Optimization of processing conditions for solid-state fermented soybean meal and its effects on growth performance and nutrient digestibility of weanling pigs

• Effects of process parameters on nutritional quality of FSBM were investigated.
• Fermented soybean meal was added to weaning pig diet at the expense of SBM.
• Achieving 40 °C and higher initial moisture content and supplementing with protease are essential to produce FSBM.
• Replacing SBM with FSBM improved average daily gain and average daily feed intake of weaning pigs.
• Replacing SBM with FSBM had no effect on nutrient digestibility and plasma urea nitrogen level of weaning pigs.

This study was conducted to investigate the appropriate processing conditions for solid-state fermented soybean meal (FSBM) using a mixed starter culture of Streptococcus thermophilus, Bacillus subtilis MA139, and Saccharomyces cerevisae (Exp. 1), and determine the effect of FSBM (produced with appropriate conditions) as a partial replacement for soybean meal (SBM) on growth performance and nutrient digestibility of weanling pigs (Exp. 2). In Exp. 1, SBM was fermented using different processing conditions, including initial moisture content, incubation temperature and duration, sugar addition, protease supplementation, and neutral protease to acid protease ratio. After fermentation, pH value and contents of crude protein, lactic acid, glycinin, and β-conglycinin in FSBM were determined. Results showed that the appropriate incubation temperature for FSBM production was 40 °C. Greater initial moisture content (60%) and protease supplementation (0.3%) improved nutritional value. The suitable neutral protease to acid protease ratio was 3:1. Five days of incubation was sufficient for production of good quality FSBM. Addition of brown sugar did not affect the glycinin, and β-conglycinin contents in FSBM. In Exp. 2, a total of 72 crossbred piglets (Duroc×Landrace×Large White) of an average weight of 8.9 kg were randomly allotted to 2 treatments with 6 replicate pens and 6 piglets per pen. Piglets were fed either a control diet with 24% SBM or a test diet with 6% FSBM added at the expense of SBM. Results from Exp. 2 showed that replacing SBM with 6% FSBM improved average daily gain and average daily feed intake (P<0.05), while feed conversion ratio was unaltered. The nutrient digestibility and plasma urea N concentration in piglets on the FSBM diet were not different from those fed the SBM diet. In conclusion, achieving a suitable incubation temperature, greater initial moisture content, and supplementing with protease are essential to obtain good quality FSBM. Feeding a diet containing 6% FSBM can result in greater growth performance in weanling pigs, implying that this new strategy has the potential to be used to produce solid-state FSBM.