Chlorella vulgaris lipid extraction side-stream enhances growth and protein enrichment in novel food Lemna minor (duckweed)

Introduction: The transition toward sustainable food systems requires strategies that simultaneously reduce bioprocess residues and enhance nutritional quality. Microalgal biorefineries generate substantial polar side-streams after lipid extraction, which remain largely underutilized despite their high nutrient content.Methods: Here, we evaluated the polar side-stream generated during lipid extraction of Chlorella vulgaris, representing the non-lipid and water-soluble fraction enriched in soluble metabolites and nutrients, as a bio-based fertilizing input for Lemna minor (duckweed), a Novel Food. The Chlorella Extraction Waste (CEW) was applied in hydroponic cultivation across a defined concentration window, and growth performance was quantified through image-based frond area analysis and kinetic modeling.Results: Within a non-inhibiting range, the side-stream significantly stimulated duckweed growth, with 0.2 g L−1 nearly doubling biomass at day 7 compared to water control. Bench-scale validation against Hoagland solution and a commercial fertilizer demonstrated enhanced protein accumulation (27.1% DW), exceeding the commercial fertilizer treatment and accompanied by reduced carbohydrate allocation, while maintaining balanced pigment profiles, antioxidant activity, and stable lipid levels.Discussion: The absence of carotenoid overaccumulation and major shifts in antioxidant activity indicates nutrient-enabled protein enrichment without detectable stress-associated metabolic reprogramming. These findings demonstrate that microalgal lipid extraction side-streams can function as nutrient-regime modulators capable of redirecting carbon–nitrogen allocation toward protein-rich biomass, coupling circular bioeconomy valorization with nutritional upgrading of a fast-growing aquatic crop. This work provides a proof-of-concept for integrating biorefinery side-streams into sustainable micro-scale photosynthetic food systems.