Potencial Citric Acid Production by Fungi Using Hemicellulosic Hydrolysate of Coffee Husk as Substrate

Abstract

Objective: The aim of this experimental assay was to produce citric acid via submerged fermentation, using hemicellulose hydrolysate from coffee husks as main substrate.   Theoretical framework: Obtaining citric acid through fermentation processes, especially submerged fermentation, has become viable due to the use of low-cost materials, such as industrial subproducts derived from green biomass.   Methodology: The hemicellulose hydrolysate was obtained from the acid hydrolysis process of the coffee husk. The strains of the fungi Aspergillus niger, Aspergillus westerdijkiae and Rhizopus sp. were employed to carry out the fermentation assays. A bioreactor consisting of a 500 ml flat-bottomed flask was used, with an inlet for supplying air and an outlet for removing samples   Results and Conclusion: The obtained results showed an increase in number of spores of the studied fungi as well as citric acid accumulation during the first 72 h of fermentation. On the other hand, after 96 h of fermentation citric acid concentration began to decrease indicating its consumption by the studied fungi, probably due to the lack of nitrogen sources and the cellular stress caused by the mixed composition of the hemicellulose hydrolysate.   Implications of the research: There is a need to study the interaction between the nitrogenous nutrients to be added to the fermentation medium and the concentration of reducing sugars as the sole carbon source in the lignocellulosic hydrolysate.   Originality/value: This work highlights the potential production of citric acid by fungi using a coffee husk as a renewable biomass.