Assessing Waste Sunflower Oil as a Substrate for Citric Acid Production: The Inhibitory Effect of Triton X-100

In this study, waste sunflower oils were evaluated as substrates for citric acid (CA) production by Yarrowia lipolytica IFP29 (ATCC 20460). This strain was selected based on its capacity to produce organic acids in a selective medium. Attempts were made to optimize the process using the Taguchi statistical method in terms of the oil polarity, oil concentration, fermentation time, and Triton X-100 concentration. The results indicated that Y. lipolytica IFP29 utilized waste sunflower oil as a substrate and produced a maximum CA of 32.17 ± 1.44 g/L. Additionally, Triton X-100 inhibited the production of CA. For this reason, this process could not be optimized. These results were obtained by periodically adjusting the pH with NaOH during the fermentation period. On the other hand, a new experimental design was created without Triton X-100. As a buffering agent, 2-morpholinoethanesulfonic acid monohydrate (MES) was used to prevent a drop in pH; the maximum concentration of CA was found to be 20.31 ± 2.76. The optimum conditions were as follows: 90 g/L of waste sunflower oil with a polarity of 16 and 12 days of fermentation. According to the analysis of variance results, the effects of factors other than polarity on CA production were found to be significant (p < 0.05).