Utilization of papaya waste and oil production by Chlorella protothecoides

Microalgae derived oils have outstanding potential for use in biodiesel production. Chlorella protothecoides has been shown to accumulate lipids up to 60% of its cellular dry weight with glucose supplementation under heterotrophic growth conditions. To reduce production costs, alternative carbon feedstocks have been evaluated and show promise as low-cost alternatives. Regional agricultural residues, such as off-quality fruits and vegetables that cannot be used as human food or animal feed, as well as inedible plant byproducts, represent an abundant and underutilized resource as a feedstock for supporting microbial production of biofuels. Here, we present the finding that C. protothecoides isolates are capable of robust cell growth and oil production in growth medium comprised of pH-adjusted puree of culled, waste papaya fruit without any additional growth supplements. Optimization of culture medium and growth conditions was used for lab-scale strain characterization and demonstration of the potential for scale-up to an industrial bioprocess. The most rapid cell doubling time observed was 6.6 h and the maximum oil production rate observed was 1.9 g/l/day.