Abstract:The potential of corn cobs as solid substrates for the production of citric acid was investigated using Aspergillus niger KA88, a local isolate as the fermenting organism. One-factor-at-a-time (OFAT) model was used to optimize the fermentation media to achieve the maximum yield of citric acid. The fermentation parameters studied and their resultant optimised levels were found to be 28 ˚C incubation temperature, 15% (w/v) sucrose for 6 days fermentation period, 50% each of (0.5-1mm and 3-5mm) particle sizes. Di-ammonium hydrogen phosphate was the preferred nitrogen source at a concentration of 4g/l. The final OFAT fermentation media gave 138.24 g anhydrous citric acid/kg dry corn cob. In general, corn cob proved to be a highly promising solid substrate for commercial citric acid production.

Samples of olewonyo from two different localities together with a laboratory produced sample were analyzed for microbial changes, pH, titrable acidity and salt tolerance. High total viable counts (TVC) of 9.99 log cfu/ml, 9.23 log cfu/ml and 5.00 log cfu/ml were observed in the Aboabo, Anloga and Lab-simulated samples respectively at room temperature at day 3 (72hours). There was no significant differences in microbial load among the various samples among TVCs, lactic acid bacteria (LAB), lactic-acid cocci, and yeasts and moulds counts as the storage time increases (p<0.001). The pH of samples from Aboabo and Anloga showed a rapid decline from 6.55 and 6.60 to 4.55 and 4.30 respectively within 24-hour of storage. The changes in the Lab-produced sample however, showed a gradual decrease from 6.55 to 4.80 for the entire period of storage. There was no significant increase in titrable acidity of the laboratory sample (p<0.02) compared to the traditional samples. Of the 15 LAB isolates from the three sites, 40% were Lactobacillus fermentatum, 26.6% Lactobacillus plantarum, 20% Lactobacillus acidophilus and 13.4% Lactobacillus brevis. In the API gallaries, the dominant species were able to ferment ribose, galactose, D-glucose, D-fructose and mannitol. The present study shows that Leuconostoc mesenteroides, Lactobacillus plantarum, L. acidophilus, L. brevis, L. fermentatum, Corynebacterium, Saccharomyces cerevisiae, Aspergillus flavus and A. parasiticus may be involved or associated in the spoilage of olewonyo.