Polyelectrolyte microcapsules built on CaCO3 scaffolds for the integration, encapsulation, and controlled release of copigmented anthocyanins
Introduction
Anthocyanins are intriguing natural compounds that are responsible for red to purple colors in many plant tissues (Lee et al., 2015). The nutraceutical and health benefits of anthocyanins in humans and animals have attracted great interests in academic and industrial research. Unfortunately, anthocyanin is highly unstable against chemical and environmental factors including pH (Ibrahim et al., 2011, Jenshi et al., 2011), temperature (Ekici et al., 2014, Jenshi et al., 2011, Stiles et al., 2007), metal ions (Sigurdson, Robbins, Collins, & Giusti, 2016), oxygen (Kalt and Lawand, 2003, Nagata et al., 2003), light (Zhao & Yu, 2010) and enzymes (Oren-Shamir, 2009), and, therefore, stabilization efforts are required to enable their utilization as nutraceuticals and food colorants.
Enhancement of anthocyanin stability has previously been demonstrated through a range of copigmentation (Trouillas et al., 2016) and encapsulation (Cortez et al., 2017, Jafari et al., 2016, Mahdavee Khazaei et al., 2014, Zaidel et al., 2014) based strategies. Copigments, like biopolymers, phenolic compounds, and metal ions can form molecular complexes with anthocyanins through various chemical interactions, including electrostatic, hydrophobic interaction, van der Waals, and hydrogen bonding interactions. The complexation can promote a shift of the flavylium cation structure in anthocyanin and confer longer stability. Encapsulation also shows potential for extending anthocyanin stability by providing a physicochemical barrier against negative environments (Akhavan Mahdavi et al., 2016, Mahdavi et al., 2014). Nevertheless, the preservation of anthocyanin for any single approach is still limited. For example, the pigmentated complex could dissociate with exposure to relatively high temperature or solvent (Boulton, 2001). Encapsulation techniques which utilize organic solvent or high energies during manufacturing process can often result in the leakage or degradation of anthocyanin, and additional challenges exists with respect to low loading and encapsulation efficiency for water-soluble substances.
Polyelectrolyte microcapsules have been recently suggested as promising delivery systems for the encapsulation of bioactive compounds, which are generally prepared by sequential deposition of opposite charged polyelectrolytes onto a molecular scaffold in a “layer-layer” (LBL) fashion (Anandhakumar et al., 2011, Grigoriev et al., 2008, Parakhonskiy et al., 2014). The unique advantages of LBL microcapsules is the easy control of the size, charge, shape and permeability of the capsules by the choice of polyelectrolyte species and number of deposited layers. After the removal of the molecular scaffold, the “hollow” microcapsules are derived. The capsule interiors can entrap small molecules (Peng, Zhao, & Gao, 2010), biomacromolecules (Balabushevitch et al., 2001, Tripathy and Raichur, 2013), and even nanoparticles (Gil, del Mercato, del Pino, Muñoz-Javier, & Parak, 2008). In particular, such hollow structures have large internal volumes, and display high potential for high loading and encapsulation of hydrophilic compounds.
Depending on the loading compounds, one has to select the sacrificial core scaffold properly, because the core removal occurring under extreme conditions could affect the stability and biological activity of loaded compounds. A range of templates including melamine formaldehyde (Liu et al., 2006), polystyrene (Johnston, Cortez, Angelatos, & Caruso, 2006), SiO2 (Wang, Angelatos, & Caruso, 2008) and carbonate particles (Ariga et al., 2011, He et al., 2009) can be used. Among them, CaCO3 can be decomposed by acidic pH which could help the preservation of anthocyanin because anthocyanin is very stable in acidic environments. Furthermore, owing to the nanoporous structure, CaCO3 particles can entrap high loadings of hydrophilic compounds like proteins and pigments regardless of their charged properties (De Temmerman, Demeester, De Vos, & De Smedt, 2011).
In this study, multi-strategy approach for anthocyanin stability by a combination of copigmentation and encapsulation techniques was developed. The strategy is centered on building all-polysaccharide based polyelectrolyte microcapsules using templated CaCO3 particles as porous scaffolds where the pigmentated complex is preloaded. The loading capacity of polyelectrolyte microcapsules to the water-soluble anthocyanin is a key issue in this study, and is addressed through use of negatively charged chondroitin sulfate (CHS) was applied to the complexes with different concentrations of anthocyanin. CHS, an acidic mucopolysaccharide with many sulfate and N-acetyl residues is a potential candidate to help the intermolecular stacking of anthocyanins (Jeong and Na, 2012, Tan et al., 2017). The copigmentation with CHS not only increased the intermolecular stacking of anthocyanin but also provide motive force for the adsorption of positive anthocyanin to the positive CaCO3. Additionally, we monitored the deposition of polyelectrolytes, i.e. CHS and chitosan (CS), upon CaCO3 surface and the following core removal by electrolyte mobility and morphological change. The influence of CHS copigmentation on the anthocyanin retaining ability of the microcapsules during the preparation process and storage were investigated.
Section snippets
Materials
Chitosan (CS) with a molecular weight range of 190,000–310,000 Da, 75–85% degree of deacetylation, and viscosity potential of 200–800 cP was purchased from sigma-Aldrich (ref 448877). Chondroitin sulfate (CHS) type A from bovine trachea cartilage (Mw = 5–10 KDa) was purchased from Bulk Supplements (Henderson, NV, US). The anthocyanin source used for all studies herein was 6:1 elderberry extract obtained from Bulk Supplements. This extract was measured to contained approximately 4.5% (w/w)
Formation of CHS/anthocyanin complexes
Polysaccharides have often been demonstrated as copigments for the stabilization of anthocyanin and can form molecular complexes with anthocyanin, preventing and maintaining the structure of the flavylium cation (Cortez et al., 2017). Furthermore, binding anthocyanin with a negatively charged polysaccharide could improve the attractive forces between positively charged anthocyanin and CaCO3 particles. In this context, we investigated the formation of complex between CHS and anthocyanin versus
Conclusions
We demonstrated the feasibility of the combination of copigmentation technique and LBL polyelectrolyte microcapsules for encapsulating high amounts of water-soluble compounds, like anthocyanins. We found that the preloading of CHS/anthocyanin copigmented complexes significantly increased the anthocyanin entrapping and loading ability in CaCO3 at a moderate concentrate range of anthocyanin. Additionally, after complexation with CHS, much smaller amounts of anthocyanin were leaked out during CaCO3
Conflict of interest
The authors have declared no conflict of interest.
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