Effect of gas nanobubbles on the efficacy of peracetic acid and chlorine against Escherichia coli and Listeria monocytogenes

Primary Author: Arshdeep Singh

Faculty Sponsor: Minto Michael

Primary College/Unit: Agricultural, Human and Natural Resource Sciences

Category: Agricultural and Natural Resource Sciences

Campus: Pullman

Abstract:

Nanobubbles are defined as fine bubbles with diameter varying from 20 to 200 nm with distinctive surfactant properties because of their small size. Nanobubbles are proven effective in irrigation systems, fisheries, wastewater treatments and dentistry. This research was conducted to study the impact of gas nanobubbles on the efficacy of commonly used antimicrobials in food industry. This study was conducted as a completely randomized block design (three replications). Air, CO2 and N2 were used to generate nanobubbles in water. Peracetic acid and chlorine were used to make the nanobubble-antimicrobial solutions and were tested against Escherichia coli O157:H7 and Listeria monocytogenes. Antimicrobials mixed with water without any gas acted as controls. Nine-milliliter of antimicrobial solutions were taken into individual test tubes and inoculated with 1 ml of individual microbial inoculum. After the holding time of 1.5 and 3 min, 1 ml of the sample was taken, neutralized with Dey-Engley broth, and plated on brain heart infusion agar. pH and Eh of antimicrobial solutions were measured before and after the addition of master inoculum. After 3 min for E. coli, CO2 nanobubbles with chlorine was the most effective treatment with 6.4 log reductions as compared to 4.2 log reductions in control. For L. monocytogenes, CO2 nanobubbles with peracetic acid was most lethal treatment with 4.6 log reductions compared to 1.9 log reduction in control. This study demonstrated that efficacy of various antimicrobials can be increased by incorporating gas nanobubbles. Further, this method can be tested against other pathogens in different food matrices.

Determination of thermal inactivation parameters of Salmonella in nonfat dry milk and whole milk powder during four months storage

Primary Author: Amninder Singh Sekhon

Faculty Sponsor: Minto Michael

Primary College/Unit: Agricultural, Human and Natural Resource Sciences

Category: Agricultural and Natural Resource Sciences

Campus: Pullman

Abstract:

Principal Topic- Foodborne pathogens such as Salmonella can endure dry environments of milk powders for extended periods of time due to increased adaptability at low water activity (aw) levels and proliferate when powders are hydrated. This study focused to compare survivability and thermal resistance of Salmonella in NFDM and WMP stored for 120 days.

Methods- This study was designed as completely randomized with three replications. Milk powders were spray inoculated with 5-serovar Salmonella cocktail and dried back to original pre-inoculation aw. The D-values of Salmonella in inoculated NFDM and WMP were determined periodically (every 30 days, starting from day-one). The D and z-values were also performed for hydrated forms of NFDM and WMP. Rehydration (13% total solids w/v) was performed on days of performing D- and z-value study. Five separate thermal death time disks containing 5g or 5 mL of respective sample were transferred into five thermal-death-time, sealed and placed in hot-water baths set at 80, 85 and 90°C for inoculated powder, and 59, 62 and 65°C for hydrated inoculated powder. Samples were held for 0 to 56 minutes in hot-water baths and quickly transferred to cold-water baths at pre-determined time intervals. The samples were enumerated using injury-recovery media, and D- and z-values were calculated.

Results- During storage, heat resistance of Salmonella in WMP was statistically higher than NFDM. D-values of Salmonella on day 120 in WMP were 24.6, 11.4, and 7.0 minutes at 80, 85 and 90°C respectively as compared to 21.9, 9.2, and 5.2 min in NFDM.