NANOENCAPSULATION OF FOOD ANTIMICROBIAL AGENTS

Many techniques have been developed for the fabrication of nanoencapsulated antimicrobials. These methods can be classified into two main categories according to whether the formulation requires a high mechanical energy (top-down method) or can be achieved directly without applying mechanical energy (bottom-up method). They can also be classified based on encapsulating materials (such as lipid, biopolymer, and inorganic material) (Jafari, 2017). The most important methods applied for antimicrobial agents are summarized below (as shown in Table 5.3).

Nanoencapsulation of Antimicrobials through Lipid-Formulation Techniques

Nanoemulsions

Among numerous nanoencapsulation techniques for antimicrobial agents, emulsions are particularly suitable for food applications due to abundant food compatible emulsion ingredients and scalable top-down approaches such as high-pressure homogenization for preparation (McClements, 2015).

Technique

Advantages

Antimicrobial Agents

Lipid-

formulation

Nanoemulsions

Small droplet size

Transparent/translucent systems suitable to use in beverages Rapid absorption Improved antimicrobial activity

Essential oils including peppermint oil (Liang et al., 2012), clove bud oil (Zhang et al., 2014a), thyme oil (Wu et al., 2014; Xue et al., 2015), sago oil (Moghimi et al., 2016)

Essential oil components such as thymol, eugenol (Ma et al., 2016), carvacrol (Chang et al., 2013)

Nystatin (Campos et al., 2012)

Nanoliposomes

Capability to encapsulate both hydrophilic and hydrophobic antimicrobial agents either in their cavity or in their bilayer High drug carrying capacity and readily tunable formulation

Antimicrobial peptides such as nisin (Colas et al., 2007; TAYLOR etal., 2008)

Anethum graveolens essential oil (Ortan et al., 2009) Rose essential oil (Wen et al., 2011)

Artemisia arborescens L. essential oil (Sinico et al., 2005) Daptomycin (Li et al., 2013)

Solid lipid

nanoparticles

Both lipophilic and hydrophilic compounds can be loaded into the solid matrix Possibility of large-scale production

Nisin (Prombutara et al., 2012)

Clove extract (eugenol) (Cortes-Rojas et al., 2014)

Biopolymer

based

Protein

Improved bioavailability and antimicrobial activity;low toxicity

Thymol (Bhavini et al., 2012;Pan et al., 2014a), carvacrol (Wu et al., 2012)

Clove bud oil (Luo et al., 2014)

Carbohydrate

Low toxicity and low cost High stability in a wide pH range

Clove bud oil (Luo et al., 2014)

Lavandin essential oil (Varona et al., 2013a)

(Continued)

TABLE 5.3 (Continued)

Technique

Advantages

Antimicrobial Agents

Good biodegradability

Essential oil components including d-limonene (Dons' et al., 2011), cinnamaldehyde, eugenol (Hill etal., 2013)

Chitosan with benzoyl peroxide(Friedman et al., 2013)

Nisin (Chopra et al., 2014)

Equipment

based

Electrospinning

and

electrospraying

Large surface area, amendable size, and morphology

Capability to carry heat-sensitive compounds Possibility of large-scale production

Bacteriocin (Heunis et al., 2010)

Peppermint oil (Ghayempour and Mortazavi, 2014)

Nanospraydrying

Preparation of nano-size ultrafine powder Good morphological properties and redispersibility

Eugenol (Hu et al., 2016) Peppermint oil (Wang et al., 2016)

Nanocomposites

Improved mechanical and barrier properties

Carvacrol (Tunc and Duman, 2011)

Rosemary essential oil (Abdollahi et al., 2012)

Clove, coriander, caraway, marjoram, cinnamon, and cumin essential oils (Alboofetileh et al., 2014)

Schematic illustration of three lipid formulations for antimicrobial agent delivery

FIGURE 5.2 Schematic illustration of three lipid formulations for antimicrobial agent delivery: (A) nanoemulsion, (B) nanoliposome, and (C) solid lipid nanoparticle.

Nanoemulsions are a specific type of colloidal dispersion containing oil, water, and an emulsifier with a remarkable small droplet size, usually covering the size range of 20—200 nm (Fig. 5.2A) (Solans et al., 2003). Depending on the nature of hydrophobicity or hydrophilicity of the antimicrobial agents, either O/W or W/O emulsions can be applied to stabilize oil-soluble or water- soluble agents, respectively. Nanoemulsions are nonequilibrium systems with a spontaneous tendency to separate into the constituent phases, while microemusions, which may appear to be similar to nanoemulsions in composition and structure, are equilibrium systems (Pan and Zhong, 2016b). Nanoemulsions can be prepared through both top-down (high-energy,) and bottom-up (low-energy) methods, while microemulsions are produced by low-energy methods only (Galanakis, 2015). The high-energy emulsification methods require a large external force by mechanical devices like high- pressure homogenization, microfludization, or ultrasonication to be applied in order to disrupt and intermingle the oil and water phases (McClements, 2012). High-pressure and high shear homogenizations are two of the most popular methods to prepare food emulsions (Pan and Zhong, 2016b).

Antimicrobial agents (e.g., nystatin, peppermint oil) can be predissolved in commonly used oils (e.g., triacylglycerol, Labrafac lipophile, soybean oil)

and then emulsified in the aqueous phase with predissolved emulsifiers using high-energy methods (Campos et al., 2012; Liang et al., 2012). Nanoemulsions of essential oils and their components (e.g., thyme oil, euge- nol) can also be formed by homogenizing them in the aqueous solutions directly, showing similar or enhanced antimicrobial properties than free essential oils (Ma et al., 2016; Wu et al., 2014; Xue et al., 2015). Compared to high-energy approaches, low-energy emulsification methods rely on the spontaneous assembling of oil droplets within mixed surfactant—oil—water systems when the conditions are altered such as phase inversion and spontaneous emulsification methods (McClements, 2012). Phase-inversion methods utilize the interfacial behavior of surfactant which are a function of composition or temperature (Pan and Zhong, 2016b). For phase-inversion composition method, essential oil microemulsions with and without other oil phase can be formed above a critical surfactant-to-oil ratio by simple mixing (Ma and Zhong, 2015; Zhang et al., 2014a). The phase-inversion temperature method applies a heating step to induce the phase inversion from crude O/W to W/O, followed by another phase inversion from W/O to O/W during rapid cooling. (Pan and Zhong, 2016b) Additionally, a self-emulsifying technique based on the deprotonation of essential oils in alkaline condition and self- assemble property of emulsion during neutralization has also be demonstrated as a successful method to form essential oil nanoemulsions (Luo et al., 2014; Zhang et al., 2016).

 
Source
< Prev   CONTENTS   Source   Next >