Optimisation of the performance of a citrus extract for biofunctionalization of spinach

• Vacuum-dried UAE lemon peel extract (V-AQ) showed high stability and Fe, Zn, Mn, and Ca content. • Application of V-AQ extract to spinach enhanced biomass, relative water content, and Fe tissue accumulation. • Upregulation of PIP2;1 in spinach leaves was related to high RWC. • Zn alone or priming extract did not enhance or exceed the biofunctional potential of the extract. Lemon ( Citrus × limon ) residues from agro-industrial processes represent a significant environmental challenge due to their high organic load and acidic pH. This study explored different extraction techniques and processing methods to obtain a stable bioactive- and mineral-rich extract from lemon peels and evaluated its biofunctional potential on spinach ( Spinacia oleracea L.). Its effect was compared to Zn by priming the extract. Vacuum-dried and ultrasound-assisted aqueous extract (V-AQ) demonstrated stability, high levels of Fe, Zn, Mn, Ca, and bioactive compounds. Foliar application of V-AQ extract enhanced spinach growth, relative water content, and mineral accumulation, while increasing aquaporin gene expression ( PIP2;1 ). Zn-primed extract did not induce into strong physiological effects, highlighting the importance of the extract matrix for full food functional activity. Overall, V-AQ lemon peel extracts combine mineral enrichment and bioactive regulation, offering a sustainable approach to enhance crop performance. These findings also support the valorization of citrus residues within circular economy strategies.