About 10,000 tonnes of okara are produced annually in Singapore. It spoils easily, has an unpleasant smell and is unpalatable, so soy food producers dispose of it — which contributes to food waste.
To reduce this wastage, Prof Liu Shao Quan and the research team from the Food Science and Technology Programme at the Department of Chemistry, National University of Singapore (NUS), have developed a biotransformation process for okara using a combination of natural microorganisms and enzymes (such as cellulase and hemicellulase) to convert it into a high-value food ingredient with better nutritional value as well as enhanced flavour.
“The biotransformation process requires adding a microbial starter to (steamed and cooled) okara, and allowing it to ferment in a clean, enclosed space for about one to two days. Okara is essentially free (or very cheap), and the starters are very affordable. The main cost involved will be in transporting the okara, steaming it and having the space for biotransformation to take place,” said Prof Liu.
Prof Liu said the starter used is the same type of mould used in the fermentation of the Indonesian soybean food tempeh: Rhizopus oligosporus.
Vong Weng Chan, a PhD student on the research team, added, "The okara can be fermented directly after it is produced, without the need for intermediate processing. Also, the high moisture content in okara promotes microbial growth, enhancing the fermentation process."
The renewed okara contains more soluble fibre, which helps to maintain gut health. Furthermore, it acquires a meaty taste, and becomes easier to digest as the insoluble fibres are broken down. This makes it suitable as an ingredient for a variety of food products, such as baked goods and meat substitutes.
“This process is straightforward, natural and does not produce waste streams. The biotransformed okara is nutritious, plant-based and has the potential to be used in a variety of food products,” said Prof Liu.
He hopes to spread the knowledge of the benefits of biotransformed okara — such as low-GI, antioxidant, high-soluble fibre — including in a talk at a roundtable discussion on “Sustainability in Food” by NUS Enterprise on November 23.
Vong WC; Lim XY; Liu SQ*, “Biotransformation with cellulase, hemicellulase and Yarrowia lipolytica boosts health benefits of okara” APPLIED MICROBIOLOGY AND BIOTECHNOLOGY. Volume: 101 Issue: 19 Pages: 1-12 DOI: 10.1007/s00253-017-8431-1 Published: 2017.