348
Although edible coatings and films have a similar definition, there is a difference.
Generally, edible films are prepared separately and then applied to the surface of the
food, whereas coatings are formed directly onto the food surfaces (Cordeiro de
Azeredo 2012). Studies have shown that both methods when rightly formulated can
improve the organoleptic characteristics of packaged food. Furthermore, they can
function to retard oxidation and/or delay microbial spoilage by the incorporation of
antibacterial and antioxidant agents. However, compared to artificial films, their
permeability and mechanical properties are generally poorer (Kester and Fennema
1986) and this will limit their use to specific applications. With further research,
some of these drawbacks will be overcome.
Edible coatings can keep fruits and vegetables fresh by improving the retention
of color, acid, sugar, and flavor components to prolong shelf life and retain nutritional quality (Fakhouri et al. 2015). Most biopolymers which are used for the formation of Edible films and Edible coatings are polysaccharides, proteins, and lipids
(Jahed et al. 2017). Among these, protein-based materials appear to be most attractive because they also provide nutritional value (Galus and Kadzinska 2016).
Protein Based Edible Films and Coatings
Proteins are good film formers exhibiting excellent oxygen, carbon dioxide, and
lipid barrier properties, particularly at low relative humidities. Edible films made of
proteins were reported to possess satisfactory mechanical properties (Peyron 1991),
but their mechanical strength limit their application in food packaging compared
toartificial polymers (Bourtoom 2009). Also, they are poor water barriers due to
their predominantly hydrophilic character (Peyron 1991; McHugh 2000). Increasing
cohesion among protein polypeptide chains by way of chemical (glutaraldehyde,
formaldehyde, glyceraldehyde, glyoxal), enzymatic (transglutaminase), or physical
(heating, irradiation) treatment was thought to be effective for modifying the barrier
properties of films as well as the mechanical properties and resistance to proteolysis
of films (Bourtoom 2009; Hernandez-Munoz et al. 2004a, b; Orliac et al. 2002;
Ouattara et al. 2002a, b; Sabato et al. 2001). Edible films from different protein
sources have been formulated. These include casein, gelatin, whey protein, corn
zein, soy protein and wheat gluten (Bourtoom 2008; Saglam et al. 2013). Table 1
illustrates various advantages and disadvantages of some protein based edible films
and coatings.
Zein
Zein, the major storage protein in corn accounts about 44–79% endosperm protein
(Lawton 2002). Zein does not dissolve in water and dilute salt solutions due to the
high composition of hydrophobic amino acids (such as leucine and alanine) and
acidic amino acid (glutamic acid, 21–26%), but dissolve in 60–95% ethanol (Chen
F. Jhan et al.
Although edible coatings and films have a similar definition, there is a difference.
Generally, edible films are prepared separately and then applied to the surface of the
food, whereas coatings are formed directly onto the food surfaces (Cordeiro de
Azeredo 2012). Studies have shown that both methods when rightly formulated can
improve the organoleptic characteristics of packaged food. Furthermore, they can
function to retard oxidation and/or delay microbial spoilage by the incorporation of
antibacterial and antioxidant agents. However, compared to artificial films, their
permeability and mechanical properties are generally poorer (Kester and Fennema
1986) and this will limit their use to specific applications. With further research,
some of these drawbacks will be overcome.
Edible coatings can keep fruits and vegetables fresh by improving the retention
of color, acid, sugar, and flavor components to prolong shelf life and retain nutritional quality (Fakhouri et al. 2015). Most biopolymers which are used for the formation of Edible films and Edible coatings are polysaccharides, proteins, and lipids
(Jahed et al. 2017). Among these, protein-based materials appear to be most attractive because they also provide nutritional value (Galus and Kadzinska 2016).
Protein Based Edible Films and Coatings
Proteins are good film formers exhibiting excellent oxygen, carbon dioxide, and
lipid barrier properties, particularly at low relative humidities. Edible films made of
proteins were reported to possess satisfactory mechanical properties (Peyron 1991),
but their mechanical strength limit their application in food packaging compared
toartificial polymers (Bourtoom 2009). Also, they are poor water barriers due to
their predominantly hydrophilic character (Peyron 1991; McHugh 2000). Increasing
cohesion among protein polypeptide chains by way of chemical (glutaraldehyde,
formaldehyde, glyceraldehyde, glyoxal), enzymatic (transglutaminase), or physical
(heating, irradiation) treatment was thought to be effective for modifying the barrier
properties of films as well as the mechanical properties and resistance to proteolysis
of films (Bourtoom 2009; Hernandez-Munoz et al. 2004a, b; Orliac et al. 2002;
Ouattara et al. 2002a, b; Sabato et al. 2001). Edible films from different protein
sources have been formulated. These include casein, gelatin, whey protein, corn
zein, soy protein and wheat gluten (Bourtoom 2008; Saglam et al. 2013). Table 1
illustrates various advantages and disadvantages of some protein based edible films
and coatings.
Zein
Zein, the major storage protein in corn accounts about 44–79% endosperm protein
(Lawton 2002). Zein does not dissolve in water and dilute salt solutions due to the
high composition of hydrophobic amino acids (such as leucine and alanine) and
acidic amino acid (glutamic acid, 21–26%), but dissolve in 60–95% ethanol (Chen
F. Jhan et al.