# Valorization of Various Natural Substrates as Alternative Carbon Sources in Fermentation Media for Pullulan Production by Domestic Aureobasidium pullulans AZ‑6

## TL;DR

This study explores using food and agro-industrial waste as low-cost carbon sources for producing pullulan, a valuable polysaccharide, using a domestic strain of Aureobasidium pullulans.

## Contribution

The study is the first to investigate sugar beet pulp, melon rind, watermelon rind, onion peel, and carrot peel for pullulan production.

## Key findings

- Molasses yielded the highest pullulan (14.55 g/L) and EPS (17.12 g/L) with a high growth rate.
- Sweet potato, onion waste, and carrot peels showed promising pullulan yields (8.24–8.70 g/L).
- Cheese whey produced the most biomass but had low pullulan productivity.

## Abstract

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.