Effect of fungal fermentation on proximate composition, physical and functional properties of five different plant proteins used in aquafeed formulation

Abstract

Five different plant proteins such as soybean meal (SBM), groundnut oil cake (GNC), rapeseed meal (RSM), sunflower oil cake (SFC) and guar meal (GRM) were tested for proximate composition as well as physical and functional properties before and after fermentation using Aspergillus niger. Fermentation was carried out in a BOD incubator at 35°C for three days after inoculating with 5% fungal suspension. Results revealed that fermentation significantly (p<0.05) increased the crude protein content and total ash by 12.5 and 10.5%, respectively, while other proximate indices, including crude fat, crude fiber and nitrogen-free extract reduced significantly. The fungal fermentation had no effect on the texture and colour of plant proteins, while fermented samples had slightly fermented odour along with their natural odour. The plant proteins such as SBM, GNC, RSM, SFC and GRM had bulk densities of 0.54, 0.62, 0.79, 0.60, and 0.71 g cm-3 and significantly (p<0.05) increased by 27.1, 0.5, 0.4, 19.9 and 12.3%, respectively. Fermentation significantly (p<0.05) reduced water holding capacity by 11.7% regardless of the ingredients, with the decrease being significantly (p<0.05) greater in GNC (17.7%), RSM (16.4%) and SBM (13.4%). After fermentation, the protein solubility index reduced significantly (p<0.05) from 77.12 to 73.59%, with SBM and RSM having a reduction of about 5.9 and 5.4%, respectively, while GNC and SFC had a reduction of 4%. The difference between fermented and unfermented GRM, on the other hand, was not significant. Results concluded that fermented ingredients could be potential protein sources rather than their counterparts based on their chemical composition and functional properties. Keywords: Aspergillus niger, Fermentation, Functional property, Physical property, Plant protein, Proximate composition