ENTHALPY - ENTROPY AND FREQUENCY FACTOR - ACTIVATION-ENERGY COMPENSATION RELATIONS FOR DEATH OF ESCHERICHIA-COLI WITH MICROWAVES IN A TUBULAR FLOW REACTOR

Kinetic analyses of death of Escherichia coli with microwaves in a tubular flow reactor were done by using the frequency factor - activation energy and activation entropy - activation enthalpy compensation relations. There was no actual isokinetic temperature for the death of E. coli, implying that the mechanisms of the death were different both in the microwave tubular flow reactor under varying experimental conditions and also in the typical constant temperature water bath. Although the death mechanisms appeared to be changing with the experimental conditions, the results implied that the compensation relations can be used in the design of the microwave pasteurization reactors

Kinetic compensation relations: Tools for design in desperation

Compensation relations are obtained for previous studies while assessing whether the compensation phenomena is real or merely a mathematical artifact. Equations concerning compensation from food and bioengineering researchers from the literature are examined as to their possible use as a tool in process design with missing data. Computer flow diagrams are given to explain this procedure and two worked sample sets of data are given as examples. Copyright (C) 1996 Elsevier Science Limite

A MODEL FOR PASTEURIZATION WITH MICROWAVES IN A TUBULAR FLOW REACTOR

Thermal death kinetics of Escherichia coli with microwaves were studied by using a tubular flow reactor with different diameters, lengths, and flow rates. Mathematical models were presented for temperature profile development and death of the microorganisms along the reactor. A first-order kinetic expression in biomass concentration simulated the death phenomena. Temperature effects on the death rate constant were expressed with an Arrhenius expression. Numerical values of the constants of this expression were found to be considerably different in microwave pasteurization experiments from those of the experiments with a constant temperature water bath. These constants were also affected by the average velocity of the medium in the reactor. Apparent death rate constants were higher with the microwave pasteurization experiments than those of the constant temperature water bath experiments at low temperatures. The results implied that tubular flow reactors may be efficiently used, especially in low-temperature pasteurization and sterilization processes

KINETIC COMPENSATION DURING HOMOGENEOUS AND HETEROGENEOUS NUCLEATION OF ICE IN AQUEOUS SYSTEMS

Homogeneous and heterogeneous nucleation rates of ice in aqueous systems are described in the literature with the equation J = A exp (B tau). There are a very large number of published data available for variation of the constants A and B with experimental conditions. Results of this study show that the parameters obtained in the experiments with differential scanning calorimeter and the microscopic technique may be described separately with an empirical compensation equation of the form In A = aB + b. The compensation equation may be used to predict the nucleation rates in design of the freezing processes. In such a design the parameters A and B are required to be evaluated under the exact experimental conditions which may not always be possible. The compensation equation may be helpful for the interpolation of experimental data when there is no information available for the specific design conditions

Construction of quality control charts with sub-optimal size samples

A case study is presented for construction of the quality control charts with suboptimum size samples obtained in a commercial brewery after measuring total acidity, apparent extract and pH of the wort; alcohol, real extract, carbon dioxide total acidity and pH of the bottled beer. Logarithmic transformation of the data was employed to construct the quality control charts, and centering of the data between the specification limits was assessed by means of the process capability index values

KINETICS OF MULTIPRODUCT ACIDOGENIC AND SOLVENTOGENIC BATCH FERMENTATIONS

Large amounts of data indicated that most of the metabolic processes of the acidogenic (acid producing) and the solventogenic (solvent producing) fermentations were regulated by product accumulation. A simple unstructured model simulated microbial growth, product formation and substrate utilization in six different fermentations, where five different microorganisms produced various combinations of ten different products. Specific growth rates of these microorganisms decreased proportionally with overall product accumulation. The products were excreted in non-growth associated pattern. Excretion of some of these products were inhibited by the overall product accumulation similarly as the microbial growth. A substrate consumption model which considered the biomass and individually all the products as separate substrate sinks simulated the data satisfactorily

ENTHALPY - ENTROPY AND FREQUENCY FACTOR - ACTIVATION-ENERGY COMPENSATION RELATIONS FOR DIFFUSION IN STARCH AND POTATO TISSUE

Diffusion of water in hydrated starch, hydrated starch plus sucrose, and diffusion of glucose, potassium, magnesium and ascorbic acid in potato tissue, i.e. a major natural source of starch, were analyzed with Eyring's diffusion theory and the compensation relations. The results implied that there may be an isokinetic temperature for the diffusion of water in amioca (amylopectin, one of the major macromolecular components of starch) and hylon 7 (native corn starch). Having an isokinetic temperature may imply that diffusional jump occurs via formation of similar activated complexes. Although the compensation relations were satisfied, there was no isokinetic temperature with diffusion of water in hylon 7 plus sucrose and diffusion of glucose, potassium, magnesium and ascorbic acid in potato tissue, therefore the compensation relations with these two systems were considered only as empirical correlations for estimating the diffusivities

STATISTICAL PROCESS ANALYSIS IN BROILER FEED FORMULATION

Statistical analysis of broiler feed production was done with data obtained in an industrial plant in an attempt to characterise the causes of variations in feed composition. Analysis of the experimental data has shown that the feed conversion ratio (FCR) for broilers was between 1.8 and 2.5. This large range of observations were thought to be caused by the wide range of variations in the composition of the feeds. The major factor contributing to the variance of the feed compositions was the variance of the raw materials. It was found that the proteins and moisture were distributed normally in most raw materials and feeds. Water molecules can diffuse in the raw materials and the feeds to make the whole batch uniform, On the other hand, the protein containing fractions tend to segregate due to density differences. Therefore, the moisture content of the raw materials tend to vary in a smaller range than those of the proteins. Mixing the feeds for three minutes or longer was sufficient to achieve suitable homogeneity, but controlling the range of the individual raw materials is recommended for further improvement of the process capability indices