Brazilian and French scientists have incorporated cellulose nanocrystals modified with pine resin into gelatin. The result was a resistant film to protect food. This technique allows the use of water-based solutions without the need to employ processing additives. Another advantage is shorter processing time, which opens up the prospect for industrial-scale production. The resulting film is safe, antimicrobial, antioxidant, stable, biodegradable and even edible. The result came through a partnership amongst Embrapa, the Federal University of São Carlos, Brazil, and the Grenoble Alpes University, France. The secular and versatile fine gelatin powder is the basis for a new edible and biodegradable film for multifunctional food packaging. Using continuous casting method, Brazilian and French researchers have incorporated cellulose nanocrystals (CNCs) that were modified with pine resin to the fragile gelatin structure in order to strengthen it and produce film, in a faster and more resistant way. The result is a biodegradable and antimicrobial film that has antioxidant properties. The material preparation by continuous rolling, known as continuous casting, is a low cost and high productivity technique that has potential to be applied in industry. It allows the use of water-based solutions or dispersions without the need to employ processing additives. The use of continuous casting had not been explored for protein film processing in pilot scale yet. This innovative work has involved researchers from Embrapa Instrumentation (São Paulo, SP, Brazil), from the Federal University of São Carlos (UFSCar) and from the University of Grenoble Alpes (UGA), in France. Currently, the most used technique for gelatin films processing is the bench casting, but this method fails due to its low productivity, since the drying stage, one of the film production stages, requires a relatively long time, up to 24 hours. Pictures of the development of the edible film made of gelatin and cellulose nanocrystals. On the other hand, the advantage of the continuous casting is that it requires a shorter processing time, thanks to the use of infrared radiation in the pre-drying stage, higher temperatures and intense air circulation. This faster film production, that takes 10 to 20 minutes, has brought about a significant increase in productivity, a performance that brings the research closer to meeting the industry's needs. This technique made it possible to produce 12 meters of film per hour on a laboratory scale. The films have appeared transparent and colorless - important characteristics that allow the consumer to view the content and quality of the product - without fractures after drying or insoluble particles on its surface, safe, stable, environmentally friendly, efficient barrier against oils and lipids, good film-forming capacity and edible nature. How continuous casting works The continuous casting method promotes high wet blade thickness control without the need for processing aids, allows the use of aqueous solutions and dispersions, and requires smaller spaces and less labor for production. 'These are very desirable characteristics, especially when we consider moving a process carried out in the laboratory to the industrial scale. The film production is carried out on a coating line, like a laminating machine', says chemist Liliane Samara Ferreira Leite, who developed the research to obtain a doctoral degree in Materials Science and Engineering at UFSCar. In this process, the solutions are continuously spread over a moving substrate such as polyester or paper coated with a height-adjustable wet sheet to control the dry film's thickness. Leite, who was supervised by researcher Luiz Henrique Capparelli Mattoso, from Embrapa Instrumentation, explains that the coated substrate then goes through a pre-drying infrared heater and drying chambers and, at the end, the dried film is cooled to room temperature and rolled up while it is still attached to the substrate. Similar to conventional plastic, but biodegradable In addition, the films were shown to have optical and mechanical properties similar to those of conventional plastics, but with the additional advantage of having natural sources as raw materials and being biodegradable. Another advantage is that the film is antimicrobial, has inhibited the growth of bacteria Staphylococcus aureus and Escherichia coli in accelerated laboratory tests and extended mozzarella cheese's shelf life by up to one month. The gelatin film presented a high barrier against ultraviolet (UV) radiation (nearly 100% for UVC, more than 93.3% for UVB and 54.0% for UVA) due to chromophore groups - part or set of atoms in a molecule responsible for its color - such as tyrosine and phenylalanine. The results obtained by the research demonstrate promising use of CNC reinforced gelatin films for applications such as packaging, whose fundamental role is to maintain the quality and safety of food products during storage and transportation. After this technology was validated in a laboratory environment and at a pre-pilot scale, next challenges include demonstration of the prototype with heat-sealable gelatin-based films (that can be closed by heat application instead of glue) intended for the storage of different food products on an industrial scale. Even though it is still on a pilot scale, the film's performance has already caught the attention of global companies that supply collagen proteins for the food industry, pharmaceutical industry, health and nutrition industry, and technical application industry. Scientific publication A good part of the research results were published in the paper Eco-friendly gelatin films with rosin-grafted cellulose nanocrystals for antimicrobial packaging in the issue 165 of the International Journal of Biological Macromolecules. The paper was authored by Liliane Leite, Luiz Mattoso, Francys Moreira, Julien Bras; as well as researchers Stanley Bilatto and Andrey C.Soares, Andrey C.Soares, who took a postdoctoral degree at the National Laboratory of Nanotechnology for Agribusiness (LNNA), located at Embrapa Instrumentation; and Rafaella T. Paschoaline and Osvaldo N.Oliveira Jr., from the University of São Paulo (USP). Doctoral Research Although animal protein can be used as a polymer mix in film production for edible and biodegradable packaging, it alone is not capable of producing films with satisfactory mechanical and barrier properties to be used as food packaging. For this reason, its use by the food packaging industry is still limited. Gelatin, once used widely in banquets in Egypt in ancient times, is a water-soluble protein derived from collagen that can be extracted from different sources. It presents poor barriers against moisture and moderate mechanical resistance under high relative humidity. However, these disadvantages can be overcome by the incorporation of reinforcement nanoparticles, such as cellulose nanocrystals (CNCs), which are incorporated into the formulations. In addition, the nanocrystals are already commercially produced in several countries, which makes them an affordable raw material. This is what chemist Liliane Leite (pictures on the right) did. At the National Laboratory of Nanotechnology for Agribusiness (LNNA), the researcher produced and characterized gelatin powder-based bionanocomposite with cellulose nanocrystals (CNCs). The researcher modified the cellulose nanocrystals, extracted from eucalyptus, with pine resin, a naturally antimicrobial material. Supported by the São Paulo Research Foundation (Fapesp), part of the study was developed at the University of Grenoble Alpes, France, under the supervision of professor Julien Bras, and co-supervision of researcher from UFSCar's Department of Materials Engineering (DEMa), Francys Vieira Moreira. The concept of the research was also to incorporate natural antimicrobial agents into packaging films in order to slow microbial growth, which is the main cause of food spoilage. In the study, gelatin of bovine origin was used, as it is one of the sources of greater production and abundance in Brazil. By using the continuous casting technique, Leite has demonstrated that, when modified with rosin (the resin extracted from pine), the cellulose nanocrystals were able to maintain antimicrobial activity in films made with gelatin and CNCs in accelerated storage tests with cheese samples. The experiment resulted in antimicrobial nanocellulose that was able to delay the appearance of microorganisms in mozzarella cheese, a perishable product that undergoes fungal and bacterial deterioration, depending on storage conditions. 'The results suggest that the incorporation of CNCs and rosin as active agents in gelatin films can be highly suitable for the production of antimicrobial packaging materials', she says. In addition to common packaging functions, such as protection, storage and practicality, the researcher says she was able to develop a film with advanced functions that has antimicrobial and antioxidant properties, called active packaging. Active packaging is an innovative concept that offers the consumer advantage such as increase of food products' shelf life, ensuring their quality, safety and integrity. 'As far as we know, the use of mechanically reinforced gelatin film with antimicrobial properties in food packaging remains unexplored. The films found in the market that are intended for the food market are of small dimensions', she explains. For that reason, the researcher says that the use of gelatin films as food packaging have been catching scientists' attention in recent years. 'Gelatin has been attracting a lot of attention as an alternative material due to its availability, low cost, biodegradability, excellent film-forming capacity and non-toxicity. It also does not present risks for application in contact with food, since it is already used widely by itself in the food industry', the chemist states. Leite says that the CNCs have proved to be effective against Gram-negative and Gram-positive bacteria. "Microbial growth can cause the development of strange taste, change in texture, loss of nutritional value, reduction of shelf live and increased risk of foodborne diseases, all of which make the product unacceptable for human consumption", she explains. Cellulose nanocrystals Chemist Liliane Leite ponders that cellulose nanocrystals, known by the acronym CNC, have been incorporated as reinforcement in films for food packaging, mainly due to their large surface area and optimal mechanical properties. Nanometric cellulose's mechanical properties, reinforcement capacity, abundance, low density and biodegradability make it an ideal candidate for the processing of polymer nanocomposites', she says. Green solution She explains that, without any additives, gelatin films become brittle and difficult to handle and that the addition of plasticizers can increase the films' flexibility, but the plasticizers decrease mechanical traction properties and reduce the barrier to gases and water vapor. Leite also says that the use of nanometric reinforcements can increase the mechanical strength, tenacity, thermal stability and barrier properties of several biopolymers such as gelatin. "Mechanical tests revealed that adding CNC to the gelatin mix led to a threefold increase in resistance to traction and a 3,5-fold increase in elastic modulus - a mechanical property that measures the stiffness of a solid material - and a 70% decrease in elongation at break, when compared to gelatin films without CNC addition" she reveals. Continuous casting enthusiast and Brazil's pioneer on this method, Liliane Leite's co-supervisor, professor Francys Vieira Moreira, from UFSCar, reports that the cellulose nanocrystals that were modified with rosin (r-CNCs) consistently improved the optical and barrier to water vapor properties of the gelatin films compared to conventional CNCs. The gelatin mix's mechanical resistance was increased and can be adjusted by varying the amount of CNCs. This study shows how surface modification reactions can extend nanocellulose's functionality for use in flexible packaging materials, which would otherwise suffer from limited physical and biological properties', says Moreira. For Leite, the study provided a comprehensive understanding of how CNCs can be explored to develop biodegradable gelatin-based films with enhanced properties or extra functionalities. CNCs are rigid rod-shaped crystalline particles extracted from cellulosic materials from plant sources. They are biodegradable, abundant, renewable and have low density, high elastic modulus and excellent mechanical properties when produced on a commercial scale. Another advantage emphasized by the researcher is that the material can be completely decomposed by the environment after disposal as a result of the properties of the ingredients gelatin and cellulose. "Thus, improving the search for more effective solutions that do not harm the environment is in synergy with the Sustainable Development Goals supported by research generated by Embrapa on various topics, both for environmental improvements and for the population. Problems with safe disposal of post-consumer plastic waste can be mitigated if biodegradable natural polymers are employed as packaging material", Mattoso says.