PROTEIN-BASED EDIBLE FILMS A REVIEW :

The edible or bio-degradable films are materials which compose of suitable means to increase the storage time of food and improve their condition externally conductive to environmental contamination. The protein, lipid and polysaccharide are materials can form the edible film. Were proteins based edible films are considered mainly appropriate in food coating. Collagen, gelatin films, corn zein, wheat gluten, soy protein, casein and mung bean protein are the most types films used in coating food. The protein edible films have remarkable gas block features equalled to films made from polysaccharides and lipids. These films have mechanical properties which make it best than polysaccharide and fat based film Although the water vapor permeability is low and the tensile strength is less than the polymers used in the packaging, many modifications have been used to improve the functional properties of the film via physical, chemical and enzymatic methods and bonding with hydrophobic materials and some polymers on (24) . (38) measured the thermogravimetric analysis TGA of 20%, 10% PVA polyvinyl alcohol and 20% 10% ka gamma irradiation with a dose of 0 - 50 kgy and found an increase in the thermal stability of radiation-treated membranes relative to non-membranes. The treatment also increased thermal stability with increased irradiation dose due to irradiation and PVA as well as increased membrane tension strength and elongation ratio with increased radiation doses and increased PVA ratio.


INTRODUCTION
An imperative role of edible films has been recorded in food industry programs to serve humankind significantly. The edible films and coatings have been used in food preservation for periods. For a long time, edible film and coating were used in food protection worldwide. The development in the food industry since more than hundred years wax was used in the coating of food to improve the storage time. The essential goal was to prevent the loss of humidity, to keep the feature and texture while the period of storage. Nowadays, waxes materials are yet used to store vegetables, fruits, and meats for elongated storage time and to long shipping time.
However, now there are extra elements prepared for the coating of edible film. These substitute origins, along with enhanced treatment techniques, have increased of using the simple moisture barriers and coating of the edible films. (23) Currently, there are more than12 kinds of commercially used edible films and coatings with sub-brands used for preserving food materials. The edible films are categorized into three groups taking into consideration, the nature of their components: hydrocolloids (containing proteins, polysaccharides or alginates), lipids (constituted by fatty acids, acylglycerols or waxes) and composites (made by combining substances from the two groups) (9) . Numerous papers have been published and reviewing the features of edible films and coatings made from bio-polymers like soy protein, wheat gluten, cellulose, starch, and casein gas, oil and water that vapour into or out of food, as well as conserving food quality).
Edible films must have some features such as mighty and soft to withstand forces adept during processing and handling (27). The edible coating can improve the presence of the goods by combining gloss or colour and making it more attractive to users. The edible film is the form adopted to investigate mechanical, block and surface characteristics, while the coating is considered as one kind of utilisation film.
Both edible films and coatings can be used as a transformer of incorporating natural or chemical antimicrobial agents, antioxidants, enzymes or functional ingredients such as probiotics, minerals and vitamins (43) .
The aim of the review was to highlight the importance of the use of plant and animal proteins in the production of edible films to reduce the environmental risks resulting from the use of plastic packaging.

Protein-based films and coatings
Protein is an imperative organic polymer in the production of films and edible coatings, along with their profusion and their sustainable kind. The numbers and types of amino acids have differed in protein materials. There is a renovated awareness in edible membranes composed of natural sustainable polymers such as proteins. These films are utilised to decrease wetness damage, oxygen and permeability, decrease lipid movement, improve mechanical features, as well as increase the qualities of food and have degradability compatible with conservational conditions (7) . Protein is also characterized by its ability to carry anti-microorganisms, flavours and colours (23) .
Protein membranes are preferred in mechanical features in comparison to membranes formed from polysaccharide and lipids. Since the proteins have a unique composition which provides a number of useful features. Therefore, these films can procedure links between several sites. The high voltage to procedure multiple cross-linkages, (45). Animal (milk and whey proteins) and plant (such as soy and zein proteins) protein films exhibit well oxygen barrier, carbon dioxide barrier and mechanical properties than polysaccharide films. However, similar to polysaccharide films, due to their hydrophilic nature, generally protein films grip poor water vapour barrier property (4)(5) . Other Studies have been shown that the concentration, structure, shape, and size of plasticizers all these features are affecting the properties of protein films .
insoluble proteins, like wheat gluten and corn zein, create insoluble coatings, while soluble proteins give coatings of unreliable solubility, depending on the type of the protein, the states of the coating process. Most of the protein in soybeans is insoluble in water but soluble in dilute neutral salt solutions, therefore, soy protein is not considered as a hydrocolloid.
From different sources such as derivatives of polysaccharides, lipids compounds, vegetable or animal proteins source, and complexes involving a combination of the preceding ingredients can produce edible films and coatings (42) . The investigate that done about the protein from different diversity to produce a variety of edible films and coating materials from different sources which played an important role in food coating whey proteins (WPC and WPI) (47,1,12).

Total milk proteins
The components of milk proteins or TMP can produce edible films and coating. A Whey proteins obtain great O 2 , odour and oil block film at minimum-to-moderate moisture. In addition, the mechanical features of whey protein film are sufficient to implement strength while utilised as a coating in food goods, films insulating layers of various food or film made into bags for food components. Irradiation and heating are one of many methods can be used to produce whey protein. Films of whey protein is a medium permeability of water vapour because it is a hydrophilic protein while it is a select barrier to O 2 as it reduces oxidation in food and decreases enzymatic attenuation reactions (32) . With less permeability to wetness and water vapour along with an acceptable barrier to smell. Whey proteins can make watersoluble films. In addition, films formed without plastic are hard and can be separated.
To increase the flexibility of the membrane plasticizer is added (37) . extracted from gelatin, such as greatest protein film, haven't a perfect water vapour limit, that restricts its utilization as edible films and bio-material.

Wheat gluten films
Gluten that produces from wheat flour consider water-insoluble protein that contained a blend of poly-peptide molecules, and deemed to be universal protein.

Corn-zein Coatings
Zein is a natural corn protein produced from corn gluten meal and is insoluble in water, but soluble in aqueous alcohol, glycol esters and glycols (11) . It has good film-forming, binding and adhesive properties. Corn-zein coating is a good barrier to oxygen. It prevents the change of the colour, loss of hardness and weight, and increases shelf life of tomatoes. Moreover, Its considered water vapour permeability, nevertheless, there were about 800 times greater than a typical shrink-wrapping film (34) , indicated that corn-zein film delayed colour changes, reduced weight loss, inhibited ethanol production, paused ripening, and reduced stiffness damage of tomatoes. the thickness of the coating affects the degree of colour change. increased levels of oxygen and carbon dioxide led to Increased thickness level of coting (41).

2-Edible protein films modified by enzymes.
To increase the functionality of protein film changing the polymer via the crosslink of the polymer chains is the alternative method that can be used.

3-Modification of edible protein films by irradiation High-energy:
One of the most common technologies used to modify the polymers is irradiation. (38) Improving the useful features of protein films or ionizing radiation have been tried, the effects of Gamma-irradiation on proteins through making conformational changes, oxidation of amino acids, and the rupture of covalent bonds and formation of protein free radicals Gamma irradiation affects the proteins by causing molecular conformational changes, oxidizing amino acids, cutting covalent bonds, forming free radicals, and free ions that lead to bonding. bonding, chain separation, and some volatile components, causing a foul smell of irradiated membranes in case of increased dose (8)(3) . Wittaya (33) Reported that the chemical stability and water vapour permeability was improved by using gamma irradiation. In addition, the results presented that water vapour permeability was reduced by using gamma irradiation. In order to induce the modifications on the protein structure, gamma irradiation application was used and indicate the more compact structure and improve block properties. Consequently, better barrier properties, proportional to the irradiation doses. Future investigations will be cured out to expand the effectiveness of gamma irradiated coating on fruits storage stage. 35.0 kGy dosage was selected as the best to achieve this study. However, the dose of 45.0 kGy reached more modifications on the film structure but produced un preferable flavour, led to difficulties to be used on food application (24) . (38) measured the thermogravimetric analysis TGA of 20%, 10% PVA polyvinyl alcohol and 20% 10% ka gamma irradiation with a dose of 0 -50 kgy and found an increase in the thermal stability of radiation-treated membranes relative to non-membranes. The treatment also increased thermal stability with increased irradiation dose due to irradiation and PVA as well as increased membrane tension strength and elongation ratio with increased radiation doses and increased PVA ratio.