Feasibility of Date Syrup as an Alternative Substrate for Bradyrhizobium japonicum Biofertilizer Production Through Submerged Fermentation

This research investigated the bioconversion of fermented date by-products into biofertilizer using Bradyrhizobium japonicum (B. japonicum). Heat-extracted date syrup (DS) or a mannitol-sucrose (MS) mixture was used as a sugar source at 12 g/L in a culture medium in a 10 L fermenter. Glucose and fructose were the only monomers identified in DS. The exponential growth phase of B. japonicum in MS began around 1 h, whereas in DS it lasted up to 3 h, resulting in substantially higher biomass accumulation. Sugar consumption stabilized at 4 h in DS, whereas it took 8 h in MS. After 12 h of fermentation, less than 1% of the sugar remained in both substrates. The findings suggest that the increased availability of glucose and fructose in DS facilitated greater sugar uptake and subsequent population growth. The DS fraction contributed to a collective mass of low-molecular-weight organic carbon, including sugars, amino acids, fatty acids, and organic acids. DS demonstrated a significantly higher yield coefficient (Yx/s) of 0.58 compared with MS 0.35, highlighting its potential for commercial production.