Practice and Progress: Updates on Outbreaks, Advances in Research, and Processing Technologies for Low-moisture Food Safety

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.

Intrinsic and extrinsic factors influencing Bacillus cereus spore inactivation in spices and herbs: Thermal and non-thermal sterilization approaches

The presence of Bacillus cereus in spices and herbs has posed a detrimental effect on food safety. The absence of thorough testing, comprehensive reporting, and vigilant surveillance of the illness has resulted in a significant underestimation of the true prevalence of foodborne illness caused by B. cereus. B. cereus spores are resistant to thermal processing (superheated steam, microwave, radiofrequency, infrared) that remains a significant challenge for the spice industry. Non-thermal techniques, such as cold plasma, gamma irradiation, and electron beam irradiation, have gained significant interest for their ability to inactivate B. cereus spores. However, these technologies are constrained by inherent limitations. The composition of B. cereus spores, including dipicolinic acid, divalent cations, and low water content in the core, contributes significantly to their resistance properties. This review delves into the different factors that impact B. cereus spores in spices and herbs during sterilization, considering both intrinsic and extrinsic factors. This review also discussed the various techniques for inactivating B. cereus spores from spices and highlighted their effectiveness and constraints. It also provides valuable insights for enhancing sterilization strategies in the spices and herbs industry.

Changes in quality characteristics and inactivation of Salmonella in cake, including oleogel used as a fat replacer, baked with two different methods

This is the first study to assess the impact of substitution of shortening (50%) with sunflower-beeswax oleogel in cake formulations on the inactivation kinetics of Salmonella spp. and the quality attributes of cakes baked in conventional (CO) and microwave (MWO) ovens. Four distinct cake samples were examined in the study: Cake samples containing oleogel prepared in two different ovens (Oleo-Cake-CO and Oleo-Cake-MWO) and control cake samples baked in two different ovens (Cont-Cake-CO and Cont-Cake-MWO). The control-batter and oleogel-batter demonstrated shear thinning behavior (pseudoplastic, n < 1), with a good fit to the Power Law model, but viscosity and viscoelastic moduli decreased when the oleogel was used in place of shortening in cake recipes. In addition, the Cont-Cake-MWO had the greatest special volume value (2.31 ± 0.04 mL/g), whereas the Oleo-Cake-CO had the lowest (1.65 ± 0.02 mL/g) (p < 0.05). Furthermore, compared to the samples baked with CO, lower water activity and moisture values (p < 0.05) were observed in the samples baked in MWO due to their higher cooking loss values (p < 0.05). In all baking techniques, the addition of oleogel to the cake formula, used as a fat substitute, resulted in higher values for cohesiveness, hardness, springiness, and chewiness (p < 0.05). As a result, the inactivation of Salmonella in cakes slightly reduced with using oleogel as a fat substitute (p > 0.05), whereas it affected some quality properties of cakes baked with both heat treatments.

Food Safety Research and Extension Needs for the U.S. Low-Moisture Food Industry

Historically, low-moisture foods were considered to have minimal microbial risks. However, they have been linked to many high-profile multistate outbreaks and recalls in recent years, drawing research and extension attention to low-moisture food safety. Limited studies have assessed the food safety research and extension needs for the low-moisture food industry. The objectives of this needs assessment were to explore the food safety culture and education needs, identify the food safety challenges and data gaps, and understand the barriers to adopting food-safety-enhancing technologies in the U.S. low-moisture food industry. This needs assessment was composed of two studies. In Study 1, food safety experts from the low-moisture food industry upper management participated in online interviews and a debriefing discussion session. In Study 2, an online anonymous survey was disseminated to a different group of experts with experience in the low-moisture food industry. The qualitative data were analyzed using deductive and inductive coding approaches, while the quantitative data were analyzed via descriptive analysis. Twenty-five experts participated in the studies (Study 1: n = 12; Study 2: n = 13). Common commodities that participants had worked with included nuts and seeds, spices, flour, and dried fruits and vegetables. A food safety culture conceptual framework was adapted, which included three main components: infrastructure conditions (foundation), individual's food safety knowledge, attitudes, and risk perceptions; and organizational conditions (supporting pillars). Major barriers to establishing a positive food safety culture were identified to be limited resources, difficulties in risk communication, and difficulties in behavioral change. For continual improvement in food safety performance, two major themes of food safety challenges and data gaps were identified: cleaning, sanitation, and hygienic design; and pathogen reduction. Participants perceived the main barriers discouraging the low-moisture food industry from adopting food-safety-enhancing technologies were: (1) budgetary priorities, (2) operation constraints, (3) technology validation, (4) consumer acceptance, and (5) maintaining desired product characteristics such as quality and sensory functionality. The findings of this needs assessment provide guidance for the food industry, academia, and government agencies about the direction of future research and the development of targeted extension programs that might help improve food safety in the low-moisture food industry.

The Use of Antimicrobial Washes to Inactivate Shiga Toxin-Producing Escherichia coli from In-Shell Pecans and Wash Water Contaminated by Different Inoculation Routes

In-shell pecans are typically harvested after falling from trees to the ground, presenting a potential route of contamination of foodborne pathogens from soil contact. In-shell pecans are often subjected to various processing or washing steps prior to being shelled. This study determined Shiga toxin-producing Escherichia coli (STEC) reductions after treatment with antimicrobial washes on direct and soil-inoculated in-shell pecans and evaluated the cross-contamination potential of the spent pecan washes after treatment. Pecans were directly and soil-inoculated with an STEC cocktail (O157:H7, O157:NM, O121, O26). Direct inoculation was achieved by spraying the STEC cocktail on the pecans. For soil-inoculation pecans, autoclaved soil was sprayed with the STEC cocktail, homogenized for 2 min, and used to coat in-shell pecans. Inoculated pecans were washed in treatments of 2% lactic acid (LA), 1,000 ppm free chlorine (sodium hypochlorite; NaClO), hot water (HW; 85 ± 2 °C), or ambient water (C [control]; 18 ± 2 °C) for 2, 5, and 10 min and diluted to enumerate STEC populations. After treatments, 100 mL of the spent wash was vacuum filtered through a 0.45-µm membrane and plated on selective agar. HW significantly reduced STEC populations from pecans with and without soil regardless of treatment time (p < 0.05), NaClO reduced STEC populations more than the ambient control wash on directly inoculated pecans, but there were no significant differences between STEC reductions from ambient water (C), LA, and NaClO treatments on soil-inoculated pecans (p > 0.05). Larger STEC populations were enumerated from ambient water wash compared to the antimicrobial washes (p < 0.05). The HW, LA, and NaClO treatments were effective at maintaining the quality of the wash water, with STEC levels being generally at or below the detection limit (<1 CFU/100 mL), while HW was the most effective at reducing STEC from in-shell pecans with and without a soil coating (>5-log CFU/mL reductions).

Demonstration of Inappropriate Validation Method for a Cracker Baking Process Using Predictive Modeling

Validation of baking processes for the inactivation of Salmonella is complicated by the combined effects of product heating and drying. The goal of this study was to quantitatively evaluate a previously disseminated approach to validating baking processes utilizing a predictive model developed using only isothermal and single-moisture inactivation data for the initially formulated dough. A simple cracker dough was formulated using flour inoculated with a five-strain cocktail of Salmonella. Side-by-side isothermal and baking experiments were performed to estimate Salmonella inactivation kinetics and to quantify survivors in a dynamic environment, respectively. Isothermal, single-moisture inactivation experiments were performed with cracker dough (water activity, aw = 0.956 ± 0.002; moisture content = 0.50 ± 0.01 dry basis) at three temperatures (56, 60, or 63°C) with ≥6 time intervals. Baking experiments were performed in a convection oven at 177°C with samples pulled every 30 s up to 360 s, with an endpoint product aw (25°C) of 0.45. The Salmonella isothermal, single-moisture inactivation kinetics in cracker dough resulted in D60°C and z-values of 4.6 min and 4.9°C, respectively; this model was then integrated over the dynamic product temperature profiles from the baking experiments. In the baking experiments, an average of 5-log reductions of Salmonella was achieved by 150 s of treatment; however, >100-log reductions were predicted by the dough-based models at that time point. This fail-dangerous overestimation of Salmonella lethality in crackers explicitly demonstrated that single-level moisture-based prediction models are inappropriate for describing inactivation in a process with both dynamic temperature and moisture, and that model-based validations must incorporate moisture/aw. Furthermore, end-users should exercise caution when utilizing unvalidated models to validate preventive control processes.

Inactivation of Desiccation-Resistant Salmonella on Apple Slices Following Treatment with ε-Polylysine, Sodium Bisulfate, or Peracetic Acid and Subsequent Dehydration

Salmonella is capable of surviving dehydration within various foods, such as dried fruit. Dried fruit, including apple slices, have been the subject of product recalls due to contamination with Salmonella. A study was conducted to determine the fate of Salmonella on apple slices, following immersion in three antimicrobial solutions (viz., ε-polylysine [epsilon-polylysine or EP], sodium bisulfate [SBS], or peracetic acid [PAA]), and subsequent hot air dehydration. Gala apples were aseptically cored and sliced into 0.4 cm thick rings, bisected, and inoculated with a five-strain composite of desiccation-resistant Salmonella, to a population of 8.28 log CFU/slice. Slices were then immersed for 2 min in various concentrations of antimicrobial solutions, including EP (0.005, 0.02, 0.05, and 0.1%), SBS (0.05, 0.1, 0.2, and 0.3%), PAA (18 or 42 ppm), or varying concentrations of PAA + EP, and then dehydrated at 60°C for 5 h. Salmonella populations in positive control samples (inoculated apple slices washed in sterile water) declined by 2.64 log after drying. In the present study, the inactivation of Salmonella, following EP and SBS treatments, increased with increasing concentrations, with maximum reductions of 3.87 and 6.20 log (with 0.1 and 0.3% of the two compounds, respectively). Based on preliminary studies, EP concentrations greater than 0.1% did not result in lower populations of Salmonella. Pretreatment washes with either 18 or 42 ppm of PAA inactivated Salmonella populations by 4.62 and 5.63 log, respectively, following desiccation. Combining PAA with up to 0.1% EP induced no greater population reductions of Salmonella than washing with PAA alone. The addition of EP to PAA solutions appeared to destabilize PAA concentrations, reducing its biocidal efficacy. These results may provide antimicrobial predrying treatment alternatives to promote the reduction of Salmonella during commercial or consumer hot air drying of apple slices.

Bootstrapping for Estimating the Conservative Kill Ratio of the Surrogate to the Pathogen for Use in Thermal Process Validation at the Industrial Scale

A surrogate is commonly used for process validations. The industry often uses the target log cycle reduction for the test (LCRTest) microorganism (surrogate) to be equal to the desired log cycle reduction for the target (LCRTarget) microorganism (pathogen). When the surrogate is too conservative with far greater resistance than the pathogen, the food may be overprocessed with quality and cost consequences. In aseptic processing, the Institute for Thermal Processing Specialists recommends using relative resistance (DTarget)/(DTest) to calculate LCRTest (product of LCRTarget and relative resistance). This method uses the mean values of DTarget and DTest and does not consider the estimating variability. We defined kill ratio (KR) as the inverse of relative resistance.The industry uses an extremely conservative KR of 1 in the validation of food processes for low-moisture foods, which ensures an adequate reduction of LCRTest, but can result in quality degradation. This study suggests an approach based on bootstrap sampling to determine conservative KR, leading to practical recommendations considering experimental and biological variability in food matrices. Previously collected thermal inactivation kinetics data of Salmonella spp. (target organism) and Enterococcus faecium (test organism) in Non-Fat Dried Milk (NFDM) and Whole Milk Powder (WMP) at 85, 90, and 95°C were used to calculate the mean KR. Bootstrapping was performed on mean inactivation rates to get a distribution of 1000 bootstrap KR values for each of the treatments. Based on minimum temperatures used in the industrial process and acceptable level of risk (e.g., 1, 5, or 10% of samples that would not achieve LCRTest), a conservative KR value can be estimated. Consistently, KR increased with temperature and KR for WMP was higher than NFDM. Food industries may use this framework based on the minimum processing temperature and acceptable level of risk for process validations to minimize quality degradation.

Rapid and sensitive detection of Salmonella in agro-Food and environmental samples: A review of advances in rapid tests and biosensors

Salmonella is as an intracellular bacterium, causing many human fatalities when the host-specific serotypes reach the host gastrointestinal tract. Nontyphoidal Salmonella are responsible for numerous foodborne outbreaks and product recalls worldwide whereas typhoidal Salmonella are responsible for Typhoid fever cases in developing countries. Yet, Salmonella-related foodborne disease outbreaks through its food and water contaminations have urged the advancement of rapid and sensitive Salmonella-detecting methods for public health protection. While conventional detection methods are time-consuming and ineffective for monitoring foodstuffs with short shelf lives, advances in microbiology, molecular biology and biosensor methods have hastened the detection. Here, the review discusses Salmonella pathogenic mechanisms and its detection technology advancements (fundamental concepts, features, implementations, efficiency, benefits, limitations and prospects). The time-efficiency of each rapid test method is discussed in relation to their limit of detections (LODs) and time required from sample enrichment to final data analysis. Importantly, the matrix effects (LODs and sample enrichments) were compared within the methods to potentially speculate Salmonella detection from environmental, clinical or food matrices using certain techniques. Although biotechnological advancements have led to various time-efficient Salmonella-detecting techniques, one should consider the usage of sophisticated equipment to run the analysis by moderately to highly trained personnel. Ultimately, a fast, accurate Salmonella screening that is readily executed by untrained personnels from various matrices, is desired for public health procurement.

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.

Inactivation of Salmonella and Shiga-toxin producing Escherichia coli on soft wheat kernels using vacuum steam pasteurization

Wheat, the raw material for flour milling, can be contaminated with enteric pathogens, leading to outbreaks linked to flour. In previous lab-scale studies, vacuum steam treatment was able to reduce Salmonella Enteritidis PT30 and Shiga-toxin producing E. coli (STEC) O121 levels on soft wheat kernels while maintaining flour quality and gluten functionality. This study used a newly designed lab-scale vacuum steam pasteurizer (VSP) to evaluate its efficacy to inactivate multiple strains of Salmonella and STEC on soft wheat by modeling the non-isothermal time-temperature history during treatment and reduction of the microbial populations. The results demonstrated that vacuum steam treatment could effectively disinfect wheat grains inoculated with enteric pathogens. In this study, Salmonella strains were less thermally resistant than STEC strains. The D75°C of Salmonella strains were 2.8 and 3.2 min, and the D75°C of STEC ranged from 3.1 to 4.6 min. E. faecium had a D75°C of 3.3 min, which indicates that it could be used as surrogate for larger scale evaluation of vacuum steam pasteurization in the future but was not conservative compared to some of the STEC strains.

Salmonella and Salmonellosis: An Update on Public Health Implications and Control Strategies

Salmonellosis is globally recognized as one of the leading causes of acute human bacterial gastroenteritis resulting from the consumption of animal-derived products, particularly those derived from the poultry and pig industry. Salmonella spp. is generally associated with self-limiting gastrointestinal symptoms, lasting between 2 and 7 days, which can vary from mild to severe. The bacteria can also spread in the bloodstream, causing sepsis and requiring effective antimicrobial therapy; however, sepsis rarely occurs. Salmonellosis control strategies are based on two fundamental aspects: (a) the reduction of prevalence levels in animals by means of health, biosecurity, or food strategies and (b) protection against infection in humans. At the food chain level, the prevention of salmonellosis requires a comprehensive approach at farm, manufacturing, distribution, and consumer levels. Proper handling of food, avoiding cross-contamination, and thorough cooking can reduce the risk and ensure the safety of food. Efforts to reduce transmission of Salmonella by food and other routes must be implemented using a One Health approach. Therefore, in this review we provide an update on Salmonella, one of the main zoonotic pathogens, emphasizing its relationship with animal and public health. We carry out a review on different topics about Salmonella and salmonellosis, with a special emphasis on epidemiology and public health, microbial behavior along the food chain, predictive microbiology principles, antimicrobial resistance, and control strategies.

Transfer of Enterococcus faecium and Salmonella enterica during simulated postharvest handling of yellow onions (Allium cepa)

Bacterial transfer during postharvest handling of fresh produce provides a mechanism for spreading pathogens, but risk factors in dry environments are poorly understood. The aim of the study was to investigate factors influencing bacterial transfer between yellow onions (Allium cepa) and polyurethane (PU) or stainless steel (SS) under dry conditions. Rifampin-resistant Enterococcus faecium NRRL B-2354 or a five-strain cocktail of Salmonella was inoculated onto onion skin or PU surfaces at high or moderate levels using peptone, onion extract, or soil water as inoculum carriers. Transfer from inoculated to uninoculated surfaces was conducted using a texture analyzer to control force, time, and number of contacts. Transfer rates (ratio of recipient surface to donor surface populations) of E. faecium (4-5%) were significantly higher than those of Salmonella (0.5-0.6%) at the high (7 log CFU/cm2) but not moderate (5 log CFU/cm2) inoculum levels. Significantly higher populations of E. faecium transferred from onion to PU than from PU to onion. The transfer rates of E. faecium were impacted by inoculum carrier (61% [onion extract], 1.6% [peptone], and 0.31% [soil]) but not by inoculation level or recipient surface (PU versus SS). Bacterial transfer during dry onion handling is significantly dependent on bacterial species, inoculation levels, inoculum carrier, and transfer direction.

Inactivation kinetics of a surrogate yield conservative predictions of foodborne pathogen reductions from low water activity foods of varying size and composition during low-temperature steam processing

There is a growing interest in using models to predict foodborne pathogen inactivation as a way to validate or verify preventive controls. Unlike liquid foods, solid, low water activity foods (LWAF) are heterogenous in composition and structure and do not transfer heat uniformly. Using models constructed from one food to predict pathogen inactivation on another LWAF is complex and may not always be possible, even if the foods have similar composition. Using models constructed from inactivation kinetics of three foodborne pathogens and a surrogate from vacuum-steam-pasteurized (72 and 82 °C) whole macadamia nuts and dried apricot halves, 3-log reductions were predicted for the same pathogens and foods of reduced size. Model fits (First-order, Weibull, and Gompertz) were significantly impacted by the food type regardless of particle size. Despite the foods being identical in composition with particle size as the only altered characteristic, best-fit models accurately predicted the 3-log reductions only 50% of the time, but the surrogate inactivation models provided conservative predictions for pathogen reductions, highlighting that a surrogate's model may be a suitable tool for predicting pathogen reduction on LWAFs.