Elsevier

Industrial Crops and Products

Volume 46, April 2013, Pages 138-146
Industrial Crops and Products

Microencapsulation of gallic acid in chitosan, β-cyclodextrin and xanthan

https://doi.org/10.1016/j.indcrop.2012.12.053Get rights and content

Abstract

The microencapsulation of gallic acid (GA) with chitosan (C), β-cyclodextrin (β-CDS) or xanthan (X) was prepared by the lyophilization method. The encapsulation was verified by Fourier transform infrared spectroscopy, UV–visible spectroscopy, scanning electron microscopy, differential scanning calorimetry and thermogravimetric analysis. Both the encapsulation efficiency and the antioxidative activity were evaluated. According to our results, the gallic acid was encapsulated by lyophilization in matrices of chitosan, β-cyclodextrin and xanthan. The encapsulated gallic acid showed no loss of antioxidant capacity and different characteristics from the pure gallic acid confirming the techniques used. With the chitosan matrix, a higher encapsulation efficiency, and capsules with characteristic shape were obtained.

Highlights

► The gallic acid was encapsulated by lyophilization method in matrices of chitosan, β-cyclodextrin and xanthan. ► With the chitosan matrix, a higher encapsulation efficiency, and capsules with characteristic shape were obtained. ► Encapsulated GA retained antioxidant capacity.

Introduction

Gallic acid (3,4,5-trihydroxybenzoic acid, GA) is a hydroxybenzoic acid biosynthesized from precursors of the shikimate pathway by the enzyme dihydroshikimate. It is found in great abundance in the plant kingdom, especially in berries, citrus fruits, cereals, tea, wine and herbs. GA occurs naturally both in the free form and as an ester or salt. The salt form is called gallate and is part of the ellagitannins structure, which is a constituent of the hydrolysable tannins (de la Rosa et al., 2010).

Gallic acid has several biochemical properties, as antioxidant (Jung et al., 2010), an antimicrobial agent (Chanwitheesuk et al., 2007), and an antihyperglycaemic agent (Punithavathi et al., 2011); it also prevents oxidative stress (Pal et al., 2010) and some kinds of cancer (Ho et al., 2010). GA retains these properties even at low amount (between 5 and 20 mg), but it is unstable at extreme temperatures or in the presence of oxygen or light, conditions which are common in food processing and storage (Jacques et al., 2010, Yang et al., 2007). Microencapsulation may maintain the bioactivity of this compound. However, the degree of protection provided by microencapsulation is determined by the choice of encapsulation method (Gouin, 2004). Lyophilization is the most efficient technique to protect GA against chemical decomposition because the low processing temperature and reduced moisture reduce the loss of bioactivity better than other methods, such as coprecipitation, neutralization, atomization and solvent evaporation (Yamada et al., 2000). Microencapsulation by lyophilization protects the compound in a polymer matrix, maintaining its bioactivity and controlling its release (Pothakamury and Barbosa-Gnovas, 1995). The composition of the coating material is a major determinant of both the capsule's functional properties and how it can be used to improve the performance of a particular active compound (Desai and Park, 2005).

Biopolymers such as chitosan have been used in previous studies to encapsulate phenolic extracts obtained from natural sources (Belščak-Cvitanović et al., 2011, Deladino et al., 2008). Chitosan is a biodegradable polymer obtained from the partial deacetylation of chitin. It has a linear structure of N-acetyl-d-glucosamine with polar groups, such as OH and NH2, which can act as electron donors (Shahidi et al., 1999). This polymer has great potential for applications in the pharmaceutical industry as a lipophilic encapsulation for drugs (Ribeiro et al., 1999) and in the food industry as an encapsulation for probiotics and prebiotics (Chávarri et al., 2010), aromatic compounds (Higuera-Ciapara et al., 2003), enzymes (Anjani et al., 2007) and antioxidants (Deladino et al., 2008, Weerakody et al., 2008).

Cyclodextrin (CDS) has been used in previous studies to microencapsulate pure phenolic compounds, such as quercetin (Pralhad and Rajendrakumar, 2004), kaempferol (Mercader-Ros et al., 2010), naringin (Sansone et al., 2011) and ferulic acid (Wang et al., 2011b). However, there are no studies of the microencapsulation of gallic acid with cyclodextrin. CDS consists of cyclic oligomers of α-d-glucose linked by glycosidic bonds. It is produced during starch metabolizing by certain bacteria, such as Bacillus macerans (Szente and Szejtli, 2004). The most common types of CDS are α, β and γ, which consist of six, seven and eight glucose units, respectively. Purification of the α and γ forms greatly increases the cost of production; therefore, the β-CDS is most widely used in commercial settings. Cyclodextrins are commonly used to protect the flavors and aromas of food (Yuliani et al., 2006) as well as vitamins (Gonnet et al., 2010, Nevado et al., 2000), antioxidants (Wang et al., 2011a, Wang et al., 2011b) and fat-soluble pigments (Blanch et al., 2007) because they form inclusion complex. In aqueous solution, the apolar cyclodextrin cavity is occupied by water molecules, which are not energetically favorable and are readily replaced by “guest molecules” that are less polar than water (Astray et al., 2009). The inclusion of polyphenols in β-CDS has the advantage of improving water solubility, especially for less soluble phytochemicals (Wang et al., 2011b).

Xanthan is an extracellular polysaccharide produced by Xanthomonas bacteria. It is chemically composed by glucose, mannose, and glucuronic, pyruvic and acetic acids. Xanthan is used in many products as a thickening (Sopade et al., 2008) or stabilizing agent (García-Ochoa et al., 2000). Xanthan has been used as an encapsulant for aromatic compounds (Secouard et al., 2007), drugs (Talukdar et al., 1998) and microorganisms (Papagiannis and Anastasiadis, 2009). However, there are no reports of encapsulating phenolic compounds with xanthan.

This study aimed to encapsulate gallic acid in chitosan, β-cyclodextrin and xanthan matrices by lyophilization, to investigate the encapsulation efficiencies and to measure antioxidant capacities of the encapsulated gallic acid. The encapsulation was evaluated by Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy (UV–vis), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

Section snippets

Materials

Molecular weight chitosan medium (C) (Sigma–Aldrich), β-cyclodextrin hydrate (β-CDS) (Sigma–Aldrich), xanthan (X) (Sigma–Aldrich), gallic acid (GA) (Fluka) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) (Sigma–Aldrich) were used in this work. All other chemicals and solvents were high performance liquid chromatography (HPLC) grade.

Microencapsulation of GA with C, β-CDS and X

The complexes were prepared in the presence of GA and C, GA and β-CDS, GA and X, according to the lyophilization methods described by Pralhad and Rajendrakumar (2004) and

Efficiency of encapsulation

Encapsulation efficiency results and antioxidant activity of encapsulated GA/C, GA/β-CDS and GA/X are shown in Table 1.The encapsulation of GA in the matrix C presented the highest values of encapsulation efficiency, being statistically different from β-CDS and X matrixes.

Gallic acid has low solubility in water (Hoepfner et al., 2002), however it can form hydrogen bonds because it has polarizable hydroxyl of phenolic and carboxylic groups both intramolecular as well as intermolecular (Carvalho

Conclusion

Gallic acid was encapsulated in matrices of C, β-CDS and X by lyophilization. The encapsulated gallic acid showed no loss of antioxidant capacity and different characteristics to the pure gallic acid that were confirmed by SEM, DSC, TGA and UV. However, with the chitosan matrix a higher encapsulation efficiency, and capsules with characteristic shape were obtained.

Further studies should be performed to measure the release of GA from the capsules, to ascertain its antioxidant activity under

Acknowledgments

To CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior), CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and LSS-UFRGS (Laboratório de Sólidos e Superfícies - Universidade Federal do Rio Grande do Sul) for their support.

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