Optimizing Medium Compositions and Fermentation Parameters for Citric Acid Production from Whey-based Medium using Response Surface Method

Abstract

This project was conducted to determine the optimum fermentation condition for the production of citric acid by Aspergillus niger NRRL 567 grown using cheese whey. A first set of experiments (Optimization 1) was studied to optimize initial level of stimulators (methanol, olive oil and phytate) for citric acid production using the central composite design (CCD). The citric acid production was identified to correlate to the initial concentration of stimulators. The application of the statistical optimization method using CCD resulted in an improvement of maximum citric acid production from 12.8 to 41.8 g/l in validation experiment. Followed a second experiment (Optimization 2) evaluated initial fermentation parameters (initial pH, fermentation time and inoculum density) on citric acid production using a CCD. The experiment indicated that initial pH and inoculum density had a significant effect on citric acid production, while fermentation time was insignificant in the tested ranges. Testing these optimal fermentation conditions using two-step optimization, a maximum citric acid concentration of 74.6 g/l was obtained after 312 h of fermentation representing a 5.8-fold increase compared to basal whey medium.