Nutrition & Food Science

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Author: search.filters.author.Tsai, Shawn

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    The effect of emulsifier type and oil inclusion on stress-related gene expression of Salmonella typhimurium in oil-in-water emulsion
    (Wiley, 2024-01-15) Tsai, Shawn; Tikekar, Rohan V.
    Salmonella has been associated with numerous outbreaks from contaminated food products, including emulsions. Emulsions are influenced by emulsifier type and oil presence, which can have varying degrees of stress or protection on bacteria. Although our previous research has shown that emulsifier solutions, rather than emulsions, provide a protective effect on Salmonella typhimurium after thermal treatment, the underlying mechanism remains unclear. This study selected S. typhimurium as the model microorganism and utilized the same emulsifiers (Tween 20, Tween 80, Triton X-100) to create emulsifier solutions and emulsions with the same oil fraction (60% (v/v)) to examine their effect on the expression of nine selected genes (rpoE, rpoH, otsB, proV, fadA, fabA, dnaK, ibpA, ompC) associated with stress response. Specifically, the study observed variations in gene expression under normal and thermal stress at 55°C. After 20-h incubation, Triton X-100 emulsion caused an upregulation of stress-related genes, rpoE, otsB, and fabA, suggesting stressful environment. After thermal treatment, S. typhimurium in Triton X-100 solution showed a longer 5-log reduction time with increased proV and decreased fabA and ompC expression, suggesting enhanced thermal protection compared to its emulsion. Conversely, Tween 80 solution increased fabA and ompC expression, indicating greater membrane fluidity and passive diffusion, potentially reducing thermal resistance. However, according to the upregulation of ibpA, this effect was likely mitigated by the overproduction of heat shock proteins. Notably, Triton X-100 environments exhibited the most significant gene expression changes after heat treatment, whereas Tween 80 without oil was the most inhospitable for bacterial survival. These findings inform bacterial responses under various conditions, aiding food safety strategies.
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    The effect of emulsifier type and oil fraction on Salmonella Typhimurium growth and thermal inactivation in oil-in-water emulsion
    (Wiley, 2023-10-13) Tikekar, Rohan V.; Tsai, Shawn
    High water activity oil-in-water emulsions can promote survival and growth of Salmonella Typhimurium. Nevertheless, the precise effect of emulsifier type and oil content on bacterial growth and inactivation is not fully understood. Here, emulsions were prepared using different emulsifiers (Tween 20, Tween 80, and Triton X-100) and different oil fractions (20%, 40%, and 60% (v/v)). TSB (control), emulsifier solutions, and emulsions were inoculated with S. Typhimurium. Bacterial growth rate was measured at 7, 22, and 37°C, whereas thermal inactivation was performed at 55°C. Growth and inactivation data was fitted into Logistic and Weibull models, respectively. At an incubation temperature of 37°C, the presence of high amount of oil (60%) in Tween 20 and Triton X stabilized emulsions extended the lag phase (5.83 ± 2.20 and 9.43 ± 1.07 h, respectively, compared to 2.28 ± 1.54 h for TSB, p < 0.05), whereas individual emulsifiers had no effect on growth behavior compared to TSB. This effect was also prevalent but attenuated at 22°C, whereas no growth was observed at 7°C. In thermal inactivation, we observed protective effect in Tween 80 and Triton X-100 solutions, where time required for five-log reduction was 1914.70 ± 706.35 min and 795.34 ± 420.09 min, respectively, compared to 203.89 ± 10.18 min for TSB (p < 0.05). Interestingly, the presence of high amount of oil did not offer protective effect during thermal inactivation. We hypothesize that oleic acid in Tween 80 and lower hydrophobicity value of Triton X-100 help maintain membrane integrity and improve the resistance of bacteria to heat inactivation.
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    Curcumin-Loaded Pickering Emulsion Formed by Ultrasound and Stabilized by Metal Organic Framework Optimization
    (MDPI, 2021-03-03) Ma, Peihua; Zhang, Zhi; Tsai, Shawn; Zhang, Hongchao; Li, Yuan; Yuan, Fang; Wang, Qin
    The ultrasound-assisted preparation of a curcumin-loaded metal organic framework (MOF) UiO-66-NH2 stabilized Pickering emulsion system was carried out in this study. A 3-level-4-factor Box–Behnken design (BBD) and response surface methodology (RSM) analysis were employed to systematically evaluate the effect of different experimental parameters (i.e., ultrasonic power, ultrasonic time, oil content, and MOF content) on curcumin loading capacity (LC) and encapsulation efficiency (EE). The results indicated that ultrasonic power and MOF content significantly affected LC and EE, whereas ultrasonic time and oil content had little effect. A mathematical model for optimizing the preparation of emulsion systems was established. Based on the ridge max analysis, an optimal condition for the newly developed curcumin-loaded MOF-Pickering emulsion was identified, i.e., ultrasonic power 150 W, ultrasonic time 11.17 min, oil content 20.0%, and MOF content 1.10%. At this condition, the LC and EE of curcumin obtained from the experiment reached 7.33% ± 0.54% and 56.18% ± 3.03%, respectively, which were within the prediction range of LC (7.35% ± 0.29%) and EE (54.34% ± 2.45%). The emulsion systems created in this study may find new applications for the delivery of bioactive compounds in food and pharmaceutical areas.
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    BACTERIAL GROWTH AND INACTIVATION IN HETEROGENEOUS ENVIRONMENT
    (2023) Tsai, Shawn; Tikekar, Rohan V.; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation explores the growth and inactivation of Salmonella enterica subsp. enterica Serovar Typhimurium in oil-in-water emulsion systems, with a particular focus on the effects of emulsifier type, oil fraction, temperature, molecular weight, and surface charge. First, investigation was conducted on the effects of emulsifier type (Tween 20, Tween 80, Triton X-100) and oil content (20%, 40%, 60%) on growth and thermal inactivation of S. Typhimurium in emulsions. The results indicated that while emulsifiers did not affect the bacterial growth rate or lag phase, the presence of high oil content (60%) prolonged the lag phase in emulsions. In addition, Tween 80 and Triton X-100 emulsifier solutions exhibited protective effects against thermal inactivation. Next chapter was focused on evaluating the impact of temperature on growth (7, 22, 37°C) and inactivation (55, 58, 60°C) kinetics of S. Typhimurium in emulsion systems with same emulsifier and oil fraction as previous chapter. The results indicated that temperature had a significant impact on bacterial kinetics, with increasing temperatures leading to faster growth and inactivation rates. Next, the effect of emulsifier molecular weight and surface charge on the growth and thermal inactivation of S. Typhimurium in emulsions was examined. To control the molecular weight with similar structure, whey protein was selected for experimentation. By adjusting the pH, it was possible to change the surface charge in whey protein. Results indicated that whey protein hydrolysate (WPH) with a lower molecular weight did not exhibit a lag phase in Salmonella growth. However, whey protein isolate (WPI) with higher molecular weight demonstrated no difference in the lag phase when compared to bacterial growth in TSB. Similar effects were observed with a positively charged emulsifier (WPI+). The findings suggest that the molecular weight of emulsifiers has a more significant impact on bacterial growth than their surface charge. Regarding the evaluation of inactivation, emulsifier solutions exhibited no significant difference compared to TSB, while emulsions stabilized by WPH and WPI+ showed some protective effects on S. Typhimurium. This observation can be attributed to the ability of positively charged emulsifiers to interact with the bacterial membrane, providing protective effects during thermal treatment. Lastly, to gain a comprehensive understanding of the mechanism concerned with the impact of emulsifier and oil inclusion on bacterial growth and inactivation behavior, S. Typhimurium was cultured in different emulsion-related environments and evaluated for nine stress-related genes (rpoE, rpoH, otsB, proV, fadA, fabA, dnaK, ibpA, ompC) after 20 hours of incubation at 37°C and after thermal treatment at 55°C for 45 min. It was found that ibpA was upregulated in all emulsifier environments, regardless of the presence of oil, indicating that IbpA was synthesized in emulsifier environments. Moreover, increased expression of fabA was also observed in Triton X-100 stabilized 60% emulsion, indicating poor heat resistance due to increased membrane fluidity. In the combination of gene expression data, our results showed that emulsifier solutions without oil exhibited a greater number of regulatory mechanisms compared to those containing oil, indicating that the presence of oil did not provide as much protection after thermal treatment. Based on these findings, the stress-related mechanism was constructed by the expression of those selected genes. Overall, this dissertation provides valuable insights into the factors influencing bacterial growth and inactivation in oil-in-water emulsion systems, as well as bacterial stress response in these systems. These findings provide important insights into the growth and inactivation behavior of S. Typhimurium in oil-in-water emulsion systems and the stress response mechanisms involved. Understanding these factors is crucial for developing effective control measures to ensure food safety and prevent foodborne illness outbreaks caused by this pathogen. This information can be used to optimize the formulation and processing of emulsion-based food products to minimize the risk of bacterial contamination and ensure their safety for consumption.
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