To study the factors and mechanisms involved in microorganisms' death or resistance to temperature in low-water-activity environments, a previous work dealt with the viability of dried microorganisms immobilized in thin-layer on glass beads. This work is intended to check the efficiency of a rapid heating-cooling treatment to destroy microorganisms that were dried after mixing with wheat flour or skim milk. The thermoresistance of the yeast Saccharomyces cerevisiae and the bacterium Lactobacillus plantarum were studied. Heat stress was applied at two temperatures (150 or 200 degrees C) for treatments of one of four durations (5, 10, 20, or 30 s) and at seven levels of initial water activity (a(w)) in the range 0.10 to 0.70. This new treatment achieved a microbial destruction of eight log reductions. A specific initial water activity was defined for each strain at which it was most resistant to heat treatments. On wheat flour, this initial a(w) value was in the range 0.30-0.50, with maximal viability value at a(w)=0.35 for L. plantarum, whatever the temperature studied, and 0.40 for S. cerevisiae. For skim milk, a variation in microbial viability was observed, with optimal resistance in the range 0.30-0.50 for S. cerevisiae and 0.20-0.50 for L. plantarum, with minimal destruction at a(w)=0.30 whatever the heating temperature is.

The occurrence of disease outbreaks involving low‐water‐activity (aw) foods has gained increased prominence due in part to the fact that reducing free water in these foods is normally a measure that controls the growth and multiplication of pathogenic microorganisms. Salmonella, one of the main bacteria involved in these outbreaks, represents a major public health problem worldwide and in Brazil, which highlights the importance of good manufacturing and handling practices for food quality. The virulence of this pathogen, associated with its high ability to persist in the environment, makes Salmonella one of the main challenges for the food industry. The objectives of this article are to present the general characteristics, virulence, thermoresistance, control, and relevance of Salmonella in foodborne diseases, and describe the so‐called low‐water‐activity foods and the salmonellosis outbreaks involving them.

This is a retrospective study describing data on the microbiological conditions of food and water obtained from analysis reports issued by the Central Laboratory of the Federal District (LACEN-DF), and information on foodborne disease outbreaks investigated by the Office of Water and Food Borne Diseases of the Federal District (NATHA), Brazil, between 2000 and 2010. A total of 4576 analysis reports were evaluated, from which 92.9% of monitoring samples and 7.1% of samples suspected to be involved in outbreaks. Of the total number of samples, 630 did not comply with Brazilian legislation (rejected). Ready-to-eat food, milk/dairy products, water, spices/seasonings, and ice cream/sorbets had the highest rejection rates among the monitoring samples (18.9–11%), with the first two groups having the highest rates among the outbreak samples (23.5 and 21.7%). Minas cheese showed to be the food with the highest rejection rate among the samples analyzed by the LACEN-DF. About 9% of the food samples were rejected due to thermotolerant coliforms and/or coagulase-positive staphylococci, and 10.5% of the water samples were rejected due to Pseudomona aeruginosa. Ready-to-eat food were the main foods involved in the foodborne disease outbreaks investigated by NATHA (51.3% of the 117 outbreaks with the food identified) and Bacillus cereus the most identified etiologic agent (41.2% of the 80 outbreaks with the agent identified). This study indicated that microbiological surveillance programs should focus on ready-to-eat food to prevent the occurrence of foodborne disease outbreaks in the region.

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.

Recent research has shown exponentially increased thermal resistance of pathogenic bacteria at a reduced water activity (aw) in thermal treatments. However, information on aw change as affected by food components at high temperatures is limited. The objective of this project was to quantify the influence of major food components on aw changes in low-moisture foods at elevated temperatures. Corn starch, soy protein, coconut, and cheddar cheese powders were selected as high-carbohydrate, high-protein, high-fat, and intermediate products. Vacuum dried powders were equilibrated in the jars containing saturated salt solutions to different aw from 0.11 to 0.84 at 25 °C. The aw of food powders were measured from 25 to 80 °C in hermetically sealed test cells using hight-temperature humidity sensors. For a given initial aw, high-carbohydrate product had more considerable aw increase than high-protein, intermediate, and high-fat foods with increasing temperature. The net isosteric heat of sorption increased from high-fat, intermediate, high-protein, to high-carbohydrate food at same moisture content. These relationships support findings in the literature that bacterial cells are more easily inactivated in high-carbohydrate and high-protein products than in high-fat foods. Understanding the correlation between food components and aw change at elevated temperatures helps predict the thermal resistance of bacteria in low-moisture foods.

Sub‐Saharan Africa (SSA) faces twin challenges of water stress and food insecurity – challenges that are already pressing and are projected to grow. Sub‐Saharan Africa comprises 43 % arid and semi‐arid area, which is projected to increase due to climate change. Small‐scale, rainfed agriculture is the main livelihood source in arid and semi‐arid areas of SSA. Because rainfed agriculture constitutes more than 95 % of agricultural land use, water scarcity is a major limitation to production. Crop production, specifically staple cereal crop production, will have to adapt to water scarcity and improved water productivity (output per water input) to meet food requirements. We propose inclusion and promotion of drought‐tolerant cereal crops in arid and semi‐arid agro‐ecological zones of SSA where water scarcity is a major limitation to cereal production. Sorghum uniquely fits production in such regions, due to high and stable water‐use efficiency, drought and heat tolerance, high germplasm variability, comparative nutritional value and existing food value chain in SSA. However, sorghum is socio‐economically and geographically underutilized in parts of SSA. Sorghum inclusion and/or promotion in arid and semi‐arid areas of SSA, especially among subsistence farmers, will improve water productivity and food security.

Water contamination by pathogenic bacteria is a global public health problem. Contamination of surface water utilized to irrigate food products, or for human consumption, causes outbreaks of foodborne and waterborne disease. Of these, those caused by diarrheagenic Escherichia coli (DEC) strains present substantial morbidity and mortality. The aim of this study was, therefore, to investigate the microbiological quality of surface water and the presence of DEC strains in different water bodies. A total of 472 water samples were collected from irrigation canal, dam, river, and dike water bodies from January through December 2015 in Sinaloa, a State located in Northwestern Mexico. Our studies demonstrated that 47.0% (222/472) of samples contained thermotolerant coliforms above permissive levels whereas E. coli strains were isolated from 43.6% (206/472). Among these E. coli isolates, DEC strains were identified in 14% (29/206) of samples including in irrigation canal (26/29) and river water (3/29) collected from the northern (83%) and central area (17%). Isolated DEC strains were classified as enteroaggregative E. coli (EAEC) 34.4% (10/29), enteropathogenic E. coli (EPEC) 31.0% (9/29), diffuse adherent E. coli (DAEC) 27.5% (8/29), and enterotoxigenic E. coli (ETEC) 6.8% (2/29). Moreover, 90% of isolated DEC strains exhibited resistance to at least one commonly prescribed antibiotic in Mexico whereas 17% were multi-drug resistant. In conclusion, the presence of DEC strains in surface water represents a potential source for human infection, and thus routine monitoring of DEC in surface water and other indirect affected areas should be considered at northwestern Mexico.

Limited food availability and altered thermal regimes (e.g. cold water releases from dams) are two common stressors threatening the persistence of fishes inhabiting anthropogenically disturbed freshwater systems. Yet, the combined effects of these stressors remain poorly characterised. To remedy this, we examined the isolated and combined effects of low temperature exposure and food restriction on specific growth rate (SGR, % body mass/day) and upper thermal tolerance (critical thermal maxima, CTMax) in larval white sturgeon (Acipenser transmontanus [Acipenseridae], 32 days post‐hatch, body mass: 0.25 ± 0.03 g, mean ± standard deviation). A 2 × 2 factorial design was implemented with fish exposed to one of two ecologically‐relevant acclimation temperatures (cold exposure: 11°C or a control temperature: 18°C) and one of two food restriction treatments designed to emulate observed declines in food availability (100% or 40% optimal feed rate) for 6 weeks (N: 3 replicate tanks/treatment, 50 fish/tank). Specific growth rate was affected by both low temperature exposure and food restriction in isolation; low temperature exposure reduced SGR by 56.5% and food restriction reduced SGR by 30.6%. Simultaneous exposure to low temperature and food restriction resulted in a greater but less than additive reduction in SGR (80.6%), indicating that the stressors interacted antagonistically. Critical thermal maxima were c. 2°C higher in 18°C‐acclimated fish (CTMax = 30.7 ± 0.4°C, mean ± standard error) compared to 11°C‐acclimated fish (CTMax = 28.6 ± 0.2°C, mean ± standard error); however, CTMax was independent of food restriction in both 11°C‐ and 18°C‐acclimated fish. These data highlight the unpredictability of stressor interactions and may guide holistic conservation strategies, which target co‐occurring stressors in freshwater habitats.

A predictive model was made for the logarithm of the thermal decimal reduction time (logD) of Salmonella enterica (D = time to 90% reduction by inactivation). The model was fitted with multiple linear regression from 521 logD-values reported in literature for laboratory media and foods highly varying in water activity and pH. The single regression model with temperature as the only variable had a high residual standard error (RSE) of 0.883 logD and no predictive value (fraction of variance explained (R²) < 0.001). Adding water activity, sugar content and pH as predictors resulted in a model with a lower RSE of 0.458 logD and an adjusted R² of 0.73. The model was validated by comparing 985 predicted with observed logD for S. enterica from other publications. The model was subsequently validated with 1498 published logD-values for inactivation of vegetative cells of nine other pathogenic bacteria genera (mainly Listeria monocytogenes, Escherichia coli, Clostridium perfringens, Cronobacter spp., Staphylococcus aureus, Yersinia enterocolitica) in or on a variety of laboratory media, meat, fish, dairy, nuts, fruits and vegetables. Regression analyses for validation with the 985 logD of S. enterica and 2483 logD of all genera show deviations from the expected slope of 1 (both 0.81) and the expected intercept of 0 (0.04 and 0.19 logD respectively). However, only 0.7% and 2% respectively of the new logD (expected: 0.5%) were observed above the 99% prediction interval of the original S. enterica model based on 521 logD. The findings suggest that i) the variability of thermal resistance of strains within species is larger than between genera and species; ii) one generic predictive model, also accounting for variability, suffices for designing the thermal inactivation of a variety of vegetative pathogenic bacteria in many food types.