USE OF MULBERRY POMACE AS SUBSTRATE FOR CITRIC ACID PRODUCTION BY Aspergillus niger MT-4

Abstract

Mulberry pomace (MP) is a waste material obtained after the production of pekmez, a traditional Turkish food. This study was performed to test the usability of MP as substrate for citric acid (CA) production by Aspergillus niger MT-4 for the first time. In the study, some culture conditions were also optimized to increase CA production in MP-based medium. Moisture, total carbohydrate, water-soluble carbohydrate, protein, lipid and ash contents of MP were determined as 31.1, 47.1, 1.3, 13.4, 1.8 and 1.4\%, respectively. Experiments were carried out in 250 mL flasks containing 100 mL of production medium. Optimal MP concentration for both fungal biomass (FB) and CA production was determined as 120 g/L. All concentrations of KH2PO4 added to MP-based medium were found to decrease CA production but increase FB production. Optimal concentrations of MgSO4 and (NH4)(2)SO4 for CA production were found as 1 and 2 g/L, respectively. The other optimal parameters were determined as an initial pH of 7.0 and an incubation period of 5 days. Under the optimized culture conditions, the amount of CA produced was determined as 24.6 g/L. On day 5, Yp/s, Yp/x and Yx/s were calculated as 0.2 g CA/g MP, 1.43 g CA/g FB and 0.14 g FB/g MP, respectively.