Date of Award

Fall 12-16-2016

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Food Science and Human Nutrition

Advisor

Balunkeswar Nayak

Second Committee Member

Aria Amirbahman

Third Committee Member

Carl Tripp

Additional Committee Members

Vivian Wu

Rodney Bushway

Abstract

Ultraviolet (UV) light-assisted titanium dioxide (TiO2) photocatalysis is an emerging technology that utilizes TiO2 photocatalysts to accelerate the reactive oxygen species (ROS) generation during UV illumination that play a major role in inactivating foodborne microorganisms. The first objective of this research was to compare different recipes of photocatalysts to identify the most efficient photocatalyst in the presence of UVA radiation for inactivation of Escherichia coli in white grape juice. The TiO2-SiO2 sol-gel coating of glass slides was identified to provide maximum inactivation (3.27±0.25 log CFU/mL) of the target microorganism in 20 min (PE. coli in white grape juice and model its inactivation kinetics.

To obtain FDA requirement for pasteurization (5-log reduction of target microorganism), the treatment duration using UVA and UVC were 60 min and 20 min, respectively. Addition of photocatalyst reduced UVA based photocatalytic pasteurization time to 40 min, whereas addition of the same photocatalyst to UVC did not demonstrate any significant reduction (P>0.05) of the pasteurization time. These results were attributed to the variation in absorbance of white grape juice (A350=1.53±0.00; A254=2.14± 0.02) at different wavelengths. The synergistic effect of UVA assisted photocatalytic (UVA-P) disinfection was estimated to be 55% based on the D-values obtained from Weibull model parameters (DUVA =5.4min; DUVA-P =2.4min). The results from this study clearly demonstrated that the composition or recipe of the photocatalytic material, the absorbance of the substrate and the wavelength of the light source used largely influence the photocatalytic process. Moreover, this study demonstrated that Weibull and/or Hom model could precisely describe the non-linear inactivation kinetics of the target microorganism during UVA assisted photocatalytic treatments (Radj2=0.979; RMSE=0.220).

To investigate the potential advantages of UVA-assisted photocatalytic treatment, the quality attributes of the UVA-P treated white grape juice were compared against that of thermal, UV-A and UV-C treated samples. Our results demonstrated that health related compounds such as vitamin C, total phenolic content and total antioxidant capacity of the white grape juice were adversely affected (P>0.05) by the UVC radiation than UVA-assisted photocatalytic disinfection. This study showed that UVA-based pasteurization of white grape juice in the presence of TiO2 photocatalysts could retain the health-related compounds that are usually lost during UVC and thermal processing of the juice. However, the efficiency of the photocatalytic disinfection needs to be improved to attain pasteurization standards in a shorter time and retain the nutrients present in the juice.

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