B); segunda fusin (C) de material a granel de cidoesterico (a granel), SL (cido esterico 5%) y SL + O (cidoesterico 4,5%, 0,5% aceite de girasol). Rango de temperatura de25 a 100 C, velocidad de calentamiento 10 C / min; velocidad deenfriamiento 12 C / min.


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beyond its limits. However, stearic acid, which is classified as class1: polar lipid (insoluble, nonswelling amphipiles) when in contactwith an aqueous surface will spread and cover the surface to form amonolayer of lipid. This reduces the surface tension of water. This phenomenon is termed the spreading pressure (S ) of oil expressedin mN/m and can be represented by the equation: S= w

m, where w = surface tension of clean air water interface and m = surface tension measured when a monolayer of lipid is in equilibrium with liquid lens of oil. This self-emulsifying property of stearic acid may be responsible for the smaller particle sizes and better monodispersity observed in dispersions produced with stearic acid as compared to the waxes.

U n s u b

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70 60 50 40 30 20 10

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A First Melting Bulk SLN SL+O NLC

Figure 7 DSC thermograph showing 1stmelting (A); crystallization (B); 2nd melting (C) of candelilla wax bulk material (bulk), SL (5 %candelilla wax), and SL+O (4.5 % candelilla wax,0.5 % sunflower oil).Temperature range from 25

to 100 C, heating rate 10

C/min; cooling rate

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Vol. 78, Nr. 7, 2013 Journal of Food Science E1005


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ms all de sus lmites. Sin embargo, el cido esterico, que seclasifica como de clase 1: lpido polar (insolubles, amphipiles nohinchable) cuando est en contacto con una superficie acuosa seextienda y cubrir la superficie de formar una monocapa de lpido. Estoreduce la tensin superficial del agua. Este fenmeno se denomina propagacin de la presin (S) de aceite expresada en mN / m, y puedeser representada por la ecuacin: S = w -

m, donde w = tensin superficial de la interfaz aire-agua limpiay m = tensin superficial mide cuando una monocapa de lpidos esten equilibrio con el lquido de la lente de aceite. Esta propiedadautoemulsionante de cido esterico puede ser responsable de lostamaos de partcula ms pequeos y mejor monodispersidadobservados en dispersiones producidas con cido esterico encomparacin con las ceras.

Figura 7-DSC termgrafo mostrando primero de fusin (A);cristalizacin (B); segunda fusin

(C) de material a granel cera de candelilla (a granel), SL (cera decandelilla 5%), y el SL + O (cera de candelilla 4,5%, aceite de girasol0,5%). Rango de temperatura de 25 a 100 C, velocidad decalentamiento 10 C / min; velocidad de enfriamiento 12 C / min.


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Montenegro and others (2003) have investigated the differences in thecrystallization process in small mini-emulsions as compared to the bulkmaterial revealed that in an emulsion system, heat-ing up samples withcrystallized droplets results in only a slight decrease of melting point ascompared to the bulk material. How-ever, there is usually a greaterdifference between the crystallization temperatures of the bulk materialand the emulsions. This means that dynamic crystallization isinfluenced much more than the melting process. The occurrence ofcrystallization in an emulsion system may be attributed to homogenousnucleation (in the case of a pure system) or heterogeneous nucleation(if added compo-nents are present which behave as nucleating sites).McClements and others (1993) and Kaneko and others (1999)suggested that the reduction in crystallization temperatures may be dueto the distribution of foreign crystallization nuclei responsible for het-

erogeneous nucleation in the bulk material among a largenumber of isolated droplets. This causes a drastic reduction inthe num-ber of heterogeneous nucleation sites in these droplets.Crystal growth is also limited to the dimension of the droplet. Ithas also been reported that triacylglycerol submicron particles prepared by crystallization using high-pressure hot melthomogenization tech-nique would typically crystallize inmetastable -form and have the tendency to transform into thestable -modification upon storage (Bunjes and others2007).

Emulsifiers have also been reported to have an effect on the

crystallization behavior of SL particles by influencing the kinet-icsin polymorphism and the crystallization temperature (Bunjes andothers 2002, 2003). In these studies, hydrophilic, nonionicemulsifiers and tripalmitin were used. Nonionic emulsifiers have been reported to retain less -modification and may result in the

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Figure 8 DSC thermograph showing 1stmelting (A); crystallization (B); 2nd melting(C) of carnauba wax bulk material (bulk), SL(5 % carnauba) and SL+O (4.5 % carnauba,0.5 % sunflower oil). Temperature range

from 25 to 100 C, heating rate 10

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Montenegro y otros (2003) han investigado las diferencias en el proceso de cristalizacin en pequeas mini-emulsiones encomparacin con el material a granel revel que en un sistema deemulsin, de calefac-cin con muestras de hasta cristalizadasgotitas resultados en slo una ligera disminucin del punto defusin como en comparacin con el material a granel. Sin embargo, por lo general hay una mayor diferencia entre las temperaturas decristalizacin del material a granel y las emulsiones. Esto significaque la cristalizacin dinmica est influenciada mucho ms que el proceso de fusin. La aparicin de cristalizacin en un sistema deemulsin puede ser atribuido a la nucleacin homognea (en elcaso de un sistema puro) o nucleacin heterognea (si se aadecompo-nentes estn presentes, que se comportan como sitios denucleacin). McClements y otros (1993) y Kaneko y otros (1999)sugirieron que la reduccin de temperaturas de cristalizacin puedeser debido a la distribucin de ncleos de cristalizacin exteriorresponsable para het-

nucleacin heterogneo en el material a granel entre un grannmero de gotitas aisladas. Esto causa una reduccin drstica en elnmero de sitios de nucleacin heterognea de estas gotitas. Elcrecimiento de cristales tambin se limita a la dimensin de lagotita. Tambin se ha informado de que las partculassubmicrnicas de triacilglicerol preparados por cristalizacinusando homogeneizacin a alta presin de fusin en calientetcnica sera tpicamente cristalizar en forma metaestable -y tienenla tendencia a transformarse en la -modificacin estable durante elalmacenamiento (Bunjes y otros 2007) .

Los emulsionantes tambin se han notificado a tener un efectosobre el comportamiento de cristalizacin de las partculas de SL alinfluir en la Kinet-ICS en polimorfismo y la temperatura decristalizacin (Bunjes y otros 2002, 2003). En estos estudios, seutilizaron hidrfilos, emulsionantes no inicos y tripalmitina.Emulsionantes no inicos se han reportado para retener menos -modificacin y pueden resultar en la

Figura 8-DSC termgrafo mostrando primero de fusin (A);cristalizacin (B); segunda fusin (C) de material a granel cera decarnauba (a granel), SL (5% de carnauba) y SL + O (4,5% decarnauba, aceite de girasol 0,5% ). Rango de temperatura de 25 a100 C, velocidad de calentamiento 10 C / min; velocidad de

enfriamiento 12 C / min.

volumen


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transformation of particles into the more stable -modification.Results from DSC thermographs (Figure6 to 8) show that almostall SL and SL+O samples, showed a peak temperature, which wasabove 65 C. This may be indicative of a transformation into themore stable -modification. However, the exact underlyingmechanisms are still not understood. Further analysis using X-raydiffraction will provide a better understanding on the morphol-ogyof these structures. In this experimental work, sucrose lau-rate (L-1695), which is a nonionic emulsifier, was used. This is ahydrophilic emulsifier with a HLB value of 16 and interfacialtension of 31.6 mN/m. It has a high-monoester concentration,

which forms 80% of its composition. According to a study con-ducted by Yanke and others (2004) on the interfacial properties ofsucrose esters, it was reported that in an emulsion system where thesucrose ester used has a high-monoester concentration, the in-terfacial properties would be dependent on the properties of thesemonoesters. Increase in the concentration of monoester contenttransformacin de partculas en el ms estable - modificacin .Los resultados de los termogramas DSC ( Figura 6 a 8) muestranque casi todas las muestras SL + O y SL , mostraron un pico detemperatura , que estaba por encima de 65 C. Esto puede s erindicativo de una transformacin en la ms estable -modificacin . Sin embargo , los mecanismos subyacentes exactosan no estn comprendidos. Un anlisis ms detallado mediantedifraccin de rayos X proporcionar una mejor comprensin de lamorfologa de estas estructuras. En este trabajo experimental , seutiliz sacarosa ( L - 1695 ) , que es un emulsionante no inico -tasa de Lau , . Este es un emulsionante hidrfilo con un valor deHLB de 16 y la tensin interfacial de 31,6 mN / m . Tiene una altaconcentracin de - monoster , que forma el 80% de sucomposicin . De acuerdo con un estudio con- canalizado porYanke y otros ( 2004 ) sobre las propiedades interfaciales de lossteres de sacarosa , se inform de que en un sistema de emulsinen donde elster de sacarosa utilizada tiene una concentracin altamonoster , las propiedades en - interfacial dependeran en las propiedades de estos monosteres . Aumento de la concentracinde contenido de monoster

increases the ability to lower the interfacial tension of a system.The above evidence shows that, in this study, the emulsifierused may have had a significant influence on the crystallizationtempera-tures. However, the whole phenomenon of the possibleinfluence of emulsifiers on surface heterogeneous nucleation isnot fully understood though there has been a suggestion of anunderlying mechanism, which involves the alignment of thedispersed material owing to the order imposed by the surfactantchains (Dickinson and McClements 1995).aumenta la capacidad de disminuir la tensin interfacial de unsistema. La evidencia anterior muestra que, en este estudio, el

emulsionante usado puede haber tenido una influenciasignificativa en la cristalizacin temperaturas. Sin embargo,todo el fenmeno de la posible influencia de los emulsionantesen la superficie de nucleacin heterognea no se entiendecompletamente, aunque ha habido una sugerencia de unmecanismo subyacente, que implica la alineacin del materialdispersado, debido a la orden impuesto por las cadenas desurfactante (Dickinson y McClements 1995)

Morphological investigations of dispersions Techniques used for investigations of particle morphology

were cryo-thin film and freeze-fracture. However, successfulresults were obtained for only 2 samples: SL+O carnauba waxusing cryo-thin film technique and SL candelilla wax usingfreeze fracture technique (Figure9).

The expected spoon-like shape (submicron spoon) which has been reported by Jores and others (2004) to be characteristic ofSL+O due to the liquid oil droplet sitting on the plate-likecrystal of the SL material was not seen here.

Investigaciones morfolgicas de dispersiones

Las tcnicas utilizadas para la investigacin de la morfologade las partculas eran de pelcula delgada y crio-congelacin-fractura. Sin embargo, se obtuvieron resultados exitosos slo 2muestras: SL + cera carnauba O utilizando la tcnica de pelcula delgada y crio-SL cera de candelilla, utilizando latcnica de fractura por congelacin (Figura 9).

La espera cuchara-como forma (submicron cuchara) que hasido informado por Jores y otros (2004) para presentar lascaractersticas de SL + O debido a la gota de aceite lquido quese sienta en la placa de cristal del material SL no se ve aqu.


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Freeze-fracture TEM Figure 10 shows the different shapes assumed by the

particles. This may be due to the effect of cooling rate and polymorphic transitions. Plate-like shapes may be attributed to

particles in the -modification; larger particles seemed to have aspheroid to irreg-ular form whereas small particles exhibitedmore isometric shape. Circular and virtually unstructured particles seen may be due to the effect of rapid cooling.

La Figura 10 muestra las diferentes formas asumidas por las partculas. Esto puede ser debido al efecto de la velocidad deenfriamiento y las transiciones polimrficas. Formas de placa pueden ser atribuidas a partculas en el-modificacin; partculas ms grandes parecan tener un esferoide de formairreg-ular mientras que las partculas pequeas mostraron forma

ms isomtrica. Partculas circulares y prcticamente noestructurado visto pueden ser debido al efecto de enfriamientorpido.

Figure 9 Cryo-thin film picture of SL+O carnauba wax showing the differ-ent structures. Structures marked (A) are artifacts; (C) indicatesparticles in top view showing a circle structure; (P) indicates particle inside view showing a plate -like structure. Scale bar: 200 nm

Figura 9-Cryo-delgada imagen de pelcula de SL + O cera carnaubamuestra las estructuras diferentes. Estructuras marcados (A) son"artefactos", (C) indica que las partculas en la vista superior que muestrauna estructura de "crculo", (P) indica partcula en vista lateral quemuestra una estructura de "placa". Barra de escala: 200 nm.

Figure 10 Freeze fracture picture of SL candelilla wax showing the differ-ent morphologies of particles. Structures marked (L) are larger particleswith striations; (S) indicates smaller particles with isometric shape and (C) indicate circular unstructured particles. Scale bar: 500 nm.

Figura 10-Freeze foto fractura SL candelilla de cera que muestra lasmorfologas diferentes de partculas. Estructuras marcados (L) son"partculas ms grandes", con estras, (S) indica que "las partculas mspequeas" con forma isomtrica y

(C) indica partculas estructuradas "circulares". Barra de escala: 500 nm.

Conclusions This research work investigated the production of SL carrier

systems using 3 high-melting SLs: stearic acid, candelilla wax, andcarnauba wax. Physical and morphological analysis was carried outto investigate phase changes undergone by these carrier systemsand, hence, predict the feasibility of their potential use as carriersystems. Finally, this work contributed in providing insight aboutthe potential use of the carrier systems in the food and cosmeticindustries, hence, widening the application spectrum.

ConclusionesEn este trabajo se investig la produccin de sistemas portadores

SL con 3 SL de alto punto de fusin: cido esterico, cera decandelilla y cera de carnauba. Anlisis fsico y morfolgico se lleva cabo para investigar los cambios de fase sufridos por estossistemas de portadora y, por lo tanto, predecir la viabilidad de suuso potencial como sistemas de portadora. Finalmente, este trabajocontribuy en proporcionar una visin sobre el uso potencial de lossistemas de portadora en las industrias de alimentos y cosmticos, por lo tanto, ampliar el espectro de aplicacin.Although the Sauter mean diameters (138 d3,2 300) werewithin the desired size range, particle size distributions revealed aminor amount of microparticles present. This was more in formu-lations using carnauba wax than in formulations based on the otherlipids. DSC thermographs revealed possible transitions into ther-modynamically stable forms resulting in high-melting peaks. Thetransition has been attributed to annealing in the colloidal stateresulting in a stable crystal modification. Incorporation of liquidlipid in the disperse phase did not seem to retard crystallinity ashigh-melting peaks were also observed for SL+O formula-tions.Underlying principles responsible for high-enthalpy valuesobtained for 1st melting peaks of SL candelilla wax and SL+Ostearic acid are still unclear and further investigations are required. Nuclear magnetic resonance, X-ray diffraction, and synchrontronradiation X-ray diffraction are options to investigate the true poly-morphic behavior of these dispersions. Light scattering techniquesmay be used in conjunction with laser diffraction to obtain a clearer picture of particle size and size distributions. Observations made inthis study confirm reports about high crystallinity when pure waxesor fatty acidstriacylglycerols are used. However, natural waxessuch as carnauba and candelilla and fatty acids like stearic acidhave proved to be useful and are difficult to replace. Further studiesshould be conducted to ascertain if the melting point and polymorphic properties of these waxes can be improved bymixing with other lower melting natural waxes or oils.

Aunque el dimetro medio Sauter ( 138 d3 , 2 300 ) estabandentro del intervalo de tamao deseado , las distribuciones detamao de partcula revelaron una menor cantidad demicropartculas presentes . Esto era ms de formulaciones con cerade carnauba que en formulaciones a base de los otros lpidos .Termgrafos DSC revelaron posibles transiciones hacia formasestables hemodinmicamente ter- resultando en picos de alto puntode fusin . La transicin se ha atribuido a recocido en el estadocoloidal que resulta en una modificacin cristalina estable . Laincorporacin de lpido lquido en la fase dispersa no pareciretardar cristalinidad como tambin se observaron picos de alto punto de fusin para SL + frmula O -ciones . Principiossubyacentes responsables de los valores de alta entalpa obtenidos

por primera picos de fusin de la cera de candelilla, SL y SL O +cido esterico an no estn claros , y se necesitan msinvestigaciones. Resonancia magntica nuclear , la difraccin derayos X y la radiacin synchrontron difraccin de rayos X sonopciones para investigar el verdadero comportamiento de poli-mrfica de estas dispersiones . Tcnicas de dispersin de luz pueden ser utilizados en conjuncin con difraccin lser paraobtener una imagen ms clara de tamao de partcula ydistribuciones de tamao . Las observaciones realizadas en esteestudio confirman los informes sobre la alta cristalinidad cuando seutilizan ceras puras o acidstriacylglycerols grasos . Sin embargo ,las ceras naturales tales como cera de carnauba y candelilla ycidos grasos como el cido esterico han demostrado ser tiles yson difciles de sustituir . Los estudios adicionales deben llevarse acabo para determinar si el punto de fusin y propiedades polimrficas de estas ceras se pueden mejorar mediante la mezclacon otros de fusin ceras o aceites naturales ms bajas .


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