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Liu S, Qiu Y, Ji K, Ozturk S, Erdoğdu F, Qin W, Yang R, Wu Q. Effect of oil exposure stages on the heat resistance of Salmonella enterica serovar Enteritidis phage type 30 in peanut flour. Food Microbiol 2023; 113:104275. [PMID: 37098433 DOI: 10.1016/j.fm.2023.104275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2022] [Revised: 04/03/2023] [Accepted: 04/03/2023] [Indexed: 04/08/2023]
Abstract
The oil in low-moisture foods (LMFs) shows protective effects on bacteria during thermal processing. However, the circumstances under which this protective effect strengthens remain unclear. This study aimed to understand which step of the oil exposure to bacterial cells (inoculation, isothermal inactivation, or recovery and enumeration step) in LMFs can enhance their heat resistance. Peanut flour (PF) and defatted PF (DPF) were selected as the oil-rich and oil-free LMF models. Salmonella enterica Enteritidis Phage Type 30 (S. Enteritidis) was inoculated into four designated PF groups representing different oil exposure stages. It was isothermally treated to obtain heat resistance parameters. At a constant moisture content (aw,25°C = 0.32 ± 0.02) and controlled aw,85°C (0.32 ± 0.02), S. Enteritidis exhibited significantly high (p < 0.05) D values in oil-rich sample groups. For instance, the heat resistance values of S. Enteritidis in the PF-DPF and DPF-PF groups were D80°C of 138.22 ± 7.45 min and 101.89 ± 7.82 min; however, the D80°C in the DPF-DPF group was 34.54 ± 2.07 min. The oil addition after the thermal treatment also helped injured bacterial recovery in the enumeration. For instance, the D80°C, D85°C, and D90°C values in the DFF-DPF oil groups were 36.86 ± 2.30, 20.65 ± 1.23, and 7.91 ± 0.52 min, respectively, which were higher than those in the DPF-DPF group at 34.54 ± 2.07, 17.87 ± 0.78, and 7.10 ± 0.52 min. We confirmed that the oil protected S. Enteritidis in PF in all three stages: desiccation process, heat treatment, and recovery of bacterial cells in plates.
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Chuang S, Ghoshal M, McLandsborough L. Oil-Based Sanitization in Low-Moisture Environments: Delivery of Acetic Acid with Water-in-Oil Emulsions. Microbiol Spectr 2023; 11:e0529322. [PMID: 37017552 PMCID: PMC10269857 DOI: 10.1128/spectrum.05293-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 03/06/2023] [Indexed: 04/06/2023] Open
Abstract
Contamination with Salmonella spp. and Listeria monocytogenes is concerning across low-moisture food (LMF)-processing environments due to the pronounced survival of these organisms under dry conditions. This study treated desiccated bacteria with acetic acid delivered by oil with and without water-in-oil (W/O) emulsion. The influences of cellular desiccation, emulsion water concentration, water activity (aw), and treatment temperature were investigated. Acetic acid dissolved in oil (i.e., acidified oil) showed low levels of antimicrobial efficacy. After treatment with acidified oil (200 mM acetic acid at 22°C for 30 min), Salmonella enterica serovar Enteritidis phage type 30 cells desiccated to 75% equilibrium relative humidity (ERH) and 33% ERH were reduced by 0.69 and 0.05 log CFU/coupon, respectively. The dispersion of a low level of water (≥0.3%, vol/vol) within the acidified oil with the surfactant (i.e., acidified W/O emulsion) significantly enhanced the antimicrobial efficacy. After treatment with the acidified W/O emulsion (200 mM acetic acid at 22°C for 20 min), desiccated Salmonella (4-strain cocktail) and L. monocytogenes (3-strain cocktail) cells were reduced by >6.52 log most probable number (MPN)/coupon, regardless of the desiccation levels. Increased efficacy was observed with temperature elevation. Reduced efficacy was observed when glycerol was added to the aqueous phase of the emulsion to decrease the solution aw, indicating that the enhanced efficacy of the acidified W/O emulsion was associated with differential osmotic pressure. The antimicrobial mechanism may be due to the membrane disruption induced by acetic acid, in combination with the hypoosmotic stress provided by W/O emulsion, creating cellular lysis, as illustrated by electron micrographs. IMPORTANCE Aqueous-based cleaning and sanitation are undesirable in processing facilities that manufacture low-moisture foods such as peanut butter and chocolate. Alcohol-based sanitization is advantageous because it leaves no residue on the contact surface but requires the processing facility to close temporarily due to flammability. At >6.52 log kill of desiccated Salmonella and Listeria monocytogenes cells, the developed oil-based formulation has the potential to be an effective dry sanitation method.
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Affiliation(s)
- Shihyu Chuang
- Department of Food Science, University of Massachusetts—Amherst, Amherst, Massachusetts, USA
| | - Mrinalini Ghoshal
- Department of Microbiology, University of Massachusetts—Amherst, Amherst, Massachusetts, USA
| | - Lynne McLandsborough
- Department of Food Science, University of Massachusetts—Amherst, Amherst, Massachusetts, USA
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Chuang S, Ghoshal M, McLandsborough L. Efficacy of acidified water-in-oil emulsions against desiccated Salmonella as a function of acid carbon chain-length and membrane viscosity. Front Microbiol 2023; 14:1197473. [PMID: 37378296 PMCID: PMC10291884 DOI: 10.3389/fmicb.2023.1197473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 05/16/2023] [Indexed: 06/29/2023] Open
Abstract
Sanitizing low-moisture food (LMF) processing equipment is challenging due to the increased heat resistance of Salmonella spp. in low-water activity (aw) environments. Food-grade oils mixed with acetic acid have been shown effective against desiccated Salmonella. In this study, different hydrocarbon chain-length (Cn) organic acids were tested against desiccated Salmonella by using 1% v/v water-in-oil (W/O) emulsion as the delivery system for 200 mM acid. Fluorescence lifetime imaging microscopy (FLIM) was utilized with a BODIPY-based molecular rotor to evaluate membrane viscosity under environmental conditions such as desiccation and temperature elevation. Drying hydrated Salmonella cells to 75% equilibrium relative humidity (ERH) increased the membrane viscosity from 1,199 to 1,309 mPa·s (cP) at 22°C. Heating to 45°C decreased the membrane viscosity of hydrated cells from 1,199 to 1,082 mPa·s, and decreased that of the desiccated cells from 1,309 to 1,245 mPa·s. At both 22°C and 45°C, desiccated Salmonella was highly susceptible (>6.5 microbial log reduction (MLR) per stainless-steel coupon) to a 30-min treatment with the W/O emulsions formulated with short carbon chain acids (C1-3). By comparison, the emulsion formulations with longer carbon chain acids (C4-12) showed little to no MLR at 22°C, but achieved >6.5 MLR at 45°C. Based upon the decreased Salmonella membrane viscosity and the increased antimicrobial efficacy of C4-12 W/O emulsions with increasing temperature, we propose that heating can make the membrane more fluid which may allow the longer carbon chain acids (C4-12) to permeate or disrupt membrane structures.
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Affiliation(s)
- Shihyu Chuang
- Department of Food Science, University of Massachusetts, Amherst, MA, United States
| | - Mrinalini Ghoshal
- Department of Microbiology, University of Massachusetts, Amherst, MA, United States
| | - Lynne McLandsborough
- Department of Food Science, University of Massachusetts, Amherst, MA, United States
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Yang R, Lombardo SP, Conway WF, Tang J. Inactivation of Salmonella Enteritidis PT30 on black peppercorns in thermal treatments with controlled relative humidities. Food Res Int 2022; 162:112101. [DOI: 10.1016/j.foodres.2022.112101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2022] [Revised: 10/26/2022] [Accepted: 10/28/2022] [Indexed: 11/09/2022]
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Yang R, Wei L, Dai J, Tang J. Thermal death kinetics of Salmonella Enteritidis PT30 in peanut butter as influenced by water activity. Food Res Int 2022; 157:111288. [DOI: 10.1016/j.foodres.2022.111288] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Revised: 04/20/2022] [Accepted: 04/21/2022] [Indexed: 11/22/2022]
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Yang R, Cheng T, Hong Y, Wei L, Tang J. The effect of dry headspace on the thermal resistance of bacteria in peanut oil and peanut butter in thermal treatments. Food Control 2022. [DOI: 10.1016/j.foodcont.2022.108851] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Liu S, Roopesh M, Tang J, Wu Q, Qin W. Recent development in low-moisture foods: Microbial safety and thermal process. Food Res Int 2022; 155:111072. [DOI: 10.1016/j.foodres.2022.111072] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Revised: 02/22/2022] [Accepted: 02/24/2022] [Indexed: 11/17/2022]
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Liu S, Wei X, Tang J, Qin W, Wu Q. Recent developments in low-moisture foods: microbial validation studies of thermal pasteurization processes. Crit Rev Food Sci Nutr 2021:1-16. [PMID: 34927484 DOI: 10.1080/10408398.2021.2016601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Outbreaks associated with low-moisture foods (e.g., wheat flour, nuts, and cereals) have urged the development of novel technologies and re-validation of legacy pasteurization process. For various thermal pasteurization processes, they share same scientific facts (e.g., bacterial heat resistance increased at reduced water activity) and guidelines. However, they also face specific challenges because of their different heat transfer mechanisms, processing conditions, or associated low-moisture foods' formulations. In this article, we first introduced the general structural for validating a thermal process and the shared basic information that would support our understanding of the key elements of each thermal process. Then, we reviewed the current progress of validation studies of 7 individual heating technologies (drying roasting, radiofrequency-assisted pasteurization, superheated steam, etc.) and the combined treatments (e.g., infrared and hot air). Last, we discussed knowledge gaps that require more scientific data in the future studies. We aimed to provide a process-centric view point of thermal pasteurization studies of low-moisture foods. The information could provide detailed protocol for process developers, operators, and managers to enhance low-moisture foods safety.
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Affiliation(s)
- Shuxiang Liu
- State Key Laboratory of Applied Microbiology Southern China, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, Guangdong Open Laboratory of Applied Microbiology, Guangdong Institute of Microbiology, Guangzhou, China.,Institute of Food Processing and Safety, School of Food Science, Sichuan Agricultural University, Sichuan, China
| | - Xinyao Wei
- College of Biological Science and Engineering, Fuzhou University, Fuzhou, China
| | - Juming Tang
- Department of Biological Systems Engineering, Washington State University, Pullman, WA, USA
| | - Wen Qin
- Institute of Food Processing and Safety, School of Food Science, Sichuan Agricultural University, Sichuan, China
| | - Qingping Wu
- State Key Laboratory of Applied Microbiology Southern China, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, Guangdong Open Laboratory of Applied Microbiology, Guangdong Institute of Microbiology, Guangzhou, China
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Xu J, Xie Y, Paul NC, Roopesh MS, Shah DH, Tang J. Water sorption characteristics of freeze-dried bacteria in low-moisture foods. Int J Food Microbiol 2021; 362:109494. [PMID: 34895752 DOI: 10.1016/j.ijfoodmicro.2021.109494] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 10/08/2021] [Accepted: 11/22/2021] [Indexed: 11/17/2022]
Abstract
Water sorption isotherms of bacteria reflect the water activity with the change of moisture content of bacteria at a specific temperature. The temperature-dependency of water activity change can help to understand the thermal resistance of bacteria during a thermal process. Thermal resistance of bacteria in low-moisture foods may differ significantly depending on the physiological characteristics of microorganisms, including cell structure, existence of biofilms, and growth state. Previous studies demonstrated that the incremental change of aw in bacterial cells during thermal treatments resulted in changes in their thermotolerance. In this study, a pathogen associated with low-moisture foods outbreaks, Salmonella Enteritidis PT30 (in planktonic and biofilm forms), and its validated surrogate, Enterococcus faecium, were lyophilized and their water sorption isotherms (WSI) at 20, 40, and 60 °C were determined by using a vapor sorption analyzer and simulated by the Guggenheim, Anderson and De Boer model (GAB). The published thermal death times at 80 °C (D80 °C-values) of these bacteria in low-moisture environments were related with their WSI-derived aw changes. The results showed that planktonic E. faecium and biofilms of Salmonella, exhibiting higher thermal resistance compared to the planktonic cultures of Salmonella, had a smaller increase in aw when thermally treated from 20 to 60 °C in sealed test cells. The computational modeling also showed that when temperature increased from 20 to 60 °C, with an increase in relative humidity from 10% to 60%, freeze-dried planktonic E. faecium and Salmonella cells would equilibrate to their surrounding environments in 0.15 s and 0.25 s, respectively, suggesting a rapid equilibration of bacterial cells to their microenvironment. However, control of bacteria with different cell structure and growth state would require further attentions on process design adjustment because of their different water sorption characteristics.
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Affiliation(s)
- Jie Xu
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA; Center for Nanotechnology and Nanotoxicology, Harvard T.H. Chan School of Public Health, Harvard University, Boston, MA 02115, USA.
| | - Yucen Xie
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA
| | - Narayan C Paul
- Texas A&M Veterinary Medical Diagnostic Laboratory, 483 Agronomy Rd, College Station, TCX 77843, USA
| | - M S Roopesh
- Department of Agricultural, Food and Nutritional Science, University of Alberta, 3-16 Agriculture/Forestry Centre, Edmonton, AB T6G 2P5, Canada
| | - Devendra H Shah
- Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-6120, USA
| | - Juming Tang
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA
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Dhaliwal HK, Gänzle M, Roopesh MS. Influence of drying conditions, food composition, and water activity on the thermal resistance of Salmonella enterica. Food Res Int 2021; 147:110548. [PMID: 34399525 DOI: 10.1016/j.foodres.2021.110548] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Revised: 06/15/2021] [Accepted: 06/16/2021] [Indexed: 10/21/2022]
Abstract
Salmonella contamination of low-water activity (aw) foods poses a serious concern worldwide. The present study was conducted to assess the effects of drying conditions, food composition, and water activity on the desiccation tolerance and thermal resistance of S. Enteritidis FUA1946, S. Senftenberg ATCC43845 and S. Typhimurium ATCC13311 in pet food, binder formulation, and skim milk powder. The samples were wet inoculated with the individual Salmonella strains and were equilibrated to aw 0.33 and 0.75, followed by an isothermal treatment at 70 °C. The thermal inactivation data was fitted to the Weibull model. Irrespective of the aw, food composition and physical structure of the selected foods, strain S. Enteritidis FUA1946 displayed the highest desiccation and thermal resistance, followed by S. Senftenberg ATCC43845 and S. Typhimurium ATCC13311. The food matrix and strain type significantly (p < 0.05) influenced the thermal resistance of microorganisms in foods along with aw change during thermal treatments. To further study the effect of food composition, an additional set of experiments using dry inoculation of the resistant Salmonella strain in the low-aw foods was designed. Significant (p < 0.05) matrix-dependent interaction on Salmonella reduction was observed. The water adsorption isotherms of selected low-aw foods were measured at 20 and 70 °C to relate the thermal inactivation kinetics with the change in the aw. The characterization of thermal resistance of the Salmonella serovars in low-aw products with different compositions and aw in this study may be used for the validation of thermal challenge studies.
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Affiliation(s)
- Harleen Kaur Dhaliwal
- Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta T6G 2P5, Canada
| | - Michael Gänzle
- Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta T6G 2P5, Canada
| | - M S Roopesh
- Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta T6G 2P5, Canada.
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Xie Y, Xu J, Yang R, Alshammari J, Zhu MJ, Sablani S, Tang J. Moisture Content of Bacterial Cells Determines Thermal Resistance of Salmonella enterica Serotype Enteritidis PT 30. Appl Environ Microbiol 2021; 87:e02194-20. [PMID: 33158899 DOI: 10.1128/AEM.02194-20] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Accepted: 11/04/2020] [Indexed: 11/20/2022] Open
Abstract
Salmonella spp. are resilient bacterial pathogens in low-moisture foods. There has been a general lack of understanding of critical factors contributing to the enhanced thermal tolerance of Salmonella spp. in dry environments. In this study, we hypothesized that the moisture content (XW ) of bacterial cells is a critical intrinsic factor influencing the resistance of Salmonella spp. to thermal inactivation. We selected Salmonella enterica serotype Enteritidis PT 30 to test this hypothesis. We first produced viable freeze-dried S. Enteritidis PT 30, conditioned the bacterial cells to different XW s (7.7, 9.2, 12.4, and 15.7 g water/100 g dry solids), and determined the thermal inactivation kinetics of those cells at 80°C. The results show that the D-value (the time required to achieve a 1-log reduction) decreased exponentially with increasing XW We further measured the water activities (aw) of the freeze-dried S. Enteritidis PT 30 as influenced by temperatures between 20 and 80°C. By using those data, we estimated the XW of S. Enteritidis PT 30 from the published papers that related the D-values of the same bacterial strain at 80°C with the aw of five different food and silicon dioxide matrices. We discovered that the logarithmic D-values of S. Enteritidis PT 30 in all those matrices also decreased linearly with increasing XW of the bacterial cells. The findings suggest that the amount of moisture in S. Enteritidis PT 30 is a determining factor of its ability to resist thermal inactivation. Our results may help future research into fundamental mechanisms for thermal inactivation of bacterial pathogens in dry environments.IMPORTANCE This study established a logarithmic relationship between the thermal death time (D-value) of S. Enteritidis PT 30 and the moisture content (XW ) of the bacterial cells by conducting thermal inactivation tests on freeze-dried S Enteritidis PT 30. We further verified this relationship using literature data for S. Enteritidis PT 30 in five low-moisture matrices. The findings suggest that the XW of S. Enteritidis PT 30, which is rapidly adjusted by microenvironmental aw, or relative humidity, during heat treatments, is the key intrinsic factor determining the thermal resistance of the bacterium. The quantitative relationships reported in this study may help guide future designs of industrial thermal processes for the control of S. Enteritidis PT 30 or other Salmonella strains in low-moisture foods. Our findings highlight a need for further fundamental investigation into the role of water in protein denaturation and the accumulation of compatible solutes during thermal inactivation of bacterial pathogens in dry environments.
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Nachtigall C, Vogel C, Rohm H, Jaros D. How Capsular Exopolysaccharides Affect Cell Surface Properties of Lactic Acid Bacteria. Microorganisms 2020; 8:E1904. [PMID: 33266168 PMCID: PMC7759885 DOI: 10.3390/microorganisms8121904] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Revised: 11/26/2020] [Accepted: 11/27/2020] [Indexed: 12/11/2022] Open
Abstract
Some lactic acid bacteria are able to produce exopolysaccharides that, based on localization, can be distinguished in free and capsular or cell-bound exopolysaccharides (CPS). Up to now, the former were the focus of current research, mainly because of the technofunctional benefits they exhibit on fermented dairy products. On the other hand, CPS affect the surface properties of bacteria cells and thus also the textural properties of fermented foods, but data are very scarce. As the cell surface properties are strongly strain dependent, we present a new approach to investigate the impact of CPS on cell surface hydrophobicity and moisture load. CPS positive and negative Streptococcus thermophilus and Weissella cibaria were subjected to ultrasonication suitable to detach CPS without cell damage. The success of the method was verified by scanning electron and light microscopy as well as by cultivation experiments. Before applying ultrasonication cells with CPS exhibiting an increased hydrophilic character, enhanced moisture load, and faster water adsorption compared to the cells after CPS removal, emphasizing the importance of CPS on the textural properties of fermented products. The ultrasonic treatment did not alter the cell surface properties of the CPS negative strains.
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Affiliation(s)
- Carsten Nachtigall
- Institute of Natural Materials Technology, Technische Universität Dresden, 01062 Dresden, Germany; (H.R.); (D.J.)
| | - Cordula Vogel
- Institute of Soil Science and Site Ecology, Technische Universität Dresden, 01062 Dresden, Germany;
| | - Harald Rohm
- Institute of Natural Materials Technology, Technische Universität Dresden, 01062 Dresden, Germany; (H.R.); (D.J.)
| | - Doris Jaros
- Institute of Natural Materials Technology, Technische Universität Dresden, 01062 Dresden, Germany; (H.R.); (D.J.)
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Yang R, Xu J, Lombardo SP, Ganjyal GM, Tang J. Desiccation in oil protects bacteria in thermal processing. Food Res Int 2020; 137:109519. [PMID: 33233153 DOI: 10.1016/j.foodres.2020.109519] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 06/30/2020] [Accepted: 07/02/2020] [Indexed: 11/30/2022]
Abstract
Edible oils have long been considered to have a protective effect on bacteria from thermal inactivation, but the mechanism for this effect remains unclear. Our recent study suggests that the water activity (aw) of oil decreases exponentially with increasing temperature. Therefore, in thermal processing, the aw of the bacteria inside oil may also decrease making the bacteria more resistant to heat. To validate this hypothesis, the equilibrium aw of bacteria (Enterococcus faecium NRRL B2354, or E. faecium) in peanut oil samples, with different initial aw (0.93, 0.75, 0.52 & 0.33) at room temperature, were measured at elevated temperatures up to 80 °C. Meanwhile, the thermal resistances of E. faecium in these samples were also tested at 80 °C. Results indicate that the aw of the bacteria-in-oil systems changed in the same manner as that of pure peanut oil; it decreased exponentially with temperature from 0.93, 0.75, 0.52 & 0.33 (at ~23 °C) to 0.36, 0.30, 0.21 & 0.13 (at 80 °C), respectively. This confirmed that bacterial cells experienced desiccation in oil during the thermal treatments. The thermal death rates of E. faecium in peanut oil samples followed first-order kinetics. The D80 value (time needed to achieve 1-log reduction at 80 °C) increased exponentially with the reduced aw at 80 °C, from 87 min at aw 0.36 to 1539 min at aw 0.13. A graphical comparison (logD80 vs. high-temperature aw) showed a similarity between the thermal resistance of E. faecium in oil and that in dry air, which supports the hypothesis that oil protects bacteria from thermal treatments through desiccation.
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Affiliation(s)
- Ren Yang
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA
| | - Jie Xu
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA
| | - Stephen P Lombardo
- Technical Innovation Center, McCormick & Company, Inc., Hunt Valley, MD 21031, USA
| | - Girish M Ganjyal
- School of Food Science, Washington State University, P.O. Box 646376, Pullman, WA 99164-6376, USA
| | - Juming Tang
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA.
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Jin Y, Tang J, Zhu M. Water activity influence on the thermal resistance of Salmonella in soy protein powder at elevated temperatures. Food Control 2020; 113:107160. [DOI: 10.1016/j.foodcont.2020.107160] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Abstract
Our recent studies and several publications suggest that the low water activity (aw) of oil in thermal processing might be a major contributing factor towards the increased thermal resistance of bacteria in oils. In this study, we developed a reliable method to measure the water activity of oil by measuring the equilibrium relative humidity in a small headspace. Using this method, water activity of peanut oil was found to decrease exponentially with increasing temperature. A model derived from excess Gibbs free energy was fitted to the observations with an R2 = 99.6% and RMSE = 0.01 (aw). Our results suggest that the sharply reduced water activity of oil resulting from a rise in temperature could cause desiccation of bacteria. This is a possible explanation for the protective effect of oil in thermal processing. A method is presented for the measurement of water activity of oil at temperatures up to 85 °C. The water activity of peanut oil is found to decrease exponentially as the temperature increases. A model is derived to predict the water activity of oil as a function of temperature. Desiccation may happen to bacteria in oil during thermal processing, which explains the protective effect of oil.
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Affiliation(s)
- Ren Yang
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA, 99164, USA
| | - Jiewen Guan
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA, 99164, USA
| | - Sicheng Sun
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA, 99164, USA
| | - Shyam S Sablani
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA, 99164, USA
| | - Juming Tang
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA, 99164, USA
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Prasad A, Gänzle M, Roopesh MS. Inactivation of Escherichia Coli and Salmonella Using 365 and 395 nm High Intensity Pulsed Light Emitting Diodes. Foods 2019; 8:foods8120679. [PMID: 31847186 PMCID: PMC6963940 DOI: 10.3390/foods8120679] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Revised: 12/10/2019] [Accepted: 12/10/2019] [Indexed: 11/21/2022] Open
Abstract
High intensity pulsed light emitting diode (LED) treatment is a novel approach to inactivate foodborne pathogens. The objective of this study was to evaluate the antibacterial potential of high intensity 365 (UV-A) and 395 nm (NUV-Vis) LED treatments against Escherichia coli and Salmonella enterica at high and low water activity (aw) conditions, and to understand the influence of different process parameters on their antibacterial efficacy. Bacteria at high (in phosphate buffer saline, PBS) and low aw (aw = 0.75) conditions were treated with both the LEDs with specific doses at a fixed distance from the LEDs. The 365 nm LED showed more effectiveness in reducing the dried bacteria compared to 395 nm LED. The dry E. coli showed more resistance to LED treatments compared to Salmonella. The 365 and 395 nm LED treatments with ~658 J/cm2 dose resulted in reductions of 0.79 and 1.76 log CFU/g of Salmonella, respectively, on 0.75 aw pet foods. The LED treatments increased the surface temperature, resulting in water loss in the treated samples. This study showed that the dose, duration of light exposure, bacterial strain, and aw played a major role in the antibacterial efficacy of the 365 and 395 nm LEDs.
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Affiliation(s)
- Amritha Prasad
- Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB T6G 2R3, Canada; (A.P.); (M.G.)
| | - Michael Gänzle
- Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB T6G 2R3, Canada; (A.P.); (M.G.)
- College of Bioengineering and Food Science, Hubei University of Technology, Wuhan 430086, China
| | - M. S. Roopesh
- Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB T6G 2R3, Canada; (A.P.); (M.G.)
- Correspondence: ; Tel.: +1-780-492-8413
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Jin Y, Tang J, Sablani SS. Food component influence on water activity of low-moisture powders at elevated temperatures in connection with pathogen control. Lebensm Wiss Technol 2019. [DOI: 10.1016/j.lwt.2019.108257] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Yadav B, Spinelli AC, Govindan BN, Tsui YY, McMullen LM, Roopesh M. Cold plasma treatment of ready-to-eat ham: Influence of process conditions and storage on inactivation of Listeria innocua. Food Res Int 2019; 123:276-285. [DOI: 10.1016/j.foodres.2019.04.065] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 04/24/2019] [Accepted: 04/29/2019] [Indexed: 11/16/2022]
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Xu J, Tang J, Jin Y, Song J, Yang R, Sablani SS, Zhu MJ. High temperature water activity as a key factor influencing survival of Salmonella Enteritidis PT30 in thermal processing. Food Control 2019. [DOI: 10.1016/j.foodcont.2018.11.054] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Misra NN, Yadav B, Roopesh MS, Jo C. Cold Plasma for Effective Fungal and Mycotoxin Control in Foods: Mechanisms, Inactivation Effects, and Applications. Compr Rev Food Sci Food Saf 2018; 18:106-120. [PMID: 33337013 DOI: 10.1111/1541-4337.12398] [Citation(s) in RCA: 133] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Revised: 09/01/2018] [Accepted: 09/10/2018] [Indexed: 12/30/2022]
Abstract
Cold plasma treatment is a promising intervention in food processing to boost product safety and extend the shelf-life. The activated chemical species of cold plasma can act rapidly against micro-organisms at ambient temperatures without leaving any known chemical residues. This review presents an overview of the action of cold plasma against molds and mycotoxins, the underlying mechanisms, and applications for ensuring food safety and quality. The cold plasma species act on multiple sites of a fungal cell resulting in loss of function and structure, and ultimately cell death. Likewise, the species cause chemical breakdown of mycotoxins through various pathways resulting in degradation products that are known to be less toxic. We argue that the preliminary reports from cold plasma research point at good potential of plasma for shelf-life extension and quality retention of foods. Some of the notable food sectors which could benefit from antimycotic and antimycotoxin efficacy of cold plasma include, the fresh produce, food grains, nuts, spices, herbs, dried meat and fish industries.
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Affiliation(s)
- N N Misra
- Center for Crops Utilization Research, Iowa State Univ., Ames, IA, USA
| | - Barun Yadav
- Dept. of Agricultural, Food & Nutritional Science, Univ. of Alberta, Canada
| | - M S Roopesh
- Dept. of Agricultural, Food & Nutritional Science, Univ. of Alberta, Canada
| | - Cheorun Jo
- Dept. of Agricultural Biotechnology, Center for Food & Bioconvergence, Research Inst. of Agriculture & Life Science, Seoul National Univ., Seoul, 08826, South Korea.,Inst. of Green Bio Science and Technology, Seoul National Univ., Pyeongchang, 25354, South Korea
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Tadapaneni RK, Xu J, Yang R, Tang J. Improving design of thermal water activity cell to study thermal resistance of Salmonella in low-moisture foods. Lebensm Wiss Technol 2018; 92:371-9. [DOI: 10.1016/j.lwt.2018.02.046] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Liu S, Tang J, Tadapaneni RK, Yang R, Zhu MJ. Exponentially Increased Thermal Resistance of Salmonella spp. and Enterococcus faecium at Reduced Water Activity. Appl Environ Microbiol 2018; 84:e02742-17. [PMID: 29439987 PMCID: PMC5881056 DOI: 10.1128/aem.02742-17] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Accepted: 02/01/2018] [Indexed: 01/13/2023] Open
Abstract
Salmonella spp. exhibit prolonged survivability and high tolerance to heat in low-moisture foods. The reported thermal resistance parameters of Salmonella spp. in low-moisture foods appear to be unpredictable due to various unknown factors. We report here that temperature-dependent water activity (aw, treatment temperature) plays an important role in the sharply increased thermal resistance of Salmonella enterica serovar Enteritidis PT 30 and its potential surrogate Enterococcus faecium NRRL B-2354. In our study, silicon dioxide granules, as carriers, were separately inoculated with these two microorganisms and were heated at 80°C with controlled relative humidity between 18 and 72% (resulting in corresponding aw,80°C values for bacteria between 0.18 and 0.72) in custom-designed test cells. The inactivation kinetics of both microorganisms fitted a log-linear model (R2, 0.83 to 0.97). Reductions in the aw,80°C values of bacterial cells exponentially increased the D80°C (the time needed to achieve a 1-log reduction in a bacterial population at 80°C) values for S Enteritidis and E. faecium on silicon dioxide. The log-linear relationship between the D80°C values for each strain in silicon dioxide and its aw,80°C values was also verified for organic wheat flour. E. faecium showed consistently higher D80°C values than S Enteritidis over the aw,80°C range tested. The estimated zaw (the change in aw,80°C needed to change D80°C by 1 log) values of S Enteritidis and E. faecium were 0.31 and 0.28, respectively. This study provides insight into the interpretation of Salmonella thermal resistance that could guide the development and validation of thermal processing of low-moisture foods.IMPORTANCE In this paper, we established that the thermal resistance of the pathogen S Enteritidis and its surrogate Enterococcus faecium, as reflected by D values at 80°C, increases sharply with decreasing relative humidity in the environment. The log-linear relationship between the D80°C values of each strain in silicon dioxide and its aw,80°C values was also verified for organic wheat flour. The results provide new quantitative insight into the way in which the thermal resistance of microorganisms changes in low-moisture systems, and they should aid in the development of effective thermal treatment strategies for pathogen control in low-moisture foods.
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Affiliation(s)
- Shuxiang Liu
- Department of Biological Systems Engineering, Washington State University, Pullman, Washington, USA
| | - Juming Tang
- Department of Biological Systems Engineering, Washington State University, Pullman, Washington, USA
| | - Ravi Kiran Tadapaneni
- Department of Biological Systems Engineering, Washington State University, Pullman, Washington, USA
| | - Ren Yang
- Department of Biological Systems Engineering, Washington State University, Pullman, Washington, USA
| | - Mei-Jun Zhu
- School of Food Science, Washington State University, Pullman, Washington, USA
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Xu J, Liu S, Tang J, Ozturk S, Kong F, Shah DH. Application of freeze-dried Enterococcus faecium NRRL B-2354 in radio-frequency pasteurization of wheat flour. Lebensm Wiss Technol 2018. [DOI: 10.1016/j.lwt.2017.12.014] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Xu J, Liu S, Song J, Tang J, Zhu M, Gray P, Villa-rojas R. Dry-inoculation method for thermal inactivation studies in wheat flour using freeze-dried Enterococcus faecium NRRL B-2354. Lebensm Wiss Technol 2018; 89:10-7. [DOI: 10.1016/j.lwt.2017.10.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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Tadapaneni RK, Yang R, Carter B, Tang J. A new method to determine the water activity and the net isosteric heats of sorption for low moisture foods at elevated temperatures. Food Res Int 2017; 102:203-212. [PMID: 29195941 DOI: 10.1016/j.foodres.2017.09.070] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2017] [Revised: 09/20/2017] [Accepted: 09/25/2017] [Indexed: 11/17/2022]
Abstract
In recent years, research studies have shown that the thermal resistance of foodborne pathogens in the low moisture foods is greatly influenced by the water activity (aw) at temperatures relevant to thermal treatments for pathogen control. Yet, there has been a lack of an effective method for accurate measurement of aw at those temperatures. Thus, the main aim of this study was to evaluate a new method for measuring aw of food samples at elevated temperatures. An improved thermal cell with a relative humidity and temperature sensor was used to measure the aw of the three different food samples, namely, organic wheat flour, almond flour, and non-fat milk powder, over the temperature range between 20 and 80°C. For a constant moisture content, the aw data was used to estimate the net isosteric heat of sorption (qst). The qst values were then used in the Clausius Clapeyron equation (CCE) equation to estimate the moisture sorption isotherm for all test food samples at different temperatures. For all the tested samples of any fixed moisture content, aw value generally increased with the temperature. The energy for sorption decreased with increasing moisture content. With the experimentally determined qst value, CCE describes well about the changes in aw of the food samples between 20 and 80°C. This study presents a method to obtain aw of a food sample for a specific moisture content at different temperatures which could be extended to obtain qst values for different moisture contents and hence, the moisture sorption isotherm of a food sample at different temperatures.
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Affiliation(s)
- Ravi Kiran Tadapaneni
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA
| | - Ren Yang
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA
| | - Brady Carter
- METER Group, Inc., 2365 NE Hopkins Court, Pullman, WA 99164-6120, USA
| | - Juming Tang
- Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA 99164-6120, USA.
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