MRI temperature mapping and finite element modeling of heat transfer in carrot particulates undergoing thermal processing

A series of experiments were conducted to test the feasibility and accuracy of using T$\sb1$ weighted magnetic resonance imaging to measure the temperature inside foods during heating. First, a steady state temperature gradient was applied to a model food gel. The T$\sb1$ temperature dependence for the gel was determined. A two dimensional Fourier transform spin echo imaging sequence was used. This method was superior to inversion recovery spectroscopic measurements when the T$\sb1$ temperature dependence is not linear.A spin echo pulse sequence allowing the shortest possible echo delay time (T$\sb{\rm E}$ = 19-21 ms) was used to obtain T$\sb1$ weighted images from whole cooked carrots at temperatures between 18.7$\sp\circ$C and 83$\sp\circ$C. The T$\sb1$ of the carrots had a linear temperature dependence over this temperature range. Sensitivity of temperature measurements ranged from $\pm 0.4\sp\circ$C to $\pm 4.2\sp\circ$C depending on the temperature of interest and the amount of signal averaging. Signal-to-noise values had a predictable dependence on voxel size and signal averaging.Dynamic images of cooked carrots during transient heat transfer were obtained with acquisition times of 12-24 seconds. The carrots were initially at room temperature and were heated with water (76-83$\sp\circ$C) from a constant temperature bath. For one set of experimental results, a finite element model was used to calculate fluid to particle convective heat transfer coefficients across the surfaces of a carrot particle. A reduced encoding by generalized series reconstruction algorithm (RIGR) was used to reduce acquisition time and improve signal-to-noise.This procedure could be used for evaluation of models and simulations used for aseptic processing systems. Currently there is no way to confirm sterilization of particulates in conventional aseptic systems. Future studies will concentrate on faster imaging techniques such as those using gradient echo pulse sequences in combination with the RIGR processing algorithm. If successful, these techniques could lead to MRI temperature measurement during actual aseptic processing.U of I OnlyETDs are only available to UIUC Users without author permissio