100A-26 |
Calorimetric evaluation of the thermal stability of ribosomes isolated from Escherichia coli and Lactobacillus plantarum |
J. LEE, Food Science and Technology, The Ohio State University, 2015 Fyffe Road, Columbus, OH 43210 and G. Kaletunc, Food , Agricultural, and Biological Engineering, The Ohio State University, 590 Woody Hayes Drive, Columbus, OH 43210. Heat inactivation of microorganisms is related to denaturation of ribosome subunits and depends on pH. Selection of appropriate processing conditions depends on the thermal stability of the target microorganism and its cellular components over the pH range found in food products. The objective of the investigation is to determine the thermal characteristics as a function of pH of whole cells and isolated ribosomes of E. coli (Gram negative) and L. plantarum (Gram positive). Differential scanning calorimetry (DSC) is used to evaluate the relationship between ribosome denaturation and cell inactivation. DSC profiles of untreated and acid-treated cells are recorded at 4oC min-1. Peaks identified as ribosome denaturation are compared for treated and untreated cells. Ribosomes isolated from both organisms are suspended in buffer at pH ranging from 3 to 7.5 and heated in the DSC to evaluate the effect of pH on ribosome thermal stability. In DSC thermograms of whole cells ribosome transition peaks are observed at higher temperature in E. coli than in L. plantarum. Similarly, the denaturation temperatures of ribosomes isolated from E. coli are higher than those from L. plantarum over the pH range examined. While the denaturation temperature of ribosomes isolated from L. plantarum decreases with pH, the denaturation temperature of ribosomes in L. plantarum cells is unchanged regardless of the pH of the surrounding buffer consistent with internal control of pH. The enthalpy change (energy required) for denaturation of isolated ribosomes is similar for both microorganisms at pH=7. However, at pH 4, the denaturation enthalpy for E. coli ribosomes is unchanged while for L. plantarum ribosomes it is reduced by half. Thermal analysis of whole cells and isolated components, including thermal stability and energy associated with the disruption of the cells, can be utilized to optimize processing conditions for manufacture of minimally processed, safe products.
Session 100A, Food Microbiology: General II
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