Investigating the effects of environmental stresses on Salmonella enterica serovar Tennessee survival in a low moisture food model

Survivability of Escherichia coli O157:H7 ATCC 43888 and Enterococcus faecium ATCC 8459 in a Hydrocolloid Gel Bar Model and Macronutrient Bar Model in Response to Vacuum Microwave Drying and Storage

This study aimed to investigate the microbial safety of Vacuum Microwave Drying (VMD) and 30 days storage at 25 °C on survivability of Escherichia coli O157:H7 ATCC 43888 and Enterococcus faecium ATCC 8459 in a nutritionally minimal bar model and macronutrient bar model. Sodium alginate hydrocolloid gel bars were inoculated with each microorganism and underwent processing in a 2 kW VMD and subsequent storage at 25 °C for 10 days in sealed bags to determine the impact of VMD on bacteria without the influence of a nutritionally dense food matrix. Additionally, the effects of macronutrient concentration on organism survivability during processing and storage were tested using a peanut butter banana bar formulated to contain high carbohydrate, high protein, or high-fat content. The macronutrient bars were inoculated with each microorganism and underwent VMD with subsequent storage at 25 °C for up to 30 days in sealed bags. Results of the hydrocolloid gel model showed that in a nutritionally minimal food matrix, both microorganisms were susceptible to VMD with additional loss of each microorganism during storage. Results showed the entire loss of E. coli O157:H7 by day 10 of storage. In the macronutrient bar study, E. faecium had minimal susceptibility to VMD and storage at 30 days while E. coli O157:H7 had minimal susceptibility to VMD with greater susceptibility to storage for 30 days. There was a significant difference (p < 0.05) in log loss comparing E. coli O157:H7 VMD processed and unprocessed bars and minimal significance comparing E. faecium VMD processed and unprocessed bars. Water activity and moisture content at storage timepoints had no observed correlation with pathogen survivability in either study.

Temperature cycling between 4 °C and 37 °C could reduce Salmonella viability in low-moisture foods

Low-moisture foods (LMFs) have been linked to Salmonella transmission due to the remarkable resilience of Salmonella against desiccation, allowing its survival for extended periods. Being metabolically inactive, Salmonella in LMFs exhibit extraordinary resistance to inactivation treatments. This study proposes a novel strategy for mitigating Salmonella in LMF products through a temperature cycling (TC) approach. Alternating the temperature between 4 °C and 37 °C on a daily basis reduced the viability of S. Typhimurium air-dried on surfaces by >4 log after 6 days. TC also diminished Salmonella resistance to acidity and reduced its virulence. The mechanism was elucidated through an integrated analysis of transcriptomics and proteomics data. Specifically, transcriptomic data revealed elevated levels of protein synthesis alongside active energy metabolism. Proteomic analysis demonstrated that these protein activities were associated primarily with the heat shock protein response. Taken together, the principal mechanism by which TC exerts its inhibitory effect appears to be the repeated induction of heat shock protein synthesis within Salmonella, ultimately leading to energy depletion. Finally, the efficacy of TC was validated on representative LMF samples, including flour, protein powder, and mixed spices. The most notable effect was observed in the mixed spices, with a reduction of 2.7 ± 0.2 log after 6 days (P < 0.05). In conclusion, the TC approach demonstrated in this study provides valuable insights into the management of foodborne pathogens in LMFs.

Glycogen plays a key role in survival of Salmonella Typhimurium on dry surfaces and in low-moisture foods

Salmonella enterica is known to survive in desiccate environments and is often associated with low-moisture foods (LMFs). In this work, S. Typhimurium ATCC 14028 was found to survive better by achieving the least reductions (3.17 ± 0.20 Log CFU reduction) compared to S. Tennessee ATCC 10722 (3.82 ± 0.13 Log CFU reduction) and S. Newport ATCC 6962 (6.03 ± 0.36 Log CFU reduction) after 30 days on surfaces with a relative humidity of 49% at ambient temperature. A metabolomic analysis revealed that S. Typhimurium was still active in energy metabolism after 24 h in the desiccate environment and glycogen, an energy reserve, was drastically reduced. We followed up on the glycogen levels over 30 days and found indeed a sharp decline on the first day. However, the glycogens detected on day 7 were significantly higher (P < 0.05) and thereafter remained stable above the original levels until day 30. The expression levels of both glycogen anabolism- and catabolism-related genes (csrA, glgA, glgC, glgX) were significantly up-regulated at all tested points (P < 0.05). The glgA and glgC insertion mutants displayed weaker survivability on both dry surfaces and in representative LMFs (flour and milk powder) compared to the wild-type strain. This work highlights the role of glycogen during different periods of desiccation, which may bring novel insight into mitigating Salmonella by disrupting glycogen metabolism.

Metabolomics insights into the potential of encapsulated essential oils as multifunctional food additives

Growing consumer concern about foodborne disease outbreaks and health risks associated with chemical additives has propelled the usage of essential oils (EOs) as novel food additives, but are limited by instability. In this regard, a series of EOs nano/micro-capsules have been widely used to enhance their stability and improve food quality. However, classical food quality assessment methods are insufficient to fully characterize the effects of encapsulated EOs on food properties, including physical, biochemical, organoleptic, and microbial changes. Recently, the rapid development of high-throughput sequencing is accelerating the application of metabolomics in food safety and quality analysis. This review seeks to present the most recent achievements in the application of non-targeted metabolomics to identify and quantify the overall metabolite profile associated with food quality, which can guide the development of emerging food preservation technologies. The scientific findings confirm that metabolomics opens up exciting prospects for biomarker screening in food preservation and contributes to an in-depth understanding of the mechanisms of action (MoA) of EOs. Future research should focus on constructing food quality assessment criteria based on multi-omics technologies, which will drive the standardization and commercialization of EOs for food industry applications.

Survival of Salmonella enterica in Military Low-Moisture Food Products during Long-Term Storage at 4, 25, and 40°C

ABSTRACT

Salmonella enterica has been increasingly implicated in foodborne outbreaks involving low-moisture foods (LMF) during the recent decade. This study aimed to investigate the potential for persistence of S. enterica in a range of LMF during storage at three temperatures. LMF products, boil-in-bag eggs (freeze-dried product), chocolate protein drink, cran-raspberry First Strike bars, mocha dessert bar, and peanut butter, were inoculated with a five-strain cocktail of S. enterica and stored at 4, 25, or 40°C for 36 months. Salmonella populations remained above 7 log CFU/g in all products stored at 4°C and above 6 log CFU/g in products stored at 25°C, excluding the cran-raspberry First Strike bars. Storage at 40°C resulted in Salmonella populations above 5.5 log CFU/g in boil-in-bag eggs after 36 months and demonstrated survivability for 12 months or less in the other five products. Additionally, a mocha bar production temperature profile study identified rapid cooling of bars in which the temperatures reached would have no measurable impact on Salmonella populations. The results indicate the ability of Salmonella to survive in a variety of LMF category foods, even under adverse storage conditions and identifies how the food matrix may affect Salmonella survivability. The data indicate the importance of establishing food processing procedures that adequately mitigate the presence of Salmonella throughout food processing systems, while also increasing comprehensive understanding of Salmonella survivability mechanisms.

HIGHLIGHTS

Morphological and metabolomics impact of sublethal doses of natural compounds and its nanoemulsions in Bacillus cereus

Microbiological safety in food industry are always a concern regarding sublethal tolerance in bacteria for common and natural sanitizers. Natural bacteriocins, such as nisin (NIS), may negatively interfere in the efficiency of major compounds of essential oils against foodborne pathogenic bacteria. However, nanoemulsioned forms increase the bactericidal potential of natural compounds acting synergistically. In this study, cinnamaldehyde (CIN), citral (CIT), and linalool (LIN) were evaluated independently, associated with NIS, and in nanoemulsions (NEs) against Bacillus cereus using untargeted-metabolomics. Results revealed morphological changes in the structure of B. cereus treated with NEs of CIN and CIT, both NIS-associated. In addition, sensibility tests and UHPLC-QTOF-MS analyses indicated that NIS might react together with CIT reducing the bactericidal efficiency, while the nanoemulsion of CIT effect was enhanced by NIS in nanoemulsioned forms. This study highlights the importance of prudent administration of natural compounds as antimicrobial agents to prevent sublethal tolerance in pathogenic bacteria.