A Comparative Study of Caffeine Degradation by Four Different Fungi

The objective of the present study is to investigate the caffeine-degrading abilities of different fungi and to apply this knowledge to environmental remediation and industrial decaffeination process. Chrysosporium keratinophilum, Gliocladium roseum, Fusarium solani, and Aspergillus restrictus were isolated from the coffee pulp obtained from a coffee estate. Pure cultures of fungi were isolated on standard conventional potato dextrose broth (PDB) medium and authenticated. Pure cultures were subjected to a caffeine tolerance study at different concentrations of caffeine (18g/L) in potato dextrose agar (PDA) and minimal media. On PDA, Fusarium solani could tolerate caffeine concentration up to 8g/L, whereas Chrysosporium keratinophilum, Gliocladium roseum, and Aspergillus restrictus could tolerate up to 6g/L. On minimal agar medium containing different concentrations of caffeine (18g/L), Fusarium solani tolerated up to 8g/L and the other fungi up to 2g/L. A time-bound caffeine degradation study was undertaken at 1g/L concentration of caffeine and glucose in nitrogen-containing and nitrogen-free liquid minimal media by subjecting the four fungi to shake flask culture at 120rpm and 30 degrees C. Degradation of caffeine up to 7days at 24-h intervals was analyzed by high-performance liquid chromatography (HPLC). Gliocladium roseum followed by Aspergillus restrictus showed maximum degradation of caffeine at 0.47 and 0.3mg/ml, respectively, by 96h in nitrogen-containing minimal medium, whereas Fusarium solani showed maximum degradation of caffeine by 48h (0.35mg/ml) and Chrysosporium keratinophilum by 72h (0.29g/ml). In nitrogen-free minimal medium, Chrysosporium keratinophilum showed maximum degradation of caffeine at 72h (0.45mg/ml), followed by Gliocladium roseum, Fusarium solani (0.3mg/ml), and Aspergillus restrictus (0.25mg/ml) at 96h. Overall, Chrysosporium keratinophilum showed a comparatively higher rate of caffeine degradation in minimal medium with or without a nitrogen source as compared with the other three fungi, indicating that nitrogen affects caffeine metabolism.