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Research progress of plant essential oils in packaging field

In recent years, the consumption of packaged foods has risen significantly, growing at an annual rate of 5% in the global packaged food market, from a value of $1.9 trillion in 2020 to an estimated value of $3.4 trillion by 2030. Food packaging can maintain food quality and safety, improve food shelf life, prevent food waste, and avoid contamination that can occur in the food supply chain. In addition to its function as a barrier, packaging also creates a medium between food and consumers, providing basic information about the food and providing consumers with a first impression of the product. Despite these benefits of traditional plastic-based packaging, there are still concerns about the entire life cycle of food packaging and its impact on the environment, as well as the inestimable harm to human health. Therefore, the demand for the development of food functional packaging is increasing, green packaging materials have become the current research hotspot, antibacterial and antioxidant biodegradable active packaging technology, including label indicators, information traceability of intelligent packaging technology has come.

Natural plant essential oil is a kind of special fragrance and rich in phenols, aldehydes and ketones. It has the characteristics of strong penetration, low molecular weight, good antibacterial effect, easy absorption and resistance. Compared with traditional chemical antioxidants, natural plant essential oil has less potential harmful side effects on the human body, and is considered to be a suitable substitute for artificial food additives. It is often used in food industry production by seasoning and preservatives, and has a good application in the field of food packaging. So far, the application of plant essential oils in antibacterial and fresh-keeping packaging has been widely concerned by relevant scholars. Researchers in the food industry are trying to mix ingredients and functional essential oils into polymer substrates as active packaging ingredients, and extend their action time by controlling the release of active ingredients, so as to achieve the purpose of preparing a new active packaging material and successfully applying it to actual industrialization.

 

Antibacterial activity of plant essential oil

Microbial pollution and nutrient deficiency are often the main factors causing food spoilage, and the higher the nutrient content of food, the more susceptible to harmful microbial pollution. Microorganisms use the nutrients in food for their own growth and proliferation, causing food spoilage. After eating such food, it is easy to cause a variety of foodborne diseases and harm human health. Natural plant essential oil has good antibacterial effect and is relatively safe to human body. Therefore, it is very important to explore the antibacterial mechanism of plant essential oils for the development of new antibacterial agents.

The antibacterial mechanism of plant essential oil can be divided into the following four points: 

(1) Plant essential oil can affect the energy metabolism of bacteria and limit their life activities. Essential oils can penetrate bacterial bodies to produce reactive oxygen compounds, cause bacterial respiratory and metabolic disorders and oxidative damage, inhibit the expression of ATPase related subunits, and thus lead to bacterial death. Li et al. found that basil essential oil increased the disturbance of phospholipid tail hydrocarbon chain, and the inhibition of bacterial respiratory metabolism was realized through the hydrophobic interaction between α-bergamin and amino acid residues of phosphofructokinase and pyruvate kinase.

(2) Plant essential oils can destroy bacterial cell walls and cause morphological changes. When the concentration difference between inside and outside cells was large, the cells burst and died. The inhibition of juniper essential oil on spore germination and mycelia growth was concentrator-dependent. When the concentration of juniper essential oil was more than 10 μL/ mL, it showed strong inhibitory effect, causing mycelia to shrink, distort and deform.

(3) Plant essential oil can destroy the structure of bacterial cell membrane and enhance its permeability by interacting with lipids in bacterial cell membrane and mitochondria, causing a large amount of cell contents to leak and cause cell death. Wang et al. showed that litsea cubeba essential oil damaged the integrity of grisea mold cell membrane, resulting in changes in soluble reducing sugar, protein and ergosterol in the cytoplasm. With the increase of concentration of litsea cubeba essential oil, the ergosterol content in grisea mold cell membrane significantly decreased.

(4) Plant essential oils have the function of inhibiting DNA synthesis or causing DNA damage. Plant essential oil can cause ribosome dysfunction and mitochondrial disturbance of fungi, thus inhibiting the growth and reproduction of bacteria. Wang et al. confirmed that ginger essential oil inhibited the expression of genes encoding cell membrane-associated proteins and enzymes related to DNA metabolism. The penicillin-binding protein and acetylglucosaminolpyruvate reductase genes were down-regulated. In addition to the above mechanisms, some compounds in the relevant plant essential oils also inhibit the activity of bacteria in other ways. For example, studies by Misharina et al. showed that carvacrol can cause the leakage of potassium ions in bacteria, affecting proton movement, ATP synthesis and membrane permeability. Clemente et al. ‘s study showed that isothiocyanate sulfides could cause cell cycle arrest of bacteria, make bacteria form filamentous, restrict the flow of bacteria to inhibit their growth and delay decay.

Antioxidant activity of plant essential oils

Food oxidation is one of the important causes of food degradation, which can lead to shorter shelf life, lower sensory standards, reduced nutritional value and potentially toxic components. Oxidation during food processing or storage can be identified by color changes and the appearance of odors, while oxidation of lipids is not obvious.

The research on antioxidant properties of essential oils has been widely reported by scholars at home and abroad. Oregano essential oil can effectively remove oxygen-containing free groups in the process of aerobic metabolism, regulate cell apoptosis, autophagy and necrosis cycle, and thus have a certain impact on the quality of meat products. At the same time, it can directly invade lipid, nucleic acid, protein and other biological macromolecules, so that the color, tenderness and wind taste of meat can be changed. Khodaei et al. explored the chemical composition and antioxidant properties of 38 essential oils, and developed a mathematical model for predicting antioxidant properties. The fitting coefficients R2 were 0.865 and 0.79, respectively, providing a solution for the digital screening of essential oils with excellent antioxidant properties.

Application of plant essential oil in fruit and vegetable packaging

Fresh fruits and vegetables are easily contaminated by microorganisms during picking, processing, transportation and storage, resulting in reduced nutritional value of fruits and vegetables and shortened shelf life. In order to improve the quality and safety of products while maintaining good nutritional and sensory properties, plant essential oils show outstanding application potential in the fruit and vegetable preservation industry due to their rich sources of bioactive compounds.

There are many forms of plant essential oil most commonly used in fruit and vegetable packaging, such as paper-based preservation form, membrane-based preservation form, fumigation treatment, soaking treatment and so on. 

Liu Guangfa et al. selected thyme essential oil and clove basil essential oil, combined with PVA to produce antibacterial paper, which maintained the sensory quality of strawberry, reduced the decay rate and inhibited the total number of colonies.

 Zhao Yazhu and others also conducted research on this, and used thyme essential oil on A-type packaging cardboard to make A carton with antibacterial property, which can extend the shelf life of strawberries by 1 to 2 days. However, due to the volatile and poor stability of essential oils, essential oils are easily released quickly in the early stage of application, resulting in limited storage of fruits and vegetables in the later stage. Studies have shown that electrospinning technology can effectively solve this problem . 

Electrospinning technology has large specific surface area, high porosity, and fiber shape in the nano to micron range, which facilitates the continuous release of active ingredients from the packaging film to the food surface. Hosseini et al. found that the encapsulation rate of rosemary essential oil in electrospinning alcohol soluble protein fibers is close to 100%. 2.5%, 5% and 10% (V/V) rosemary essential oil loaded electrospun fibers have encapsulation rates up to 99.5%±1.3%, 99.7%±1.9% and 99.3%±2.5%, respectively. 

They can be used as active food packaging coatings to control the release and delivery of rosemary essential oil to food and gastrointestinal tract. Zhou Yunling et al. developed an emulsion electrospinning film with carboxymethyl chitosan as the outer layer and clove basil essential oil as the core, which reduced the weight loss rate and soluble solid content of cherry fruit, and had a good fresh-keeping effect. 

At the same time, electrospinning technology also has problems related to scaling up production and safety, the product yield is low and the electrospinning process requires high voltage, which can pose potential hazards to workers.

In the context of commercialization, microencapsulation technology requires simple equipment and can be used to improve the stability, water solubility and antibacterial properties of essential oils.

 The embedding rate and release rate of thyme essential oil microcapsules obtained by Cai et al. by co-precipitation method were 87.61% and 53%, which could inhibit the growth of Staphylococcus aureus and Bacillus anthracis, and had good potential in food packaging when used together. Cai et al. also confirmed the effect of starch film of thyme essential oil microcapsules on the quality and physical and chemical properties of mango, making the shelf life of mango at 25 ℃ up to 10 days, proving the potential of developing thyme essential oil microcapsules for fruit preservation. 

Microencapsulation of essential oils can also be produced using different methods such as emulsification, spray drying, freeze-drying, composite coacervation and melt extrusion. Li et al. prepared oregano essential oil microcapsules by spray drying method, and added Oregano essential oil into polyethylene film by melt blending and extrusion casting method, which enhanced the moisture permeability and air permeability of the film, effectively regulated the respiration of strawberries, and delayed the accumulation of CO2 and the release of O2 in the packaging. Song Wenlong et al. 

prepared the active packaging of polyethylene-ginger essential oil microcapsules, using chitosan-gelatin and ginger essential oil as the core material, and prepared ginger essential oil microcapsules by spray drying method. Compared with the film of the control group, the gas content in the packaging bag could be effectively controlled. 

The product can significantly delay the decline of quality, hardness and malondialdehyde content of okra, maintain its binding moisture content, delay the aging process of okra, maintain its good sensory quality and extend the shelf life of okra.

It also has unique advantages in the preservation of food and meat

 

summarize

The global demand for functional, environmentally friendly and efficient antibacterial food packaging continues to increase, and the development of more effective, sustainable and safe antibacterial materials has become a research hotspot in the field of food packaging. At the same time, food corruption and waste, human and animal poisoning and even death caused by foodborne microorganisms are widely concerned in the field of food safety.

 This paper focuses on the effects of plant essential oils on the antibacterial, antioxidant and pharmacological activities of packaged products, and evaluates the possibility of using essential oils in the packaging field according to the main deterioration mechanism and intended use of food and the different packaging requirements of different foods. 

Plant essential oils offer a safer alternative to the development of new functional packaging materials.
Despite these potential benefits of essential oils, there are many issues related to food packaging materials that must be overcome before their widespread commercial application. 

First of all, this type of food packaging is mainly prepared in small molds in research laboratories, without taking into account manufacturing costs. Therefore, more research needs to be invested in the future to reduce the processing and manufacturing costs of refined oil-based packaging materials in the future. Second, deeper applied research is needed on a wider variety of foods, especially high-value foods. 

Because for these foods, the additional cost of using this functional packaging technology is more reasonable. Ideally, future refined oil-based packaging materials should meet the conditions of being reusable, easy to recycle, and not causing damage to the environment after disposal and abandonment. 

At present, the relevant scholars on refined oil-based food packaging research is still in its infancy, but its antibacterial, antioxidant and prolong the shelf life of food has been fully verified, we believe that with the development of this field will bring a new generation of economic, convenient and sustainable packaging materials.

 

The above information is from Modern Food Science and Technology, DOI:10.13982/j.mfst.1673-9078.2023.10.0934 Author: Mohan LI , Liyong JIAO

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