Modelling release mechanisms of cinnamon (Cinnamomum zeylanicum) essential oil encapsulated in alginate beads during vapor-phase application

Highlights

• Cinnamon essential oil was efficiently encapsulated in alginate beads.

• Cinnamon essential oil-alginate beads exhibited antifungal activity in vapor phase.

• Water release from beads in vapor phase was described with two first order models.

• Essential oil release in vapor phase was described with second order dynamic model.

• Temperature and relative humidity affected essential oil release in vapor phase.

Abstract

Encapsulation efficiency of Cinnamomum zeylanicum essential oil (EO, at 5% v/v) in sodium alginate beads and its controlled release was determined. Composition of vapors generated by the beads was assessed by solid-phase microextraction. Water and EO released from the beads in the vapor phase were determined at 59% or 88% relative humidity at 4 °C or 25 °C. First and second order dynamic models appropriately described release mechanisms of water and EO, demonstrating Fickian behavior in both cases, in which diffusion mainly depends on EO concentration gradients. Encapsulation efficiency was 85.43% ± 4.97%, volatile components (cinnamaldehyde, caryophyllene, and α-caryophyllene) were detected in the vapor phase. Water and EO release rates were higher at the higher temperature, while a higher relative humidity led to lower water release but greater EO diffusion. Furthermore, enhanced antifungal (against Botrytis cinerea, Penicillium expansum, Alternaria alternata, or Colletotrichum gloeosporioides) activity of encapsulated EO was observed in vapor phase.

Introduction

The need to expand the spectrum of safe antimicrobials for use in the food industry has led to the examination of essential oils (EOs) as a potential candidate. Consequently, numerous studies have tested the antimicrobial properties of these oils both in vitro and in food (Lorenzo-Leal et al., 2019; Reyes-Jurado et al., 2019).

Chen et al. (2018) and Lorenzo-Leal et al. (2019) provide recent outcomes on the antimicrobial effectiveness of EO in the vapor phase. In some cases, EO has proved to be more efficient in the vapor phase than with direct application (Aguilar-González et al., 2015; Reyes-Jurado et al., 2019). Besides their low water solubility and high hydrophobicity, EO components responsible for antimicrobial activity are mainly volatile, which improves their activity in the vapor phase (Goni et al., 2009). Furthermore, as the antimicrobial is not in direct contact with food and is required only in small concentrations, sensory properties are less affected (Lorenzo-Leal et al., 2019).

The integration of EO into carriers for application in the vapor phase has also been considered (Noppakundilograt et al., 2015; Sangsuwan et al., 2016), and in some cases activity comparable to conventional antimicrobials has been observed (Baldim et al., 2019; Radünz et al., 2019). Current studies suggest the application of EO into polymeric carriers in the form of capsules, particles, or films with the purpose of protecting the oils against external factors (such as oxygen and light), to disguise their strong odors, or simply to provide a practical way of holding or handling the EO (Baldim et al., 2019; Radünz et al., 2019). In fact, studies have been conducted to provide better stability to bioactive substances in different encapsulation systems. Conjugates obtained through Maillard reaction of whey protein hydrolysates and linear dextrin, with different degrees of polymerization, were tested for the stabilization of oil in water emulsions; the augment of the degree of polymerization of dextrin improved storage, oxidative and physical stabilities of emulsions (Pan et al., 2020). Essential oils entrapment into polymers also helps to overcome their high volatility, which otherwise would increase their loss or uncontrolled release into the surrounding environment (Sangsuwan et al., 2016).

Alginate is an interesting option as an EO carrier due to its gelling capacity, biocompatibility, and low toxicity properties (Lee and Mooney, 2012). There has been much investigation into the properties of alginate, and the polymer is widely available at an affordable price (Lee and Mooney, 2012).

Authors such as Benavides et al. (2016), Ke et al. (2019), and Volić et al. (2018) have highlighted the importance of studying the EO release profile of carrier polymers, as well as the mechanisms governing the release. For hydrophobic components (such as EO), swelling or matrix erosion are important phenomena (Benavides et al., 2016). While most studies concerning EO release have used a liquid medium as the surrounding environment (Ke et al., 2019; Volić et al., 2018), some studies have been performed in the vapor phase (Cevallos et al., 2010; Noppakundilograt et al., 2015). However, there is a lack of information regarding the understanding of the mechanisms governing the release of EO from alginate beads during the vapor phase. During release, conditions such as temperature and the relative humidity of the surrounding environment could influence diffusion. Ke et al. (2019) stated that the contribution of increasing temperature to an improved diffusion of cinnamaldehyde into a 95% ethanol solution was most likely due to increased polymer mobility and expansion at higher temperatures. Ayala-Zavala et al. (2008) and Cevallos et al. (2010) emphasized the importance of studying the effects of relative humidity in the essential oil release from β-cyclodextrins. Cevallos et al. (2010) observed that cinnamaldehyde release was governed by the shape of the water vapor isotherms. Using different supersaturated salt solutions to generate different relative humidity environments, Ayala-Zavala et al. (2008) studied the effects of water presence on the release of cinnamon (Cinnamomum zeylanicum) leaf EO from β-cyclodextrin capsules. Understanding the mechanisms of the water release itself, its behavior in the vapor phase, and the beads' weight loss are also important factors to comprehending EO release, since water content and movement might influence the beads’ structure and consequently, the release of EO (Lai et al., 2007; Zhou et al., 2018).

In this study, cinnamon EO, which is an effective antimicrobial against foodborne molds and bacteria (Chuesiang et al., 2019a), was encapsulated in alginate beads. Water and the EO release profile were studied and modelled at different temperatures, relative humidities, and chamber headspace volumes that mimicked real fruit storage conditions. Finally, the effectiveness of the alginate–cinnamon EO beads in the vapor phase was tested against Botrytis cinerea, Penicillium expansum, Alternaria alternata, and Colletotrichum gloeosporioides, and was compared with the antimicrobial activity of free cinnamon EO against the same molds.