Antibacterial efficacy of Satureja montana L. essential oil encapsulated in methyl-β-cyclodextrin/soy soluble polysaccharide hydrogel and its assessment as meat preservative

Highlights

• Satureja montana L. essential oil (SEO) have a good inhibitory effect on S. aureus.

• Methyl-β-cyclodextrin inclusion complex (MCD-IC) improved the solubility and stability of SEO.

• MCD-IC enhanced the mechanical strength and release characteristics of the hydrogel.

• MCD/SEO-soy soluble polysaccharide hydrogels can be used as antibacterial packaging material.

Abstract

As an emerging packaging material, hydrogels have been attracting attention to inhibit foodborne pathogens by encapsulating antimicrobial substances. Herein, an antibacterial packaging material was prepared via incorporation of methyl-β-cyclodextrin/Satureja montana L. essential oil inclusion complexes (MCD/SEO-ICs) into soy soluble polysaccharide (MCD/SEO-SSPS) hydrogel. During, the addition of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) facilitated the formation of amido linkage between -NH2 and –COOH. Compared with SSPS hydrogel, the MCD/SEO-SSPS hydrogel exhibited a more compact structure. What's more, physical characterization indicated that combining MCD/SEO-ICs with SSPS could improve the hardness, adhesiveness and springiness of hydrogel. More importantly, a good antibacterial activity of SPSS hydrogel was obtained with the addition of MCD/SEO-ICs. On this basis, the application test demonstrated that the prepared MCD/SEO-SSPS hydrogel could reduce the visible count of Staphylococcus aureus (S. aureus) in meat samples by 3.5 Log CFU/g during 7-days storage, which retained the freshness of chilled pork and extended the shelf life. The above results indicated that MCD/SEO-SSPS hydrogel can be used as a safe and effective active packaging material for chilled meat preservation.

Introduction

Microbial infection and changes in sensory characteristics are the two significant factors affecting the quality of food during storage and preservation. Food spoilage causes many problems, including mass wastage, environmental pollution, and disease (Li et al., 2021; Omerović et al., 2021). Packaging can prevent external factors from directly contacting the food matrix, but the extensive use of synthetic petroleum-based packaging materials has caused environmental pollution (Al-Tayyar et al., 2020; Trajkovska Petkoska et al., 2021). Natural biopolymer coatings or packaging films have gradually attracted people's attention due to their biodegradability and functional adjustability (Feng et al., 2017; Zhao et al., 2019). Hydrogel composed of protein or polysaccharides can be used as a biocompatible material to replace traditional packaging (Gul et al., 2021). Hydrogels based on polysaccharides from a wide range of sources have been reported in the literature for packaging. For example, hydrogel based on bagasse nanocellulose have been studied for their applicability as additives in intelligent packaging, and it also showed rapid responses to meat deterioration (Lu et al., 2020). Bi et al. (2020) successfully loaded an antimicrobial peptide into polyvinyl alcohol (PVA)/chitosan (CS) hydrogel, which can inhibit the growth of microorganisms in salmon muscles and improve texture properties. The excellent dispersibility, emulsification and adhesive properties of soy soluble polysaccharides (SSPS) with their low cost make them attractive alternative materials in the field of packaging materials (Chivero et al., 2014; Liu et al., 2020). SSPS is a polysaccharide composed of rhamnogalacturonan and polygalacturonic acids as the main chain and galectin and arabinose as side chains (Nakamura et al., 2001). Combining antibacterial substances with SSPS can make it effect long and endow the hydrogel packaging materials with some functional properties.

However, the use of hydrogels was still limited by certain properties, such as drug loading, controlled release, and mechanical strength (Kim et al., 2019). In the preparation of drug-loaded hydrogels, chemical crosslinking has better properties than the hydrogel formed by physical crosslinking (Rodriguez Vilches et al., 2011). However, the residues of some toxic and harmful crosslinking agents have potential safety hazards, the drug loading capacity of the hydrogel was limited, and the loading effect of hydrophobic drugs was not satisfactory (Torres-Luna et al., 2020). Among the chemical cross-linking agents, EDC is considered to have the characteristics of non-toxicity and good biocompatibility, and it is often used in combination with NHS to improve coupling efficiency (Yang et al., 2020).

In addition, during the fabrication of functional hydrogels, to further improve the solubility, stability and effect of hydrophobic substances, they can be embedded in certain drug carriers, such as nanoemulsion, nanofibers, and β-cyclodextrins (Feng et al., 2020; Muñoz-Shugulí et al., 2021). Due to the hydrophilic outer surface and hydrophobic inner cavity of cyclodextrin, β-cyclodextrins can form stable inclusion complexes (ICs) with many molecules, including essential oils (Astray et al., 2009; Zhu et al., 2021). β-cyclodextrin can be modified by introducing various groups to produce a variety of derivatives, and the derivatives have better water solubility and low toxicity than the original cyclodextrin (Hu et al., 2021; Zhao et al., 2020). Among these derivatives, methyl-β-cyclodextrin (MCD) has attracted considerable attention due to its high water solubility and entrapment rate (Shlar et al., 2017; Siva et al., 2020).

Hydrogels containing nanoparticles can offer outstanding mechanical performance and improved controlled-release of the drugs (Jiang et al., 2020). The combination of β-cyclodextrin and hydrogel can also be used in polysaccharide-based hydrogels, which can load hydrophobic drugs and exert a controlled-release effect, and the mechanical strength of composite hydrogel will be higher than single component hydrogel (de Oliveira et al., 2021; Gupta et al., 2019). Moradi et al. (2020) manufactured a chitosan/polyvinyl alcohol hydrogel and thyme oil/cyclodextrin IC as a drug carrier used in different fields. β-cyclodextrins can easily be functionalized, have inherent biocompatibility with hydrogels, and form a host-guest (HG) inclusion structure (van de Manakker et al., 2009). Whereas, there are limited studies on the hydrogel containing MCD and SSPS via EDC/NHS cross-linking method, so its application potential can be explored in the field of food packaging.

Inspired by previous studies, an antibacterial SSPS hydrogel was constructed in this study with the addition of MCD/SEO-ICs as the prominent antibacterial regent. The characteristics of this material were clarified by scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR), fluorescence spectroscopy, and texture measurement. In addition, the chemical composition and antibacterial activity of SEO were also studied, and the successful synthesis of MCD/SE-ICs was verified. There are many hydroxyls and amino groups on the SSPS polymer chain to provide cross-linking basis. As a non-toxic and biocompatible cross-linking agent, EDC and NHS promoted the formation of a hydrogel structure by forming amide bonds between SSPS molecules (Graphical abstract). Its impact on meat quality has been evaluated by the applied research in chilled pork meat.