Survival of acid-adapted or non-adaptedSalmonellaEnteritidis,Listeria monocytogenesandEscherichia coliO157:H7, in traditional Greek salads

Survival of Salmonella spp., Escherichia coli O157:H7, and Listeria monocytogenes in Ready-to-Eat "Guacamole": Role of Added Antimicrobials

Ensuring the microbiological safety of food products is majorly important to regulatory agencies, producers, and consumers. This study aimed to examine the effects of three different antimicrobial agents, including chitosan (CH), mastic oil (M), and citric acid (CA), individually or as a combination, against Salmonella spp., Escherichia coli O157:H7, and Listeria monocytogenes (artificially inoculated) in Guacamole, a ready-to-eat (RTE) avocado-based salad. The Guacamole samples included untreated samples, designated as CNL, and samples treated as follows: CA 0.15% and CA 0.30% with citric acid added at 0.15% and 0.30% v/w; CH 0.5% and CH 1% with chitosan at 0.5 and 1% v/w; M 0.2% and M 0.4% with mastic essential oil (EO) at 0.2% and 0.4% v/w; CACH with CA 0.30% and CH 1% v/w; CAM with CA 0.30% and M 0.4% v/w; CHM with CH 1% and M 0.4% v/w; and CACHM with CA 0.30%, CH 1%, and M 0.4% v/w. Microbiological evaluation, monitoring of the pH values, and proximate analyses (moisture, fat, protein, ash, and water activity) were performed at different time intervals (days 0, 1, 3, 5, and 7) at two storage temperatures (4 and 10 °C). Antimicrobial treatments, particularly CH 1% and CACHM, effectively (p < 0.05) reduced Salmonella spp. and E. coli O157:H7 populations at 4 °C, while CACHM showed the most efficacy against L. monocytogenes. However, at 10 °C, antimicrobials had limited impact, and the bacterial counts exhibited an increasing trend during storage. The pH values in the avocado-based salad samples showed, in general, higher decreases at 10 compared to 4 °C, with the CHM combination showing the highest antimicrobial effect.

A current insight into Salmonella's inducible acid resistance

Salmonella is a diverse and ubiquitous group of bacteria and a major zoonotic pathogen implicated in several foodborne disease outbreaks worldwide. With more than 2500 distinct serotypes, this pathogen has evolved to survive in a wide spectrum of environments and across multiple hosts. The primary and most common source of transmission is through contaminated food or water. Although the main sources have been primarily linked to animal-related food products, outbreaks due to the consumption of contaminated plant-related food products have increased in the last few years. The perceived ability of Salmonella to trigger defensive mechanisms following pre-exposure to sublethal acid conditions, namely acid adaptation, has renewed a decade-long attention. The impact of acid adaptation on the subsequent resistance against lethal factors of the same or multiple stresses has been underscored by multiple studies. Α plethora of studies have been published, aiming to outline the factors that- alone or in combination- can impact this phenomenon and to unravel the complex networking mechanisms underlying its induction. This review aims to provide a current and updated insight into the factors and mechanisms that rule this phenomenon.

Oxidative and Microbial Stability of a Traditional Appetizer: Aubergine Salad

An eggplant-based salad, called aubergine salad (AS), is a traditional appetizer and as such, is quite popular in the Mediterranean area. It is widely produced either on a home scale or on an industrial scale and widely consumed. However, there are cases where preservatives (such as sodium benzoate and potassium sorbate) are added in order to extend the shelf life of the product. In the present study, the stability of this delicatessen against oxidation and microbial spoilage was evaluated, with or without preservatives. The physicochemical properties of the salad were evaluated, along with the tocopherol content, resistance to oxidation, and microbial count. According to the results, it is evident that the induction period of AS is 16% (in the case that preservatives were used) and 26% (in the case without preservatives) increased, compared to a control sample (plain soybean oil). This can be attributed to the increased content in tocopherols, and more specifically to α-tocopherol. Furthermore, the addition of preservatives resulted in increased storage days and a reduction of microorganisms. However, in both cases, the AS-prepared salad exhibited a self-stabilization ability after 13 days, negating the need for preservatives.

Listeria monocytogenes Biofilms in the Food Industry: Is the Current Hygiene Program Sufficient to Combat the Persistence of the Pathogen?

Biofilms contain microbial cells which are protected by a self-produced matrix and they firmly attach themselves to many different food industry surfaces. Due to this protection, microorganisms within biofilms are much more difficult to eradicate and therefore to control than suspended cells. A bacterium that tends to produce these structures and persist in food processing plants is Listeria monocytogenes. To this effect, many attempts have been made to develop control strategies to be applied in the food industry, although there seems to be no clear direction on how to manage the risk the bacteria poses. There is no standardized protocol that is applied equally to all food sectors, so the strategies for the control of this pathogen depend on the type of surface, the nature of the product, the conditions of the food industry environment, and indeed the budget. The food industry performs different preventive and corrective measures on possible L. monocytogenes-contaminated surfaces. However, a critical evaluation of the sanitization methods applied must be performed to discern whether the treatment can be effective in the long-term. This review will focus on currently used strategies to eliminate biofilms and control their formation in processing facilities in different food sectors (i.e., dairy, meat, fish, chilled vegetables, and ready-to-eat products). The technologies employed for their control will be exemplified and discussed with the objective of understanding how L. monocytogenes can be improved through food safety management systems.

Prior exposure to different combinations of pH and undissociated acetic acid can affect the induced resistance of Salmonella spp. strains in mayonnaise stored under refrigeration and the regulation of acid-resistance related genes

The innate and inducible resistance of six Salmonella strains (4/74, FS8, FS115, P167807, ATCC 13076, WT) in mayonnaise at 5 °C following adaptation to different pH/undissociated acetic acid (UAA) combinations (15mM/pH5.0, 35mM/pH5.5, 45mM/pH6.0) was investigated. The inherent and acid-induced responses were strain-dependent. Two strains (ATCC 13076, WT), albeit not the most resistant innately, exhibited the most prominent adaptive potential. Limited/no adaptability was observed regarding the rest strains, though being more resistant inherently. The individual effect of pH and UAA adaptation in the phenotypic and transcriptomic profiles of ATCC 13076 and WT was further examined. The type (pH, UAA) and magnitude of stress intensity affected their responses. Variations in the type and magnitude of stress intensity also determined the relative gene expression of four genes (adiA, cadB, rpoS, ompR) implicated in Salmonella acid resistance mechanisms. adiA and cadB were overexpressed following adaptation to some treatments; rpoS and ompR were downregulated following adaptation to 15mM/pH5.0 and 35mM/pH5.5, respectively. Nonetheless, the transcriptomic profiles did not always correlate with the corresponding phenotypes. In conclusion, strain variations in Salmonella are extensive. The ability of the strains to adapt and induce resistant phenotypes and acid resistance-related genes is affected by the type and magnitude of the stress applied during adaptation.

Physicochemical Analysis and Essential Oils Extraction of the Gorse (Ulex europaeus) and French Broom (Genista monspessulana), Two Highly Invasive Species in the Colombian Andes

Gorse (Ulex europaeus) and French broom (Genista monspessulana) are two highly invasive species that have become a threat to tropical countries, especially in Andean ecosystems. This research focused on providing a physicochemical characterization and essential oils extraction of both species to better understand their potential valorization and guide further environmental management efforts. For this purpose, the following analyses were conducted for both species: higher heat value (HHV), elemental analysis, proximate analysis, thermogravimetric analysis to obtain constituent natural polymers (hemicellulose, cellulose, and lignin), and extraction of essential oils and other interest chemical compounds through supercritical fluids. Ecological closeness was found between the two species mostly regarding HHV, fixed carbon, and volatile matter, which calls for similar potential uses. Both species were also found to be suitable for combustion processes, gasification, extraction of chemical compounds, and use of lignocellulosic content; however, only U. europaeus appeared suitable for activated carbon obtention. Therefore, this work provided relevant data that can be used as preliminary basis to establish strong scientifically-based management and control strategies for these two invasive species. We recommend focusing primarily on thermal processes such as pyrolysis, gasification, or combustion, and also essential oils extractions of acetic acid, dodecanoic acid, anagyrine, amylene hydrate, caulophylline, and maltol in the future.

Fate of Listeria monocytogenes in Ready-to-Eat Refrigerated Dips Treated with High Pressure Processing

Various outbreaks and recalls have been associated with Listeria monocytogenes contamination of ready-to-eat (RTE) food products, including dips. High pressure processing (HPP) is useful for reducing levels of bacteria in many RTE food products, but its efficacy for reduction of pathogens in RTE dips is not well understood. In this study, laboratory-prepared hummus, tahini, baba ghanoush, guacamole, and pesto were initially treated with HPP at 350 MPa for up to 240 s to assess L. monocytogenes inactivation and determine D-values. D_350 MPa-values in hummus, guacamole, and baba ghanoush were 105.3, 71.3, and 34.0 s, respectively. No significant reduction in L. monocytogenes levels was observed in tahini or pesto at 350 MPa for 240 s or after additional treatment for up to 600 s at 600 MPa (P > 0.05). Overall, the results of this study highlight the efficacy of HPP for reducing L. monocytogenes levels in certain RTE dips and but not in others.

Lactobacillus plantarum 5BG Survives During Refrigerated Storage Bio-Preserving Packaged Spanish-Style Table Olives (cv. Bella di Cerignola)

This paper proposes bio-preservation as a tool to assure quality and safety of Spanish-style table olives cv. Bella di Cerignola. Lactobacillus plantarum 5BG was inoculated in ready to sell olives packaged in an industrial plant by using a half-volume brine (4% NaCl; 2% sucrose). The samples were stored at 4°C. The survival of the inoculated strain, the microbiological quality, the sensory scores and the survival of a strain of Listeria monocytogenes inoculated in brines were evaluated. The persistence of the Lb. plantarum bio-preserving culture was confirmed on olives (≥6.5 Log CFU/g) and in brine (≥7 Log CFU/ml). Bio-preserved olives (SET1) showed a better sensory profile than chemically acidified control olives (SET2) and the texture was the real discriminative parameter among samples. Bio-preserved olives recorded better scores during storage because of their ability to retain good hardness, crunchiness, and fibrousness without cracks. The inoculation of Lb. plantarum positively acted on the safety of olives, as the D-value of L. monocytogenes was reduced from 40 (SET2) to 5 days (SET1). In conclusion, Lb. plantarum 5BG and the physico-chemical conditions achieved in the settled procedure are suitable for the industrial packaging of Bella di Cerignola table olives, improving the process by halving brining volumes and avoiding chemical stabilizers, and significantly reducing the salt concentration. The final product is also safely preserved for almost 5 months as suggested by the reduction of the survival rate of L. monocytogenes.

Viability of and Escherichia coli O157:H7 and Listeria monocytogenes in a delicatessen appetizer (yogurt-based) salad as affected by citrus extract (Citrox©) and storage temperature

The antimicrobial effect of citrus extract (at 1 mL/kg [C1] and 2 mL/kg [C2]) on naturally occurring microbiota and inoculated pathogens (E. coli O157:H7 and L. monocytogenes at ca. 6 log cfu/g) in the traditional Greek yogurt-based salad Tzatziki stored at 4, 10, or 21 °C, was examined. Lactic acid bacteria (LAB) were high (8.0-8.5 log cfu/g) and varied only minimally for both the control (untreated) and the citrus extract-treated salad samples, whereas the higher citrus extract concentration yielded the lowest yeast populations, irrespective of temperature, during the entire storage period. Populations of inoculated E. coli (6 log cfu/g) declined in both untreated and citrus extract-treated samples from day 0-70, 35, and 15 at 4, 10, and 21 °C, respectively. Citrus extract had a significant effect on the survival of the inoculated E. coli O157:H7, with reductions of 2.8-4.8 log cfu/g in the citrus extract-treated samples at the end of the storage period. Our data show that L. monocytogenes survived in both untreated and citrus extract-treated samples during the entire storage period, irrespective of the storage temperature. The higher concentration of citrus extract had a significant effect on the survival of L. monocytogenes in the treated samples, and reductions of 1.5-3.0 logs were noted on final day 70, 35 and 15 at 4, 10 and 21 °C, respectively. The results of our study demonstrated the potential of citrus extract as a natural compound that can control the growth of food-borne pathogenic bacteria, such as E. coli O157:H7 and L. monocytogenes in Tzatziki, a yogurt-based salad.

A Review of Temperature, pH, and Other Factors that Influence the Survival of Salmonella in Mayonnaise and Other Raw Egg Products

Salmonellosis is one of the main causes of foodborne illnesses worldwide, with outbreaks predominately linked to contamination of eggs and raw egg products, such as mayonnaise. This review explores previous studies that have investigated Salmonella control mechanisms utilized in the production of raw egg mayonnaise and other food products. Apart from the use of pasteurized eggs, the main control mechanism identified is the pH of the raw egg products, which plays an important role in the consistency and stability while affecting the survival of Salmonella spp. However, currently there is no consensus regarding the critical pH limit for the control of Salmonella. The effectiveness of pH as a control mechanism is influenced by the type of acid used, with the effectiveness of lemon juice compared with vinegar highly debated. Additionally, Salmonella susceptibility to pH stresses may also be influenced by storage temperature (in some studies refrigeration temperatures protected Salmonella spp. from acidulants) and is further complicated by the development of Salmonella cross-tolerance-induced responses, pH homeostasis achieved by the cellular antiport and symport systems, and acid tolerance response (ATR). These mechanisms all provide Salmonella with an added advantage to ensure survival under various pH conditions. Other confounding factors include the fat content, and the addition of NaCl, garlic and plant essential oils (PEOs) from mint, cinnamon, cardamom and clove.

Survival and growth of Salmonella Typhimurium, Escherichia coli O157:H7 and Staphylococcus aureus in eggplant dip during storage

Eggplant dip is an internationally popular appetizer, prepared in some instances under uncertain hygienic conditions with inconsistent refrigeration. This study examined the effects of citric acid on the survival of pathogenic microorganisms (Salmonella Typhimurium, Escherichia coli O157:H7 and Staphylococcus aureus) and naturally present organisms (lactic acid bacteria, LAB, aerobic bacteria, APC and yeast and mold, YM) in eggplant dip during storage. Eggplant dip with 0, 0.2, 0.4, 0.6 or 0.8% citric acid was inoculated with S. Typhimurium, E. coli O157:H7 or S. aureus and stored at 4, 10 and 21 °C for ≤15 d. Throughout the study, the survival of the inoculated microorganisms was monitored, and LAB, APC, YM numbers and pH were determined. There was no significant (p>0.05) effect of citric acid on inoculated S. Typhimurium and E. coli O157:H7. Salmonella and E. coli O157:H7 survived >7d with little reduction in viability. Reduction of S. aureus viability increased with citric acid concentration and reached>3.0 log10 CFU/g by 15 d at 4 °C. Citric acid had no effect (p>0.05) on the background YM during storage at 4, 10 and 21 °C or LAB stored at 4 and 10 °C, while at 21 °C, 0.6 and 0.8% citric acid significantly reduced LAB. Citric acid had no effect (p>0.05) on the APC in samples stored at 4 °C but it had significant effects on samples stored at 10 and 21 °C. Work reported showed that the use of citric acid at 0.4-0.8% can inhibit the growth of S. aureus in eggplant dip, but adequate refrigeration is essential to minimize risk from this and other pathogens in this product.