Release kinetics of cinnamaldehyde, eugenol, and thymol from sustainable and biodegradable active packaging films

Highlights

• NAC addition decreased crystallization temperature of SLN in films 50 %.

• The decrease was similar between NAC added.

• Crystallization of SLN results in expulsion NAC from the particles.

• The film formation did not affect particle functionality.

• The release kinetics controlled by the number and crystallinity of carrier particles.

Abstract

Active packaging films can be formulated with biodegradable polymer loaded with natural antimicrobial compounds (NAC) as biodegradable alternatives to traditional plastic packaging for food. Essential oil compounds, naturally found in the plants, have antimicrobial activity against microorganisms. In this work, they are encapsulated in liquid lipid nanoparticles (LLN) or solid lipid nanoparticles (SLN) to control and enhance their solubility and stability and control kinetic release. In this study, the release kinetics of thymol, cinnamaldehyde, and eugenol, from pullulan-based films were studied as a function of lipid structure (liquid vs solid) and carrier particle concertation. The crystallization temperature of SLN (10.2 °C) decreased with incorporation of NAC (6.8 °C in SLN loaded with 1 % cinnamaldehyde). Increasing NAC significantly decreased (p < 0.05) the crystallization temperature of SLN. The SLN structure was similar in films to emulsions as their melting and crystallization temperatures were similar (p > 0.05). The NAC release rate from SLN films was twice than that from LLN films due to higher aqueous partitioning. The release rate in SLN films increased 100 %, 50 %, and 5 % for thymol, eugenol, cinnamaldehyde, respectively, when NAC concertation in the particles increased from 1 % to 2 %. Thymol had highest release rate (0.93 ppm/min) from SLN loaded with 2 % NAC films than that of eugenol and cinnamaldehyde (0.40 and 0.15 ppm/min, respectively). This study shows that the NAC-loaded pullulan films can be used as active antimicrobial packaging film for food applications with controlled release of active compounds.

Introduction

The main purpose of food packaging is to protect the food enclosed beside its other functions such as handling, and communication with the customers (Guarda, Rubilar, Miltz, & Galotto, 2011; Ribeiro-Santos, Andrade, Melo, de, & Sanches-Silva, 2017). There is a large need to design active packaging systems with antimicrobial activity from Generally Recognized as Safe (GRAS) ingredients to further improve their protective function, preferentially using sustainable and economical sources.

Recently, biodegradable packaging films increasingly gaining attention in the food industry. They are often based on biopolymers that are sustainable, environmentally-friendly and cost-effective alternatives to traditional plastic packaging materials (Del Nobile, Conte, Incoronato, & Panza, 2008; Hassannia-Kolaee, Khodaiyan, Pourahmad, & Shahabi-Ghahfarrokhi, 2016; López, Sánchez, Batlle, & Nerín, 2007; Ma, Hu, Wang, & Wang, 2016; Noronha, De Carvalho, Lino, & Barreto, 2014). Biodegradable films were successfully formulated by using polysaccharides, such as pullulan (Hassannia-Kolaee et al., 2016; Trinetta, Cutter, & Floros, 2011), carrageenan (Shahbazi, Rajabzadeh, Ettelaie, & Rafe, 2016), starch (Basiak, Galus, & Lenart, 2015; Jaramillo, Gutiérrez, Goyanes, Bernal, & Famá, 2016; Qiu et al., 2015; Saberi et al., 2016), and chitosan (Bonilla, Poloni, Lourenço, & Sobral, 2018; Noshirvani et al., 2017; Rao, Kanatt, Chawla, & Sharma, 2010; Robledo et al., 2018). In particular, pullulan is a water soluble polysaccharide produced by fungus Aureobasidium pullulans, and known for its good film-forming abilities (e.g., oral film strips) (Kristo & Biliaderis, 2007). It was also used in the food industry for thickening and encapsulation purposes (Hassannia-Kolaee et al., 2016). Pullulan-based films are transparent, tasteless, odorless, and have good oxygen barrier properties (Hassannia-Kolaee et al., 2016; Trinetta et al., 2011). The functional properties of these films may be enhanced by blending pullulan with other polymers (i.e., gums) (Trinetta et al., 2011).

The biopolymer-based films can further be functionalized to have antimicrobial activity using, natural antimicrobial compounds (NAC) such as essential oils (Noshirvani et al., 2017; Robledo et al., 2018). There is a plethora of articles on the antimicrobial effectiveness of essential oils as they are sustainable and GRAS compounds (Kuorwel, Cran, Sonneveld, Miltz, & Bigger, 2011). This form of active packaging shown promising results on controlling the growth of microorganism (Kuorwel et al., 2011).

The essential oil compounds, thymol, eugenol, and cinnamaldehyde, which are naturally found in thyme, clove, and cinnamon essential oils, respectively, were shown to have strong antimicrobial effectiveness due to their phenolic structures (Del Nobile et al., 2008). The antimicrobial mode of action is related to their ability to disturb the cell membrane of microorganisms (Del Nobile et al., 2008; Marchese et al., 2017; Noshirvani et al., 2017; Robledo et al., 2018). These compounds are hydrophobic in nature, and therefore, need a form of delivery strategy to homogenously incorporate them into largely aqueous matrixes. At the same time, they are labile to thermal and chemical stresses (Trinetta, Morgan, Coupland, & Yucel, 2017). We previously showed that encapsulating these active compounds in liquid lipid nanoparticles (LLN) can improve their stability and control their release (Trinetta et al., 2017; Yucel, Elias, & Coupland, 2012). The encapsulated systems enhanced antimicrobial activity by controlling the distribution of the active ingredients throughout the system (Trinetta et al., 2017; Yucel et al., 2012). This enhancement is related to increased surface area-to-volume ratio and homogenous distribution (Donsì & Ferrari, 2016; Trinetta et al., 2017).

Furthermore, solid lipid nanoparticles (SLN) can be formed by crystallization of lipid droplets in fine emulsions to further control the distribution and release of encapsulated ingredients (Yucel, Elias, & Coupland, 2013). The crystallization even can lead to expulsion of the ingredients from the droplet core, a phenomenon known as the burst release. Although it is often regarded as an instability problem, this instantaneous release of active compounds can enhance their antimicrobial effectiveness (e.g., limonene) by increasing their availability via interfacial interactions (Trinetta et al., 2017). Therefore, the antimicrobial activity of these compounds are largely determined by the release kinetics of entrapped active agents from film matrices.

Other researcher investigated release of thymol from zein films (Del Nobile et al., 2008), citronella essential oil from soy protein lignin blend (Arancibia, Giménez, López-Caballero, Gómez-Guillén, & Montero, 2014; Arancibia, López-Caballero, Gómez-Guillén, & Montero, 2014), and cinnamon essential oil from polysaccharide bilayer films (Arancibia, Giménez et al., 2014; Arancibia, López-Caballero et al., 2014). Overall, conflicting results have been reported in the literature for the antimicrobial effectiveness of these compounds even in a liquid model environment (i.e., emulsions). Some of this discrepancy is related to the lack of knowledge for the release of these compounds as a function of physicochemical properties of the carrier systems; yet none in active packaging films formulated with liquid or solid lipid nanoparticles to encapsulate NAC and compound concentrations. Recently, our group studied the application of pullulan-based films to control postharvest disease in small berries, where the enhanced antimicrobial activity of NAC was greatly enhanced by controlling the internal structure of the carrier particles (McDaniel, Tonyali, Yucel, & Trinetta, 2019). Therefore, the objective of this work was to investigate the release kinetics of selected natural antimicrobial compounds (thymol, cinnamaldehyde, and eugenol) from the pullulan-based biodegradable films as a function of lipid nano-particles structure and crystallinity, and compound concentration.