Located in 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.
Local starch production
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.