Industrially scalable complex coacervation process to microencapsulate food ingredients

Highlights

• ‘Coco process’ - in situ complex coacervation microencapsulation by spray-drying

• Insoluble, dry, food ingredient microcapsules formed sans chemical cross-linking.

• Industrially-scalable with high retention of volatile limonene during spray drying

• Up to 80% total limonene retained in CoCo microcapsules over 72 days on the shelf.

Abstract

Microencapsulation by conventional complex coacervation, though highly effective and achievable at the bench-scale, is challenging to scale-up because of the complexity of the process. A novel, industrially-scalable microencapsulation process by in situ complex coacervation during spray drying (the ‘CoCo process’) is introduced, where the multiple steps are collapsed into one, to form dry complex coacervated (CoCo) microcapsules by spray drying. The CoCo process was used to encapsulate d-limonene in CoCo microcapsules using alginate and gelatin as wall materials. Insoluble CoCo particles were produced without chemical cross-linking, with extents of complex coacervation of 75 ± 6% and 64 ± 6% for CoCo particles with and without d-limonene, respectively. Up to 82.7% of d-limonene was retained during spray drying; moreover, the CoCo matrix exhibited excellent barrier properties, retaining up to 80.0% of total d-limonene over 72-day storage in sealed vials at room temperature.

Industrial relevance

Commercialization of microencapsulation of bioactives by complex coacervation in agricultural and food applications is hindered by the high-cost and time-intensive multistep process consisting of emulsification, coacervation, shell hardening and drying. In this work, we overcome these limitations by developing an industrially scalable in situ complex coacervation process during spray drying (‘CoCo process’). One-step complex coacervation during spray-drying opens the door to cost-effective, high-throughput, high-volume production of bioactive-containing microcapsules. The protective matrix microcapsules formed by this novel process stabilize and protect the bioactive, while allowing controlled release of the cargo for various applications in the food and many other industries.

Introduction

Microencapsulation facilitates successful incorporation of bioactive compounds in many industries such as food, pharmaceutical, cosmetics, agriculture and functional materials (Carvalho, Estevinho, & Santos, 2016; Gharsallaoui, Roudaut, Chambin, Voilley, & Saurel, 2007; Martins, Barreiro, Coelho, & Rodrigues, 2014; Prajapati, Jani, & Kapadia, 2015). As utilization of bioactive compounds are usually limited by their susceptibility to external environmental degradation, microencapsulation can provide a protective barrier, desirable release profile and compatibility with different media. Complex coacervation is a particularly promising microencapsulation system. It is a phase separation process where an immiscible phase is produced mainly through electrostatic interactions between two oppositely charged polymers (e.g. proteins and anionic polysaccharides) (Warnakulasuriya & Nickerson, 2018; Yan & Zhang, 2014). Microencapsulation by complex coarcervation is of high interest in many industrial sectors because of high payloads achievable and controlled release possibilities (Eratte, Dowling, Barrow, & Adhikari, 2018; Gouin, 2004). However, potential commercial application of the conventional process is limited by the multiple steps required for emulsification, coacervation, shell hardening and drying (Lemetter, Meeuse, & Zuidam, 2009; Timilsena, Akanbi, Khalid, Adhikari, & Barrow, 2019). Moreover, a crosslinking step using toxic agents such as formaldehyde or glutaraldehyde is often necessary to stabilize polymer associations, which is especially incompatible with food systems. Alternatively, non-toxic natural cross linker such as genipin or enzymatic cross linker such as tranglutaminase have also been studied. However, no matter what type of cross linker is used, cross linking requires precise adjustment of pH and/or temperature and typically takes hours to complete (da Silva et al., 2019; Dong et al., 2011; Saravanan & Rao, 2010; Yang et al., 2014).

Complex coacervation is particularly suited to encapsulate volatile oils as the coacervates effectively trap the oil emulsion to minimize volatile losses (Eghbal & Choudhary, 2018). In one example, peppermint oil was encapsulated by conventional complex coacervation with gelatin and gum arabic (Dong et al., 2011). The encapsulation process required sequential steps including emulsification of the peppermint oil in a gelatin solution, combining with the gum arabic solution, pH adjustment using acetic acid to induce complex coacervation, enzymatic cross-linking with transglutaminase to harden the microcapsule wall, and finally, spray drying of the mixture to obtain dry complex coacervates microcapsules. In another example, whey protein and gum arabic were used to encapsulate orange essential oil. Here again, the complex coacervation suspension was formed first and then spray dried to obtain complex coacervated microcapsules (Rojas-Moreno, Cárdenas-Bailón, Osorio-Revilla, Gallardo-Velázquez, & Proal-Nájera, 2018).

Although effective, the conventional multistep process of microencapsulation of volatile oils in complex coacervation microcapsules remains an obstacle for commercialization. To overcome this barrier, we developed a process that enables in situ complex coacervation during spray drying (Tang, Scher, & Jeoh, 2018). In this process, the feed emulsion is prepared with two negatively charged matrix polymers and a volatile base. Atomization of the feed volatilizes the base, lowering the pH to below the isoelectric point of one of the polymers to allow complex coacervation between the oppositely charged polymers. Concurrent rapid moisture removal enhances associations between the polymers to form dry complex coacervation microcapsules that are collected at the outlet of the spray dryer. This novel process microencapsulates emulsions in complex coacervation microcapsules by a low-cost, industrially-scalable spray drying process in one step without the use of a crosslinking agent (Fig. 1). Spray drying is the most common and cheapest way to produce microencapsulated food products at industrial scales (Gharsallaoui et al., 2007; Jacobs, 2014; Sosnik & Seremeta, 2015).

The objective of this study was to investigate the potential of this novel, industrially-scalable complex coacervation process (herein referred to as the ‘CoCo process’, Fig. 1) to microencapsulate bioactive compounds. We demonstrate and characterize CoCo microparticles formed by spray drying using a widely-used combination of protein and polysaccharide, gelatin and alginate, as matrix polymers (de Kruif, Weinbreck, & de Vries, 2004; Schmitt & Turgeon, 2011; (Yan and Zhang, 2014)). Alginate and gelatin are commonly used in various food products. A linear polysaccharide derived from algae cell wall, alginate is a good microencapsulation material in food systems due to its biocompatibility, biodegradability and nontoxicity (de Oliveira, Paula, & de Paula, 2014). Alginate is composed of alternating blocks of 1–4 linked α-L-guluronic and β-D-mannuronic acid residues (Gombotz & Wee, 2012). The charge density of this linear chain polymer makes it a very promising matrix building polymer. Gelatin is obtained from the hydrolysis of collagen extracted from skin, white connective tissue, and bones of animals and it is a popular ingredient in food (Haug & Draget, 2011; Liu, Li, & Guo, 2008; Meng & Cloutier, 2014; Zhou, Mulvaney, & Regenstein, 2006). Gelatin has very good film-forming properties during spray drying which facilitates the rapid formation of a dense film to provide good protection of the core ingredient (Matsuno & Adachi, 1993).We further demonstrate the potential of the CoCo process to encapsulate d-limonene, a volatile oil. d-limonene is a monocyclic monoterpene with a pleasant citrus-like smell and many bioactivities such as antifungal, bacteriostatic and bactericidal properties, making it appealing in many industries (Ciriminna, Lomeli-Rodriguez, Demma Cara, Lopez-Sanchez, & Pagliaro, 2014; Espina, Gelaw, de Lamo-Castellví, Pagán, & García-Gonzalo, 2013). Microencapsulation can facilitate broad application of limonene by preventing volatile loss and degradation during processing and storage and by enabling controlled release of the oil.