Valorization of Various Natural Substrates as Alternative Carbon Sources in Fermentation Media for Pullulan...

This study investigates the potential of various agro-industrial and food wastes as alternative carbon sources for cost-effective and sustainable pullulan production by a domestic, melanin-free strain of Aureobasidium pullulans AZ-6. Nine natural substrates, including cheese whey, molasses, grape pomace, sugar beet pulp, melon rind, watermelon rind, onion waste, carrot peels, and sweet potato, were pretreated and used in supplemented fermentation media. Batch fermentations were carried out under optimized conditions (pH 6.48; 24.2 °C; 100 strokes per minute), and biomass, extracellular polysaccharides (EPS), pullulan yields, and sugar consumption kinetics were evaluated. Among the tested substrates, molasses exhibited the highest EPS (17.12 g/L) and pullulan titers (14.55 g/L), as well as the greatest specific growth rate (0.104 h^-1). Although cheese whey supported the highest biomass (13.03 g/L), its pullulan productivity was relatively low (4.98 g/L). Other substrates, such as sweet potato, onion waste, and carrot peels, also showed promising pullulan yields (8.24-8.70 g/L) and substrate utilization rates. This study evaluates the potential of several waste-derived substrates for pullulan biosynthesis and contributes to the circular bioeconomy by valorizing underutilized resources. To the best of our knowledge, sugar beet pulp, melon rind, watermelon rind, onion peel, and carrot peel have been investigated as substrates for pullulan production for the first time in the literature.