Authors: Apurva Sharma, Priti Saha and Vankayala Jaya Sravani
Introduction
Edible films can be prepared from protein, polysaccharide and lipid materials. Among them, protein based edible films are the most attractive. These films have impressive gas barrier properties compared with those prepared from lipids and polysaccharides. The mechanical properties of protein-based edible films are also better than those of polysaccharide and fat-based films because proteins have a unique structure (based on 20 different monomers) which confers a wider range of functional properties, especially a high intermolecular binding potential. However, the poor water vapour resistance of protein films and their lower mechanical strength in comparison with synthetic polymers limit their application in food packaging.
What is edible film?
It is defined as thin continuous layer of edible material formed on or placed between food and food components. Selection of edible film material is based on moisture barrier properties and gas barrier properties also mechanical strength of the bio material and type of food where the edible film is going to be coasted.
Advantages of edible film
- Can be consumed with food
- Eco-friendly
- Non toxic
- Reduce cost utilization of by products
- Increases nutritional properties of food.
Classification of edible films and coatings
Edible films can be produced from materials having film forming ability. During manufacturing, film materials must be dispersed and dissolved in a solvent such as water, alcohol or mixture of water and alcohol or a mixture of other solvents. Plasticizers, antimicrobial agents, colours or flavours can be added in this process. According to the biomaterial/base material used film are classified into four types –protein based, lipid based, polysaccharide based and composite based.
Two or more base material used for improving the quality of edible film called composite film. Generally one type of base material is mixed with other type of base material in different fraction.
Main components generally used for film formation
The main components include base material (carbohydrate, lipid, protein), solvent (water, ethanol and ethanol-water mixtures) and structure or shape forming material (plasticizer or cross linking agents).
Principle of film formation
By applying heat, acid and enzyme treatment to base material (carbohydrate, lipid, protein), its native state changes to film forming state and this process is called co-aceravation. Edible film coatings are formed by simple, complex and thermal co-acervation.
Properties of edible films
Moisture barrier
Edible films based on milk proteins have a limited capability to retard moisture loss. They are generally not suitable for the situation in which control of water vapor transmission is the primary objective. Incorporation of lipid materials to protein based films can effectively improve moisture barrier. The water vapor transmission of edible films can be improved by using both ultrasound and microfluidization treatments.
Gas barrier
Milk protein based films shows excellent gas barrier properties, especially at low humidity. It can be used as main oxygen barrier material in regulating respiration and oxidation. The major advantage of whey protein based films over polysaccharide based films is lower gas permeability. Gas barrier properties of milk protein based films are also better than those of several commonly used inedible, synthetic films. This feature can be used to form integrated packages of milk protein films and synthetic polymer films.
Mechanical strength
Milk protein based films have relatively smaller stretch-ability than high density polyethylene and low density polyethylene. It was also found that the elongation, tensile load and loading strength of milk base edible film are poor than synthetic film. The mechanical strength of edible films based on milk proteins improved by using micro fluidization technique. Plasticizer and cross linking agents are also increases the mechanical strength of film.
Applications
- As edible packaging material for packing nuts and tomato
- Prevents the oxidation of fruits
- Microencapsulation of fat
- Enzyme immobilization
- Wrap and pouches.
About Author / Additional Info:
PhD. Scholar at National Dairy Research Institute