VALORIZATION OF SOYBEAN MEAL FOR PRODUCTION OF HIGH PROTEIN ANIMAL FEED AND VALUE-ADDED PRODUCTS USING NEW STRAIN OF AUREOBASIDIUM PULLULANS

Abstract

By-products of soybean oil production are high-quality protein supplements for animal feed. However, they are rich in anti-nutritive factors and indigestible components, among which the special attention is focused on galactooligosaccharides, due to lack of αgalactosidase in monogastric animals. Enzymatic treatment of soy-based products and microbial fermentation are employed for overcoming these issues. The main goal of this study was to apply fermentation with a selected strain of black yeast-like fungus (Aureobasidium spp.) of the soybean products in order to obtain highprotein soy-based animal feed. First, screening for an appropriate strain of microorganism among ten natural isolates from grapes has been performed. Keeping in mind complex structure of soybean polysaccharides the first selection criterion was the ability of growth in the presence of arabinose, xylose, galactose, mannose, raffinose, or soybean oil as sole carbon source. More important, enzymatic activity of α-galactosidase was detected in new isolates. The highest α-galactosidase producer was selected for cultivation on soybean meal. The selected strain was characterized in terms of physiological and technological properties and identified as Aureobasidium pullulans P8. In order to obtain high protein soybean meal, it has been utilized in two types of fermentation, i.e. solid state (SSF) and submerged (SMF) under varying conditions. Maximal protein content (61.11% based on dry weight) was obtained after 5 days of SMF at 30 °C and 10% of dry matter, while SSF produced 57.78% protein after 7 days of incubation at 30 °C with substrate contained 30% of dry matter. Extracellular enzymatic activities of cellulase, pectinase, amylase, xylanase and αgalactosidase were detected in supernatant after SMF, indicating its potential reusability for hydrolysis of new batch of soybean substrate. This investigation revealed the versatile extracellular enzymatic potential of newly isolated black yeast-like fungus Aureobasidium pullulans P8 and its potential for production of high protein soybean meal.