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Biofuel

Sweet cassava ethanol

A variety of the sweet root reduces the number of stages in the production of fuel alcohol

eduardo cesarMore than 600 products can be obtained from cassava starch for use in several industrial sectorseduardo cesar

During a trip to collect plants in the Amazon, researcher Luiz Joaquim Castelo Branco Carvalho, from Embrapa Genetic Resources and Biotechnology, of Brasília, came across a variety of cassava that had a high concentration of sugar rather than starch in its root. Most of this sugar is glucose, the substrate used in the fermentation process for ethanol production. The variety discovered by the researcher is actually a genetic mutation, kept and used by the native Brazilian Indians to obtain an alcoholic beverage, even before the Portuguese arrived in Brazil. “They used the drink, called caxirim, in religious ceremonies and celebrations”, says the researcher.

The mutant plant, after undergoing the traditional process of selecting varieties and crossing with plants adapted to areas chosen for future plantations, resulted in a variety that does not require the cassava starch hydrolysis process for transformation into sugar and conversion into alcohol, including the fuel. “The elimination of starch hydrolysis reduces energy consumption by approximately 30% in the process of ethanol production from cassava,” says Carvalho.

The root of the sweet cassava variety is harvested, ground, pressed, and the juice is ready to be used for alcohol production, which makes it different from the other raw materials used to the same end. “The existing substrates in the vegetable kingdom are either sucrose, from sugarcane, beet and sweet sorghum, for instance, or starch, from corn, cassava root, rice grains and sorghum grains. Ethanol can also be made out of sugarcane bagasse, grasses and crop residues,” says Carvalho, who in addition to his degree in Agronomy from the Federal University of Viçosa, Minas Gerais, also holds a master’s degree in Genetics, a PhD in biochemistry and a post-doctoral degree in evolution genetics and molecular biology. It is necessary to use enzymes to transform the starch into sugar in the traditional cassava alcohol production process.

Agricultural niches
The proposal to produce alcohol from sweet cassava does not necessarily mean competition with sugarcane ethanol, but the possibility of occupying other agricultural niches, such as the Amazon and the Northeastern and Midwestern regions of Brazil. These were the regions chosen by Carvalho to begin the varietal test, the first step toward finding out whether the characteristic of producing glucose instead of starch was maintained in all the areas. Because the cassava cycle from planting to harvesting is long – for conventional cassava, it can take from eighteen to twenty-four months – the tests were carried out between 2001 and 2004. “The ideal time to harvest sweet cassava is ten months after it was planted,” says Carvalho. This is the case because the root is very soft and has a high sugar content, so that if it is not harvested at the right time, the roots are attacked by ants and rodents, pests that seldom attack traditional cassava.

The results of the three year experiment points to a volume of production that ranges from 8 to 60 tonnes of roots per hectare, depending on the variety planted. The variety with the best performance was used for auto-pollination crossings and conventional crossings with local varieties, to transfer the high glucose concentration characteristic of the plants already adapted to different regions. Depending on the place, the variety can already be used for large scale production with the agricultural technology used for conventional cassava. “We can now carry out the cloning propagation and begin the plantations in the Amazon region,” says the researcher. For the Cerrado (savannah) region, an estimated three years are necessary for plantation in a large area, while in the Northeast, the estimate indicates five years.

Fourteen cubic meters (m³) of alcohol per hectare per year was obtained from the tested variety, through a fermentation process that lasts only ten hours. The conventional cassava starch hydrolysis process results in approximately 6.43 m³ of alcohol by means of a fermentation process that lasts from sixty to seventy hours, whereas the traditional sugarcane process resulted in 8m³ in forty-eight hours. “In order to obtain the 14m³, we carried out improvements derived from knowledge of one of the plant’s biological processes, in which it hydrolyses the starch after a certain stage of development, and we used biotechnology to identify the mutation that took place in the genes where the sugar had originated in the roots of the sweet cassava,” says Carvalho. The same functional and proteomic genomic biotechnology tools used by the Embrapa team that identified the mutation in the sweet cassava genes were also used to select the same characteristic in commercial varieties.

Viable alternative
Producing fuel alcohol from cassava is not new in Brazil. Since the days of Pró-Álcool implementation, a Brazilian fuel alcohol development program established in late 1975, the plant was considered a viable alternative for ethanol production. At that time, six plants for cassava alcohol production were set up in Brazil. From 1978 to 1983, Petrobras produced the fuel in a unit in the state of Maranhão. However, these plants were built in areas where the plant is not traditionally produced, rendering them unfeasible. “Although there were several cassava study projects at the time, only some of them had scientific bases,” says agronomy engineer Teresa Losada Valle, a researcher at the IAC Agronomy Institute of Campinas, state of São Paulo. She has researched the tuber for the past twenty-three years. “Moreover, there was no efficient technology for large scale cultivation.”

Since then, the cassava cultivation scenario has undergone changes as well as the substantial technological development of the crop, especially in the states of Paraná, São Paulo and Mato Grosso do Sul. “An industrial complex has been established on the border area between the three states and it currently processes about six tonnes of cassava roots for flour and starch,” says Teresa. Moreover, a Brazilian inputs industry specializing in cassava cultivation has also been established, and the region has become a worldwide reference in this respect. “Brazil is a large exporter of cassava technology, both in the agricultural and in the industrial areas,” says the researcher, whose project was recently approved by CNPq , the National Council of Technological and Scientific Development, to study the tuber for alcohol production.

“Based on industrial technologies, more than 600 products can be obtained from cassava starch and used in several fields, ranging from the food, steel, pharmaceutical, animal feed, and textile industries to the paper industry,” says Carvalho. The plant has once again become an issue in the ethanol production discussion since the search for renewable and non-polluting fuels has been stepped-up. Starch is also one of the most often mentioned raw materials to replace plastic products produced from petroleum derivatives.

In relation to processing, much like all the other starchy staples (sweet potato, corn), cassava must have its starch broken down into smaller molecules so that it can be transformed into alcohol by the yeast. In the 1970’s, this process was very limited; however, the enzymes currently used in the process are efficient and easy to purchase, though expensive. Moreover, the process might be improved further, since the United States is developing new technologies for ethanol production from corn. “Starch is a type of temporary sugar storage for plants,” explains Teresa. Cassava stores this polysaccharide in its roots, formed by the linking of several glucose molecules; in the event of need, when there is a shortage of water or light for photosynthesis, it works as an energy reserve.

For the researcher, while sugarcane has been developed on a large scale production system, as in the case of rubber and coffee in the past, cassava for ethanol production can be based on a completely different model, through extremely efficient small farms. “This is possible for two reasons: because of the physiology of the plant and because of technological development that has created machinery, equipment and management systems for small properties,” says Teresa.

eduardo cesarTraditional variety of mandioca leaveseduardo cesar

One of the most significant features of cassava is its production capacity, even under adverse conditions. “In poor soil that is not very fertile, where other crops are either unfeasible or high risk, the plant has a very satisfactory performance,” explains the researcher. This is due to the efficient synergism of fungi with the cassava roots, referred to as mycorrhiza, and to association with other nitrogen fixating microorganisms. The plant is also resistant to lack of rain, during both the planting and the productive seasons.

Cattle food
Cassava is a perennial plant, and as of the moment in which the roots reach a production deemed satisfactory, after approximately two years, they can be harvested; if they remain planted, they continue to accumulate starch. Aside from the root for ethanol purposes, the haulm can be used as animal feed. For every 50 tons of root, 40 to 50 tonnes of haulm are produced and usually abandoned on the fields. “This haulm is excellent food especially for cattle, as it contains a lot of fiber, starch, protein, minerals and sugars,” says Teresa. To use it, it must be chopped up in order to allow for the evaporation of hydrogen cyanide, which is toxic.

One of the chief advantages of cassava exploration for ethanol production is that no other country in the world has such significant genetic diversity of this plant as Brazil, for it was domesticated here. The plant’s starch is a highly efficient source of energy. “While one tonne of sugarcane yields 85 liters of alcohol, one tonne of cassava with 33% of starch and 2% of sugars can yield 211 liters of fuel alcohol, but there are also varieties with 36% of starch,” says Teresa.

Despite such favorable results, the main disadvantage of cassava in relation to sugarcane for ethanol production is low agricultural productivity. Data from the IBGE, the Brazilian Institute of Geography and Statistics, indicates that in 2006, average Brazilian cassava productivity was of 14 tonnes per hectare (t/ha), while sugarcane yielded 74.4 t/ha in the same period. In the state of São Paulo, average cassava productivity for industrial purposes was about 26 t/ha, practically twice the national average.

Sugarcane production costs are lower than cassava production costs. According to data released by Cepea, the Center for Advanced Studies on Applied Economics of the Luiz de Queiroz Agronomy School of the University of São Paulo in Piracicaba, for the region of the city of Assis, state of São Paulo, the cost of the tonne of sugarcane stood at R$ 37.60 in the 2005 harvest, whereas the cost of cassava was R$ 84.52 per tonne in the same period. “The fact that cassava is not feasible when compared to sugarcane is due to the high investment made in the sugar-alcohol sector, which provided for gains both in agricultural productivity and industrial results,” says researcher Fábio Isaias Felipe, from Cepea, who published studies with Lucilio Rogério Aparecido Alves, from the same institution, on cassava alcohol as a source of energy. The researcher believes that it is possible to render the production of ethanol from cassava feasible by carrying out the necessary crop treatments and investing in agricultural technology. “We will certainly get more favorable results for cassava, but one must think of specific market niches, and not about competition with sugarcane alcohol.”

Domestication by the native Indian population
Evidence obtained from DNA tests and archeological studies shows that the origin and domestication of cassava (Manihot esculenta) in a region that includes the states of Acre, Rondônia and Mato Grosso dates back some 10 to 12 thousand years. “The ancestor of cassava came from that region, indicating that the domestication process was carried out in the Amazon,” says researcher Luiz Joaquim Castelo Branco Carvalho, from Embrapa. The Manihot genus consists of 98 species, of which 80 are found in Brazil, 12 in Mexico and the rest in Central and North America.

“The possible domestication hypotheses are based on the geographic distribution of the species in the Americas and their number in specific places,” explains Carvalho. Of the 98 species of this genus, only one of them, found in Brazil, was domesticated and cultivated by man.

Based on DNA technology, it was possible to establish that the cultivated cassava derives from one species only that would be its ancestor, referred to as Manihot esculenta ssp. flabellifolia.

“Archeological research reports the finding of cassava residues at a site that dates back more than 8,400 years ago in a region of the Amazon, on the border between Brazil, Bolivia and Paraguay,” says Carvalho. This finding confirms the DNA studies that indicate the plant, from which cassava originated around 10 to 12 thousand years ago, was found in this area, in addition to the beginning of its domestication by man. “Cassava is one of the most significant contributions of native populations to the modern world,” says researcher Teresa Losada Valle, from IAC. The native populations whose staple food was cassava helped domesticate other plants that can currently be identified as extremely useful and sophisticated biological and biochemical processes in modern agriculture. “The extremely toxic root of the bitter cassava, a variety that contains a high level of hydrogen cyanide, was transformed into cassava flour without any toxic traces and could be easily stored,” says Teresa. The same process is still used nowadays. On the border between Brazil and Paraguay, native populations developed other varieties with very little toxic substances in them. Cassava became such an efficient plant that it became a basic food group in the pre-colonial Amazon area, much as what happened with corn in Mexico and potatoes in the Andes.

The projects
1.
Influence of population density during different harvesting periods upon the production and quality of cassava roots – Manihot esculenta Crantz); Type Regular Research Grants; Coordinator Teresa Losada Valle – IAC; Investment R$ 11,250.00 and US$ 537.40 (FAPESP)
2. Collection of germplasm and recognizing the center of origin and domestication of the cassava (from 1996 to 2001);  Generation and use of biotechnological tools for the identification of mutations (2002 to 2004); Genetic functionality tests of the mutation and creation of commercial varieties (since2005); Coordinator Luiz Joaquim Castelo Branco Carvalho – Embrapa; Investment US$ 180 thousand (Rockefeller Foundation),  R$ 194 thousand (Embrapa Recursos Genéticos e Biotecnologia); R$ 160 thousand (CNPq); € 160 thousand (International Atomic Energy Agency)

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