3 May, 2019
Meeting Ethiopia's growing demand for starch using mango seeds
Arba Minch Town, Ethiopia, is a known
source for various fruit, including mangoes. It is the chosen
site for the
proposed strach extraction plant because of the steady supply of the raw
material in the town.
the Horn of Africa, Ethiopia currently imports 45% of its starch needs and,
with the demand for starch expected to increase, this figure could become much
higher. "A local supply of starch that does not compete with the food market is
needed," says Dr Tamrat Tesfaye, a researcher in the Department of Science and
Technology-CSIR Biorefinery Industry Development Facility (BIDF). Tesfaye is
originally from Ethiopia, where he completed his undergraduate and MSc degrees
before joining the CSIR to undertake a PhD programme in chemical engineering at
the University of KwaZulu-Natal. He explains that of the most common types of
mangoes grown and consumed in Ethiopia, thousands of kilograms of mango seeds
are thrown away annually.
The BIDF collaborated with
the University of KwaZulu-Natal and the Ethiopian Institute of Textile and
Fashion Technology to extract starch from waste mango seeds. The team of
chemists and engineers also conducted a techno-economic analysis for the
establishment of a facility to extract starch from mango seeds in Ethiopia and
estimated that the return on investment would be visible within a two-year period.
Starch, commonly found in
potatoes, rice, maize and wheat, is used in the beverage, food, textile, pharmaceuticals,
paper and pulp and cosmetics industries. Malnutrition in Ethiopia has been
widely documented and the production of starch for non-edible uses from foods
such as potatoes, maize and rice only exacerbates the country's food security
challenges. The team believes that starch extraction from mango seeds will
benefit the local agricultural sector and create employment opportunities.
A techno-economic analysis
conducted by the team concluded that establishing a plant in Ethiopia to extract
starch from mango seeds at an industrial scale could be viable. "The supply of
raw material is a key factor in ensuring the success of the operation," says
Tesfaye. He says that the team considered the major mango growing zones of the
country and settled on Arba Minch Town as a site to establish the starch extraction
plant because of its close proximity to market centres and labour, as well as
the availability of utilities and transportation infrastructure.
Some of the industrial
equipment required includes a washing machine, a desander, a grinder, and a
packing machine. After a process of washing and destoning mango seeds, they are
crushed to produce a slurry of starch granules. "The slurry is then sieved and
washed, making this a water-intensive exercise," says Tesfaye.
After a series of processes
of washing and dewatering, the dewatered starch cake is then dried in a flash
dryer, yielding a commercial-grade starch product.
The project team tested extracted
starch and found it to be comparable with a standard starch sample used in the
local textile industry. The starch consumption of several textile, paper and
pulp and starch manufacturing industries was considered in the plant design.
The proposed plant is envisaged to produce 500 tons of starch per annum, operating
for eight hours a day, 300 days per annum.
Seeds, peels and pulp from
the fruit industry contribute significantly to the country's waste streams.
Removing mango seeds from waste streams and beneficiating them for high-value materials
is one way of reducing the environmental and health risks associated with
incinerating, composting and landfilling waste from the fruit industry.
Additionally, Tesfaye states
that using mango seeds - which are discarded as waste - instead of food-based
materials, such as potatoes, rice and maize, has economic benefits and adds to
the country's food security. "If these food materials are consumed for industrial
applications, we need to plant additional starch sources for human
consumption," he adds, citing the use of fertilisers and pesticides that impact
the environment negatively. Thus, using mango seeds instead reduces the
environmental burden on ecosystems and adds significant economic value.
"This is another way in which
the recently launched biorefinery facility is facilitating the removal of organic
waste products from waste streams and biorefining them into higher value
products," says the facility director, Prof. Bruce Sithole.
The weight of a mango seed
constitutes up to 25% of the total weight of the fruit, meaning that a quarter
of the fruit is thrown away. A team of chemists and engineers have successfully
developed starch from waste mango seeds.