Abstract The antimicrobial effect of free and encapsulated (carrier agent: gum Arabic) commercial nisin (Nisaplin®) against Listeria monocytogenes ATCC 7644 (Lm) and Bacillus cereus IAL 55 (Bc) in refrigerated (6 ± 1 °C) milk was determined throughout 21 days (d). Skim and whole milk samples containing free and encapsulated commercial nisin (0.25–1.0 mg/L, alone and combined) were contaminated, individually, with Lm or Bc (vegetative cells and spores) and the microorganisms' counts assessed every 3 d. Encapsulated commercial nisin presented characteristic traits of spray-dried products and stable antimicrobial activity under refrigeration (90 days). In both skimmed and whole milk, free and encapsulated Nisaplin® combined (0.5 mg/L each) exhibited the strongest antilisterial effect (d21 – d0; P