Turning Mushy Lipids into Fruity Notes: Unlocking Lactone Biosynthesis Potential in Fat Industry Lipid Waste.

Waste from the fat-processing industry represents a challenging stream due to its physicochemical properties and environmental impact. Valorization through recovery and reuse offers ecological, economic, and social benefits. This study focused on mushy lipid residues generated during cold pressing of oilseeds (sunflower, flax, blue poppy, hemp, black cumin, and walnut) and evaluated their potential for lactone biosynthesis. The waste was analyzed for protein and fat content, while fatty acid profile, acid and peroxide values, oxidation stability, and health-related indices characterized the extracted oils. Polyphenol content and antioxidant activity of the residues were also determined. Subsequently, the waste was used as a substrate in biotransformation processes with Lactiplantibacillus plantarum and Yarrowia lipolytica. The results showed high protein (13.1-19.4%) and fat levels (65.0-77.3%) across all residues. The lipid fractions were rich in monounsaturated and polyunsaturated fatty acids, comprising nearly 90% of the total fatty acids, with oleic and linoleic acids being the dominant components. These features highlight their strong valorization potential, particularly for the microbial synthesis of aroma-active lactones. Under the applied conditions, the production of γ-dodecalactone and δ-decalactone reached 0.76 g/L and 1.62 g/L, respectively, confirming the suitability of cold-press residues as substrates for sustainable biotechnological applications.