A new use of the cassava plant—a woody shrub grown in tropical or subtropical regions of the world—could mean an increase in the availability of food, while at the same time providing a new source of biofuel, whether solid, liquid or gaseous, a team of Swedish and Chinese researchers have found. Starch grains in cassava stem SX 913Starch grains seen in a cross section of a cassava stem. Photo by courtesy of Shaojun Xiong.

“Cassava stems have previously been overlooked in starch and energy production”, the researchers, of whom two of Bio4Energy, say in a study freshly published in the online version of Global Change Biology Bioenergy, a peer-reviewed scientific journal.

Today the cassava plant is extensively cultivated for its starchy tuberous root and is the third-largest source of food carbohydrates in the tropics after rice and maize, according to online encyclopedias. Being drought tolerant by nature and capable of growing on marginal soils, it is a major food staple in the developing world, providing a basic diet for over half a billion people. Countries like China have turned their interest to cassava for its suitability as a feedstock in bioethanol production.

However, because so many less well-to-do people rely on the cassava—alternatively called manioc, yuca, balinghoy, mogo, mandioca, kamoteng kahoy, tapioca or manioc root plant; depending on where in the world it is grown—biofuel making based on the cassava root could easily been seen as an example of one man’s food being turned into another man’s fuel. This week the European Parliament voted to prevent such displacement of food production, or of land used to grow food or feed, by capping the use of so-called first-generation biofuel in the EU at six per cent of its goal to have ten per cent of final energy use in automotive transport come from renewable sources by 2020.

Environmental and development campaigners, as well as an increasing number of international research organisations, have said the issue ties in with the question of whether land fit for food production, or hosting forests serving as a carbon sink and a haven of biodiversity, are being claimed for biofuel production.  

In the case of the cassava plant, however, there could be a way around these issues, the Sino-Swedish research group said, resulting in more food and biofuel being made available, with “no” net displacement of land or "indirect land use change", as the phenomenon is called in European Union and United Nations' policy papers.

"The cassava roots on which biofuels and other products are based can be replaced by cassava stems without land use expansion, making root starch available as food for [an] additional 30 million people today", the researchers' study says.

Their contention is that the possibility of using the stem for fuel production has largely been overlooked. They say this is because a certain type of tissue in the cassava which produces starch in the late stages of the plant's maturation has not traditionally been the focus of research investigations.

However, up to 15 per cent of the stem biomass, mainly from this 'xylem' tissue (which, by the way, is where the biomass polymer lignin is formed) could be extracted by an uncomplicated and energy-efficient method for use in the production of solid, liquid or gaseous biofuels, the researchers hold.

"Research efforts have traditionally focused on the phloem [tissue] and its sugar pathways. What we are saying is to use [starch from] the stems instead", said study co-author This email address is being protected from spambots. You need JavaScript enabled to view it., who is a B4E PI affiliated with the Swedish University of Agricultural Sciences (SLU), and a close colleague of Shaojun Xiong who led the research team.

In their article Cassava stems: a new resource to increase food and fuel production, which includes further estimates of untapped capacity corresponding to more than a tripling of the yield of food carbohydrates from cassava roots in 2030, the researchers paint a bright future for the use also of the stem of the tropical shrub of many names;

"The cassava is cultivated on 19 million hectares for its high starch content [approximately 70 per cent] in the roots and used as food for 500 to 1000 million people in tropical and subtropical regions in Africa, Asia and South America.

"We found that cassava stems, now regarded as... waste of no use, have [a] surprisingly high content of starch at the time when roots are harvested.

"The cassava feedstock resources can be utilised more efficiently within the combined Food & Fuel concept where both starch and fuel production are increased and, in addition, waste is minimised when the stems are integrated into the combined starch and fuel model according to one scenario (starch + solid biofuel + biogas) [described in the researchers' scientific article]".

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About cassava research in Bio4Energy

The cassava stem project was coordinated by doctor This email address is being protected from spambots. You need JavaScript enabled to view it.of Bio4Energy and of the Unit of Biomass Technology and Chemistry, BTC, SLU Umeå. From the same institution, doctor Torbjörn Lestander, PhD student Björn Hedman and agronomist Håkan Örberg also took part.

From the China Agricultural University (CAU) in Beijing, lead author Wanbin Zhu and his colleague Maogui Wei were part as current or present postdoctoral students at SLU Umeå. CAU professor Guanghui Xie and doctoral student Jiwei Ren made contributions.

The article Cassava stems: a new resource to increase food and fuel production was published in the online version of GCB Bioenergy 10 September 2013.

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