The antimicrobial properties of chitosan in mayonnaise and mayonnaise-based shrimp salads.

The potential for using chitosan glutamate as a natural food preservative in mayonnaise and mayonnaise-based shrimp salad was investigated. Mayonnaise containing 3 g/liter of chitosan combined with acetic acid (0.16%) or lemon juice (1.2 and 2.6%) was inoculated with log 5 to 6 CFU/g of Salmonella Enteritidis, Zygosaccharomyces bailii, or Lactobacillus fructivorans and stored at 5 and 25 degrees C for 8 days. In mayonnaise containing chitosan and 0.16% acetic acid, 5 log CFU/g of L. fructivorans were inactivated, and numbers remained below the sensitivity limit of the plate counting technique for the duration of the experiment. Z. bailii counts were also reduced by approximately 1 to 2 log CFU/g within the first day of incubation at 25 degrees C, but this was followed by growth on subsequent days, giving an overall growth delay of 2 days. No differences in counts of Z. bailii in mayonnaise stored at 5 degrees C or of Salmonella Enteritidis stored at either temperature were observed. In mayonnaise containing lemon juice at both 1.2 and 2.6%, no substantial differences were observed between the controls and the samples containing chitosan. In shrimp salads stored at 5 degrees C, the presence of a coating of chitosan (9 mg/g of shrimp) inhibited growth of the spoilage flora from approximately log 8 CFU/g in the controls to log 4 CFU/g throughout 4 weeks. However, at 25 degrees C, chitosan was ineffective as a preservative. The results demonstrated that chitosan may be useful as a preservative when combined with acetic acid and chill storage in specific food applications.