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From field to table

Using nanotechnology to make edible films and fertilizers

Eduardo Cesar Edible packaging made from guava and chitosanEduardo Cesar

Fruit, plants and agricultural waste, when processed on a nanometric scale, show great potential to be used in edible films to protect vegetables, in reinforced and biodegradable plastics, in fertilizers and even to degrade pesticides. The universe that is emerging for nanotechnology applied to food and agriculture is vast. In Brazil, research groups have been achieving fairly promising results, some with immediate application, such as a biofilm with silver nanoparticles (structures about 10 to 40 nanometers in diameter), synthesized from the extract of a regional Indian plant (Ocimum sanctum) and silver nitrate, and developed at the Chemistry Institute at the State University of Campinas (Unicamp) along with researchers from Amravati University in India. The polymer mixture obtained from a vegetable and the silver nanoparticles result in a solution in which to immerse fruit to protect them, thereby extending their shelf life.

After this immersion, the fruit are wrapped in a thin film that works as a protection barrier, reducing the amount of oxygen coming in and carbon dioxide going out, which avoids water loss. When the fruit is washed in running water, the biofilm is eliminated entirely. “It’s an excellent platform to protect fruit and vegetables transported for a long time in tropical climates, like India and Brazil,” says professor Nelson Duran, from Unicamp, the research coordinator, who had collaboration, in Brazil, from the Natural and Human Sciences Center at the Federal University of the ABC Region, in the city of Santo André.

The biofilm was tested on various fruits, including guavas. Among the items assessed were weight loss, protein loss and bacterial infection. “The protected fruit lost virtually no weight or protein and remained infection free for the fortnight of the study,” says Durán. The fruit ripened, but did not rot. Known for its antibacterial properties, the silver nanoparticles used in the composition of the biofilm were obtained via biological synthesis, whereas the commercial ones are obtained by chemical or physical processes. “The biopolymer used is edible, non-toxic and approved by the FDA, the United States government agency that regulates food and drugs, as well as by Anvisa, the Brazilian National Sanitary Surveillance Agency,” says Durán .

The researchers tested the biogenic silver nanoparticles for their cytotoxicity in vitro and toxicity in vivo in animal trials and for their penetration of human tissues as well. “At the concentrations used, they don’t penetrate the skin and aren’t toxic.” The joint study with the Indian researchers is included in a bi-national collaboration effort approved in 2008 and initiated in 2009, and is part of a project financed by CNPq (the National Council for Scientific and Technological Development) involving research into silver nanoparticles generated by fungi, bacteria and plants.

Researchers from Embrapa – Empresa Brasileira de Pesquisa Agropecuária [an enterprise specializing in crop and livestock research], are also working on developing surfacing films based on tropical fruit, and processing residues of cotton and coconut, chitosan and other raw materials. One of the films developed by the researcher Henriette Azeredo, from Embrapa Agroindústria Tropical, in the city of Fortaleza, Ceará state, is based on mango pulp plus cotton cellulose fibers. “The toughest component in vegetable fibers and in wood itself is cellulose,” says the researcher Luiz Henrique Mattoso, head of Embrapa Instrumentação Agropecuária, in the city of São Carlos, inner-state São Paulo. In her study, Henriette tested the addition of different concentrations of cellulose nanofibers, reaching a maximum of 36 percent , to assess the behavior of the films. “With about 10 percent , results were already very good,” says the researcher, who conducted the research during her post-doctoral studies, which she completed in 2008, at the US Department of Agriculture, as part of an agreement with Embrapa. The mango pulp films with nanofibers had better mechanical resistance, formed a better barrier to moisture and provided better temperature stability. “The technology can’t be applied yet because the potential adverse effects of the nanofibers, even of cellulose ones, on humans isn’t known yet,” she says. Therefore, another project, conducted by the researcher Morsyleide Rosa, also from Embrapa Agroindústria Tropical, will focus on the toxicological analysis of the new material.

Regulating the use of agronanotechnology is a discussion that has been under way for several years in many countries. In Europe, for instance, five conferences have already been held on this issue, the last of which took place in November 2009. During the International Conference on the Application of Nanotechnologies in Food and Agriculture, held in the town of São Pedro, inner-state São Paulo, the researcher Steven Robert, from the Institute for Agriculture and Trade Policy of the United States, stressed three approaches that should be considered in relation to regulating the use of agronanotechnology. The first depends on the government’s voluntary orientation and on voluntarily presenting data on nanotechnology products for regulation by the agencies; the second refers to compulsory submission of products developed by the industry to the regulating bodies; and the third, the most radical, proposes the suspension and non-approval for sale of products until there is sufficient reviewed data to conduct the risk evaluations required to establish a suitable overarching set of regulations.

Tina Williams / US Department of Agriculture Nanofibers made from coconut wasteTina Williams / US Department of Agriculture

Morsyleide is also working with the waste of regional industries – such as green coconut and cotton residues – to obtain cellulose nanofibers from various sources. “Another interesting raw material for sourcing nanocellulose is the patties left over from pressing palm to extract dendê biofuel,” she says. The pseudo-trunk of the banana tree, which has a high cellulose content, has also yielded fairly promising results for the production of nanocomposite films that can be used for packaging or other applications. One of the lines of research is coordinated by the researcher José Manoel Marconcini, from Embrapa Instrumentação Agropecuá¬ria. He mixes plastics with vegetable fibers or nanosylica extracted from rice husks to increase the mechanical resistance of both conventional and recycled plastics. Preliminary results indicate that these nanostructured materials change the optical properties and improve the mechanical properties of the materials. “In the case of cellulose, the crystalline region has a mechanical resistance and elasticity similar to Kevlar, a material that’s stronger than steel,” says Marconcini. “It’s a technology that the entire world is trying to learn.” Canada is ahead of the game. In July, the Canadian firm Domtar and the research institute FPInnovations launched a project to build a factory that is to produce only nanocrystalline cellulose, the output of which is expected to reach a ton a day.

Marconcini is also working with biodegradable plastics strengthened with nanocellulose fibers, which can be used for tubes in which seedlings are grown, in films to protect plantations or even to repel insects on cultivated land, using pheromones. For this application, all that is required is to tie a strip of a certain biodegradable plastic in the plantation for it to release the necessary substances into the environment. At the University of Marburg, in Germany, for example, researchers are testing in the field a prototype made with nanometric filaments from biodegradable plastics. These filaments were manufactured with a process known as electrospinning, based on the application of an electric current. The prototype, which is similar to a spider’s web in miniature, when placed on the soil releases the active ingredients selected, little by little, until it eventually disintegrates.

Since 2006, Embrapa has been in charge of coordinating the Network of Nanotechnology Applied to Agribusiness, headquartered at its São Carlos unit and involving 150 researchers from 53 institutions, of whom 14 work for research centers and 39 for universities. Last year, the National Laboratory of Nanotechnology for Agribusiness was instituted, with investments in excess of R$10 million. The funding comes from Finep (the Studies and Projects Finance Agency), CNPq (the National Council for Scientific and Technological Development) and FAPESP. The research lines range from nanobiosensors and electrochemical sensors to monitor processes and products used in crop and livestock farming, to edible nanofilms, the production of fertilizers, pesticides and pharmaceutical products for animals. Researchers from Embrapa Gado de Corte, in Campo Grande (Mato Grosso do Sul state), and from Instrumentação Agropecuária, jointly with the University of São Paulo in São Carlos, are working on nanobiosensors to detect pathogens such as foot and mouth disease and other viruses in animals, as these diseases cause producers major losses.

Another nanotechnology that is directly applicable in the field consists of fertilizers encapsulated within zeolites, a group of minerals with nanometric cavities in their porous structure. “When the fertilizer is added to the soil, its release occurs gradually,” says Marconcini. The objective of the project, which is coordinated by the researcher Alberto Bernardi, from Embrapa Pecuária Sudeste, in São Carlos, is to improve dispersion of nutrients and their absorption by plants. A new research frontier is using nanocomposites based on these materials for the controlled release of fertilizers, a project coordinated by the researcher Cauê Ribeiro, from Embrapa Instrumentação Agropecuária, together with Pecuária Sudeste. “As yet, there’s no product in the market to fertilize the soil and the leaves,” says Marconcini. In the area of leaf fertilizers, the trend points to nanoemulsions. “As the drops are smaller, one uses less of the active principle,” explains Mattoso.

The same nanostructures are used in pesticides already found on the market. “A small one-liter bottle can replace a 20-liter drum of poison,” compares Marconcini. Nanotechnology is also being used to degrade conventional pesticides. One of the technologies that Embrapa is studying is to use catalysts made from titanium oxides and tin, of nanometric size, in conjunction with ultraviolet light, to break down pesticide molecules in water faster.

Scientific articles
DURÁN, N.; MARCATO, P. D. et al. Potential use of silver nanoparticles
on pathogenic bacteria, their toxicity and possible mechanisms of actionJournal of the Brazilian Chemical Society. v. 21, p. 949-59. 2010.
AZEREDO, H. M. C; MATTOSO, L. H. C. et al. Nanocomposite edible films from mango puree reinforced with cellulose nanofibersJournal of Food Science. v. 74, n.5, p. 31-35. 2009.