Symbiotic fermentation characteristics of biotransformed maize pulp for biofertilizer production

Maize deep processing has been the second-largest agricultural processing industry in the world. The products (such as starch sugar, maize oil, and crude fiber) have been very important food and chemical raw materials. Among them, maize starch is currently the main resource for the production of glucose syrup and various sugar derivatives. However, the preparation process of maize starch can produce a large number of by-products, such as Maize Steep Liquor (MSL). Alternatively, the maize pulp has been confined during processing, due to the dark color, heavy taste, high toxin content, and difficult handling. Particularly, maize pulp presents great potential in the field of bio-exploitation, due to a large number of nutrient contents with more than 40% nitrogen and more than 25% carbohydrates. Therefore, a cheap nitrogen source can be served for the fermentation production of bioproducts. This study aims to develop microbial fertilizers using the abundant source of fast-acting nitrogen in the maize pulp and the growth-promoting factors of microorganisms. The slow release and degradation of toxins by soil were avoided to reduce the direct toxicity of biotoxins to humans and livestock. A systematic evaluation was made on the high-density fermentation of three strains of plant inter-rhizosphere growth-promoting bacteria (PGPMs) in the maize pulp. The fermentation characteristics were investigated via the symbiotic fermentation of three strains of PGPMs that screened in the previous stage. The experimental results showed that the three species significantly increased the biomass in the fermentation system after the symbiotic fermentation. The flow addition of starch industrial waste (crystalline glucose mother liquor) was taken as a supplement during the simulation. The total biomass was elevated from 6.6×109 to 2.17×1010 CFU/mL in the fermentation system. The maximum viable bacterial count and amino acid nitrogen were obtained at the end of 45 h fermentation. Meanwhile, the glucose was added in the mimic crystalline glucose mother liquor flow in the symbiotic system. Then, there was a significant increase in the utilization of total sugars and soluble phosphorus. Specifically, the soluble phosphorus utilization increased by nearly 50%. The addition of glucose also maintained the stable pH value in the fermentation system, particularly for the stable production of bacterial fertilizer. This finding can provide a better solution and practical basis for the reuse of maize pulp in the production of low-cost biofertilizers using a variety of bacteria. The high value-added reuse of crystalline glucose mother liquor can be produced using the waste of maize starch.