Soy protein is a protein obtained from a soybean after it has been dehulled and defatted. The use of soy protein in edible coating is characterized by many restrictions due to the allergic reactions associated with it. Potato pellet chips coated with soy protein isolate reduced more fat than all different concentrations of Carboxymethyl Cellulose (2 percent, 6 percent, 10 percent, and 14 percent w/v). Application of soy protein at 10 percent edible coating in doughnut mix resulted in 55.12 percent fat reduction.
Wheat gluten is a general term for water-insoluble proteins of wheat flour that is composed of a mixture of polypeptide molecules, considered to be globular proteins. A 2009 issue of Food Chemistry studied the impact of wheat gluten-based edible coating on dough sheets during deep-fat frying. High gluten content resulted in lower oil uptake in products with low moisture content.
Casein forms 80 percent of milk protein and has three principal components: α, β, and k-casein. A 2002 issue of Food Research International reported the failure of milk casein in reducing fat uptake, in which cereals coated with it rather had higher fat content than uncoated cereals. On the contrary, a 2005 issue of Food Science and Technology International found that potato chips coated with casein had 14 percent less oil than those that were not coated. Therefore, product type and characteristics could furnish a reason for differences in oil uptake observed by both research works. Authors also reported that potato slices coated with whey protein resulted in 5 percent reduction in fat uptake. The binding property of whey protein improved in the presence of sodium bisulphite in blanching a solution. Wheat flour battered chicken strips coated with 10 percent denatured whey protein isolate resulted in staggering 30.68 percent reduction in fat uptake as compared to coating without whey protein.
Lipids, unlike hydrocolloids exhibit good moisture barrier properties because of their hydrophobic nature. Generally, films made from lipid lack the structural integrity that films from protein or polysaccharide have. Also, they are not able to form cohesive films and have been used as coatings or incorporated into biopolymers to form composite films. This gives a better water vapor barrier due to their low polarity. Although incorporation of lipids into biopolymers may decrease the water vapor property of the film, it will create a film with non-uniform structure, according to an April 2012 issue of Journal of Food Engineering. Wax, acetoglycerides, etc. are the different types of lipids used in edible coating. Wax coatings have been reported to be substantially more resistant to moisture transport than most other lipids or non-lipid coatings. Nevertheless, coatings made from wax and other fat and oil materials are characterized by challenges like cracking, greasy surface, homogeneity, and undesirable organoleptic problems.
In summary, the superimposing characteristic feature of edible coating used in deep-fat frying is its ability to deter water escape from the product and oil imbibition by the product, which can be explained by their thermogelling and crosslinking characteristics. This feature helps to improve nutritional value of food products by reducing oil uptake during frying. They improve the sensory qualities of the food and can be used as a vehicle for incorporating other useful ingredients, such as antimicrobial and antioxidant agents. Oil absorption in deep-fat frying has been linked to water escape through the pores and consequent oil occupation of the voids created. When coating is applied to food, it forms a film on the surface of the product serving as a barrier to prevent water and fat movement during frying. As frying progresses, water loss is imminent, but the film formed reduces the size and number of pores. The amount of water loss from the surface consequently restricts fat inflow because coating makes the surface of the food stronger and more brittle during frying, improving the water-holding capacity of the product. Edible coating also works by changing the surface hydrophobicity of the food products.