Pioneering hydrothermal treatment is applied to banana peels. The method is simple and does not generate waste. Innovative use of banana peels can reduce food losses and environmental issues. Bioplastic film can be used as primary packaging. Product has excellent antioxidant properties and protection against solar radiation, which helps to extend the life of food. Some of the mechanical properties of the films are comparable to those of low density polyethylene. Banana peels are the raw material used by researchers from Embrapa Instrumentation and the Federal University of São Carlos (UFSCar) to create bioplastic films with potential application as active food packaging. Through a simple process involving mild pretreatments that use only water or a dilute acid solution, the researchers fully and pioneeredly converted banana peels into bioplastic films with excellent antioxidant properties, protection against ultraviolet (UV) radiation, and no waste generation. The films performed the same or even better than many similarly prepared bioplastics made of other types of biomass but through other methods, including more complex, expensive, time-consuming and thus less productive processes for the transformation of agri-food waste. The banana value chain particularly generates a significant amount of by-products that are currently underused or improperly discarded, resulting in losses and environmental issues. According to Brazilian researchers, up to 417 kg of peels can be generated for each ton of bananas processed. That was the motivation to reduce the waste generated by the disposal of peels by making full use of them, including their numerous bioactive compounds, such as phenolics and pectin, an important polysaccharide that can be used to produce biodegradable films. “Therefore, the use as a bioplastic film is an opportunity to create value for this waste and reduce the environmental impact associated with the use of non-biodegradable plastics,” states chemical engineer Rodrigo Duarte Silva, who developed the film during his postdoctoral studies under the supervision of Embrapa researcher Henriette Monteiro Cordeiro de Azeredo (pictured on the right). Azeredo explains that the film - which is brown and prepared on a laboratory scale with micrometric thickness - can be used as a primary packaging for products that are prone to oxidation reactions. The promising experimental results encouraged the researchers to continue the studies to further improve some of the film's properties. Such properties include interaction with water, a research challenge due to the high affinity for water that the molecules present in the biomass have. In addition, in approximately one and a half years the researchers intend to develop the bioplastic film on a pilot scale to make the process even more interesting from an industrial standpoint. Photo by: Mariana Franzoni Researchers explain how the banana-based film is fabricated The banana film process The study, which was funded by the São Paulo State Research Foundation (Fapesp) and the National Council for Scientific and Technological Development (CNPq), set out to offer a simple process to prepare bioplastic films directly from banana peels. At the National Laboratory of Nanotechnology for Agribusiness (LNNA), the researchers used peels of the Cavendish banana variety (the most consumed and cultivated one in the world and known as dwarf bananas), whose annual production is estimated at 50 million tons, according to 2022 data from the Food and Agriculture Organization of the United Nations (FAO). To obtain the films, Silva explains that the banana peels were dried and ground, resulting in a powder. Two types of powders were prepared: one from unblanched banana peels, which eventually darkened during the drying due to the action of enzymes such as polyphenol oxidase, and another from banana peels that had been subjected to a previous blanching process – boiling in a diluted citric acid solution – to deactivate such enzymes. “This way, it was possible to analyze the influence of the enzymes on the final properties of the films”, the researcher reports. In addition, the researchers investigated the impact of the type of pretreatment applied to banana peels (hydrothermal, water-based, or with dilute sulfuric acid), and the addition or non-addition of carboxymethylcellulose – a biodegradable polymer made of cellulose that works as a binding agent – at low concentration in the films. According to Silva, the goal of the pretreatments, performed in an autoclave at 121° C for only 30 minutes, is to change the structure of the biomass to allow the films to form. Through the two pretreatments, the pectin present in the banana peels was successfully solubilized. According to Azeredo, the hydrothermal treatment has stood out as an ecologically friendly process as it only uses water as a reagent, and it has already been used to convert orange byproducts into bioplastic films. However, it had not been applied to banana peels yet. The few studies in the literature on films prepared from banana peels intended for packaging were developed without the application of pre-treatments, which can compromise the properties of the final material. “Both the hydrothermal and the sulfuric acid pretreatments have been shown to be effective for the preparation of banana peel films. Although we have used the peels as a powder, which offers advantages in terms of storage and preservation of the raw material, it is possible to adapt the process to use wet peels, which can further simplify it”, the postdoctoral researcher says. Photos by: Maria Fernanda Photo by: Maria Fernanda Promising results For Henriette Azeredo, the study showed that the films' mechanical properties, which are positively affected by the incorporation of carboxymethylcellulose, are comparable to those of other films made from other whole byproducts, such as avocado-based ones, which had added pectin. Moreover, some mechanical properties of the films were comparable to those of low density polyethylene (LDPE). Another advantage is that the films blocked over 98% of the ultraviolet radiation in the UVA range and over 99.9% in the UVB range. This type of radiation is well known to cause skin burns after sun exposure, for example, but it also promotes the oxidative deterioration of foods. According to the researchers, such benefit offsets the films' limited transparency, making them suitable to protect food against this type of radiation. The films showed excellent functional properties, as they retained at least 50% of the antioxidant activity of the starting raw material. According to the researchers, these properties were strongly influenced by the blanching process, which helped to prevent the degradation of the phenolic compounds present in the banana peels. In addition, some of the films had hydrophobic surfaces, i.e. push water molecules away, which is particularly interesting in the context of materials for food packaging. “Hydrothermally pretreated banana peels have proven to be a promising biomass to produce bioplastics that are suitable for food packaging applications, due to their excellent antioxidant and surface properties, which can contribute to the transition to a circular bioeconomy,” Henriette Azeredo underscores. She also recalls that the films can contribute to avoiding food waste and possibly extending the shelf life of food if the bioplastic is used as packaging, since they have light-barrier antioxidant properties. Photo: Maria Fernanda Paper The study “From bulk banana peels to active materials: Slipping into bioplastic films with high UV-blocking and antioxidant properties” was published on the Journal of Cleaner Production, in January. The paper is authored by Rodrigo D. Silva and Henriette M. C. Azeredo (Embrapa Instrumentation), Thályta F. Pacheco (University of Brasília/Embrapa Agroenergy), Amanda D. de Santi (University of São Paulo, São Carlos campus), Fabiana Manarelli, Breno R. Bozzo and Caio G. Otoni (Federal University of São Carlos), and Michel Brienzo ("Júlio de Mesquita Filho" São Paulo State University).