The effect of fermentation by Bacillus subtilis and Aspergillus niger on the nutritional value of date palm kernels

This study was performed to investigate the effect of fermentation by Bacillus subtilis (B. subtilis) and Aspergillus niger (A. niger) and alkaline processing on the nutritional value and chemical composition of date palm kernels (DPK). DPK was fermented for 28 days under solid-state fermentation culture with two different microorganisms (B. subtilis and, or A. niger). Alkaline processing was performed by soaking DPK in NaOH solution for 24 hours. In this experiment, eight treatments were used: DPK (control), DPK fermented by B. subtilis, and A. niger separately or in combination, and processed with NaOH, alone or with B. subtilis or A. niger or both. Digestibility and gas production of fermented and processed DPK were performed using the batch culture and gas production techniques. The results showed that there was an increase in crude protein (CP) and a decrease in crude fiber concentrations due to the fermentation of DPK with B. subtilis and A. niger (P < 0.05). Total phenol content in fermented DPK (FDPK) with B. subtilis and A. niger was significantly lower than the control. Gas production significantly increased in FDPK compared to control and NaOH-treated samples (p <0.05). All treatments significantly increased the in vitro digestibility of DM (IVDOD) and OM (IVOMD) compared to the control (p < 0.01). Among the treatments, simultaneous fermentation of DPK with B. subtilis and A. niger had the most significant effect on increasing the microbial CP (MCP) and its efficiency (EMCP; p <0.01).