Influence of Fat and Emulsifiers on the Efficacy of Nisin in Inhibiting Listeria monocytogenes in Fluid Milk

Abstract

The recent FDA affirmation of nisin, an antimicrobial peptide, as a GRAS (generally recognized as safe) additive in pasteurized cheese spreads has renewed interest in its potential application in US dairy products. Fluid milks were prepared with varying concentrations of milk fat (0 to 12.9%) and of nisin (0 to 50 U/ml). Biological activity assays using a sensitive indicator microorganism in a well diffusion system indicated that initial nisin activity (50 U/ml) decreased by about 33% when it was added to skim milk and by more than 88% when added to milk containing 12.9% fat. Nisin activity decreased by ca. 50% in milk containing 1.29% fat. Milks containing 0, 10, or 50 U/ml of nisin and varying fat percentages were challenged with approximately log10 7 to 7.5 cfu/ml of log phase Listeria monocytogenes Scott A or Jalisco. At 2 h after inoculation, the viable count of L. monocytogenes Scott A decreased to log10 .30 cfu/ml in skim milk with 50 U/ml of nisin, decreased to log10 2.90 cfu/ml in skim milk with 10 U/ml of nisin, and increased slightly (log10 7.8 cfu/ml) in skim milk without nisin. In half-and-half (12.9% milk fat), nisin was far less effective in inhibiting Listeria with populations decreasing to log10 6.57 cfu/ml for 10 U/ml of nisin and log10 5.87 cfu/ml for 50 U/ml. Similar results were obtained with L. monocytogenes Jalisco. The nonionic emulsifier, Tween 80, partially counteracted decreases of nisin activity in milks, whereas the anionic emulsifier, lecithin, had no effect. Addition of Tween 80 significantly increased the activity of nisin against L. monocytogenes in milk regardless of fat content.

Application of lactococcin BZ and enterocin KP against Listeria monocytogenes in milk as biopreservation agents

“…The addition of 160 AU ml -1 cerein 8A produced by B. cereus to UHT milk resulted in a decrease of 3 log cycles in the cell counts of L. monocytogenes within the 14-day period at 4 °C (BIZANI et al, 2008). Nisin (50 IU ml -1 ) caused 7, 3, and 1 log reduction in the counts of L. monocytogenes Scott A in skim milk (0% fat), milk with 4% fat, and milk containing 12.9% fat, respectively (JUNG et al, 1992). Most of the studies declared that cell counts of L. monocytogenes in milk challenged with different concentrations of nisin (BHATTI et al, 2004;KIM et al, 2008;YOON et al, 2011) or pediocin 5 (HUANG et al, 1994) decreased to an undetectable level at the beginning of the incubation, but then increased during the incubation period.…”

“…This result indicates that lactococcin BZ could be a good alternative antimicrobial agent to control pathogens in foods containing fat. Similar to enterocin KP, the inhibitory activity of nisin (JUNG et al, 1992;BHATTI et al, 2004;MEENA et al, 2004;YOON et al, 2011) and pediocin 5 from Pediococcus acidilactici UL5 (HUANG et al, 1994) declined by increasing fat content of dairy products. According to those authors, the decrease in bacteriocin activity was probably due to the fact that bacteriocin might be adsorbed to the milk fat globules and become unavailable to destroy bacterial cells.…”

Characterization of Antimicrobial-bearing Liposomes by ζ-Potential, Vesicle Size, and Encapsulation Efficiency

“…17,18 Nevertheless, loss of antimicrobial activity was reported when nisin was directly added to foods. Jung et al 19 found significant loss of nisin activity in milk because of interactions with milk fat globules. Apparently, nisin preferentially adsorbed at the milk fat droplet surface to maximize interaction of the hydrophobic side chains with lipid phase molecules.…”

Nisin released from immobilization matrices as antimicrobial agent

“…The polypeptide nisin is a GRAS (generally recognized as safe) additive (Jung et al, 1992) which shows antimicrobial activity chiefly against a range of Gram positive bacteria, particularly spore-formers {Delves-Broughton, 1990). The potential applications of nisin in food preservation i.e.…”