Adding value to the by-products of cereal processing by fungal production of highly unsaturated fatty acids

Abstract

The processing of cereals as agricultural crops or biofuels generates millions of tons of byproducts annually. The South African beer brewing industry alone produces approximately 520 000 tons of brewers’ spent grain per year. These residues not only lead to economic losses for the industry, but constitute an environmental hazard. Currently cereal by-products are mainly utilised as animal and fish feeds. This application is limited by the high fibre and low protein levels generally present in these by-products. The presence of antinutrients (phytic acid, chlorogenic acid and other phenolic compounds) and the low levels of highly unsaturated fatty acids (HUFA) in most of these by-products also limit its use, especially as feeds for monogastric animals and fish. HUFA such as eicosapentaenoic acid (EPA) are essential to the regulation of the cardiovascular, immune, digestive and neurological systems in mammals and fish. Arachidonic acid (ARA) is of nutritional importance in fish egg and larvae development (Ogata et al., 2004). These long chain fatty acids have to be included in the diets of mammals and fish (Dyal and Narine, 2005). Currently the main dietary source of HUFA is marine fish oil. As demand for crude fish oil for the aquaculture industry increases and the market for dietary omega-3 supplements expands by 24% annually, there are concerns over the sustainability of marine and fish sources of HUFA (Jang et al., 2000). Recent research has focused on HUFA production by micro-organisms as a sustainable and safe alternative to fish oil (Ward and Singh, 2005). Fungi of the genus Mortierella are used for industrial production of some of these valuable HUFA and could be grown directly on the cereal by-products. The aim of this study was to enhance the quality of the by-products and to provide an alternative application for cereal by-products as a source of HUFA. Cereal by-products enriched with HUFA could find applications as food, feed, or pharmaceutical or veterinary products.