Olive waste valorization: advances in nutrient optimization and microbial engineering for lipid production

Olive waste is an abundant and renewable substrate with strong potential for microbial lipid production, yet its efficient utilization remains limited by nutrient imbalances and inhibitory compounds. This review synthesizes recent advances in nutrient optimization and microbial engineering strategies aimed at enhancing lipid biosynthesis from olive mill residues. Key developments include tailored medium formulations to correct carbon-nitrogen ratios, co-culturing systems that promote metabolic cross-feeding, and genetic engineering approaches that overexpress fatty acid biosynthetic enzymes. Studies report lipid contents of up to 60% (w/w) in optimized fungal and yeast systems, underscoring the feasibility of process enhancement through nutrient control. Despite these advances, challenges persist in large-scale process integration, including inhibitor detoxification, bioreactor oxygen transfer, and cost-efficiency. Environmental implications and sustainability assessments through life-cycle and techno-economic analyses remain limited, indicating a gap in translating laboratory successes to industrial applications. Overall, this review highlights the synergistic role of nutrient optimization and metabolic engineering in converting olive waste into high-value lipids, while identifying future priorities in process automation, genetic containment, and industrial scalability toward circular bioeconomy goals.