SINGAPORE - Two local scientists have devised a novel process that can turn prawn shells into a drug that treats Parkinson's disease, and pruned tree branches into a nutritional supplement, among other quests to unlock the value hidden in discarded waste products.
The researchers from the National University of Singapore (NUS) first use chemical processes to break down the waste products into substrates that can then be transformed by bacteria into useful substances.
For instance, washed and dried prawn shells are ground and broken down into a paste that can be digested by bacteria such as E.coli in a process similar to grape fermentation to make wine, and after a few days, a highly valuable amino acid called tyrosine is produced.
Tyrosine is an important component of animal feed for chickens, pigs and fish, as the amino acid helps to enhance the animals' growth rate and protein quality.
However, the scientists' research has gone even further, using catalysts produced by the bacteria to then convert the tyrosine to L-dopa, a medicine that can be used to treat Parkinson's disease, a neurological condition.
The bacteria, including E.coli, were enhanced through genetic engineering to optimise the novel transformation process, said Assistant Professor Zhou Kang from NUS's department of chemical and biomolecular engineering, one of the two lead scientists in the project.
Their research on producing L-dopa from crustacean shells was published in the scientific journal Proceedings of the National Academy of Sciences in March this year.
"Singapore is very focused on developing sustainable ways of producing proteins, such as through aquaculture, and animal feed will play important roles there," added Prof Zhou.
The scientists also found that the raw materials for their process were cheaper than conventional raw materials. For instance, L-dopa is traditionally made from glucose, which costs between US$400 and US$600 per ton, whereas prawn shells cost about US$100 per ton.
However, it will take another five to 10 years before prawn shell-based Parkinson's disease drugs can reach pharmacy shelves, said the NUS scientists.
For one thing, the L-dopa made in the lab needs to be purified before it can be sent to pharmaceutical companies to develop them into pills. It will also take a few years to scale up the manufacturing process and eventually commercialise the prawn-based medicine, said Prof Zhou.
He added that L-dopa can be further converted to other substances such as painkillers.
In their drive to upcycle unwanted waste, the team used similar chemical and fermentation processes to convert wood waste such as pruned branches and sawdust into proline, a supplement for healthy joints.
It is planning to work with industrial partners to commercialise their conversion technology, which took four years to develop, to manufacture L-dopa, tyrosine, and proline.
This year, the researchers also started working on converting carbon dioxide - the main greenhouse gas causing climate change - into ethanol, an alcohol, by pumping in hydrogen.
They hope to transform the ethanol into protein-enriched biomass, such as yeast strains, that has a nutritional value comparable to beef. The product can be a form of alternative proteins, the scientists said.
"Once the chemical process (to make ethanol) is done, we will add microbes and convert it into "beef", and that will be our next step. That's the plan," said Associate Professor Yan Ning, the other lead scientist in the project.
Prof Zhou added: "There is great interest to produce proteins from sustainable sources, so we believe it would be best if we can produce it from carbon dioxide."
Recently, the team also started work on converting wastepaper and expired meat into tyrosine.
"Tyrosine is one of the most valuable amino acids out there, and it costs between $30 and $50 per kilogram," said Prof Zhou.
"We are trying to make valuable products from the waste stream. We hope that this technology could be improved to expand the spectrum of products for society."
