Functional Characterization of Antimicrobial and Antioxidant Properties of Whole Lemon Pulp and Depectinized Lemon Pulp as Circular By-products in Animal Nutrition

The increasing demand for sustainable livestock production underscores the need to explore innovative solutions that enhance resource efficiency and minimize waste. Agricultural by-products offer a valuable source of nutrients and bioactive compounds that can be effectively valorised for animal nutrition. This study investigated the nutritional composition, antioxidant, and antimicrobial properties of whole lemon pulp (WLP) and depectinized lemon pulp (DLP) as functional feed ingredients for animal health. WLP and DLP were characterized for bromatological composition through chemical analysis. Acetone (70 %, v/v), methanol (50 %, v/v), and water were used as extraction solvents before testing antioxidant capacity using the 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation decolourisation assay and evaluating O138 Escherichia coli inhibitory activity through the microdilution method, monitoring bacterial growth spectrophotometrically. Obtained findings revealed that both WLP and DLP exhibited antioxidant activity, particularly for acetone and methanol extracts, showing markedly higher radical scavenging capacity than water extracts (p < 0.0001). Notably, WLP demonstrated increased antioxidant ability and inhibitory effects against verocytotoxic E. coli strain compared to DLP (p < 0.0001), likely due to the solubilization or denaturation of several functional compounds during the depectinization process in DLP. Despite this reduction, DLP retains residual antioxidant and antibacterial activity, potentially offering a cost-effective opportunity for utilization in animal nutrition within a circular economy strategy. These findings underscore the nutritional and functional potential of lemon by-products, suggesting further research into their applications in promoting animal health and sustainability in livestock production.