Introduction: Edible films are on every day food products consumed by millions of
consumers. So what might an edible film be that is covering your food products ? Edible
films are made up of biopolymer and polymers the film is then obtained by drying a thin
layer of film-forming material which is then applied to a food surface.1 There are many
different types of films some are made from fruit purees, carbohydrates, protein, and lipid
or resin. Examples of a carbohydrate polymer include forms of cellulose, starch and dextrin,
pectin, and alginates. Proteins include albumen, corn zein, soy protein isolate, collagen and
whey.2
Edible films are put on foods to help them from lipid oxidization and growing
harmful bacteria that can contaminate the food during transportation. Edible films also
offer longer shelf life in foods like apples and bananas to keep them from ripening. The
most important part why an edible film is applied to food is how well it can keep
permeability such as, the transfer of gas, water vapor, oxygen, and carbon dioxide from
going to one side of the film to the other. Another important way to determine the different
types of edible films is the tensile strength and flexibility .Barriers are also either watersoluble or solvent-soluble. The more water-soluble a film the more permeable to water
vapor it is, and the more solvent-soluble a film is the best moisture barrier since water
vapor does not pass through them as readily.2
Plasticizers: Edible films and coatings need to have good elasticity and flexibility, a low
brittleness, a high toughness and to prevent cracking during handling and storage. Plasticizers of
low molecular weight are typically added to hyrocolloid film forming solutions to modify the
flexibility of edible films. Plasticizers with characteristics such as small size polar groups high
polarity, generally impart greater plasticizing effects on a polymeric system. Plasticizers are
required for polysaccharides or proteins based edible films. The most common used plasticizers
are polyols, glycerol, sorbitol, and polyethylene glycol.3
Film Forming Material Carbohydrates: Hydrocolloids which are the
carbohydrate based films are fully or partially soluble in water and are used principally to
increase the viscosity of the continuous phase like a gelling agent or thickener it can also be
used as an emulsifier. Cellulose derivatives are polysaccharides composed of linear chains
of Beta glucosidic units with methyl, hydroxyproyl or carboxyl substituent. Only four
cellulose derivative forms are used for edible coatings or films they are Hydroxypropyl
cellulose or HPC, Hydroxypropyl methycellulose or HPMC, Carboxymethylcellulose or
CMC, and Methyl cellulose or MC. Cellulose derivatives exhibit thermo-gelatin therefore
when suspensions are heated they form a gel whereas they returns to originally
consistency when cooled. The films that cast from aqueous solutions are MC, HPMC, HPC,
and CMC tend to have moderate strength, are resistant to oils and fats, and are flexible,
transparent, flavorless, colorless, tasteless, water- soluble and moderate barriers to oxygen.
In a case study it was seeing if CMC had a longer shelf life with the coating of potassium
sorbate on pistachios. All concentrations of sorbate showed no growth of molds on the
pistachios.4MC is the most resistant to water and it is the lowest hydrophilic cellulose
derivatives. However cellulose films are poor water vapor barriers because of the inherent
hydrophilic nature of the polysaccharides and they posses poor mechanical properties.
Edible coatings made of CMC, MC,HPC, and HPMC have been applied to some fruits and
vegetables for providing barriers to oxygen, oil, or moisture transfer.3
Chitosan which is mainly made from crustacean shells, is the second most abundant
natural and non-toxic polymer in nature after cellulose. Chitosan shows antifungal and
antibacterial properties, which are believed to be originated from its polycationic nature.3
In a case study it talks about adding in antimicrobial agents to help provide microbiological
stability to extend shelf life. The aim of the study was to evaluate inhibition by vapor
contact of Aspergillus niger and Penicillium digitatum by selected concentration of Mexican
oregano added to chitosan .The overall study showed that adding the oregano oil helped
chitosan film exhibit better antifungal properties.5 Some major drawbacks of chitosan is its
poor solubility in neutral solutions. The required degree of deacetylation to obtain a
soluble product must be 80-85% or higher. Chitosan products are highly viscous,
resembling natural gums. Chitosan can form transparent films to enhance the quality and
extend the storage life of food products. Pure chitosan films are generally cohesive
compact, and the film surface has a smooth contour without pores or crack. Chitosan films
tend to exhibit fat and oil resistance and selective permeability to gases but lack resistance
to water transmission shelf life of fresh strawberries would be a good example or even
slices of mango fruit.3
Gums in edible films are used for their texturizing capabilities. All gums are
polysaccharides composed of sugars other than glucose. Two important film forming gums
are guar gum and xantahn gum. Guar gum is used as a water binder, stabilizer and viscosity
builder. Xanthan gum is readily dispersed in water, this makes it high consistency rapidly
in both hot and cold systems of food products. 3 Xanthan gum were studied about in a case
study on a antioxidant composite film from defatted mustard meal. In the study it coated a
smoked salmon that used heat treatment and high pressure homogenisation .The Xanthan
gum mainly retarded lipid oxidation in the study.6In another case study is showed
characterize physical properties in gums including thickness, color, water vapor sorption
kinetics and isotherms, water vapor permeability, tensile strength, and microstructure of
composition films prepared by casting sodium alginate and low methoxy pectin. The gums
had good properties to keep water vapor and had low tensile strength.7
Starch is the major carbohydrate reserve in plant tuber and seed endosperm where
it is found as granules, each typically contain several million amylopetcin molecules and
much larger number of smaller amylose molecules. Amylose is responsible for the filmforming capacity of starch. Starch is used to produce biodegradable films to partially or
entirely replace plastic polymers. The films are transparent or translucent, flavorless,
tasteless, and colorless. The down fall to starch films is that they are not efficient barriers
against low polarity. Starch films are limited to poor mechanical strength and its efficient
barrier against low polarity compound. Films of high amylose corn starch or potato starch
were more stable during ageing, and lost little elongation and had not or a slight increasing
in tensile strength. Plasticizer is generally required for a starch based edible film to
overcome film brittleness. The most common used plasticizers for starch films are glycerol
and sorbitol.3 Starch films can also be beneficial to the environment instead of plastic films.
In a peer reviewed article it talked about using a tapioca starch film. The objective of the
study is to develop models and study the individual and interactive effects of the process
variables on the mechanical properties of tapioca starch base edible films. The study
measured the tensile strength, elongation, and puncture force to see if the eco friendly film
was overall a good source. The study was proven that is had poor water permeability but
had good moisture barriers. 8
Film Forming Material Proteins: Animal milk whey proteins and plant like soy
and zein proteins films exhibit better oxygen barriers, carbon dioxide barrier and
mechanical properties than polysaccharide films. Protein films also generally posses poor
water vapor barriers. Proteins that are insoluble in water, like corn zein and wheat gluten
produce insoluble coatings. Other soluble proteins produce water soluble coatings of
varying solubility depending on the protein in soybeans is insoluble in water but soluble in
dilute neutral salt solutions. 3
Gelatin is prepared by the thermal denaturation of collagen isolated from animal
skin bones and fish skins. The physical properties of gelatins are related not only to the
molecular weight distribution but also to the amino acid composition. Gelatin is readily
soluble in water at temperatures above 40 degrees Celsius forming a viscous solution of
random coiled linear polypeptise chains. Mamalian gelatins commonly have better physical
properties and thermostability than most fish gelatins this is because due to the factor of
higher amino acid content.3 A study looked at how physical and mechanical properties of
edible films based on blends of sago starch and fish gelatin plasticized with glycerol or
sorbitol were investigated. Film forming solutions of different ratios of sago starch to fish
gelatin were used and cast at room temperature. The findings of this study showed that the
addition of fish gelatin in starch solutions has a significant effect resulting in films with
lower tensile strength and higher water vapor permeability.9
Whey protein isolate produces totally water-soluble coatings but heat denatured
solutions of whey protein isolate produced coatings in which whey protein is insoluble.
Whey proteins can produce transparent, flexible, colorless, and flavorless films, with a poor
moisture barrier. Protein based films posses a good aroma barrier and low oxygen
permeability. Whey protein films produce without addition of any plasticizers are very
brittle and the addition of plasticizers provides flexibility to the films but also increases
their water vapor permeability. Increased concentration of plasticizers in edible whey protein
films decreased tensile strength but increase in elongation. The water vapor permeability can also
be improved by the incorporation of hydrophobic materials such as lipids.3 Whey proteins also
have good properties and preventing microbial growth in Listeria and Staphylococcus
Aureus.10In a case study is describes characterization of edible films made from two different
whey proteins one being whey protein isolate and whey protein concentrate added with three
levels of glycerol. The molecular structure, as well as a barrier, tensile, thermal, surface and
optical properties of films were determined in attempts to provide a better film. The outcome of
the study showed that the whey isolate edible film had better properties then the whey protein
concentrate.11
Antimicrobial Agents: Edible films and coatings are being especially designed to
increase functionalities by incorporating natural or chemical antimicrobial agents or functional
ingredients such as probiotics, minerals and vitamins. Antimicrobial agents slow down the
diffusion of the active compounds from the surface of the food. Common chemical antimicrobial
agents used in food systems are benzoic acid, propionic acid, sodium benzoate, sorbic acid, and
potassium sorbate. These help to inhibit the outgrowth of both bacterial and fungal cells. They
also inhibit the growth of microorganism present on the surface.3 In a peer review case study is
took table grapes and coated them with hydroxypropylmethylcellulose contain ethanolic extract
of propols . In order to improve quality and shelf life during storage and also using the health
properties of propolis. In seven day storage the soluble content increased, and in ten days of
storage coated samples had a better microbial safety than uncoated samples.12However, due to
health concerns to chemical preservatives the demand for a more natural film has become more
popular.
Benefits of Edible Films: Edible films have many positive implications on the foods we
consume. Positive factors that edible films bring to food is keeping negative microbial growth
that could be harmful to the gut. One important main functions of edible films are to keep
microbial growth from mostly happening during long distance transportation from field to stores
and storage. A very big benefit in improving edible films would be making more biodegradable
films versus plastic non biodegradable films. This is important on the environment and coming
up with producing better alternative for edible films. A peer review journal article stated that
plastic packaging has come into widespread use, thanks to its good mechanical properties and
effectiveness as a barrier to oxygen and water. However, synthetic packaging material have led
to the serious ecological problems due to their non-biodegradability. The study choose a film
forming solutions based on myofibrilar proteins isolated from chicken breast muscles in distilled
water, plasticizer and either HCl or NaOH. The end result of making the biodegradable film that
it was strong and flexible enough to be peeled and handled. The film solubilized under the acidic
conditions were generally transparent and smooth.13 A negative benefit for people who are
consuming edible films could be allergic reactions to films made of whey protein or other
materials such as casein could be harmful.
Conclusion: Edible films are made with many different materials but the ones I choose to
talk mostly about are carbohydrates and protein based films. The carbohydrate films are widely
used in reducing lipid oxidation and reducing water vapor and permeability. One last case
mentioned packaging films were prepared from water soluble chitosan and MC methylcellulose.
Composite films were prepared by directly blending chitosan with MC in water, followed by
cross-linking the composites films with calcium ions. The microstructure, water vapor
permeability and mechanical strength of the composites was significant in using this edible film.
The film also showed significant inhibitory effect on lipid oxidation.14 Protein based films are
good in reducing antimicrobial growth on food, and has good natural alternatives to making
edible films.15 Overall the use of edible films can be positive if made non synthetic and
biodegradable to help in the reduction of microbial growth and lipid oxidation, and to also
manage longer shelf life.
Application to Dietetic Practice: In practice what might be important information to a
client is explaining what an edible film is and why it is on food. It is also important in explaining
the difference in natural or synthetic films. Since more people are going away from harsh
processed foods it is easy to cut out the synthetic films, but some meats and fresh produce in
stores can still have a synthetic film. So to insure a client is to educate them on the difference of
films for an example collagen gelatin films are natural and still hold antimicrobial growth
properties and help with lipid oxidation. It might also be important to a client if a film is
synthetic of natural due to the negative environmental factors that synthetic edible films have.