Isolation and identification of Aspergillus niger from some fruits and use for sodium gluconate production

Sodium gluconate is an auxiliary chemical used in the food, chemical, construction and environmental sectors. Aspergillus niger strains have the ability to produce gluconic acid by oxidizing glucose. The aim of this thesis is the isolation and identification of candidate Aspergillus niger strains from various fruits for the biotechnological production of sodium gluconate, followed by the identification of high sodium gluconate producers and the production of sodium gluconate in batch and semi-batch system at pilot scale. In the study, 46 typical Aspergillus colonies were collected from PDA medium, and then 25 ribosomal ITS regions were identified according to their morphological features according to the results of the sequence analysis. Accordingly, it was determined that 21 of the collected isolates belonged to the Aspergillus niger species, with homology higher than 97%. In the presence of 1% glucose, the highest sodium gluconate yield (Ys/p, >0.5) among these strains was determined in A. niger SG3 and SG21 strains. 61.14 g/L sodium gluconate could be produced at the end of the pilot scale 40 hours of intermittent fermentation. In addition, 105.30 g/L sodium gluconate could be produced in semi-batch fermentation. The sodium gluconate produced at the end of both fermentations was recovered by crystallization and characterized by comparing it with the standard in the HPLC system. At the end of this study, the locally sourced Aspergillus niger SG21 strain was determined for the production of ready-to-use sodium gluconate for industrial use. It has also been shown that sodium gluconate can be produced in pilot scale systems with this strain.