Assessment of the inhibitory effect of free and encapsulated commercial nisin (Nisaplin®), tested alone and in combination, on Listeria monocytogenes and Bacillus cereus in refrigerated milk

• Antimicrobial effect of free and encapsulated (gum Arabic) Nisaplin® was tested.
• Listeriamonocytogenes and Bacilluscereus inoculated in chilled milk were the test organisms.
• Spray-dried commercial nisin had antimicrobial effect under refrigeration (90 days).
• Free and encapsulated Nisaplin® combined showed the strongest antilisterial effect.
• Both forms of Nisaplin® controlled B. cereus spores germination and outgrowth.

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 < 0.05), although Lm resistant cells were observed. Free and encapsulated commercial nisin (0.25 mg/L) were highly effective against Bc spores germination and for the pathogen outgrowth inhibition (d21 – d0; P < 0.05) in both types of milk, improving the food product microbiological safety.