Packaging Innovations of Meat and Meat Products: Comparison
Please note this is a comparison between Version 1 by Marian Gil and Version 2 by Catherine Yang.

In edible packaging, the application of natural and renewable biopolymers is gaining popularity as, unlike petroleum-based plastic packaging materials, they do not cause environmental problems. Packaging using active compounds further extends the shelf life of food products compared with traditional packaging by reducing the adverse effects during storage, such as oxidation, microbial growth, and moisture loss. On the other hand, the inclusion of natural bioactive substances in packaging provides an opportunity to increase the shelf life of food products and/or decrease the use of preservatives.

  • active packaging
  • electrospinning
  • bioactive substances

1. Natural Polymers in Food Packaging

The environmental problems caused by conventional polymers have necessitated the search for alternative packaging materials. Biodegradable films based on biopolymers have become such an alternative [1][31]. In 2020, bio-based plastics used in food packaging amounted to 0.99 million tons, accounting for 47% of the total production of bio-based plastics [2][1]. The raw materials for the production of biopolymers are relatively plentiful, and the production of biopolymers consumes agricultural waste, which, together with the environmental benefits, makes the production of biopolymers profitable [3][32].
Biopolymers are popular in food packaging because they are edible and safer for humans. For applications in food packaging, the most frequently studied nanocomposite biomaterials are proteins, carbohydrates, and their derivatives [4][5][6][7][33,34,35,36]. To achieve an environmentally friendly alternative and promote sustainability goals, cellulose- and starch-based nanocomposites can be incorporated into packaging systems [8][37]. Examples of natural antioxidants for lipid food include, among others, edible films and coatings with an active coating based on cellulose derivatives, chitosan, alginate, galactomannans, or gelatin [9][38].
Cellulose is the most abundant biopolymer in the world, making it an ideal raw material for use in sustainable packaging materials. Cellulose ethers, such as methylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, and carboxymethylcellulose, are suitable for the production of packaging films [10][11][7,39]. Cellulose is obtained from natural sources such as wood, cotton and food waste, agricultural waste, cereal bran, and fruit skins [12][40]. Its availability from many different sources and being biodegradable, environmentally friendly, and inexpensive have made cellulose an often-preferred material in packaging [13][41]. Besides being edible and biodegradable, its sensory and organoleptic properties are beneficial; therefore, cellulose can be used in the encapsulation of bioactive substances to enhance the nutritional properties of food products [12][40].
Starch is one of the most crucial biodegradable polymers because of its abundance, low cost, biodegradability, and renewability [14][15][42,43]. Starch-based films have been used in food packaging and preservation technologies as they show excellent film-forming ability and unique gelatinization properties, along with their odorless, tasteless, and colorless nature [16][17][5,44]. So far, starch-based films have been extensively used in the packaging of different types of food products (such as meat, fruit, oil, and cheese) as they have good organoleptic and gas barrier properties [18][19][45,46]. However, starch-based materials are brittle and hydrophilic, which limits their processing and use. Starch is mixed with various synthetic and natural polymers to improve its properties; this increases the strength of the processing properties of the materials [20][47].
Another biopolymer is chitosan, which is derived from chitin. Chitosan films have shown good antibacterial and antioxidant performance for food packaging. The amino and hydroxyl groups in the structure of chitosan affect its antimicrobial activity against gram-positive and gram-negative bacteria [21][48]. Chitosan-based films have a high gas barrier. Their brittleness eliminates the use of plasticizers such as polyols (glycerin, sorbitol, and polyethylene glycol) or fatty acids (stearic and palmitic) [20][47].
Being a water-soluble natural polymer, gelatin is a protein of biological origin, which shows high biodegradability, biocompatibility, water absorption, nonimmunogenicity, and commercial availability. Thanks to these properties, various forms of gelatin (e.g., foils, scaffolds, capsules, filters) are used in cosmetics, pharmacy, medicine, food, and water filtration [22][49]. However, due to its hydrophilicity, its structure needs to be stabilized because, in the absence of biopolymer stabilization, gelatin-based materials tend to dissolve and lose their structure [23][50].
Among the methods available for gelatin structure stabilization, protein crosslinking is one of the most commonly used approaches to achieving hydrolytic stability of samples based on gelatin [24][51]. Crosslinkers such as glutaraldehyde and genipin are extensively used in this regard. However, there exist potential toxicity issues, along with the need for intensive detoxification strategies considering residual unreacted glutaraldehyde groups. In addition, the high cost of genipins is one of the primary disadvantages while using these crosslinkers [24][25][51,52]. The gelatine-based packaging material has a good oxygen barrier compared to other biopolymers and has the ability to be welded, which is important in the production of packaging. The production of gelatin foils is relatively simple; it does not require special conditions for drying and forming the foil [26][53]. To prevent the risk of toxicity and achieve cost-effectiveness, heat treatment of gelatin along with sugar particles has recently been introduced as an alternative chemical crosslinking method [27][28][54,55]. The resulting condensation reaction between proteins and sugar is called the Maillard reaction (MR) [23][50].
Gelatin-based materials show different properties (e.g., solubility, swelling, antioxidant activity, preservation of morphology after immersion) based on the degree of MR, which depends on parameters such as type of sugar, reaction time, temperature, and pH of the solution. As crosslinkers, pentoses (e.g., ribose) are more reactive than hexoses (e.g., glucose) and disaccharides (e.g., lactose) [29][56], whereas an increase in the percentage of sugar (up to a certain point), temperature, or pH of the solution induces a further extended response [23][30][31][50,57,58].
To enhance the bioavailability and stability of thiamine in raw and cooked red meat and salmon samples, the thiamine nanofiber nanocoating process has been successfully applied. Specifically, for salmon samples, this process is found to be more effective regarding bioavailability. In addition, it ensures a continuous increase in the thiamine content in red meat and fish samples under cold storage conditions for 3 days. Whereas a maximum bioavailability of 87% was reported for nanocoated red meat samples, for salmon samples, a 94% bioavailability was achieved. Therefore, given these results, in future, this nanotechnology application may play a leading role in the food industry [32][59].
The most successful edible protein film available on the market is a sausage casing made of collagen. The films reduce leakage and prevent discoloration and fat oxidation of thawed and chilled beef steaks. Collagen-based films are used for processed meats to increase juiciness, reduce drip. For many years, the Japanese meat industry has commercially used films and coatings based on polysaccharides. During processing, the coatings dissolve and integrate with the meat, which has a positive effect on the texture and reduces weight loss, ensuring higher yield [33][60].

2. Electrospinning

Nanofibers are obtained using electrospinning techniques that use electrostatic forces to form fibers and non-electrospinning techniques that use mechanical force. These include phase separation, drawing, template synthesis, self-assembly, etc. [34][61].
Electrospinning is a versatile, cost-effective, and convenient method to produce nano-/microfibers with a high surface-area-to-volume ratio, controlled dimensions, high load capacity, low weight, and wide-ranging flexibility [35][62]. Furthermore, with decades of evolution, electrospinning nanofibers can now be designed with various structures and morphologies to perform specific functions, such as uniaxial [36][63], hollow [37][64], core–shell [38][65], and porous structures [39][66].
Electrospinning is an easy and versatile nanotechnique for producing nonwoven nanofiber films. Its advantages are as follows: a high surface-area-to-volume ratio, increased porosity, small interfibrous pore size, and high gas permeability. It is widely used in natural and synthetic polymers [16][40][5,67]. Thus, electrospinning has gained interest in, among others, textiles, agriculture, water treatment, air filtration, energy storage, cosmetics, electronics and sensors, pharmaceuticals, biomedical products, and packaging [22][23][41][49,50,68].
Among innovative approaches to packaging, electrospinning has gained huge interest in the biomedical and the food industries, especially in meat packaging [42][43][44][45][46][23,69,70,71,72]. The rapid development of electrospinning has resulted in numerous applications in various fields, including biomedicine [47][73], food packaging [48][74], sensors [49][75], protective materials [50][76], textiles [51][77], energy [52][78], oil–water separation, and others [53][54][17,79]. Several applications of electrospinning have been found in food science, e.g., protecting bioactive ingredients from external factors by encapsulating them [55][56][57][80,81,82] and extending the shelf life of a food product by improving its bioavailability and controlled release of biomolecules [58][59][60][83,84,85].
Compared with traditional casting films, electrospun nanofibers show numerous unique characteristics such as high surface-area-to-volume ratio, nanoporous structure, high porosity, and high absorption capacity [35][61][62,86], which make them more sensitive to the surrounding changes in acidity/alkalinity and make it possible to control the release of the contained bioactive compounds. Thus, of late, electrospun nanofibers have gained much attention in developing food packaging films [62][63][64][14,87,88].
In addition, being a nonthermal process, electrospinning helps maintain the structure stability, particularly when using additives with low thermal stability at high temperatures. The process of electrospinning can be briefly divided into three steps as follows: (1) formation of a conical shape (“tailor’s cone”) by a charged drop of a polymer solution; (2) formation of a jet at the end of the cone if the electric field strength is sufficient to overcome the viscoelastic force of the solution; and (3) deposition of a solid jet on the collector surface and production of many fibers, with rapid volatilization of the solvent [16][65][5,89]. To obtain fibers using solution electrospinning, various materials—including synthetic and natural polymers and their combinations—can be utilized. Among them, synthetic polymers such as polystyrene and polyvinyl chloride, biocompatible and biodegradable synthetic polymers like polylactic acid and polylactic-co-glycolic acid, conductive polymers such as polyaniline and polypyrrole, and natural polymers such as chitosan, alginate, collagen, and gelatin can be directly electrospun into nanofibers [23][66][67][68][69][70][50,90,91,92,93,94].
The electrospinning technique has been used to develop high-performance packaging materials in the food industry, due to its unique advantages: it can produce (1) micro-/nanofibers to encapsulate unstable bioactive molecules and load with nanoparticles; (2) edible packaging nanofibers from biopolymers, which show excellent biosafety; and (3) nanofibers for the controlled release of bioactive compounds under a specific stimulus [53][17].
Natural polymers, especially polysaccharides and proteins, are frequently used to produce nanofibers due to their biocompatibility, nontoxicity, food-grade properties, and biodegradability [71][95]. In addition, their diversity of functional groups enables a wide range of active ingredients to be bound or trapped using molecular interactions [72][96]. Functional electrospun mats can be used to develop nanocomposite material from a diverse range of performance-enhanced plastics for packaging applications. In addition, they can be used to reinforce the physical properties of both plastics and bioplastics as transparent gas barrier layers or even as new technologies for designing bioactive packaging with antimicrobial protection and delivering nutraceuticals to food products [73][97]. Numerous electrospinning stimuli-responsive materials have recently been synthesized, which can achieve the controlled release of active substances, thus producing a long-term biological effect [74][75][98,99].
Nanofiber mats are promising candidates in AP [76][100]. In the AP industry, nanofibers are highly useful tools to protect and deliver bioactive compounds to their destination at the desired time [77][78][101,102]. Electrospun nanofibers can improve the barrier and antimicrobial properties of materials in food packaging depending upon their functional properties. These nanofibers can also be utilized as nanosensors to detect and monitor the conditions of the food product during transport and storage [79][103]. These biological polymers can be based on proteins, lipids, or polysaccharides [80][81][82][104,105,106]. This advanced technology is originally derived from the enrichment of antioxidants in packaging designs [83][84][85][86][107,108,109,110].
Electrospun fibers show a good capacity to charge active substances, and their huge surface area leads to a rapid response to internal and/or external factors by releasing/activating the trapped compounds in a timely manner [66][71][87][90,95,111].
Thus, as a new technology, electrospinning can improve the overall quality and extend the shelf life of fresh or packaged meat products [71][95], including (1) protecting products from microbial contamination [45][88][89][3,71,112], (2) preventing lipid and protein oxidation [90][91][113,114], (3) developing sensory properties [44][59][70,84], and (4) improving the functional and nutritional characteristics of meat products [92][22]. Electrospinning enables the incorporation of antimicrobial compounds into the matrixes/or packaging mats and allows for a functional effect on the surface of meat or products—where the microbiological activity is located—instead of mixing them directly with food [93][115].
Starch-based films with nanofibers show an extremely high surface activity, which makes them potential candidates for active food packaging due to their nanosize [53][17]. In addition, the morphology and structure of electrospun starch fibers can be easily altered to protect numerous active substances and enhance the mechanical and barrier properties [94][116]. Several factors like fiber orientation, additional ingredients [95][96][117,118], and final processing [97][119] can influence their properties required for food packaging [16][5].
Results show that zein-based coatings are more suitable in the packaging of food products with a high water content [98][120]. Yildiz et al. [99][121] developed an electrospun chitosan/polyethylene/curcumin nanofiber to monitor the freshness of chicken meat. Duan et al. [62][14] showed that curcumin-loaded nanofibers provide the ability to monitor chicken spoilage in the real world.
The challenge is to overcome the unreliability of bio-based plastics. There is a need to develop a multilayer mixture using additives [2][1]. In conclusion, electrospinning seems to be a promising technique with potential applications in the fields of functional food products and AP [78][102]. The advantage of electrospinning is its simplicity, the possibility of using it in a wide range of materials, and its low cost [34][61].

3. Antioxidant and Antimicrobial Compounds

Many meat products are considered highly perishable because of their high nutrient content. Temperature is the major factor in the activation of the growth of microorganisms and chemical reactions; thus, the cooling temperature has a significant impact on their properties. However, variations in the temperature during storage and transport can impair the quality of the products, e.g., by increasing microbial growth and chemical reactions such as increasing peroxides and thiobarbituric acid (TBA) values [100][101][122,123].
To increase the commercial value and safety of beef, cold storage methods and cold chain logistics have been developed and widely used. These methods are used in preserving raw beef, especially in freezing and chilling [102][103][124,125]. Freezing below −18 °C significantly extends the shelf life of meat products but degrades the quality of the meat in the freezing–thawing process. In comparison, storage at 4 °C can preserve the sensory quality of meat and lower the energy consumption; however, it cannot inhibit the growth of microbes completely, in particular some psychrophiles, so the shelf life of the products is limited [102][104][28,124].
The meat industry is interested in achieving packaging durability goals and producing modern solutions based on bio-based, biodegradable, compostable, recyclable, or reusable materials [105][126]. Increasing demand for meat has urged significant advances in meat packaging, guaranteeing healthy and safe products. Meanwhile, the safety and quality of meat are dependent on the packaging materials and technologies applied [89][106][112,127].
Innovations in food packaging nanomaterials are primarily attributable to their following distinct characteristics: excellent optical, barrier, and thermal properties, antimicrobial activity, and advanced sensing properties affecting their chemical, physical, and biological potential unlike their bulk counterparts [8][107][37,128].
Nanomaterials consisting of TiO2 [108][109][129,130], SiO2 [110][111][131,132], AgNPs [112][133], graphene [113][134], and nanocellulose [114][135] possess remarkable characteristics such as high catalytic activity and conductivity, which make them quintessential candidates for biosensory abilities [8][37].
Exemplary electrochemical immunosensors that are appropriate for the detection of Salmonella in meat samples have recently been found in the literature [115][136]. For example, graphene is a fully reliable biosensing nanomaterial that can be easily integrated with smart packaging systems. Graphene-based nanofibers and electrodes are applied in the development of a flexible detector for ethanol [116][137], histamine [117][138], and ammonia [8][118][37,139]. Among these films, pigment-based natural colorimetric films have gained considerable attention due to their nontoxicity, biocompatibility, nature of pH sensing, and others [119][120][140,141]. These pH-sensitive colorimetric films can show visible color changes while reacting with non-neutral volatile gases generated from high-protein degraded food products, which can provide visual information about the quality and microbial contamination of the food product [61][62][121][122][14,86,142,143].
To delay lipid oxidation and reduce chemical additives causing health disorders, functional packaging using natural antioxidants is applied to extend the shelf life of meat products [89][123][124][112,144,145].
Antioxidant and antimicrobial compounds used in food packaging are of different origins: natural, such as essential oils, nisin, curcumin, α-tocopherol and vitamins, phenolic-rich plant and pomace extracts, allyl isothiocyanate, and chitosan [125][126][146,147]; synthetic antioxidants, such as butylhydroxytoluene and its analogs, butylhydroxyanisole, and t-butylhydroxyquinone [42][23]; or antimicrobial, such as organic acids (acetic, sorbic and ascorbic, benzoic and propane), nitrites, and nitrates [127][128][148,149].
Thymol, which is the primary component of thyme oil (classified as Generally Recognized As Safe by United States Food and Drug Administration), is a promising alternative to chemical preservatives with good antimicrobial and antioxidant properties [129][150]. Although thymol’s potential as a food preservative has been widely discussed, its use in film/coating formulations is highly limited due to its high volatility and hydrophobicity [130][151]. Given these issues, particular attention has been paid to the encapsulation of plant-derived bioactive compounds in biopolymer nanocarriers [104][131][26,28]. Lin et al. [132][152] used gelatin nanofibers that contain thyme essential oil/ε-polylysine β-cyclodextrin nanoparticles to control the growth of Campylobacter jejuni on the surface of poultry with no effects on the sensory and textural properties and color. The packaged chicken samples showed lower aerobic bacteria counts, total volatile basic nitrogen, trimethylamine and TBA content, and pH values [101][123].
Cinnamaldehyde (3-phenyl-2-propenal), a component of natural cinnamon oil with a common flavor, is one of the important antioxidant and antimicrobial agents. It can be used to improve the quality of food products and extend their shelf life. Its sensitivity to heat, light, humidity, oxygen, and liquid form at room temperature necessitates its encapsulation. Zein nanofiber mass containing 1000 ppm loaded with cinnamaldehyde showed good bactericidal activity against Staphylococcus aureus PTCC 1337 (Persian Type Culture Collection (PTCC)) and Escherichia coli O157:H7 with no significant adverse effects on texture or color in nitrite-reduced sausages [101][123]. The number of E. coli and S. aureus (colony-forming unit/g samples) decreased in all sausages during storage due to the presence of zein nanofibers with cinnamaldehyde as an antibacterial agent and nitrates [101][123]. Many studies [59][133][134][135][84,153,154,155] reported that cinnamaldehyde, zein nanofibers with cinnamaldehyde, and nitrites show long-term growth inhibition of S. aureus and E. coli. After 10 days of storage, samples with packages containing phase change materials used for temperature buffering did not contain E. coli and S. aureus bacteria [101][123].
Using unstable substances in AP, positive results are observed in nanoencapsulation techniques, including nanoparticles, nanoemulsions, and nanocapsules. This prevents the degradation of, for example, saffron bioactive compounds under adverse conditions until they are delivered for physiological purposes [136][156]. In this context, electrospinning and electrospraying have recently gained increased interest in encapsulating bioactive ingredients and food packaging. These methods are simple, versatile, nonthermal, and thus highly suitable for the encapsulation of heat-sensitive compounds [137][138][139][157,158,159]. Studies [139][159] have indicated that electroyarn containing 30% zein and 10% saffron extract show great potential in extending the shelf life of seafood products and delaying their spoilage during cold storage.