M.J. Madibana1*, C.H. Fouché1, J.J. Davids2, S.T. Mthembu2, M.H. Motubatse2, Z. Poni2, E.A. Thomas2, O. Nyengule2, R.L. Nemakhavhani2
1Department of Forestry, Fisheries and the Environment, Martin Hammerschlag way, Foreshore, Cape Town, 8001
2Department of Conservation and Marine Sciences, Cape Peninsula University of Technology, P.O. Box 652, Cape Town 8000, South Africa
(Manuscript received 9 July; accepted for publication 22 August 2022)
Abstract. Soybean has shown over the years to be a reliable plant protein source to excellently substitute the high cost fishmeal in aquaculture diets. However, antinutritional factors (ANFs) limit its usage in aquaculture feeds. Therefore, the current study was designed to test the efficacy of three substrates containing different microorganisms that are capable of reducing soybean ANFs in a 3-month period at a low pH of 2.8. Full fat soybean (USB) was fermented using Anaerobic waste extract from Recirculating Aquaculture System sludge trap (RASW); Biocentric® Feed probiotic powder (BIOP); Oakland® double cream yoghurt (3x 106 CFU ml-¹) (OY), Control treatment which had no substrate that contained fermenting microorganism (SRR). Each treatment was conducted in three replicates at 2.8 pH. The untreated soybean granules recorded a numerical protein content of 48.56%. The BIOP fermented soybean recorded significantly higher protein content as compared to the other soybean meal fermented with the other substrates. There was also a significant decrease in the soybean content of the amino acid lysine upon fermentation with the four treatments. Fermentation of the soybean with the four treatments was not significantly different in relation with their soybean lipid content, crude fibre content, methionine + cysteine, dry matter content, urease activity and gross energy content (P>0.05). There was an overall significant decrease in the ANFs when soybean was fermented with the four treatments, with four out of six analysed ANFs parameters content showing a significant decrease upon fermentation (P<0.05). Fermentation of the soybean with RASW resulted in a significant decrease of trypsin inhibitor content as compared to the rest of the treatments. The USB recorded a numerical value of 43.80 for trypsin inhibitor, whereas RASW fermented soybean recorded least trypsin inhibitor of 3815±010 mg/g. In conclusion, the current study showed that the fermentation substrates used are capable of reducing soybean ANFs, with a slight decrease in soybean protein content.