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GROWTH, INACTIVATION, AND SURVIVAL OF SALMONELLA ON SESAME SEEDS DURING TAHINI PROCESSING AND REFRIGERATED STORAGE OF TAHINI
Title
GROWTH, INACTIVATION, AND SURVIVAL OF SALMONELLA ON SESAME SEEDS DURING TAHINI PROCESSING AND REFRIGERATED STORAGE OF TAHINI
Creator
Zhang, Yangjunna
Date
2016, 2016-05
Description
Salmonella can survive for long period of time in low-moisture foods and cause human illness after consumption of contaminated foods. Recently...
Show moreSalmonella can survive for long period of time in low-moisture foods and cause human illness after consumption of contaminated foods. Recently, sesame seeds and tahini (sesame seeds pasta), have been identified as unusual sources of salmonellosis. Controlling specific steps during tahini processing and storage of tahini may minimize the risk of Salmonella contamination. This study examined the fate of Salmonella in different steps of tahini processing and refrigerated storage of tahini. A four serovar cocktail of Salmonella was used for inoculation of sesame seeds and tahini. Bacterial populations were determined by aerobic plate counts on both selective and non-selective media. Water activity of samples was determined during processing and storage. For the soaking step during tahini processing, unhulled dry sesame seeds with aw of 0.1 were inoculated with Salmonella, held 24 h, and then soaked in water at ambient temperature. Populations were monitored at 0, 18, 22 and 24 h. Salmonella decreased by 2 - 3-log CFU/g during drying and then increased by 5 log CFU/g after rehydration. Separately, inoculated de-hulled seeds with two different initial aw were roasted at three different temperatures (95, 110, and 130 ºC) for 90 min. Both the Salmonella populations and aw were determined at 10 min intervals during roasting. Finally, inoculated sesame seeds were processed into tahini. As a comparison, the same quantity of uninoculated roasted sesame seeds were processed into tahini, and then inoculated post-processing. Tahini was stored at 4 ºC for 17 weeks. Approximately 8 log CFU/g of Salmonella was detected initially in the sesame seeds prior to roasting with a 1-log CFU/g reduction after 20 min at 95 ºC when the aw of seeds decreased quickly. For different roasting temperatures, the aw declined much faster and stopped decreasing during roasting, while populations continue decreasing throughout the whole roasting. To investigate survival of Salmonella during refrigerated storage of tahini, approximately 9 log CFU/g of Salmonella was inoculated onto sesame seeds or into processed tahini without significant reduction throughout 17 weeks (p > 0.05). These results suggest that Salmonella contamination can be an issue at any step of tahini manufacture.
M.S. in Food Safety and Technology, May 2016
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THERMAL INACTIVATION OF SALMONELLA AGONA IN LOW-MOISTURE FOOD SYSTEMS AS INFLUENCED BY WATER ACTIVITY
Title
THERMAL INACTIVATION OF SALMONELLA AGONA IN LOW-MOISTURE FOOD SYSTEMS AS INFLUENCED BY WATER ACTIVITY
Creator
Jin, Yuqiao
Date
2016, 2016-07
Description
Salmonella can survive in low-moisture, high-protein and high-fat foods for several years. Despite nationwide recalls for Salmonella in low...
Show moreSalmonella can survive in low-moisture, high-protein and high-fat foods for several years. Despite nationwide recalls for Salmonella in low-moisture products, information on survival of Salmonella during high-protein and high-fat food processing is limited. This project evaluated Salmonella enterica serovar Agona 447967 thermal inactivation kinetics in a high-protein and a high-fat matrix using a defined matrix composition, varying water activities and process conditions. A high-protein matrix, composed of 60:6:25 weight ratio of flour: oil: protein, and a high-fat matrix, composed of 60:25:6 weight ratio of flour: oil: protein was studied. Each matrix was inoculated with Salmonella enterica serovar Agona 447967 at activities of 0.5, and 0.9. Samples were packed in aluminum test cells and heat treated over a range of temperatures and time intervals. Survival of Salmonella Agona was detected on trypticase soy agar with 0.6% yeast extract. The average z-values for the high-protein matrix at the water activity (aw) of 0.5 and 0.9 were 9.01ºC, and 7.51ºC, respectively. The average z-values for the high-fat matrix was 11.91ºC at aw 0.5, and 7.08ºC at aw 0.9. Results showed that the z-value at aw 0.5 was significantly different from the z-value at aw 0.9 (p < 0.05) in both the highprotein and high-fat matrices. Critical process factors associated with pathogen destruction were identified during thermal treatments in this project. Results indicated that a correlation existed between temperature and water activity and must be accounted for when predicating inactivation of Salmonella enterica in these model matrices under dynamic process conditions.
M.S. in Food Process Engineering, July 2016
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