Elsevier

Food Hydrocolloids

Volume 107, October 2020, 105865
Food Hydrocolloids

Corn fiber gum-soybean protein isolate double network hydrogel as oral delivery vehicles for thermosensitive bioactive compounds

https://doi.org/10.1016/j.foodhyd.2020.105865Get rights and content

Highlights

  • Corn fiber gum -soy protein double network (DN) hydrogels were developed at 25 °C.

  • The DN gels released riboflavin more efficiently as compared to soy protein gel.

  • CFG delayed proteolysis of DN gels in stomach but promoted that in intestine.

  • The release profile of riboflavin was influenced by microstructure of hydrogel.

Abstract

Corn fiber gum (CFG)-soybean protein isolate (SPI) double network (DN) hydrogels, with varied concentrations of CFG, were fabricated at room temperature in order to develop a biocompatible vehicle for the oral administration of thermosensitive bioactive compounds. Riboflavin (vitamin B2) was encapsulated in the gel as a model bioactive compound. The compound release properties of these DN hydrogels were investigated in simulated gastric and simulated intestinal fluids (SGF and SIF). DN hydrogels with 0.25% of CFG were found to be the most desirable of those assayed for the oral administration of bioactive compounds. The results of low-field nuclear magnetic resonance (LF-NMR) relaxometry measurement showed that the pH-responsive DN hydrogels exhibited low swelling ratio in the SGF but larger swelling ratio in the SIF. The results of degree of proteolysis and scanning electron microscopy (SEM) showed that significant release of riboflavin from DN hydrogels in the SIF was due to large swelling, CFG matrix erosion and the proteolysis of SPI. The release mechanisms of riboflavin through the DN hydrogels in the simulated intestinal fluid followed non-Fickian diffusion based on Peppas' semi-empirical equation.

Introduction

Bioactive compounds, such as bioactive peptides, vitamins, and probiotics, are nutraceuticals widely reported to have beneficial effects on human health. The incorporation of such bioactive compounds into food systems thus provides a promising way to develop novel functional foods that deliver health benefits beyond nutrition and/or reduce the risks of diseases (Elliott & Ong, 2002). However, a large number of these bioactive molecules remain poorly bioavailable via oral administration, due to factors such as low solubility within the gut, lack of stability under the environmental conditions encountered in food processes (such as light, temperature and oxygen levels) or those in the gastro-intestinal tract (digestive enzymes, pH, or the presence of other nutrients) (Arbos, Arangoa, Campanero, & Irache, 2002). Various protection and delivery strategies have been developed to overcome these limitations. One well-studied strategy is trapping molecules of interest in biodegraded hydrogel matrices (Brannon-Peppas, 1993; Kamath & Park, 1993; Park & Park, 1996). Hydrogels are three-dimensional cross-linked networks of natural macromolecules that are able to swell in water and retain a significant quantity of water without dissolving. Hydrogels can protect bioactive compounds from hostile environments in the gastrointestinal tract, thus potentially preventing their loss. Moreover, degradable hydrogels are able to accomplish the controlled release of these bioactive compounds due to their sensitivity to environmental stimuli, such as pH and digestive enzymes (Maltais, Remondetto, & Subirade, 2010).

Among the ingredients that can be used to form hydrogel, proteins and polysaccharides are particularly attractive owing to their biodegradability, biocompatibility and nontoxicity features. Protein-based hydrogels, such as whey protein gel and soybean protein gel, have been popular choices for constructing mixed hydrogels due to their high nutritional value, excellent functional properties and amphiphilic nature (Abaee, Mohammadian, & Jafari, 2017). Many polysaccharides, known as dietary fibers, are not digested by human enzymes but could be degraded by microbiota in the colon, e.g., alginate, k-carrageenan, pectin and arabinoxylan (McClements, 2017). The erosion of these polysaccharide hydrogels via microbial fermentation is specifically used for colon-targeted delivery (Cao & Mezzenga, 2020). Corn fiber gum (CFG) is an arabinoxylan (AX) isolated from corn bran through an alkaline extraction process (Qiu et al., 2015). CFG consists of a linear backbone of β-(1–4)-d-xylopyranose to which α-l-arabinofuranose substituents are attached through O-2 and/or O-3 (Izydorczyk, Biliaderis, & Bushuk, 1990). Ferulic acids (3-methoxy, 4 hidroxy cinnamic acid) are ester-linked to arabinose side chains and CFG can be used to form hydrogels by covalent cross-linking involving ferulic acid (FA) oxidation by laccase (Niño-Medina et al., 2009). Laccase can promote the oxidation of FA, enabling the coupling of AX chains through the formation of diferulic and triferulic acids (di-FA and tri-FA), thereby generating a three-dimensional network hydrogel of CFG (Berlanga-Reyes, Carvajal-Millan, Lizardi-Mendoza, Islas-Rubio, & Rascón-Chu, 2011). Covalently cross-linked CFG gels have been found to be little affected by the conditions in the gastric-intestine tract, although they can be degraded by a mixture of Bifidobacterium from the colon (Martínez-López et al., 2016). Previous studies have demonstrated that covalently cross-linked CFG gels could be used for the entrapment of biomolecules, such as insulin and Bifidobacterium, for therapeutic purposes (Berlanga-Reyes et al., 2009; Martínez-López et al., 2019; Paz-Samaniego et al., 2018).

Soybean protein isolate (SPI) is applied extensively in the food industry due to their low cost, abundant availability, high nutritional value and functional properties, including emulsifying and gelling (Nishinari, Fang, Guo, & Phillips, 2014). SPI hydrogels can wrap nutraceutical substances in their network and be used as oral delivery vehicles due to their biodegradability, adjustable swelling and release characteristics (Chen, Remondetto, & Subirade, 2006). However, as nutrient carrier matrices, protein gels tend to have a poor transport efficiency in the body because they are degraded rapidly by pepsin under gastric acid environment (Luo, Borst, Westphal, Boom, & Janssen, 2017).

In order to overcome the limitations exhibited by protein gels and utilize the functional properties of polysaccharide gels, the development of polysaccharide-protein double network (DN) hydrogel systems as oral delivery vehicles for bioactive compounds is of high interest. Double network hydrogels are composed of two interpenetrating polymer networks with unique properties, wherein the rigid and brittle network serves as the first network while the second network is ductile and flexible (Gong, Katsuyama, Kurokawa, & Osada, 2003). The DN hydrogel exhibited high mechanical strength because its first network effectively dissipated energy while the second network maintained hydrogel integrity during deformational process (Sun et al., 2013; Zhang et al., 2009). Compared with hydrogels with protein as their only constituent, polysaccharide-protein DN hydrogels are more efficient in transporting nutrients in the intestine, because the polysaccharide network in the gels protects protein from pepsin degradation and acidic environment in the stomach (Alavi et al., 2018). However, few examples have been reported of polysaccharide-protein DN hydrogels used as nutrient carriers, with investigations to date mainly focused on DN hydrogel preparation. Deng, Liu, Li, Yadav, and Yin (2018) developed corn fiber gum (CFG)-soybean protein isolate (SPI) double network (DN) hydrogels with laccase and a heat treatment. However, the heating process is not conducive for encapsulating thermal-sensitive nutraceutical substances, such as some vitamins and probiotics. Therefore, the purpose of the present work was to develop a novel CFG-SPI double hydrogel as a delivery vehicle for thermosensitive bioactive compounds, using riboflavin as a model. CFG-SPI DN hydrogels with different concentrations of CFG were induced by laccase and D- (+)-gluconic acid δ-lactone (GDL) at room temperature. Their microstructure changes were analyzed and controlled release kinetics were explored in simulated gastric and intestinal fluids.

Section snippets

Materials

SPI was obtained from Pine Agritech Ltd. (Beijing, China). Corn bran samples were kindly provided by COFCO Corporation (Beijing, China). Laccase from Trametes versicolor (E.C.1.10.3.2), porcine pepsin, porcine pancreatin (4 × USP specifications) was purchased from Sigma-Aldrich (St. Louis, MO, USA). D-(+) -gluconic acid δ-lactone (GDL), riboflavin and heat-resistant α-amylase were purchased from Aladdin Industrial Corporation (Shanghai, China). Hexane, sodium hydroxide and hydrochloric acid

Release profiles in the simulated gastro-intestinal tract

The release profiles of riboflavin from the different CFG-SPI double network hydrogels in simulated gastric fluids (SGF) with or without addition of 0.1% pepsin for 2 h and in simulated intestinal fluids (SIF) with or without addition of 1.0% pancreatin for another 4 h at 37 °C, are shown in Fig. 1. It was found that SPI gels released riboflavin slowly under SGF without pepsin, with initial rates of approximately 0.83%/min over the first 30 min of incubation (Fig. 1A). The initial release rates

Conclusion

This work developed and examined CFG-SPI double network hydrogels as oral delivery systems for thermosensitive bioactive compounds. Pure SPI hydrogel exhibited a poor transport efficiency of riboflavin in SIF due to a high swelling ratio in the SGF and susceptibility to enzymatic degradation by pepsin. LF-NMR relaxometry results showed that CFG-SPI DN hydrogels were sensitive to pH. They exhibited lower swelling ratios in SGF but higher ratios in SIF in comparison to the SPI hydrogel.

CRediT authorship contribution statement

Wenjia Yan: Methodology, Validation, Formal analysis, Investigation, Data curation, Writing - original draft, Writing - review & editing, Visualization. Boya Zhang: Formal analysis, Investigation. Madhav P. Yadav: Conceptualization, Visualization, Writing - review & editing. Liping Feng: Investigation, Validation. Jinxin Yan: Investigation, Formal analysis. Xin Jia: Supervision, Writing - review & editing. Lijun Yin: Supervision, Project administration, Funding acquisition.

Declaration of competing interest

All authors declare that there is no conflict of interest related to this article.

Acknowledgements

This work was funded by the National Science Foundation of China (No. 31771934) and the National Key Technologies R&D Program (No. 2016YFD0400804).

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