Effect of oregano essential oil and resveratrol nanoemulsion loaded pectin edible coating on the preservation of pork loin in modified atmosphere packaging
Introduction
Meat such as pork is a highly perishable product because it is rich in nutrients and contains high levels of polyunsaturated fatty acids and protein, which are susceptible to oxidation and microbial spoilage (Huang et al., 2014). A variety of innovative meat packaging technologies have been developed, and modified atmosphere packaging (MAP) has been a widely used packaging for fresh meat preservation. The high oxygen (80% O2 and 20% CO2) MAP (HOMAP) is commonly used in retail meat markets to maintain the bright red colour of the meat to attract consumers while shifting the dominating bacteria to less spoilage flora to prolong the shelf-life (McMillin, 2008). However, the high levels of oxygen can also increase the oxidation of meat and lead to discolouration and off-flavour (McMillin, 2008) as well as increased toughness (Frank, Kaczmarska, Paterson, Piyasiri, & Warner, 2017).
Edible coating is another effective packaging to improve the quality and shelf-life of fresh produce, which can be used as a hurdle technology for HOMAP to solve its shortcomings. Among the edible coating materials, pectin has received much attention due to its non-toxic, odourless, renewable and biodegradable properties, and coatings made of pectin have low gas permeability and hence is a good barrier to prevent gas exchange (Espitia, Du, de Jesús Avena-Bustillos, Soares, & McHugh, 2014). Also, pectin coating can act as a good carrier for the bioactive compounds, such as antioxidants and antimicrobials, to further enhance food safety, quality and health benefits (Espitia et al., 2014).
Bioactive compounds from natural sources are increasingly popular with consumers, due to perceived health concerns associated with synthetic compounds; essential oils and polyphenols are the two main types of natural bioactive compounds used in edible coating to improve food preservation (Zambrano-Zaragoza et al., 2018). Oregano essential oil (OEO) is considered as one of the most powerful antioxidant essential oils, as it has been well documented to extend shelf-life of fresh meat by controlling both lipid and protein oxidation (Fasseas, Mountzouris, Tarantilis, Polissiou, & Zervas, 2008) and inhibiting microbial growth (Sivropoulou et al., 1996). Resveratrol (RES) is also a potent antioxidant and has been demonstrated to be more effective against meat oxidation than other well-known polyphenols such as carnosine, quercetin and rutin (Bekhit, Geesink, Ilian, Morton, & Bickerstaffe, 2003). It is also a phytoalexin, synthesised by plants against the attack by bacteria, viruses or fungi (Mora-Pale et al., 2015). However, direct application of OEO and RES may compromise the sensory quality of foods due to their intense and unique flavour and bitter taste (Fasseas et al., 2008, Koga et al., 2016).
Oil-in-water (O/W) emulsion is a promising system for loading these bioactive compounds into an edible coating, via encapsulation of the bioactives. This can not only minimise the direct impact of bioactive compounds on the sensory attributes, but also provide protection for these compounds (Davidov-Pardo and McClements, 2014, Koga et al., 2016). In addition, by reducing the particle size of the emulsion to the nano-scale (i.e. nanoemulsion), the functionality of the emulsion as a carrier can be further improved, resulting in better solubility and stability (Zambrano-Zaragoza et al., 2018). However, the use of nanoemulsion as an encapsulation system is still limited in pharmaceutical applications such as drug carriers (Jaiswal et al., 2015, Liu et al., 2014). The nanoemulsion encapsulation system has great potential to be developed in food applications. Therefore, the objective of this study was (1) to prepare OEO and RES active emulsion/nanoemulsions and investigate their stability at different temperatures (4 °C and 25 °C) during storage (15 days); and (2) then load the emulsion/nanoemulsions into pectin biopolymer matrix to develop edible coatings, and to investigate the effect of the coating on the fresh pork quality in HOMAP (80% O2 + 20% CO2) during cold storage (4 °C, 20 days).
Section snippets
Materials
Pectin from citrus peel (galacturonic acid ≥ 74.0% dried basis), food grade polysorbate 80 (Tween 80), ethanol and oregano essential oil were purchased from Sigma-Aldrich (Castle Hill, NSW, Australia). Pharmaceutical grade resveratrol (99% pure trans-resveratrol powder) was purchased from Megaresveratrol (Danbury, Connecticut, USA). All other chemicals were analytical grade and were purchased from Sigma-Aldrich (Castle Hill, NSW, Australia).
Preparation of emulsion and nanoemulsion
An oil-in-water (O/W) system was chosen to make the
Particle size and stability of emulsion and nanoemulsion
Nanoemulsion is defined as an emulsion with the particle size less than 100 nm (Gupta, Eral, Hatton, & Doyle, 2016). The particle size of the nanoemulsion and emulsion and their polydispersity index (PDI) are presented in Table 2. The initial particle size of the OEO nanoemulsion, OEO-RES nanoemulsion and OEO-RES emulsion were 48.49, 53.09 and 220.01 nm respectively. The particle size of the nanoemulsions (OEO and OEO-RES) were significantly smaller (P < 0.05) than that of the emulsion
Conclusion
Nanoemulsions (OEO and OEO-RES) with particle size about 50 nm were successfully prepared by a high-speed homogeniser and were demonstrated to be stable at 4 °C for 15 days. The prepared emulsion and nanoemulsions were successfully incorporated into the pectin matrix and then coated on fresh pork loins. Pectin coating (Solu-PEC) alone was effective in extending the shelf-life of pork, by minimising pH change, retarding lipid and protein oxidation, maintaining meat tenderness, and inhibiting
CRediT authorship contribution statement
Yun Xiong: Writing - original draft, Data curation, Visualization, Formal analysis. Shumin Li: Methodology, Investigation, Writing - original draft, Data curation. Robyn Dorothy Warner: Resources, Writing - review & editing. Zhongxiang Fang: Supervision, Conceptualization, Methodology, Writing - review & editing, Funding acquisition, Resources.
Declaration of competing interest
None.
Acknowledgement
This work was financially supported by the Australian Pork CRC LTD Scholarship.
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