Production of gluconic acid from sweet potato peels using naturally occurring fungi by submerged fermentation

The oxidation of glucose produces gluconic acid, a significant organic acid. The aim of this study was to produce gluconic acid from sweet potato peels by submerged fermentation. Isolation and identification of fungi were done using standard microbiological methods. Proximate analysis of substrate and screening of fungal isolates for gluconic acid production was done using standard procedures. Gluconic acid yields were determined using High Performance Liquid Chromatography. A standard gluconic acid producer, Aspergillus niger ATCC 10577, was used as control. A sum of six different fungal species were isolated and identified. They included Aspergillus niger, Aspergillus flavus, Penicillum sp., Cladosporium sp., Rhizopus stolonifer and Aspergillus terreus. Proximate composition of the sweet potato peels showed percentage carbohydrate of 20.81 ± 0.07, percentage moisture of 64.02 ± 0.27. Screening for gluconic acid production showed that Aspergillus niger had the highest zone of clearance and identified as Aspergillus niger UFMGCB 14248. Our data further showed that gluconic acid concentrations (mg/ml) was highest at substrate concentration 50 g/L, carbon source starch, incubation day 7 and pH 6 for both Aspergillus niger UFMGCB 14248 and Aspergillus niger ATCC 10577. The findings showed that the fungal isolates used in this study were good gluconic acid producers