Encapsulation of flavonoid in multiple emulsion using spinning disc reactor technology
Graphical abstract
Highlights
► Encapsulation of flavonoid in multiple emulsion using spinning disc reactor (SDR). ► SDR is capable of producing stable multiple emulsion with mono-disperse droplets. ► Flavonoid can be encapsulated in multiple emulsion with high degree of retention. ► SDR offers cost effective and energy saving process for making multiple emulsion.
Introduction
Multiple emulsions have a number of potential benefits over the conventional oil-in-water (O/W) emulsions for certain applications such as reducing fat content (Gaonkar, 1994; Lobato-Calleros, Rodriguez, Sandoval-Castilla, Vernon-Carter, & Alvarez-Ramirez, 2006) or encapsulation of the functional food components (Benichou, Aserin, & Garti, 2004) and active molecules (Kanouni, Rosano, & Naouli, 2002; Laugel, Chaminade, Baillet, Seiller, & Ferrier, 1996; Tokimitsu, Kobayashi, Uzu, & Arisawa, 1990) in the inner aqueous phase. Thus, multiple emulsions have potential as micro carriers of hydrophilic or lipophilic ingredients entrapped in their internal droplets which are subsequently released. Encapsulation within the inner emulsion can allow the masking of odour or taste and protection against oxidation by light or enzymatic degradation, to prolong shelf-life. Controlled release of the active ingredients can be produced by dilution, shear, or other agitation (Kanouni et al., 2002; Muschiolik, 2007).
Generally, multiple emulsions are prepared by a two stage emulsification process: firstly, a simple W/O emulsion is made using a low HLB (hydrophilic-lipophilic balance) emulsifier under intense homogenization conditions. In the second stage, the primary water-in-oil (W/O) emulsion is dispersed in an aqueous phase containing high HLB emulsifier under lower shear conditions, preventing rupture of the internal droplets as far as possible, to produce a W/O/W multiple emulsion (Pal, 2008).
The loss of the internal phase due to the excessive shear stress during the production of the secondary emulsion is a major problem and much research has been carried out to try to overcome this difficulty (Liu, Ma, Meng, & Su, 2005). The release rate of the internal droplets is directly proportional to the applied shear stress and only moderate shear can be applied in order to produce multiple emulsions that retain a significantly high percentage of the internal phase (Van der Graaf, Schroen, & Boom, 2005).
Hence it is desirable to use low shear device to prevent expulsion of the internal droplets to the external continuous phase in order to produce highly stable multiple emulsions (Pal, 2008). However, low-shear conditions cannot be used with most conventional emulsification equipment without yielding droplets that are unacceptably large or have an unacceptably wide droplet distribution, which eventually leads to unstable products (Van der Graaf et al., 2005).
In the recent years, there has been growing interest in the role of flavonoids in maintaining human health. Flavonoids have become a regular part of the human diet (Havsteen, 1983; Pierpoint, 1986) and are of importance as antiscorbutic (anti-scurvy) agents added to food (Roger, 1988).
Rutin (quercetin-3-rutinoside) is one of the primary flavonoids in a number of plants (Kim et al., 2005) such as buckwheat. It has numerous biological activities which are beneficial to human health such as antioxidant effect (Gao, Xu, & Chen, 2003; Kozlov, Ostrachovitch & Afanas, 1994), protective effect against hepatotoxicity (Janbaz, Saeed, & Gilani, 2002), and anti-inflammatory effect (Cruz et al., 1998; Guardia, Rotelli, Juarez, & Pelzer, 2001). Reynolds (1996), pp. 1679–1680 suggested that rutin can be used to improve capillary function by reducing abnormal leakage and it has been administered to reduce capillary impairment and venous insufficiency of the lower limb. However, the solubility of rutin and many other flavonoids in water (or oil) is low (Luo et al., 2011; Luo et al., 2012).
The only group of flavonoids that has reasonable solubility in water is the anthocyanins. Anthocyanins have a high potential for use as natural colourants due to their attractive orange, red, purple, and blue colours. However, they can be quite unstable chemically (Fennema, 2008) depending on the flavonoid concentration, pH, temperature, light intensity, the presence of metallic ions, enzymes, oxygen, ascorbic acid, sugars and their degradation products and sulphur dioxide, among others (Cevallos, Bolyvar, & Cisneros-Zevallos, 2004). The colour stability is generally more stable at low pH, e.g., pH 2 (Selim, Khalil, Abdel-Bary & Azein, 2008).
Anthocyanins are also good natural antioxidants which may provide an array of health promoting benefits (Tsuda, Kato, & Osawa, 2000). Almajano, Carbo, Jimenez, and Gordon (2008) reported that W/O emulsions containing tea extracts have shown strong antioxidant activity against oil oxidation. However, anthocyanins have received less attention than other flavonoids; despite their widespread occurrence, possibly due to their instability. Multiple emulsions are a way of possibly protecting anthocyanins in foods.
Extracts of Hibiscus sabdariffa are known to contain a significantly high amount of anthocyanins and have been reported to decrease blood pressure (Haji Faraji & Haji Tarkhani, 1999; Onyenekwe, Ajani, Ameli & Garnamel, 1999) and have anti-tumour, immune-modulating and anti-leukaemic effects (Muller & Franz, 1992; Tseng et al., 2000). Wang et al. (2000) have reported protective effects against oxidative stress in rats.
In previous work (Akhtar & Dickinson, 2000) water-in-oil-in-water multiple emulsions were prepared via a two stage emulsification process using a jet homogeniser alone. The jet homogenisation produced multiple emulsions with a wide range of droplet sizes (0.5–16 μm), a highly poly dispersed system which had lower encapsulation efficiency (40–60%) due to high shear mixing. The aims of this study were to test the advantages of combining SDR technology with a jet homogenizer for producing multiple emulsions for effective encapsulation and protection of some of these flavonoids. The jet homogenizer is capable of reproducibly fine aqueous (or oil) droplets of a narrow size distribution, whilst the SDR can provide very controllable and low shear conditions for producing the secondary emulsion. The SDR equipment used for processing multiple emulsions is shown elsewhere (Akhtar, Blakemore, Clayton, & Knapper, 2009). The SDR is essentially a 20 cm diameter rotating disc heated up to 250 °C with a speed range of 200–3000 rpm. In the SDR, the emulsion phases are fed into the centre of the disc and the centrifugal force drives the emulsion phases towards the edge of the disc as a thin film. When the film breaks at the edge of the disc, it creates uniform emulsion droplets with a narrow droplet size distribution. The multiple emulsions formed were characterized and tested for their stability via particle size analysis, creaming, confocal microscopy and spectrophotometry.
Section snippets
Materials
The low HLB lipophilic polymeric emulsifiers Arlacel P135 (polyethylene-30 dipolyhydroxystearate), HLB = 4–5, and Cithrol PG3PR (polyglycerol-3 polyricinoleate), HLB = 2–2, were purchased from ICI (Middlesbrough, England) and Croda (Hull, England), respectively. The high HLB hydrophilic emulsifiers, Brij 78 (polyoxyethylene (20) stearyl ether), HLB = 15.3, and Synperonic PE/F127, HLB = 16, were purchased from Croda Ltd (Hull, England). A pH 7 buffer was prepared from sodium dihydrogen
Particle-size distribution of emulsions with and without flavonoids
The particle-size distributions of the primary 20 vol% W/O emulsions stabilised by 1.6 wt% polymeric emulsifier with and without rutin are shown in Fig. 2. Both the primary emulsions showed very similar monomodal distributions with z-average of 128 nm and polydispersity index of 0.034. Thus, including 90 μM rutin in the aqueous phase did not change the water droplet size significantly. The particle-size distributions of the W/O/W multiple emulsion with and without rutin are compared in Fig. 3.
Conclusions
The SDR technology is capable of producing moderately mono-disperse and stable multiple emulsions as a result of the relatively gentle continuous emulsification processing that can be applied. Using this technology, it has been shown that rutin and Rosella extract flavonoids can be successfully encapsulated within multiple emulsions with a high degree of retention and protection. Thus, using these methods, other flavonoids or nutrients could be encapsulated in order to enhance their
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