Composition of Edible coating for Minimally Processed Fruit and vegetables.

 

Polysaccharides based coating

Polysaccharides such as starch and starch derivatives, cellulose and cellulose derivatives, alginates, carrageenan, various plant and microbial gum, chitosan and pectinates.These films are excellent oxygen, aroma and oil barriers and provide strength and structural integrity; but are not effective moisture barriers due to their hydrophilic nature. The O2 barrier properties are due to their tightly packed, ordered hydrogen bonded network structure and low solubility. These coating may retard ripening and increase shelf life of coated produce, without creating severe anaerobic conditions Chitosn (deacetylated form of chitin) inhibits the growth of several fungi. Chitosan is used to coat pepper, cucumber, strawberry and raspberry. It reduces water loss and maintain quality. Cellulose edible films are tough and flexible.They.  are resistant to O2 and lipid  migration.Example of some polysaccharides that have been successfully used to coat MPF are: carrageenan, maltodextrin, methylcellulose, CMC, pectin, alginate and microcrystalline cellulose.These coatings can be utilized to modify the internal atmosphere, thereby reducing respiration of fruits and vegetables.

Protein based coating

Edible coatings made of animal proteins (such as milk protein) and plant proteins (such as zein, soy protein and wheat gluten) . Protein can be classified into water soluble and water insoluble. Soy protein and whey proteins are example of water soluble proteins, while wheat gluten and corn zein are water insoluble proteins .These are excellent aroma, oxygen, and oil barriers and provide strength and structural integrity but are not effective moisture barriers. Their O₂barrier properties are due to their tightly packed, ordered hydrogen bonded network structure, low solubility and the presence of several side residue of amino acids (cysteine, in particular) which can inhibit polyphenoloxidase(Dhall et al, 2008). Protein that are made from animal product may raise issues for certain consumer groups (Baldwin et al, 1995). Whey protein concentrate, whey protein isolate, casein, and soy protein concentrate are some examples of proteins also used to coat minimally processed fruits.

Lipid based coating

Lipid based coatings are made from waxes and oils, such as paraffin wax or oil, beewax, carnauba wax, candelilla wax, mineral oil, vegetable oil, actylated monoglyserides, stearic acid, lauric acid, or sucrose esters of fatty acids .lipids can be included in the formulation of edible coatings in the form of a single layer of lipid based film, as lipids distersed in a network formed by hydrocolloids, or as a secondary layer(a lipid layer over a hydrocolloid layer).Lipids offer limited oxygen barrier properties, due to the presence of microscopic pores and elevated solubility and diffusivity. Lipid films have good water vapor barrier properties, due to their low polarity, but are usually opaque and relatively inflexibl.

Composite or bilayer coatings

The composite coating are any combination of polysaccharide, protein and lipid based coatin. The use of composite or bilayer coating is beneficial to fresh produce, because each ingredients function synergistically to provi0de a barrier for protection. Gracia et al in 2000 found that using lipids with polysaccharides in coating produced excellent barrier properties to water vapour. The composite coating adhere better to to a large number of surfaces due to both polar and non polar characteristiscs. Improved moisture barrier properties of composite coating have made them promising candidates for coating fresh  and Minimally processed  fruits and vegetables . The example of composite coating are plasticized protein film, film formed by milk protein (Casein) and lipids (Acetylated monogylceride)