Date of Award:

5-2024

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biological Engineering

Committee Chair(s)

Luis J. Bastarrachea

Committee

Luis J. Bastarrachea

Committee

Silvana Martini

Committee

David Britt

Abstract

Dehydration is one of the most prevalent forms of food preservation, with approximately 85% of food is hot air drying due to the simplicity of the process. The high temperatures employed in this method may also induce a loss in nutritional quality, which involves destruction of micronutrients (vitamins), and loss of color.

The aim of this work is to develop a low energy, non-thermal method of food dehydration that results in a high-quality product through the application of Ultraviolet light, within the UV-A range. UV light can be separated into its 3 categories based on the wavelength of light from longest to shortest they are A, B and C. UV-A has a longer wavelength and thus has low energy compared to UV-C or UV-B, but that longer wavelength equates to a deeper penetration ability within food materials. The UV-A light is hypothesized to supply the needed energy beneath the surface of the food samples for the release of water in a dry environment without the need for added heat. This supplied energy is also hypothesized to be able to reduce the microbial load present in the food.

The pairing of UV-A light and low relative humidity air for 10 h was applied to purple potatoes, mangoes, apples, and sweet potatoes to evaluate the dehydration kinetics this method of dehydration has on produce as well as how it effects the chemical and physical structure. The control samples of purple potato that were dehydrated without exposure to UV-A light retained 133% more moisture than the samples treated with UV-A exposure. The work done on mangoes and apples was to better observe the effectiveness of UV-A dehydration on fruit with a high-water and sugar content relative to the purple potatoes. The control samples of mango and apple resulted in a moisture content that was 85% and 55% greater than the content of the samples that were dehydrated with exposure to UV-A, respectively. Electron microscopy, infrared spectroscopy and differential scanning calorimetry confirmed the preservation of the physical and chemical integrity of the purple potatoes, mangoes and apples that were UV-A dehydrated even after extended storage time in a range of relative humidity levels (11.3% - 86%). Additional work was done on sweet potatoes to determine the antimicrobial effectiveness of the 10 h UV-A dehydration process by monitoring the change in bacterial load of samples inoculated with ~ 6 log(CFU/gDry solids) of E. coli K12 and L. innocua L2 individually. There was a significant (P < 0.05) reduction found for both bacteria after the 10 hours of treatment compared to the control samples not treated with UV-A light. The samples inoculated with E. coli K12 were reduced by 99.9 ± 0.1% as a result of the 10 h of UV-A exposure with only a 92.2 ± 0.1% reduction in the control samples. For samples inoculated with of Listeria innocua L2 there was a 99.2 ± 0.5% reduction at the end of the 10 h UV-A dehydration where the control samples treated with the absence of UV-A light had only a 60.9 ± 10.3% reduction.

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