29F-13 |
Antimicrobial efficacy of native and enzymatically degraded chitosans against Listeria innocua and Pseudomonas aeruginosa |
T. A. Nicholas, D. I. SKONBERG, and A. A. Bushway. Dept. of Food Science & Human Nutrition, Univ. of Maine, 5735 Hitchner Hall, Orono, ME 04469-5735 Pseudomonas and Listeria are two common bacterial genera found in most foods and are often responsible for spoilage and human illness, respectively. Many current shelf life extension and pathogen inhibition methods employ the use of various chemical preservatives. Chitosan, an abundant natural polysaccharide, possesses antimicrobial as well as functional properties. These properties may be influenced by a number of factors which must be studied before determining the most useful food applications of chitosan. Our objective was to study the effects of native and enzymatically degraded (with alpha amylase) chitosans on two common bacteria found in foods. We also investigated the effects of media type on the antimicrobial properties of chitosan in vitro. A 1.0% chitosan solution was degraded by 10% alpha amylase for 10 min, 1 hr or 24 hrs. The degraded and native chitosans were added to the nutrient (NB) or tryptic soy (TSB) broths at levels of 0.5, 1.0, or 2.0% v/v and the pH was adjusted to 5.5 (controls were non-acidified broth or broth at pH 5.5). Broths were autoclaved and then inoculated with cultures of Listeria innocua or Pseudomonas aeruginosa and incubated for four days at 4°C. Bacteria were enumerated daily. Chitosan treatments effectively reduced Listeria counts in TSB by at least one log, but only significantly so on day three. The 24 hour degraded chitosan and lower percentage chitosan treatments were the least effective. No significant reductions in Pseudomonas counts were observed in TSB for any treatment. In NB all the chitosan treatments had significantly (p£ 0.05) lower (up to 3.4 logs) Pseudomonas counts than both controls on all four days. Log reductions increased with increasing chitosan percent. Ten minute degraded chitosan had slightly greater log reductions compared to other treatments. The results of this experiment indicate that chitosan can easily be degraded with alpha amylase and that the antimicrobial effectiveness of chitosan depends on the nutrient matrix, chitosan percentage, degradation time, and type of bacteria.
Session 29F, Food Microbiology: Control of foodborne microorganisms by antimicrobials
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