Packaging plays a vital role in preservation of term and extent of shelf life of meat. Without packaging, the processing of food can become compromised as it is contaminated by direct contact with physical, chemical, and biological contaminants. In recent years, the development of novel food packaging (modified atmosphere and active packaging) has increased the shelf life and quality of food, thereby bringing convenience to consumers. However, most of the food packaging materials have developed from non-biodegradable and non-renewable materials. These non-biodegradable packaging materials cannot imbibe preservatives and can only pose barrier properties to moisture, air and gases. Majority of these packaging materials used are different types of plastics viz. polyethylene, nylon, polyester etc.
In recent years, the usage of plastics for the packaging of food products has increased many folds. It is increasing at an alarming rate of 4 percent and is estimated at 310 million tonnes annually around the globe (Plastics Europe, 2014). This has posed serious environmental threats and loss of precious fossil fuels. Per capita consumption of plastic in India is around 5kg/year and of the world is 25 kg each year, expected to increase in the coming years. Synthetic plastics pose the problem of disposability after their use by consumers. The problem of plastics is not only limited to land but also threatens aquatic/sea life and land animals as well. Further, it is a common practice to burn the wastes including plastics in the open area on the road sides. This causes emission of harmful gases and volatile products in the environment, that are even more dangerous than the plastics in their native form.
Development of bio-based plastics from the by-products of dairy and animal industries is an innovative concept. This will have a dual beneficial impact in comparison to non-biodegradable plastic, in the form of environmental protection, effective utilization of waste from dairy/animal industry and revenue & employment generation. Therefore, the problems of environmental pollution and the 79 limited petroleum resources have encouraged scientists to develop ‘bio-based plastics’, meaning plastics derived from bio-based materials such as polysaccharides, proteins and lipids etc. While these are renewable resources, a lot of research is required to develop and improve the quality characteristics of such packaging materials.
These biodegradable films have a variety of advantages such as biodegradability, edibility, biocom-patibility, aesthetic appearance and barrier properties against oxygen and physical stress.
Characteristics of Biodegradable Films
An edible (biodegradable) film is a thin continuous sheet formed from a biopolymer matrix that is cohesive enough to have the physical integrity to stand-alone and possesses biodegradability. One of the most familiar examples of edible packaging is natural casing for sausages. These have been used in food preservation since the 12th century, when wax coatings were used on vegetables and fruits, for larding of meat products, for lengthening of shelf life, and to avoid drying of food products. Corn zein was employed commercially as a food coating since World War II to enhance food appearance (Lawton 1992).
Polysaccharides have been extensively used as study material for biodegradable packaging. Various natural cross linking agents used are sodium alginate, CMC, cellulose, gelatin, etc. Linking of proteins with polysaccharides can improve barrier properties of the developed films. They also provide strength to the film matrix. Addition of polysaccharides in the film matrix improves the physical and mechanical properties.
Chitin, the second most abundant natural polysaccharide on earth after cellulose, is the structural component of the exoskeletons of crustaceans, insects, mushrooms and cell walls of certain fungi and green algae. Crustacean shells are regarded as the main source of chitin for the chemical industry. Chitin is insoluble in water, in common organic solvents as well as in acidic, basic and neutral aqueous solutions. Chitosan [poly-?-(1 ? 4) N-acetyl-D-glucosamine], is the N-deacetylated derivative of chitin. Chitosan is of special interest in biodegradable antimicrobial (bioactive) packaging, because it is cationic and naturally antimicrobial. Chitosan based films have antimicrobial activity mainly due their protonated amino group, which interferes with negatively charged ions. The properties that make chitosan commercially important are biodegradability, biocompatibility (in both plant and animal tissues), non-toxicity, allerginicity and the ability to transform into gels, beads, fibres, colloids, films, flakes, capsules and powders.
In recent years, protein-based films have gained more importance and use as bio-degradable packaging material because of their advantage as edible packaging over synthetic films. Protein-based films are hydrophilic in nature, which limits their use in high moisture food systems, causing poor performance as barrier materials. Hydrophilicity and thus barrier properties can be improved by addition of structuring agents such as lipids and emulsifiers that increase structural complexity, gel strength and resistance to heat denaturation. Furthermore, protein-based edible films can function as carriers of antimicrobial and antioxidant agents. Animal proteins (whey, casein, zein, ossein, egg proteins) based films have better mechanical and barrier properties than polysaccharide based materials and other plant protein based films. The mechanical and barrier properties of biodegradable films is directed by quality of raw material and additives, as the presence of triglycerides in milk protein networks significantly improves water vapour properties, due to low polarity. In addition, the incorporation of natural antimicrobial and antioxidant substances in the milk-based films may help in the extension of storage life of meat products.
Whey proteins have excellent intrinsic nutritional as well as functional properties, which are required for formation of edible films and coatings, both in the denatured as well as native forms. The film forming properties include water solubility, gelation and emulsification properties. Since whey protein based films are water based, they are generally flavourless, tasteless and flexible in nature. However, important factors which affect the physical features of the film are purity, composition of protein sources and formulation of the film.
Film formation requires the necessity of the initial unfolding (partial or total) of the proteins, thus resulting in protein aggregation and finally gel formation. The various methods employed for film formation are heating, ?-irradiation, cross-linking of agents (enzymes), addition of chemicals, change in net charge, and increase in hydrostatic pressure, cooling, or partial enzymatic hydrolysis.
Lipid-based films are mostly used as moisture barriers, especially for fresh fruits and vegetables. Lipid based films have improved water vapour permeability, however they significantly affect the young’s modulus, tensile strength, elongation. The amount and type of lipids used are critical determining factors of the water vapour permeability value of films formed from protein-lipid emulsions. Crystalline lipids provide better barrier characteristics to moisture transport than liquid lipids.
Application of Bio-based Packaging in Meat Industry
Protein and lipid based polymers have good potential as bioactive packaging due to their mechanical and barrier properties. Such films can mechanically protect foods and can prevent quality losses of foods due to mass transfer (e.g. moisture, gases, flavours, etc.). In fact, they can also prevent surface as well as post processing contamination from microorganisms. Indeed, these films can be used as excellent carriers of natural or chemical antimicrobial agents, antioxidants, enzymes or functional ingredients such as probiotics, minerals and vitamins and other food additives. Raw meat and meat products have been successfully coated and preserved for sufficient periods of time (Chatli et al. 2014) with satisfactory sensory acceptability and shelf stability. Jandyal, 2016 also used soy protein isolate based films for the protection of egg koftas incorporated with cinnamon oil and liquorice extract which was able to extend their shelf life up to 20 days under aerobic and 35 days under vacuum packaging conditions.
Biodegradable packaging films offer alternative ways of packaging without adversely affecting the environmental costs while maintaining ecological balance. These can be incorporated with antioxidants, antimicrobials or natural extracts in the film formulation. They can be wrapped on ready-to-eat products for extending their shelf-life and for widening their marketability. They can serve to protect the food quality during storage, transportation and retail merchandising while ensuring food safety and decreasing the environmental burden.
The Authors are from Division of Livestock Products Technology, Indian Veterinary Research Institute, Izatnagar Bareilly-243122, Uttar Pradesh