Researchers from Embrapa Instrumentation and Federal University of São Carlos, both located in São Paulo state, Brazil, elaborated a short and illustrative graphical review to present possible uses of edible films and coatings, as well as their advances and challenges. The didactic content also helps to understand their function.

Edible films and coatings can be used as a primary package to maintain water activity levels among food components, control mass transfer in processed foods, diffuse active components, or act as sources of sensory appeal. 

However, researchers clarify that these structures, formed by thin macromolecular-based layers, are not simple packaging materials and, at times, they do not even perform packaging-related roles. They can simultaneously perform two or more functions, depending on the application. 

Henriette Monteiro Cordeiro de Azeredo, a food engineer at Embrapa Instrumentation, gives the example of using a film as a pizza component. The researcher is the first author of the graphical review Edible films and coatings – Not just packaging materials, published in volume 5 of the scientific journal Current Research in Food Science.

Graphical reviews summarize schematically key concepts and novel ideas. In this type of material, researchers present results of studies in different ways, such as graphics, tables, images, and schemes. 

According to the researcher, it is used to elaborate short and structured articles to transmit ideas on a topic of great interest, aiming to facilitate the reader’s comprehension, as well as to be used as a teaching tool in class, for instance.

Uses of edible films and coatings

“Designed to work as a barrier against moisture, the film can be made with attractive sensory ingredients to enrich the pizza properties, but it can also contain an antimicrobial compound to extend the microbiological stability of susceptible components like cheese and tomato sauce”, Azeredo explains. 

According to Caio Gomide Otoni, professor of the Department of Materials Engineering of the Federal University of São Carlos and one of the paper’s authors, edible films and coatings have been studied as protective layers to be used with food to extend its stability, especially given their role as protective barriers. Films differ from coatings due to their type of application.     .

“Films are anatomic structures formed separately, whereas coatings are formed directly on the food surface”, explains the professor, who is a collaborative researcher at the National Laboratory of Applied Nanotechnology to Agribusiness (LNNA), located at Embrapa Instrumentation.

The researchers state edible films and coatings should be considered as part of the food rather than part of the package system, although they can be, as they often are.

For Luiz Henrique Caparelli Mattoso, another researcher at Embrapa Instrumentation and co-author, the possible roles of edible films and coatings should be explored to maximize their benefits to food stability and safety, to be part of consumers’ sensory experience, and to provide health benefits.

Mattoso points that one of the functions of edible films and coatings is as primary packaging, but there must be a secondary one. “The primary packaging is the one directly in contact with the food. Some products have both a primary and a secondary external package”, the researcher explains.

Breakfast cereals, for instance, are packed in a plastic bag, which is the primary package. According to Mattoso, primary packaging works mainly as a barrier against vapor, minimizing texture changes. Each bag is placed inside a cardboard box, which is the secondary packaging. This second one provides mechanical protection, works as a barrier against light, and contains information on the product, such as name of the product, nutritional facts, and other data printed on the package.

Another example is a chocolate box. Each chocolate is individually wrapped in a primary packaging inside a secondary one, the box, to group them together in a salable unit and protect them against contamination. “In this case, edible films and coatings are more appropriate to replace primary packaging”, Mattoso states. 

Sensory appeal

She says a sachet matrix should take various factors into consideration, including heat sealability, tensile properties to support the contents, and barrier properties to minimize the chemical degradation of the contents.

Rheological properties should also be considered, since viscosity changes may be desirable or not, depending on what is expected from the final result of the product. 

The researchers also report that edible films and coatings might reduce water migration in multicomponent food products, such as pizzas, ice-cream cones, and frozen desserts. Additionally, they can reduce mass transfer during food processing like deep-frying, for example. 

“It is possible to coat French fries before frying them with a layer of hydrophilic macromolecules to create a barrier and reduce oil absorption, considered an undesirable side effect. Oil excess makes French fries soggy and less crunchy, besides being unhealthy”, the food engineer states. 

Edible films and coatings can also have components with sensory appeal, such as the ones made of fruit and/or vegetable purees, which can be consumed as snacks.

“In addition to desirable sensory properties, they may contribute to improve the mechanical properties of the material, since they contain film-forming biomacromolecules and plasticizing sugars”, Azeredo states.

Another role of edible films and coatings is to carry active components. In that capacity, the researchers say they are capable of extending food stability by mechanisms other than those of mere barrier effects .

“Active edible films and coatings can release compounds that increase food stability (e.g., antimicrobials and antioxidants) or that absorb compounds that reduce food stability (e.g., ethylene, water vapor and oxygen)”, the researcher evaluates

The researchers state that edible films and coatings can also incorporate bioactive compounds with benefits to consumers’ health, such as the ones containing probiotics. 

However, the researchers encourage further studies in order to increase the feasibility of large-scale processing of edible films, as well as to improve the physical performance of the materials, maintaining their characteristic food quality and safety.

“One of the biggest challenges is to create biomimetic edible structures that reproduce the mechanic and barrier performance of fruit peels, trying to imitate mother nature”, they conclude.

Limitations

Mattoso, who recently received the prize ABPol “Profª. Eloisa Mano” 2023 from the Brazilian Association of Polymers (ABPol) due to his work on materials science, says the main component of the edible films and coatings is an edible biomacromolecule, usually a polysaccharide and or a protein, capable of forming a continuous and cohesive layer.

“Although the resulting material is a cohesive layer that can benefit food stability, edible films and coatings are generally not able to fully replace conventional fossil-based plastics for packaging”, the material engineer states.

To work as packaging, the obstacle highlighted by the researcher is the limitation of the biomacromolecules to fully substitute conventional polymers, since most of them degrades at temperatures close or lower than its melting points, making traditional thermal processing methods challenging.

“The hydrophilic nature of most biomacromolecules is another disadvantage, making the films highly permeable to water vapor and sensitive to contact with wet surfaces, which restricts some applications”, UFSCar professor Caio Otoni observes.

The use of biomacromolecules is still limited due to their relatively high cost, although they can be isolated from cheap and abundant raw materials, such as food losses and waste. However, isolation processes involve time-consuming and expensive methods.

The study was supported by National Council for Scientific and Technological Development (CNPq) and by Nanotechnology Applied to Agribusiness Network (Rede Agronano), led by Embrapa Instrumentation..

Avante-garde research

Edible films and coatings have been a research topic at Embrapa Instrumentation for nearly two decades. As a result of the introduction of nanotechnology and studies with new materials carried out by Mattoso, innovations in various areas of knowledge, based on sustainable raw materials, have advanced and are able to preserve the quality and extend the shelf life of fruits and vegetables.

An example is the nanoemulsion of carnauba wax, a commercial-scale coating used in Brazil and in other countries to preserve fruits, such as mangoes, limes, peppers, and tomatoes.