Biovalorisation of okara (soybean residue) for food and nutrition
Abstract Background Okara is the soybean residue that remains after the manufacture of soymilk or soybean curd. The high moisture content (70 80% makes it susceptible to spoilage, and so it is often discarded. Yet, okara still holds many nutrients (on a dry weight basis, approximately 50% carbohydrates, 20 30% proteins and 10 20% lipids, as well as minerals and phytochemicals) making it a suitable substrate for biovalorisation. Scope and approach The composition of okara is assessed with respect to its potential for biovalorisation to obtain bioactive substances and food products. Studies on okara fermentation by fungi, bacteria and yeasts are highlighted, with their main drawbacks and challenges critically discussed and the research gaps identified. Key findings and conclusions Studies to date have demonstrated the feasibility of okara fermentation to produce a variety of functional ingredients and foodstuffs. The health benefits and nutritional quality of okara are often enhanced by fermentation, and the fermented okara is also an inexpensive substrate for extraction of bioactive substances. Present research remains largely at bench scale, and the main challenges are related to scaling up, efficiency and/or yield. There is much scope for further exploration into various aspects of okara biovalorisation, including applying bioprocessing treatments as a pre fermentation step, using combinatorial microbes or enzymes, and evaluating organoleptic property, dietary effects and potential allergenicity of the fermented products.