Thermal processing involves application of heat to destroy pathogenic microorganisms of public heath concern and to reduce the activity of microorganisms and enzymes that spoil the food. However, the technique is associated with considerable degradation of taste, color, texture, flavor and nutritional quality of processed foods. Data on kinetics of changes in quality factors and their temperature dependence, as well as the heat penetration behavior of the food during processing are necessary to predict and optimize the extent of quality retention. The objectives of this study were: (a) to evaluate the kinetics of thermal softening, color degradation and loss of ascorbic acid in potato (Solanum tuberosum) at selected temperatures (70--100°C) and to evaluate their temperature dependence; (b) to evaluate the effect of process variables (temperature, rotational speed, can size and nature of the covering fluid) on heating behavior of canned potatoes and (c) to determine the influence of the above process variables on process time and product quality.

No description available.

Graduation date: 1951

Ultrasonic techniques were investigated for non-invasive quality evaluation of selected fruits and vegetables. An ultrasonic non-destructive evaluation system was developed and used to investigate physical and acoustical property changes for the selected fruits and vegetables non-invasively. The system included a high power burst pulser, a broadband receiver, a digital storage oscilloscope, two pairs of transducers of 250 kHz and 1 MHz, and a microcomputer system, which was interfaced with the ultrasonic equipment through a General Purpose Interface Board (GPIB), for data acquisition and analysis. Using potatoes and apples, several forms of the acoustic indices were investigated using the system. Investigation of “Yukon-Gold’ potatoes concentrated on the physical and acoustical property changes during the storage period of approximately five months. The tests were conducted at regular intervals. Ultrasonic velocity, attenuation coefficient, modulus of elasticity, and tissue density were determined for each potato along two different orientations — longitudinal and transverse. Three varieties of apples, ‘Golden Delicious’, ‘Red Delicious’, and ‘Granny Smith’, were tested to detect their physiological changes with ripeness. The tests were conducted at two different stages of ripeness. In each test, ultrasonic velocity, attenuation coefficient, modulus of elasticity, and tissue density were determined along longitudinal and radial directions of the apples. Frequency analysis of the transmitted ultrasonic signals through potato and apple samples was also conducted using Fast Fourier Transform (FFT) techniques. The experimental results for the potatoes and apples indicated the measured acoustical and physical properties differed along different orientations; i.e., potato and apple tissues are anisotropic materials. Apple tissues transmitted much lower frequency components than potato tissues and the transmitted frequency range was much narrower due to the much higher percentage of intercellular void space in apple tissues (24%) than in potato tissues (2%). The ultrasonic measurements were able to detect physiological changes and physical heterogeneities in fruit and vegetable tissues. Therefore, the ultrasonic technique can be a useful and quick method for evaluating firmness as well as textural and rheological property changes during storage of fruits and vegetables. Hollow hearts in ‘Atlantic’ potatoes were successfully detected using the ultrasonic nondestructive evaluation system at 250 kHz. A objective this work was to develop a quantitative, non-invasive method for hollow heart detection in potatoes, and to provide information for designing evaluation equipment which could serve as an automatic quality control step in the production process. The analysis of the transmitted ultrasonic signals through the potatoes was carried out in both time and frequency domains. The results of the investigation of ‘Atlantic’ potatoes showed that the waveform of transmitted ultrasonic signals through a hollow heart potato differed significantly from that of a normal potato. Further, the defective potatoes could be separated on the basis of the amount of ultrasonic power transmitted through a potato. By means of digital Fourier analysis, the 0^th spectral moment, M₀, was determined from the power spectral density curve of a transmitted ultrasonic signal. The spectral moment represents the amount of ultrasonic power transmitted through a tested potato, and was chosen as the basis for quantitative, non-invasive method for hollow heart detection, since power transmission of ultrasonic wave was affected by the presence of hollow heart in potatoes. Potatoes with hollow heart transmitted much less ultrasonic power than normal potatoes — approximately 89% less on average. There was a distinct separation between the normal potatoes and hollow heart potatoes. The reliability of this method was confirmed. Among 41 ‘Atlantic’ potatoes tested, all 26 hollow-heart potatoes were identified without exception. Therefore, the parameter M₀ could provide an effective method of analyzing the ultrasonic measurements for quantitative, non-invasive evaluation of hollow hearts in potatoes. This non-invasive method could be used to identify internal quality of potatoes that is difficult to evaluate from external appearance. Such a measurement offers promises for the development of equipment that would sort potatoes with hollow heart automatically. / Ph. D.

Boron deficiency or toxicity can reduce yield and quality of vegetables. Seven vegetable crops, varying from low to high boron requirements were grown in field plots at Corvallis in 1987. Leaf-B and yield components of green bean, cucumber, potato, carrot, tomato, broccoli and table beet were examined under conditions of fall or spring soil applied B at a 5 kg/ha rate on two soil types. Soil tests on control plots indicated B levels of .39 mg/kg and .20 mg/kg in the top 23 cm of soil in the silty clay loam and sandy loam soil, respectively. Fall or spring application of B increased soil B levels in the top 23 cm on the silty clay loam soil to .68 mg/kg and .37 mg/kg, and on the sandy loam soil to .81 mg/kg and .42 mg/kg, respectively. Boron application had no effect on yield or yield components except in green beans where spring applied B on the sandy loam reduced percent of premium grade pods (sieve sizes 1-4). Leaf-B levels were not affected in cucumber, carrot, or tomato on either soil. Boron application on both soils had a significant effect on leaf-B levels in bean, broccoli and table beet. Potato leaf-B was significantly affected only on the sandy loam soil. / Graduation date: 1993

The contamination of street vended vegetables may occur through the usage of manure and contaminated irrigation water, and the consumption of these vegetables, such as ready-to-eat salads, can cause foodborne diseases in consumers. The objective of this study was to investigate the Enterobacteriaceae diversity in vegetables sold at informal markets in the Johannesburg Metropolis. A total of 201 vegetable samples were purchased from randomly selected street vendors from different regions in the Johannesburg Metropolis and analysed for aerobic growth count and Enterobacteriaceae contamination using Plate Count Agar (PCA), and violet red bile glucose agar (VRBGA), respectively. The diversity of bacterial isolates was analysed using sequencing and phylogenetic analysis. The aerobic bacterial growth counts of vegetables from all the regions ranged from 7.66(±0.759) to 8.37(±0.347) log10 cfu/g and the mean aerobic growth counts of vegetables from Soweto and Yeoville were significantly different (p ≤ 0.05) from those of the other regions, but were not significantly (p > 0.05) different across different vegetable types. The Enterobacteriaceae growth counts in vegetables from all the regions ranged from 5.05 (±0.647) to 5.45 (±0.693) log10 cfu/g. The mean Enterobacteriaceae growth counts of vegetables were not significantly (p > 0.05) across each region and different vegetables types. The predominant Enterobacteria genera were Serratia (35%), followed by Hafnia (21%), Aeromonas (17%), and Pseudomonas (5%). In conclusion, this study shows that the vegetables sold at the informal markets in the Johannesburg Metropolis have high aerobic bacterial growth and Enterobacteriaceae contamination due to poor hygiene practices. The dominant Enterobacteriaceae genera isolated are Aeromonas, Hafnia, Serratia, and Pseudomonas, which could be opportunistic pathogens. It is recommended that the Department of Health improves vending and sanitation facilities, to prevent cross contamination. / Life and Consumer Sciences / M. Sc. (Life Sciences)