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The technical feasibility of ohmic heating was evaluated for viscous liquids in static ohmic heating cells in three stages. First, electrical conductivities and time/temperature profiles were measured and compared for selected hydrocolloids (carrageenan, gelatin, pectin, starch and xanthan) in water at various concentrations (1--6%). Of the thickening agents examined, carrageenan gave the highest value for electrical conductivity and the shortest time to raise the temperature from 20 to 100°C. It was followed by xanthan. Pectin and gelatin samples were found to exhibit lower, but similar electrical conductivities and heating profiles. Starch samples had the lowest electrical conductivity and the temperature of starch solutions never exceeded 62°C within the specified time limit of 10000 s. / In the second stage, the effect of salt and acid concentration was evaluated on electrical conductivities and time/temperature profiles of the above selected hydrocolloids in water solutions at a concentration necessary to achieve a similar apparent viscosity of 0.2 Pa.s at 300 s-1 and 20°C (carrageenan 1.7%, pectin 2.5%, starch 4.3% and xanthan 2%). / In the third stage, measurements of electrical conductivities, time/temperature and heating rate profiles were performed applying six voltage gradients (5.26, 7.14, 13.16, 17.86, 21.05 and 25 V/cm), with two electrode cross-sectional surface areas (19.84 and 37.95 cm2) and the electrodes separated at three specific distances (10.05, 14.33 and 20.01 cm) at 150 V. Applied voltage gradients had a major effect on temperature and heating rate profiles but no effect on electrical conductivities. / Rheological properties of carrageenan, pectin, starch and xanthan solutions were investigated at various temperatures (20--80°C) and concentrations (carrageenan 1.5, 1.7 and 1.9%; pectin 2.3, 2.5 and 2.7%; starch 3.8, 4 and 4.2%; xanthan 1.6, 1.8 and 2%) in the presence of 1% salt. Both temperature and concentration influenced the rheological properties of solutions. / Finally, electrical conductivity measurements and rheological properties of starch at 4% and 1% salt were used as input to evaluate a theoretical model for the electrical, thermal and flow behaviour in a continuous ohmic heating unit. (Abstract shortened by UMI.)

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Call number: LD2668 .T4 1984 J32 / Master of Science

Thesis (MTech (Consumer Sciences: Food and Nutrition))--Cape Peninsula University of Technology, 2006 / Fruit and vegetables are the major antioxidant contributors to the diet Antioxidants assist in the prevention of oxidative damage in the body and may as a result prevent the causation of degenerative diseases. Thermal household processing plays an integral part in South African consumers' lives, as most fruit and vegetables consumed are processed at home. Consumers' perceptions that food processing causes nutrient losses, especially of vitamin C, have been corroborated by studies that investigated thermal household processing of single foods or that of industrial processing. No studies have determined the effect of thermal household processing on mixed dishes. A popular consumed South African mixed dish, namely, stewed tomato and onion flavoured with parsley, was investigated by using three recipes, each using a different preparation method. The traditional recipe for the preparation of stewed tomato and onion was modified (control recipe) to contain parsley. Two other recipes (Recipe 1 and 2) were compiled based on the recipe formulation of the control recipe but differed in the preparation methods used. In Recipe 1, raw onion was added to cooked tomato and in Recipe 2, sauteed onions were added to cooked tomato.

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The major objective of this project was to evaluate the feasibility of artificial neural networks (ANNs) and genetic algorithms (GAs) for modeling and optimization of food thermal processing. The specific objectives were: (1) to develop a comprehensive computer simulation program for thermal processing, (2) to apply ANNs and GAs for modeling and optimization of constant retort temperature (CRT) thermal processing and variable retort temperature (VRT) thermal processing, (3) to develop dynamic models for thermal processing using ANNs, and (4) to explore ANN-model-based analysis of critical control points for deviant thermal processes. / As a preliminary research, neural network models were successfully developed for modeling of residence time distribution (RTD) under aseptic processing conditions. The main configuration parameters of neural networks such as the number of hidden layers and their neurons, learning runs, choice of transfer functions and learning rules were optimized. / In order to provide experimental data needed for developing and testing of ANN models and GA optimization, a comprehensive finite difference computer simulation program for thermal processing was first developed in MS Visual Basic language, which could be used for simulating different thermal processes such as constant retort temperature (CRT) and variable retort temperature (VRT) thermal processing. / The second objective was focused on developing modeling and optimization methods for CRT thermal processing using ANNs and GAs. The ANN models were developed for predicting process time, average quality retention, surface cook value, final temperature difference, lethality ratio, and equivalent energy consumption. Using this optimization program, the effects of process variables on the optimal retort temperature and the maximum average quality retention were investigated. / The final part of the thesis research was focused on applying ANN methods for the analysis of critical control points (CCPs) for deviant thermal processes, one of the important steps required for developing hazard analysis of critical control points (HACCP) program. The results indicated that ANN models could be efficiently used for the analysis of CCPs of thermal processing. Such a concept can be expanded for developing an ANN based HACCP expert system for thermal processing. (Abstract shortened by UMI.)

Although radio-frequency (RF) methods have been used for decades in many heating and drying processes, there is still a need for more engineering design data related to the design of the applicators and the performance of these systems before costly prototypes are built. Energy, temperature, and the effect produced by the high frequency field parameters on biological materials need to be examined with regard to their effects on the resulting processing requirements. / Wheat-seed infection by a fungus such as Fusarium graminearum can considerably lower the seed germination and the quality of the harvest. A study was thus conducted to determine the combined effect of different levels of RF power, temperature, and moisture content on the quality of seed-grade wheat and fungus inactivation. Similar treatment combinations were studied with seed-grade soybean in view on improving germination. With higher power, higher temperature (90°C) and higher moisture content (14%), the fungus mortality significantly increased, with a fungal vigour of less than 0.1, and the germination quality of the seeds decreased to a germination vigour below 0.3. For soybean seeds, only treatments of low RF intensity (60°C) were successful in improving germination vigour especially at lowest moisture content typically found in stored seeds. / RF treated wheat was studied to identify the relationship between heating conditions and grain quality categorized in terms of kernel viability and structural damage. / The potential of an RF thermal treatment to improve and extend the storability of vacuum packaged carrot sticks was investigated. The results have shown that it is possible to treat carrot sticks to 60°C in less than 2 min to reduce the initial microbial load. The RF-treatments maintained colour, the vacuum of the packages, and the excellent taste of the carrot sticks. / RF heating was studied for the pasteurization of prepared samples of ham. The ham samples were brought to internal temperatures of 75 and 85°C, by RF heating with a 10 min residence time. The study indicates that radio-frequency heating can improve the storability of re-packed hams by reducing the bacterial load, reducing moisture loss during storage and maintaining an overall greater product quality. (Abstract shortened by UMI.)