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Call number: LD2668 .T4 1958 L33 / Master of Science

Pasteurization radiation offers a new means of extending the refrigerated storage life of foods. This procedure avoids many of the undesirable changes which result when sterilization radiation is used and still eliminates most of the spoilage organisms. Shrimp was treated with 5 ppm chlortetracycline and subjected to pasteurization levels of gamma radiation and stored at 38°F. The levels of irradiation used were 0.5 and 0.75 megarad. These levels were based on the flavor threshold of irradiation intensity. The quality of the stored irradiated shrimp was determined by subjective evaluation, chemical analyses and microbiological examinations. The storage life of the shrimp irradiated at 0.5 megarad was extended to 5 weeks, compared with 1 week for the unirradiated samples held at the same temperature. Throughout the ten week storage period, the samples which received doses of 0.5 megarad and CTC and those which received 0.75 megarad with and without CTC remained in good condition. / Graduation date: 1963

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

No description available.

Continuous thermal pasteurisation of various bulk liquid media is an important step in the food and allied industries. The design of a continuous flow pasteuriser is typically predicated on mathematical models developed from experimental data - usually batch, bench - scale, ethods. Of particular interest is the effect of combined pasteuriser temperature ( T ) and liquid pH on inactivation and survivor of contaminants. However, bench - scale thermal survivor data may not adequately mirror those in a continuous flow pasteuriser. This research presents the development and experimental validation of rigorous models for thermal pasteurisation of bacteria as affected by combined process T - pH in both batch, bench - scale capillary studies ( static ) and in a pilot continuous flow pasteuriser ( dynamic ), within a defined liquid and range of exposure time, temperature and pH ( t - T - pH ). Five integrated stages in synthesis and model analysis were undertaken using stringent criteria for goodness of fit of an adequate model established. First, four published predictive models were assessed against published static data ( n [subscript T] = 248 ) for the thermal inactivation of Escherichia coli ( ATCC 25922 ) in a Carbopol ® 941 liquid food simulant in batch capillaries over a range of t - T - pH. The models tested were the Classical Arrhenius, Davey Linear - Arrhenius ( D - LA ), Square - Root ( Belehradek ) and a third - order Polynomial model ( nOP ). Analysis showed the D - LA model best satisfied the criteria for model selection and explained 96.0 % V in the thermal inactivation rate coefficient. Second, the D - LA model was assessed against limited, published dynamic data ( n [subscript T] = 109 ) for the same E. coli strain in identical food simulant. The model explained 60 % V in the thermal inactivation rate coefficient. On average, model predictions of survivor numbers from the dynamic data were less than that predicted from the static data, i.e. for a given ( t - T - pH ) more bacterial cells were apparently inactivated in the continuous flow pasteuriser than in bench - scale, batch capillary studies. Overall, however it was not clear from extensive analyses of available data whether there is a statistically significant difference in survivor numbers of viable E. coli between batch static and continuous flow dynamic data. Third, although the D - LA model best satisfied the criteria for goodness of fit of a model, it failed to accurately predict the observed tails in the static survivor data. New models ( KDT and a modified KDT ) were synthesised to predict tails and shoulders in survivor data. The modified KDT ( MKDT ) form gave improved predictive capability over the KDT model when assessed against published static survivor data for E. coli and L. monocytogenes ( n [subscript T] = 355 ) in the Carbopol food simulant. This model, however, could not be readily integrated with equations describing the performance of a continuous flow pasteuriser. Analyses indicated that a greater density of dynamic survivor data for E. coli was needed. Fourth, a pilot continuous flow pasteuriser was constructed and used to generate a greater density of dynamic survivor data of E. coli ( ATCC 25922 ) in a Carbopol ® 941 carrier liquid for rigorous comparison with predictions from the Lin ( 1976 ) isothermal continuous laminar flow process model. Direct steam injection heating was used. Extensive dye and digital - video studies, in a section of glass holding tube confirmed the practical implementation of the assumptions of laminar flow and rapid condensation of steam. Extensive practical experiments highlighted a non - isothermal condition along the holding tube. A highly linear dependence ( R ² > 0.90 ) of exposure temperature with holding tube length, i.e. exposure time, was demonstrated. This was accounted for using mathematical approaches and quantitatively incorporated into a D - LA model for the rate coefficient in an extended Lin process model. A block experimental design of 4 T ( 54, 56, 58, 60 ° C ) x 4 pH ( 4.5, 5.5, 6.5, 7.5 ) x 3 replicates with a total of ( n [subscript T] = 834 ) exposure times ( 16 - 198 s ) was carried out in the pilot continuous flow pasteuriser. Findings highlighted that greater numbers of E. coli were thermally inactivated in the flow pasteuriser than predicted. From a practical operating view, the predictions from the extended Lin model were therefore conservative - with reduced risk to public health. Highly significant differences in the rates of heat - up of bacteria in the pilot pasteuriser ( dynamic ) ( 0.0104 s ) compared with that in the batch ( static ) capillary tubes ( 1.6 s ) and, mode of heat transfer, together with partial effects of dispersion with increasing length of pasteuriser holding tube, are postulated to be the controlling process influences for the difference between the experimental survivor data and the extended Lin model predictions. The lack of agreement between the continuous pasteuriser data and predictions from the extended Lin model indicated that this model cannot be practically applied. A direct comparison of the experimentally derived dynamic survivor data from the pilot pasteuriser ( as ln N / N [subscript 0] ) was also made with both the published static and dynamic data at a number of defined t - T - pH. This comparison revealed that overall, more E. coli were inactivated in the pilot continuous flow pasteuriser than described by published batch static capillary and dynamic data. Importantly, these comparisons showed that batch thermal survivor data for E. coli do not adequately mirror those obtained in continuous flow systems. Fifth, in a search for an improved model for the inactivation data, the newly derived MKDT model was assessed against the experimental pilot pasteuriser data. This model was rejected, however, because it could not account satisfactorily for all tails in survivor curves. A Weibull form model with two coefficients ( a scale factor ( α ) and a shape factor ( β ) ) also did not adequately predict tailing and could not be reliably extrapolated with holding time. However, a modified Weibull form, also with two model coefficients ( β [subscript 0], β [subscript 1] ), did give an improved fit to available experimental data. This research highlighted statistically significant differences between the dynamic thermal survivor data for E. coli and standard bench - scale static capillary data for a defined liquid and range of t - T - pH. It is likely that findings from this study can be generalised. However, validation should be carried out for a range of common indicator micro - organisms in a range of liquid foods. / Thesis (Ph.D.)--School of Chemical Engineering, 2006.

No description available.

Fluid-to-particle heat transfer coefficients (h$ rm sb{fp}$) associated with food and model particles under simulated aseptic processing conditions were experimentally evaluated, and verified using measured inactivation kinetic parameters of the enzyme trypsin. Convective heat transfer coefficients were determined initially using two methods: a rate method based on evaluated heating/cooling rate indices (f$ rm sb c$/f$ rm sb h$) and a ratio method based on the ratio of temperature difference between the medium and particle locations. / Carrot and potato tissue in the form of finite cylinders of different lengths (0.02-0.04 m) and diameters (0.016-0.023 m) were used for evaluating h$ rm sb{fp}$ associated with aqueous CMC solutions (0-1.0% w/w) at temperatures ranging from 50 to 80$ sp circ$C and at relatively low fluid flow (0.2 to $0.7 times10 sp{-3}$ m/s) conditions. Carrots generally gave higher h$ rm sb{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$) greater than 0.80. / A pilot scale holding tube simulator was designed and fabricated for routine/rapid gathering of heat penetration data which may be experienced in high temperature short time processing conditions. / Using the simulator under conditions comparable to industrial applications, and a full factorial experimental design, h$ rm sb{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$ sp circ$C, and flow rate was varied from 1.0-$1.9 rm times10 sp{-4} m sp3$/s. Average h$ rm sb{fp}$ values ranged from 56 to 966 W/m$ sp2$C depending on size, shape, fluid concentration, particle orientation, and tube diameter. Differences caused by different particle materials were accounted for by introducing a thermal diffusivity ratio in developed dimensionless correlations for both mixed and forced convective heat transfer to spherical and finite cylindrical particles under simulated aseptic processing conditions. / Thermal inactivation of trypsin (bovine pancreas type III) in low and high pH media was studied at temperatures ranging from 90-130$ sp circ$C. Comparative studies of its kinetic data with other bioindicators indicated the enzyme to be suitable for HTST verification/validation purposes. Further studies revealed, probably depending on pH, that trypsin was more susceptible to thermal inactivation at temperatures around 70$ sp circ$C. (Abstract shortened by UMI.)