Antimicrobial activity of nisin-adsorbed silica and corn starch powders

The antimicrobial peptide nisin is an effective bacterial inhibitor and has been adsorbed onto various surfaces and added to packaging films. In the present study, nisin was adsorbed onto food-grade powders then evaluated for nisin activity in a series of three experiments. Adsorbent powders used were calcined diatomaceous earth, synthetic calcium silicate, hydrate, two diatomaceous earth, and corn starch powders. Adsorption was conducted by placing the powders in agitated nisin solutions, followed by dehydration of the powder pellet after centrifugation. The dehydrated powders were then tested for inhibitory activity against either Lactobacillus plantarum or Listeria monocytogenes. Activity was measured by placing the nisin-adsorbed powders in solutions of 0.1% peptone water inoculated with one of the test bacterial strains. Cel-pure 65 adsorbed then released from 74.7% to 94.7% of the nisin activity contained in the original solution (500-800 IU/ml) in which the powders were agitated. Corn starch adsorbed then released from 45.4% to 60.5% of nisin activity when from 300 to 700 IU/ml nisin activity adsorbing solutions were utilized. One percent of nisin-absorbed Celpure 100 and Celpure 65 powders in 30 ml of log 4.5 cfu/ml L. monocytogenes inoculum reduced populations to below detection levels (<101 cfu/ml) within 24 and 6 h, respectively. Thus, nisin-adsorbed powders were highly efficient at both adsorption and release of antimicrobial activity.