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

Gender is correlated with body mass index, eating habits and exercise frequency in students attending a private university in western Turkey

Influence of gender on body mass index (BMI), eating habits and exercise frequency are evaluated in students attending a private university in Istanbul, Turkey. Males had a significantly higher mean BMI value. Among male students, 27.89% were overweight, and 6.11% were obese, while only 2.63% of females were overweight, and 0.87% were obese.Significantly higher percentage of females than males were underweight (23.70% versus 0.56%, respectively). Male students ate more in a typical day. Breakfast was the most often skipped meal for both genders. Females preferred to consume fruits and vegetables, whereas males preferred more meat and bread. Although the frequencies were significantly different, dairy consumption was low, and fast food and soda consumptions were high for both genders. The majority of university students were insufficiently active. Females were physically less active compared to males

SOLUBILIZATION AND RHEOLOGICAL BEHAVIOR OF RAISIN SUSPENSIONS

Solubilization of raisins is the first step in the production of raki or similar anise flavoured spirits. It is a two-phase process. Components in direct contact with water dissolve at a constant rate in the first phase. The rates of the first phase and final amounts of the solubilized components increase with temperature and stirring rate and decrease with particle size and volume of dissolving water. In the second phase of the solubilization phenomena, the driving force was the deviation of the solubilized solids contents from the finally attainable value. A loose net-like structure was established in this phase; therefore, the mass transfer rates were not affected by the actual size of the particles

EFFECTS OF SUBSTRATE CONCENTRATION ON GROWTH AND LACTIC-ACID PRODUCTION BY MIXED CULTURES OF LACTOBACILLUS-BULGARICUS AND STREPTOCOCCUS-THERMOPHILUS

The kinetics of growth and lactic acid production by mixed cultures of Lactobacillus bulgaricus and Streptococcus thermophilus were modeled with a set of modified logistic and Luedeking-Piret equations. The specific growth rates and the inhibitory effect of each individual species on the mixed culture growth were found to be determined by the media composition. The kinetic analysis clearly showed that the contribution of each microbial species to the mixed culture growth process changed drastically when the substrate concentration was about 15%. This optimum initial substrate concentration was in agreement with the results of the previous studies and the optimum found by trial and error procedure in commercial yogurt production

Kinetic analysis of aspergillus oryzae cultivations on starch

Cultivation of Aspergillus oryzae on starch is described as a combination of two rate processes: Starch hydrolysis and the cellular activities of the fungi including growth, enzyme production and maintenance. Kinetic models are presented to describe growth, enzyme production, starch hydrolysis and uptake of the hydrolysis products. Numerical values of the model parameters indicated that the rate controlling step of A. oryzae growth on starch was not starch hydrolysis, but the substrate uptake process. Glucose was one of the starch hydrolysis products. About 35% of the substrate consumed for biomass synthesis was glucose. Its accumulation in the medium did not cause repression of the starch hydrolysing enzymes. Steady state starch hydrolysis rates increased with initial starch concentration in the medium. Starch hydrolysing enzymes of A. oryzae have extensive industrial uses. This study may help in a more detailed understanding of the kinetic aspects of the production of these enzymes