18D-1 |
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J. KAISER and P. D. Courtney. Department of Food Science and Technology, Ohio State University, 2015 Fyffe Ct., Parker Food Science Bldg., Columbus, OH 43210 Probiotic bacteria, such as some Lactobacillus acidophilus strains, can be freeze-dried into powder form and mixed into liquid or dry food products to provide live bacteria to consumers. The objective of this study was to determine the role of the bacterial phospholipid membrane saturation as it relates to viability of freeze-dried bacteria over time while held under different storage conditions. Lactobacillus acidophilus NCFM was grown to the stationary phase in MRS broth with 0, 100, 250, or 500 ug/ml of stearic, linoleic, or linolenic acids. Cells were harvested, washed and re-suspended in phosphate buffer saline, pH 7.4. Suspensions were freeze-dried and stored at 4, 22, and 37 °C in air or nitrogen in the dark. Cell viability was assessed twice per week for the first 3 weeks and then at 1 and 3 months. The membrane fatty acid profile was measured by gas chromatography of fatty acid methyl esters at 0, 1 and 3 months. Results showed that cells grown with the higher fatty acid concentration (500 ug/ml) grew poorly compared to cells grown in lower fatty acid concentrations. The lipid saturation level in the cell membrane affected the viability over time during the storage of freeze-dried cells with the more saturated fatty acids promoting viability. Additionally, cell cultures that were exposed to ambient air and light died within one week of storage; whereas cell cultures stored in nitrogen in the dark remained viable for up to several months. Results suggest that oxidation mechanisms within the membrane contribute to cell death. Membrane fatty acid saturation affects viability of freeze-dried L. acidophilus. Growth medium may be modified to alter cell membrane lipid saturation to promote viability.
Session 18D, Food Microbiology: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |