Evaluation by differential scanning calorimetry of the effect of acid, ethanol, and NaCl on Escherichia coli

Abstract

The influence of acid, ethanol, and NaCl on the cellular components and inactivation of Escherichia coli were evaluated using differential scanning calorimetry. Cell viability was assessed using plate counting. The thermal stability for ribosomal subunit denaturation and the total apparent enthalpy decreased with increasing ethanol, salt, and acid concentrations. The reduction of the ribosomal subunit denaturation peak was the primary contributor to the decrease in the total apparent enthalpy. Thermograms indicated that even at concentrations at which less than a 0.4-log reduction of cell viability with a concomitant minimal reduction of total apparent enthalpy occurred, a decrease in onset temperature of ribosomal transition was evident. Acid treatments at pH 3 induced by HCl and by 0.4 M acetic acid caused the DNA denaturation temperature in vivo to decrease. Application of chemical treatment prior to heat treatment noticeably reduced the viability of E. coli cells at all the heat treatment temperatures (60, 62.5, and 65°C) compared with that of heat treatment alone, suggesting an increased sensitivity of bacteria to heat treatment. Differential scanning calorimetry in vivo can be used to assess the effectiveness of hurdles when thermal processing technologies with hurdles are designed. Copyright ©, International Association for Food Protection.