Calculating temperature lag for the correction of D values obtained from differential scanning calorimetry

Abstract

A heat flux differential scanning calorimeter (DSC) was involved in a new method of determining thermal inactivation kinetic parameters ( D - and z -values) for a bacterial suspension in skim milk. Validating the method against an established method led to the realization that the required sample size caused the sample temperature to appreciably lag that of the DSC cell, leading to consistent but inaccurate D-values. However, only the temperatures of the sample sensor and the DSC cell were available once this was realized. In this report, an analysis is introduced to determine the lag by using only the sensor temperature beneath the sample pan. It relies on equations based on Newton's law of cooling employed elsewhere in the DSC literature. They are used to analyze the sample sensor temperatures at the start of the scan, before a linear temperature rise in the sample is established, along with the constant temperature difference between the DSC cell and that of the sample sensor after the linear temperature rise is established. The analysis was applied to correct the temperatures leading to the D-value, which aligned it with the established value. • A novel approach calculates a mass average temperature lag in a DSC sample using only the sample surface temperatures. • A unique nondimensionalization of the equations for temperature lag halved the number parameters that were required to calculate it. • The approach is shown to give consistently accurate results for the lag.