89D-22 |
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L. M. MICHAEL1, D. A. Golden1, and S. Zivanovic2. (1) Department of Food Science and Technology, University of Tennessee, 2605 River Drive, Knoxville, TN 37996-4591, (2) Dept. of Food Science & Technology, Univ. of Tennessee, Food Chemistry & Biophysics Labs., 2605 River Dr., Knoxville, TN 37996-4591 One of the possible mechanisms of chitosan antimicrobial activity is its interaction with the cell wall of microorganisms causing the disruption of normal transfer of nutrients and flocculation of cells. The objective of this study was to determine flocculation rates of yeasts as affected by chitosan. Specifically, we investigated flocculation kinetics of Saccharomyces cerevisiae, Candida krusei, and Zygosaccharomyces bailii in medium molecular weight chitosan solutions (0.0001 to 0.1%). Yeasts were cultured in YM broth at 25C for 24 hr with orbital shaking. During the early stationary growth phase, cells were centrifuged, washed in 0.1M NaCl, and resuspended in 0.1M acetate buffer (pH 4.0). Chitosan stock solution (1% chitosan in 1% acetic acid) was added to cell suspensions to achieve chitosan concentration of 0.0001, 0.001, 0.01 and 0.1% and the volume was adjusted with acid solution. Cell suspension with addition of the same volume of acetic acid, but with no chitosan, served as control. Flocculation of microbial cells during 24 hr incubation at 25C was measured as a decrease in absorbance at 600nm. The highest rate of flocculation of yeast cells was achieved with 0.01% chitosan. After 60 min incubation, absorbance of S. cerevisiae suspensions decreased for 0, 0, 9, 39, and 6 % for control, 0.0001, 0.001, 0.01, and 0.1% chitosan, respectively. However, after 2 hr, absorbance for 0.01% and 0.1% decreased by 61 and 27%, respectively, while for lower concentrations of chitosans and control, absorbance did not change significantly. Although antimicrobial effect was achieved, delay in flocculation with the highest tested concentration of chitosan was caused by increased viscosity that stabilized the suspensions. These data contribute to understanding of the flocculation patterns of yeasts and assist in determining the binding and clarifying attributes of chitosan.
Session 89D, Food Microbiology: Antimicrobial effects on foodborne microorganisms
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |