The total water uptake, rate of water uptake, extract release volume and maximum shear force were measured on a series of samples of irradiated freeze-dried beef. Forty seven pieces of round steak (2.5 cm x 2.5 cm x 10.4 cm or 1" x 1" x 4") were irradiated at one, three and five megarad. The control samples were not irradiated. Half of the samples were irradiated when fresh, and the other half were irradiated after freeze drying. This procedure has been defined as the "fresh-dry" irradiation sequence throughout the report. The samples were frozen in an air blast at two temperatures (-22.2°C and -56.1°C). Freeze-drying was carried out below 300 microns of Hg and a maximum shelf temperature of 15.6°C (60°F). There appears to be three phases of water uptake: 1) A very rapid, almost instantaneous, absorption. 2) A more gradual uptake (called Part.1 in the report). 3) A relatively slow asymptotic approach to an equilibrium condition (Part 2). These two last phases are shown to be straight lines when the logarithm of the water uptake is plotted against the logarithm of the immersion time. Irradiation level has no significant effect on the final water content or on the slow asymptotic absorption (Part 2) or the extract release volume, but has a significant effect on the gradual water uptake (Part 1) and on the shear press force. Fresh-dry irradiation sequence (and freezing rate) have a significant effect on the total water uptake and on the slow asymptotic water (Part 2) uptake, but not on the gradual water uptake (Part 1), or on the extract release volume or on the shear press forces. Freezing rates have a significant effect on the total water uptake, but not on the slow asymptotic water uptake (Part 2), on the gradual water uptake (Part 1), on the extract release volume or on the shear press forces. The highest total water uptake was found for the meat irradiated when fresh, and slow frozen at -2 2.2°C. The mechanism of the gradual absorption appears to follow a phenomena of water flow, as evidenced by the straight line relationship found in the plots of logarithm water uptake versus logarithm immersion time. / Land and Food Systems, Faculty of / Graduate

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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.)

Ohmic heating is an electrical resistance heating resulting from the passage of electrical current through an electrically conductive material offering some resistance. Most food products possess sufficient electrical conductivity to be able to take advantage of ohmic heating. This research was undertaken to evaluate the quality changes associated with fine ham emulsions prepared under ohmic heating conditions as compared to those produced by conventional heating. / In the first part of the study, kinetics of quality changes (color, texture, water holding capacity, cooking loss and water activity) associated with fine ham emulsion subjected to conventional heating conditions were evaluated. The second part of the study was to standardize ohmic heating conditions for achieving target time-temperature combinations. It was desired to achieve cooking conditions (temperature come-up and hold times) both similar to and faster than conventional heating so that meaningful quality comparisons could be made between the two. / The final part of the study was to compare the quality changes of fine ham emulsion subjected to ohmic heating under different rates, and to compare them with conventional heating. (Abstract shortened by UMI.)

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