Effect of the weight ratio of alginate-modified tapioca starch on the physicochemical properties and release kinetics of chlorogenic acid containing beads

Highlights

• Calcium alginate beads filled with modified tapioca starch were studied.

• Chloragenic acid was used for testing the release characteristics.

• Bead properties are controlled by starch content.

• Release dynamics are dominated by diffusion transport.

Abstract

Sodium alginate (SA)-modified tapioca starch (TS) solutions (R_SA/TS) in different weight ratios (1/0, 0.75/0.25, 0.5/0.5 and 0.25/0.75), added with chlorogenic acid (CGA), were dripped into CaCl₂ solution for obtaining calcium alginate (CA) hydrogel beads filled with TS containing chlorogenic acid (HB_CA/TS). The beads size, morphology, encapsulation efficiency, textural and viscoelastic properties, CGA release in simulated gastrointestinal conditions, and the molecular interactions between beads components using DSC and FTIR were evaluated. The sphericity of the HB_CA/TS filled with TS was lower than that made with only calcium alginate, but the diameter was larger. CGA release from the beads was due to a complex interplay between matrix porosity and tortuosity. Highest release % of CGA occurred for HB_0.75/0.25 which showed the lowest Tan δ-strain %, hardness and cohesiveness values. The diffusion-relaxation model involving two mechanisms described better the CGA release experimental data.

Introduction

The roles of antioxidants on human health have been widely recognized by numerous researches, and there has been an increasing interest by the food industry and a growing trend in consumer preferences for natural antioxidants over synthetic compounds for food applications (Fu et al., 2011, Xi and Shouqin, 2007). However, natural antioxidants are easily oxidized and sensitive to heat and light, which limit their application in the food industry (Chao, Wang, Zhao, Zhang, & Zhang, 2012). Thus, the development of carriers systems for these compounds that may help to protect them against deleterious environmental factors and to incorporate them into more complex food systems in an efficient manner is a current topic of study.

Microencapsulation is a reliable technique that has been in use for many decades for protecting bioactive compounds from degrading under the influence of environmental factors. This technique relies on surrounding the bioactive compounds with a semi-permeable biopolymeric matrix, avoiding or retarding their coming into contact with the deleterious environmental factors. An ongoing research topic is how to improve the physicochemical, functional, and release properties characteristics of these biopolymeric matrices, and to make them more cost efficient.

The most widely used encapsulating material is alginate, a natural anionic polyelectrolyte extracted from various species of algae, and composed by (1-4)-linked β-d-mannuronate (M) and α-l-guluronate units (G), which are present in the linear macromolecule in homopolymeric blocks of each monomer, together with blocks of alternating sequence (Donati et al., 2005). Alginate has several features that make it a suitable choice material for encapsulation such as low cost, simple use, biodegradability, biocompatibility, capability to undergo chain–chain association and forming three dimensional gels in the presence of divalent cations (e.g., Ca²⁺) (Fang et al., 2008). However, alginate gels are susceptible to disintegrate in the presence of excess monovalent ions, Ca²⁺-chelating agents, and harsh chemical environments (Smidsrod & Skjak-Braek, 1990). They also present high permeability, due to their porous and hydrophilic structure which causes rapid release of entrapped materials (Chan et al., 2011, Hosseini et al., 2014, López-Córdoba et al., 2013, Martin et al., 2013), which may be considered a drawback in some applications. Some authors have reported that alginates can form matrices with improved structural and functional properties by the addition of other polymers as fillers (Chan et al., 2011, López-Córdoba et al., 2014, Wu et al., 2014). Hosseini et al. (2014) informed that the presence of resistant starch in alginate microcapsules resulted in higher nisin encapsulation efficiency and loading capacity, while López-Cordoba et al. (2013) found that the incorporation of starch granules improves the release characteristics of alginate-based capsules.

There are very few researches about the combination of alginate with chemically modified starch. It is interesting to note that chemically modified starches exhibit reduced digestibility, so they qualify as resistant starches, and may have an important role in human health (Chung, Shin, & Lim, 2008). No reports are available characterizing the effect of the alginate-chemically modified starch weight ratio on the structural, mechanical, loading, and release properties of microcapsules containing bioactives. This knowledge is relevant considering that the most important mechanisms that regulate the release rate of bioactive compounds (diffusion, swelling, biodegradation/erosion and osmotic pressure) will depend on the composition of the biolymeric matrix and the surrounding fluid (Barba et al., 2009, Pothakamury and Barbosa-Cánovas, 1995).

Chloragenic acid (CGA, 5-caffeoylquinic acid) is a widely used bioactive in functional foods due to its antioxidant activity and scavenging of reactive oxygen species capacity (Pal et al., 2012, Pal and Mitra, 2010, Sato et al., 2011), and for preventing diverse health conditions (Shin et al., 2015). CGA is easily oxidized and sensitive to heat and light (Chao et al., 2012), and for this reason was chosen as the bioactive to be encapsulated in this work.

The objectives of this work were to: (a) encapsulate chlorogenic acid (CGA) in modified tapioca starch-filled calcium alginate hydrogel beads (HB_CA/TS); (b) evaluate the size, textural, microstructural, and viscoelastic properties of the beads; (c) determine the CGA entrapment efficiency, antioxidant activity, and release kinetics under simulated gastrointestinal conditions; and (c) evaluate the starch-alginate-CGA interactions on the beads.