Natural Antimicrobial Activity of Nettle (Urtica dioica L.) Leaf Extract for Shelf-Life Extension of Mashed Potatoes.

The growing demand for minimally processed clean-label foods has intensified interest in natural antimicrobials as alternatives to synthetic preservatives. However, very little is known about the antimicrobial potential of several wild edible plants when incorporated into food matrices. This study evaluated the antimicrobial activity of nettle (Urtica dioica L.) leaf extract and as a clean-label preservative for extending the shelf life of fresh mashed potatoes. The extract exhibited strong antioxidant activity, with DPPH, ABTS, and FRAP values of 21.96 ± 0.76 μmol Trolox/mL, 17.51 ± 0.90 μmol Trolox/mL, and 5.93 ± 0.65 Fe(II)/g, respectively. In vitro antimicrobial testing confirmed broad-spectrum activity, with minimum inhibitory and bactericidal concentrations indicating pronounced susceptibility of Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes) and notable effects on Gram-negative pathogens (E. coli, Salmonella enterica serovar Typhimurium). Cytotoxicity assessment using L929 fibroblast cells showed the extract was non-toxic at concentrations effective for antimicrobial application. When incorporated into mashed potatoes at 0.5%-2.0% (w/v), nettle extract achieved preservative effects comparable to 0.025% commercial nisin. Treated samples exhibited significantly delayed increases in total viable counts, psychrotrophs, Enterobacteriaceae, B. cereus, S . aureus , P. aeruginosa, and spoilage fungi during storage at 4°C and 25°C. Electronic tongue analysis differentiated treatment groups, revealing mild bitterness and astringency at increasing nettle leaf extract incorporation, but these effects were less detrimental than spoilage-related off-flavors in untreated controls. Overall, nettle leaf extract provides combined antimicrobial and antioxidant functionality, enhances microbial stability, and maintains acceptable sensory quality, supporting its potential as a natural alternative to synthetic preservatives in ready-to-eat mashed potato products.