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 (δ 13C) 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 δ 13C values of the mycelium: C4-glucose diets led to more negative ∆ 13C values (δ 13CMYCELIUM-δ 13CDIET) compared to C3-glucose diets. Nitrogen sources also affected isotopic fractionation, with KNO3 leading to negative ∆ 15N (δ 15NMYCELIUM-δ 15NDIET) and NH4Cl yielding positive ∆ 15N. Conversely, pH and temperature showed negligible effects on δ 15N, while continuous aeration during growth significantly decreased δ 15N, 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 δ 15N 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.