Influence of Diet and Growth Conditions on the Carbon and Nitrogen Stable Isotopic Composition of Aspergillus niger Mycelium: Insights for Fungal Chitosan Characterization

This study investigates, for the first time, the relationship between carbon (δ13C) and nitrogen stable isotopic composition of Aspergillus niger mycelium, used as chitin and chitosan sources, and the fungus diet under controlled cultivation conditions. Four diets were tested, combining different carbon (C3- and C4-glucose) and nitrogen sources (KNO3 and NH4Cl). Results showed that carbon sources significantly influenced δ13C values of the mycelium: C4-glucose diets led to more negative Δ13C values (δ13CMYCELIUM-δ13CDIET) compared to C3-glucose diets. Nitrogen sources also affected isotopic fractionation, with KNO3 leading to negative Δ15N (δ15NMYCELIUM-δ15NDIET) and NH4Cl yielding positive Δ15N. Conversely, pH and temperature showed negligible effects on δ15N, while continuous aeration during growth significantly decreased δ15N, possibly due to partial assimilation of atmospheric nitrogen. These findings demonstrate that both nutrient and cultivation parameters can modulate the isotopic fractionation in A. niger, particularly for nitrogen. Although a direct correlation between diet composition and δ15N could not be established, this work provides the first experimental link between fungal metabolism and its isotopic fingerprint. The results offer a scientific foundation for applying stable isotope ratio analysis to authenticate and trace fungal-derived chitin and chitosan, with potential applications in food and winemaking industries.