Lipid Insights Encapsulation of Polyunsaturated Fatty Acid Esters with Solid Lipid Particles

Lipid Insights OPEN ACCESS Full open access to this and thousands of other papers at SHORT REPORT http://www.la-press.com. Encapsulation of Polyunsaturated Fatty Acid Esters with Solid Lipid Particles Ronald Holser Russell Research Center, Agricultural Research Service, United States Department of Agriculture, Athens, Georgia, USA. Corresponding author email: [email protected] Abstract: Encapsulation of structurally sensitive compounds within a solid lipid matrix provides a barrier to prooxidant compounds and effectively limits the extent of oxidative degradation. This offers a simple approach to preserve the bioactivity of labile structures. The technology was developed for cosmetic and pharmaceutical products but may be applied to additives used in food and feed formulations. The encapsulation of docosahexaenoic acid (DHA) and α-linolenic acid (ALA) was examined as model compounds of current interest in functional foods and feeds. Solid lipid particles were prepared from triglycerides containing saturated and unsaturated fatty acids and evaluated by differential scanning calorimetry. The thermal characteristics of the lipids used to form the particle were related to molecular structure and could be adjusted by selection of the appropriate component fatty acids. Encapsulation by solid lipid particles provides a method to inhibit oxidation and improve shelf life of products formulated with DHA and ALA. Keywords: calorimetry, docosahexaenoic acid, linolenic acid, nanoparticles, oxidative stability Lipid Insights 2012:5 1–5 doi: 10.4137/LPI.S7901 This article is available from http://www.la-press.com. © the author(s), publisher and licensee Libertas Academica Ltd. This is an open access article. Unrestricted non-commercial use is permitted provided the original work is properly cited. Lipid Insights 2012:5 1 Holser Introduction This report describes how lipid particles were prepared The health benefits associated with the polyunsatu- from binary mixtures of saturated and unsaturated trig- rated acids such as α-linolenic acid (ALA) and doco- lycerides and used to encapsulate omega 3 fatty acid sahexaenoic acid (DHA) have generated interest in esters. Thermal properties of the lipid particles were formulating foods and dietary supplements with these characterized by differential scanning calorimetry. The compounds. However, the highly unsaturated structure physical stability of the particles was examined by par- of these compounds is prone to oxidation and loss of ticle size analysis and the chemical stability of encapsu- bioactivity. Encapsulation techniques can inhibit deg- lated material was monitored by infrared spectroscopy radation and preserve the quality of products formu- while heating to induce degradation. lated with these compounds.1,2 The capsule or coating acts as a barrier to prevent reaction of the encapsulated Materials and Methods compound. The capsule may also be designed with Preparation additional chemical functionality that provides bind- Lipid standards used in this investigation were at least ing sites for cellular recognition, response to changes 99% pure and included docohexaenoic acid methyl in pH conditions, or additional protective groups.3,4 ester, linolenic acid methyl ester, palmitic acid methyl Solid lipid particles consist of a solid lipid matrix ester, stearic acid methyl ester, trimyristin, triolein, tri- with the bioactive component dispersed throughout palmitin, and tristearin (Nu-Check Prep, Inc., Elysian, the solid phase. There are a variety of techniques used MN USA). Tween 80 (Fisher Scientific, Fair Lawn, NJ, to manufacture these materials including high pres- USA) was used as the surfactant. Encapsulated materi- sure homogenization and solvent diffusion.5–9 The als were prepared by heating a mixture of the selected first method requires more mechanical energy input lipids together and generating the corresponding oil-in- than the second method but does not depend on the water emulsion. A typical experiment combined 50 mg use of an organic solvent which can be a limitation tripalmitin and 50 mg tristearin with 10 mg doco- for certain products or markets. Solid lipid particles hexaenoic acid methyl ester. The lipids were heated at found initial applications for the delivery of thera- 75 °C for 2 minutes. A 4 mL volume of aqueous Tween peutic agents and represented an alternative to the 80 (0.5 wt%) was quickly added to the melted lipids use of liposomes for the encapsulation of bioactives. and homogenized for 90 seconds at 20 K RPM with a Pharmaceutical applications for solid lipid particles tissue homogenizer (Omni, Waterbury, CT, USA). This include oral, parenteral, and topical drug delivery.7,10–18 emulsion was further processed by a laboratory micro- Advantages include improved bioavailability, con- fluidizer (Microfluidics, Newton, MA, USA). trolled release, and stabilization. Limitations include drug loading capacity and reports of drug expulsion Characterization during storage. However, these properties are related Particle size distributions were measured with a to compatibility between the solid lipid matrix and Nicomp model 380 ZLS particle size system (Nicomp the bioactive compound which can be controlled by PSS, Santa Barbara, CA, USA). Measurements were careful selection of the lipid matrix. taken at 23 °C using a 635 nm source and a scatter- The current study is motivated by the development ing angle of 90°. Samples were prepared for measure- of solid lipid particles for food and feed applications. ment by dilution in deionized water. Calorimetry data The primary benefit expected from the use of these were collected with a TA Instruments model Q20 dif- materials is the increased stability of the encapsulated ferential scanning calorimeter (TA Instruments, New compound leading to extended shelf life of formulated Castle, DE, USA). The instrument was calibrated with products. The selection of triglycerides for such appli- an Indium standard. Aluminium sample pans were cation is determined by melting point range which may used and samples were scanned at 5 °C/min over the be adjusted by blending the appropriate structures to temperature range of 25 °C to 90 °C. provide the desired property for the specific application. Oxidative Stability Degradation of encapsulated A secondary benefit can be realized in terms of sensory DHA was monitored by mid infrared (MIR) spectros- properties where adverse flavour attributes of the encap- copy using attenuated total reflectance (ATR). Spectra sulated compound may be masked by the lipid matrix. were collected with a Tensor 27 FT-IR system (Bruker 2 Lipid Insights 2012:5 Encapsulation of polyunsaturated fatty acid esters Optics, Billerica, MA) equipped with a Model 300 lowered approximately 5 °C by blending a saturated lipid Golden Gate diamond ATR and temperature control- with the unsaturated lipid triolein. The melting point of ler (Specac, Ltd., London, England). A sample was the lipid matrix used for encapsulation may be changed placed on the ATR crystal and heated from 25 °C in a predictable manner through selection of the appro- to 120 °C at 5 C°/min while spectra were collected priate mixture of lipid components. The performance of at 5 minute intervals. Samples were scanned over the lipid particle used to form the matrix can be related the range 4000–600 cm−1 at a resolution of 4 cm−1. The to structure and readily described in terms of melting spectrum was the result of 128 co-added scans. The point. This offers a simple approach for product devel- instrument was controlled by OPUS v 5.0 software opers or formulators to exploit the melting properties of and spectra were processed using Grams/AI v 8.0 solid fats and vegetable oil blends. (Thermo Fisher Corp., Waltham, MA, USA). The influence of triglyceride structure on melting point is clearly demonstrated in Figure 2 which shows Results and Discussion the variation in melting point for blends of tristearin and Lipid particles generated from fluidized mixtures soybean oil.19 Modification of tristearin by the intro- of saturated lipids such as tripalmitin and tristearin duction of an unsaturated fatty acid ester at the second or trimyristin and tripalmitin exhibited unimodal carbon of glycerol reduces the melting points for all particle size distributions with mean diameters of blend ratios. As the degree of unsaturation is increased 277.6 ± 15.6 nm or 270.2 ± 13.8 nm, respectively. from one double bond in oleic to three in linolenic the Particles prepared from mixtures of saturated and unsat- melting point is further reduced. Comparable results are urated lipids such as tripalmitin and triolein exhibited observed with tripalmitin (Fig. 3) but over a lower tem- slightly smaller mean diameters of 220.1 ± 13.1 nm. perature range.20 Such structured triglycerides are typi- The particle size distributions were unchanged over cally prepared in small quantities for research purposes 6 months storage at ambient conditions which dem- and are not economical for low cost applications.21 onstrates the physical stability of the lipid particles. However, commodity oils such as coconut and palm Thermal properties of these lipid particles were that contain a high level of saturation and offer measured by differential scanning calorimetry. Figure 1 similar opportunities to control the melting point of compares results obtained for lipid particles prepared mixtures. Figure 4 presents results obtained for blends from binary mixtures of the triglycerides. The melt- of these oils with soybean oil. These curves provide ing points of the individual components measured guidance for product design and development. The use 59.6 °C, 68.0 °C, and 74.5 °C for tristearin, tripalmitin, of commercially available edible oils will facilitate the and trimyristin, respectively. The melting points of the adoption of this technology and avoid potential delays solid lipid particles prepared from binary mixtures were associated with the regulatory process. 80 0 70 −5 60 SSS 50 SOS SLS −10 SLnS 40 Temperature (°C) 30 Heat flow (W/g) −15 Trimyristin/Triolein Tripalmitin/Triolein 20 Tristearin/Triolein 10 −20 0 20 40 60 80 100 20 30 40 50 60 70 80 90 Blend (wt%) Temperature (°C) Figure 2.

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