| Fluid-to-particle heat transfer coefficients (h$rmsb{fp}$) associated with food and model particles under simulated aseptic processing conditions were experimentally evaluated, and verified using measured inactivation kinetic parameters of the enzyme trypsin. Convective heat transfer coefficients were determined initially using two methods: a rate method based on evaluated heating/cooling rate indices (f$rmsb c$/f$rmsb h$) and a ratio method based on the ratio of temperature difference between the medium and particle locations.;Carrot and potato tissue in the form of finite cylinders of different lengths (0.02-0.04 m) and diameters (0.016-0.023 m) were used for evaluating h$rmsb{fp}$ associated with aqueous CMC solutions (0-1.0% w/w) at temperatures ranging from 50 to 80$spcirc$C and at relatively low fluid flow (0.2 to $0.7times10sp{-3}$ m/s) conditions. Carrots generally gave higher h$rmsb{fp}$ values (100-550 W/m$sp2$C) compared to potatoes (80-450 W/m$sp2$C). Laminar flow natural convection dominated the flow regime. Hence, the Nusselt number was modeled as a function of Rayleigh's number which resulted in coefficients of determination (R$sp2$) greater than 0.80.;A pilot scale holding tube simulator was designed and fabricated for routine/rapid gathering of heat penetration data which may be experienced in high temperature short time processing conditions.;Using the simulator under conditions comparable to industrial applications, and a full factorial experimental design, h$rmsb{fp}$ values were estimated using finite cylinders of Teflon and potato tissue of different sizes (length: 0.020-0.0254 m; diameter: 0.0159-0.0254 m), and spherical Teflon particles (diameter 0.0191 m) in food grade CMC solutions (0-1.0% w/w). Operating temperatures were 90, 100 and 110$spcirc$C, and flow rate was varied from 1.0-$1.9rmtimes10sp{-4} msp3$/s. Average h$rmsb{fp}$ values ranged from 56 to 966 W/m$sp2$C depending on size, shape, fluid concentration, particle orientation, and tube diameter. Differences caused by different particle materials were accounted for by introducing a thermal diffusivity ratio in developed dimensionless correlations for both mixed and forced convective heat transfer to spherical and finite cylindrical particles under simulated aseptic processing conditions.;Thermal inactivation of trypsin (bovine pancreas type III) in low and high pH media was studied at temperatures ranging from 90-130$spcirc$C. Comparative studies of its kinetic data with other bioindicators indicated the enzyme to be suitable for HTST verification/validation purposes. Further studies revealed, probably depending on pH, that trypsin was more susceptible to thermal inactivation at temperatures around 70$spcirc$C. (Abstract shortened by UMI.). |
