Date of Award

Summer 8-11-2017

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)


Food Science and Human Nutrition


Vivian C.H. Wu

Second Committee Member

Benildo G. de los Reyes

Third Committee Member

Cheng-An Hwang

Additional Committee Members

Dorothy Klimis-Zacas


Gaseous sanitizers have been considered for the control of foodborne pathogens to ensure food safety without affecting the moisture content of the food. This study focused on the use of gaseous chlorine dioxide (ClO2) and ozone (O3). The objective was to evaluate the efficiency of gaseous ClO2 and O3 against Shiga-toxin producing Escherichia coli, Salmonella and Listeria monocytogenes on low moisture foods like almonds, black peppercorns, and produce like baby spinach. Gaseous ClO2 was generated on site using a dry precursor method and tested at various concentrations and time durations depending on the food models used. Gas was flowed through an air circulation contraption in the case of low moisture foods and a bucket tumbler in the case of baby spinach. Almonds were treated at 0.27mg of ClO2/g of almonds for 4hr and 0.40 mg of ClO2/g of almonds for 6hr. Peppercorns were exposed to 0.29 mg of ClO2/g of sample for 2.5hr and 0.40 mg of ClO2/g of sample for 4hr. Baby spinach was exposed to 0.015 mg of ClO2/g of sample for 15min, 0.02 mg of ClO2/g of sample for 15min, 0.03 mg of ClO2/g of sample for 30min, and 0.04 mg of ClO2/g of sample for 30min. Gaseous O3 was generated using corona discharge, where dry oxygen was fed into an ozone generator. This was fed into the low moisture food circulation contraption and the bucket tumbler through a thin pipe hose. The concentrations were 17.83mg O3/g of almonds for 6hr in the case of almonds, and 2hr and 4hr in the case of peppercorn. Concentrations used for baby spinach were 15.28 and 6.11mg O3/g of spinach exposed for 15 and 30min. Treatments for almonds were hurdled with post-treatment heat at 50oC and 65oC for both gases. In the case of peppercorns, the importance of increase in relative humidity was studied at 45% and 80% in case of ClO2. Gaseous ClO2 combined with heat gave over 4 log CFU/g reductions for all pathogens tested on almonds. Treatment of 0.27mg of ClO2 for 4hr and further heating at 65oC resulted in 4.58 ± 0.32 and 4.10 ± 0.27log CFU/g reduction for STEC and L. monocytogenes, respectively. 4.29 ±0.61log CFU/g of Salmonella reduction was achieved at 0.40mg of ClO2 for 6hr and heating at 65oC. For peppercorns, the highest concentration (0.4mg of ClO2/g of peppercorn) and longest time (4hr) tested under 80%RH had 3.68, 3.72 and 2.97 log CFU/g reductions for STEC Salmonella, and L. monocytogenes, respectively. Baby spinach was treated using shorter time duration since they are delicate and get damaged easily. Reductions of pathogens from the highest concentration and longest treatment time were above 2log CFU/g with STEC being the highest at 4.45log CFU/g. Gaseous O3 when hurdled with heat, reduced pathogens on almonds with 2.46, 2.18 and 2.45 log CFU/g for STEC, Salmonella and L. monocytogenes. When treating alone, O3 resulted in < 1log CFU/g pathogen reduction on almonds, pepper and spinach. None of the above treatment conditions contributed to visual quality damage on the food models. In conclusions, treatments with ClO2 was more effective than O3. It can be implemented into the existing industrial processing to replace the harmful sanitizers that have been used.