Edible Coatings- An emerging preservation protocol


Authors: Loveleen Kaur Sarao1  and Ajay Singh2

Extending the shelf life of the perishable food products such as raw fruits and vegetables, milk, meat, fish, eggs is the biggest challenge being faced by the food preservation technologies.  The extension of shelf life assists in meeting the daily nutritional demand. The presently used preservation techniques focus on the suitability of the process in use and the production of environment friendly products.  Such products should have added nutritional benefits without imparting any adverse effect on the health. 
An emerging preservation protocol is the one which employs the use of edible films and coatings. The use of films and edible coatings are an alternative to the conventional packaging.  This provides the main features for these biodegradable packaging which should be met towards specific uses for the conservation and improvement of different food products. The commonly used components are the biopolymers, additives, bioactive components and probiotics. 
An edible film or coating is the material having a thickness of less than 0.3 mm. This film or coating is formed by combining biopolymers with different types of additives. The edible coating is formed directly on the food itself. On the contrary, the edible film is first made and then adhered to the product. Rigid matrices with similar characteristics are formed via both these methods.

Often, edible films and coatings undergo evaluation for their mechanical properties, such as elasticity modulus (EM), elongation at break (E), and tensile strength (TS). This refer to their elasticity and rigidity and the force required to break them. They display similar mass transfer phenomena (i.e., permeation, adsorption, and diffusion), which is related to the transport of solutes between food and the atmosphere. However, both mechanical properties and mass transfer phenomena are impacted by the type of material and manufacturing protocol which allows the generation of different structures of biopolymeric matrices.

One of the universal biopolymer for bio-packaging is starch.  It has been widely used for decades owing to its characteristics and gelatinization properties. Another important biopolymer having the ability to form hydrogels and encapsulation barriers is alginate. Recently, chitosan has gained attention for the elaboration of edible films and coatings. This is so as it is a gelling agent and has desirable chemical (forms hydrogen bonds and hydrophobic interactions) and biological (biocompatibility, biodegradability and bioactivity) properties. Other natural components for the formulation of packaging includes proteins (collagen and protein isolates), lipids (canola oil and cinnamon bark oil), amongst the other unconventional materials (e.g.,smooth-hound protein and papaya puree)  for producing  bio-packaging with targeted characteristics.

The role of additives such as plasticizers or stabilizers in the formulation of edible films and coatings is to modify the mechanical properties (for increasing the E and decreasing TS and EM) and mass transfer phenomena. In addition to this, the incorporation of antioxidant, fungicidal, or microbial additives allows obtaining bioactive bio-packaging. 
Following are the main benefits offered by the edible films and coatings:

1.protection against UV light
2.barrier against mechanical damage such as  dents or cuts
3.increasing  the shelf-life of the product
4.transport of solutes ( salts, additives and pigments) water vapor, organic vapors (aromas and solvents) and gases (oxygen,carbon dioxide, nitrogen, and ethylene) between food and the atmosphere
5.bioactive components (antioxidants) 
6.antimicrobial effect against bacteria and fungi (silver nanoparticles) 
7.healthy microorganisms ( probiotics) that confer benefits to the consumer
8.biodegradable natural materials

In the present times, bioactive compounds and microorganisms such as probiotics are added into sustainable packaging for extending the functionality and nutrition of perishable and natural foods. They influence the product quality, shelf-life, maturation, darkening effect, and the inhibition of pathogens. Bio-packaging meets the requirements for the protection of minimally processed foods. Their usage indicates an economic saving related to the loss of food due to natural maturation, managing to extend the shelf-life of the product. Based on the biomaterials employed and the types of biologically active compounds, specific properties, such as sensorial, physicochemical and nutritional characteristics, in coated products can be improved.

Author’s Bio
Affiliations: 1. Punjab Agricultural University, Ludhiana
2 Head, Department of Food Technology, Mata Gujri College, Fatehgarh Sahib.