Search

The survival of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes was determined on almonds pistachios held at typical storage temperatures. Almond kernels and inshell pistachios were inoculated with four- to six-strain cocktails of nalidixic acid-resistant Salmonella, E. coli O157:H7, or L. monocytogenes at 6 log CFU/g and then dried for After drying, inoculated nuts were stored at -19, 4, or 24°C for up to 12 months. During the initial drying period after inoculation, levels of all pathogens declined by 1 to 2 log CFU/g on both almonds and pistachios. During storage, moisture content (4.8%) and water activity (0.4) of the almonds and pistachios were consistent at - 19°C; increased slowly to 6% and 0.6, respectively, at 4°C; and fluctuated from 4 to 5% and 0.3 to 0.5 at 24°C, respectively. Every 1 or 2 months, levels of each pathogen were enumerated by plating; samples were enriched when levels fell below the limit of detection. No reduction in population level was observed at -19 or 4°C for either pathogen, with the exception of E. coli O157:H7-inoculated almon stored at 4°C (decline of 0.09 log CFU/g/month). At 24°C, initial rates of decline were 0.20, 0.60, and 0.71 log CFU/g/month almonds and 0.15, 0.35, and 0.86 log CFU/g/month on pistachios for Salmonella, E. coli O157:H7, and L. monocytogen respectively, but distinct tailing of the survival curves was noted for both E. coli O157:H7 and L. monocytogenes. [ABSTRACT FROM AUTHOR]

Abstract: Salmonellosis outbreaks from consumption of raw almonds in 2001 and 2004 led to regulations that require mandatory treatment of almonds sold in North America to give a minimum 4-log reduction of Salmonella. This study aims to: 1) assess the risk of salmonellosis associated with almond consumption in North America, with current treatments in effect; 2) determine the resilience of the current production system to increases in prevalence or concentration of Salmonella on almonds; 3) assess the impact of treating less than 100% of the crop; and 4) investigate conditions that could explain the number of cases associated with the 2001 outbreak. Risk was assessed using a Monte Carlo simulation, based on an established dose–response relationship. Data for almond amounts sold, Salmonella prevalence and concentration on almonds, storage time and temperature at different handling steps, population reductions during storage at various temperatures and with different treatments, and consumer handling were based on data from published sources and almond industry or academic expert opinion. What-if scenarios were evaluated for Salmonella prevalence varying from 1 to 65%, concentrations of Salmonella varying from 1 to 120MPN/100g, and portions of untreated crop varying from 0 to 10%. The estimated incidence of salmonellosis in North America from almonds as currently treated is on average 0.008 cases per billion servings (with an estimated 6.6billion servings consumed annually). Increases in Salmonella prevalence to 25%, mean concentrations above 25MPN/100g, or leaving 0.05% of the crop untreated all resulted in an arithmetic mean risk greater than 1case/year (with geometric means remaining below 1case/year for all variables). Assuming 4000kg at a prevalence of 65% (observed in recalled lots) and an average concentration of 120MPN/100g in raw almonds (back calculated from levels in recalled almonds) predicted over the 2800 cases estimated for the 2001 outbreak. Applying a 4-log reduction to these almonds reduced the average number of predicted cases to less than a single case. The current regulation is effective in maintaining the risk of salmonellosis from consumption of almonds below an arithmetic mean of 1case/year, although significant increases in either prevalence or concentration, or small increases in proportion of untreated almonds would frequently lead to exceeding this threshold. [Copyright &y& Elsevier]

Pathogens occurring in particulate foods may be unevenly distributed, which may impact interpretation of most-probable-number (MPN) values. The MPN analysis of Salmonella in naturally contaminated raw almonds was conducted using two sample preparation methods. Raw almond kernels (3,698 samples) and inshell almonds (455 samples) were collected from almond processors throughout California during the 2006 and 2007 harvests, and l00-g samples were enriched for Salmonella. The prevalence of Salmonella on kernels and inshell almonds was 1.6 and 0.9%, respectively, in 2006, and 0.83 and 2.2%, respectively, in 2007. Almond kernel samples from 2006 were further enriched for Salmonella, and levels of the organism were determined for positive samples by three-tube MPN analysis (25 g, 2.5 g, 0.25 g). Almonds were either divided into subsamples prior to blending and enrichment (method A), or samples were blended in enrichment broth prior to preparation of subsamples (method B). Salmonella was not isolated (<1.2 MPN/100 g) upon retesting of 19 of 31 (method A) or 23 of 29 (method B) positive samples. When detected, levels were 1.4 to 15.5 MPN/100 g (average 2.3 MPN/100 g) or 1.4 to 18.3 MPN/100 g (average 2.1 MPN/100 g) using methods A or B, respectively. A total of 23 different Salmonella serovars were identified from the original almond samples. Salmonella Muenchen was the most frequently isolated serovar (15%) from the 53 Salmonella-positive samples, followed by Newport (12%), Enteritidis (10%), and Typhimurium (8%). No correlation was found between presence of Salmonella and E. coli levels, aerobic plate counts, or counts of yeasts or molds. [ABSTRACT FROM AUTHOR]

Large volumes of fine particulate matter or “dust” (soil, hulls, and shells) generated when hulls and shells are removed from almond kernels complicate cleaning and sanitation procedures in the huller-sheller (HS) environment. This study evaluated the efficacy of 3 aqueous quaternary ammonium sanitizers (AQuats) and an isopropyl alcohol-based quaternary ammonium sanitizer (IPAQuat) for reducing Salmonella in dust collected from 2 HS facilities. Dust (1 g) was thoroughly mixed with 1 to 2 mL of inoculum (1 to 5 log CFU/g) before adding 1 to 7 mL of water, an AQuat (200 or 1000 ppm), or IPAQuat (200 ppm, 58.6% isopropyl alcohol) and incubated at 15 and 30 °C for up to 21 d. At either 15 or 30 °C increases in Salmonella populations in the dust were not significantly different following addition of either water or AQuats. No significant differences were observed upon water or AQuat addition, either among the 3 AQuats tested, the concentration or volume of AQuat, or the initial level of Salmonella. When IPAQuat was added to dust inoculated at 1 to 7 log CFU/g, Salmonella levels were reduced to less than 1.3 log CFU/g after treatment and after incubation at 30 °C for 48 h. IPAQuat was an effective sanitizer compared to the AQuats, even in the presence of high levels of organic material. Recent large-scale outbreaks of salmonellosis with low-moisture foods have increased concerns regarding their safety. Little research or guidance is available on appropriate cleaning and sanitation programs for these food types. This research is focused on an evaluation of sanitation options for low-moisture foods, in particular almonds. The information should be applicable and useful to the nut industry and to other low-moisture foods. Practical Application: Recent large-scale outbreaks of salmonellosis with low-moisture foods have increased concerns regarding their safety. Little research or guidance is available on appropriate cleaning and sanitation programs for these food types. This research is focused on an evaluation of sanitation options for low-moisture foods, in particular almonds. The information should be applicable and useful to the nut industry and to other low-moisture foods. [ABSTRACT FROM AUTHOR]

The ability of Salmonella,to migrate from an external aqueous environment through the almond hull and shell, and to colonize the kernel, was evaluated in two ways. First, the outer surface of shell halves from five varieties of almonds that differed in shell hardness were placed in contact with a suspension of Salmonella enterica serovar Enteritidis phage type 30 for 24 h at 24°C. Salmonella Enteritidis was isolated from the inside of these almond shells in 46 and 100% of the samples, by direct swabbing of the inner surface of the shell and by enrichment from the swab, respectively. These findings suggested that hardness of the shell is not a significant factor in the migration of the pathogen through that tissue. In addition, both motile and nonmotile strains of S. enterica serovar Typhimurium migrated through the almond shells to the same extent under the conditions of this assay, indicating that bacterial migration through the wet shell may be a passive process. Second, whole almonds (intact hull, shell, and kernel) were soaked for 24 to 72 h at 24°C in a suspension of Salmonella Enteritidis phage type 30 labeled with the green fluorescent protein. Green fluorescent protein-labeled Salmonella cells were observed on the outer and inner surfaces of both the almond hull and shell, and on the kernel, by confocal laser scanning microscopy. Our data provide direct evidence that wet conditions allow for Salmonella migration through the hull and shell and onto the almond kernel, thus providing a means by which almond kernels may become contaminated in the field. [ABSTRACT FROM AUTHOR]

Data on the prevalence and populations of pathogens in individual foods are critical to the development of product-specific quantitative microbial risk assessments. An outbreak of salmonellosis associated with the consumption of raw almonds in 2000 to 2001 provided an opportunity to evaluate the levels of Salmonella in the recalled product. Duplicate 100-g samples from each of fifty 22.7-kg boxes of recalled almonds were enriched by one of two methods. Salmonella was isolated by at least one method from 42 boxes (84% positive). The levels of Salmonella determined by a three-tube most-probable-number (MPN) method were 8.5 ± 1.3 MPN/100 g. In a subsequent study, raw almonds that arrived at almond processors were sampled from 2001 through 2005 to determine the overall prevalence and levels of Salmonella and to characterize the Salmonella isolates obtained. Aerobic plate counts, coliform counts, and MPN levels of Escherichia coli were also determined on positive samples. An isolation frequency for Salmonella of 81 (0.87% ± 0.2%) of 9,274 samples tested (100 g) was determined for raw almonds sampled from throughout California over the 5-year period. Salmonella was not isolated upon retesting in 59 of 65 positive samples. When detected, levels were 1.2 to 2.9 MPN/100 g. Of the 81 total isolates, 35 different serotypes of Salmonella were represented. Aerobic plate counts, coliform counts, and E. coli levels did not correlate with the presence of Salmonella. [ABSTRACT FROM AUTHOR]

To evaluate die survival of Salmonella on raw almond surfaces, whole almond kernels were inoculated with Salmonella Enteritidis phage type (PT) 30 collected from a 24-h broth culture or by scraping cells from an agar lawn. Kernels inoculated with lawn-collected cells to 8, 5, 3, and 1 log CFU per almond after a 24-h drying period were stored for 161 days at 23 ± 3°C. Calculated rates of reduction were similar for the four inoculum levels (0.22. 0.28, 0.29, and 0.22 log CFU/month, respectively). Kernels inoculated to 7.1 or 8.0 log CFU per almond after drying were stored for 171 or 550 days, respectively, at selected temperatures, including -20 ± 2°C, 4 ± 2°C, 23 ± 3°C, and 35 ± 2°C. No significant reductions of Salmonella were observed during storage at -20 and 4°C over 550 days. At 35°C, a biphasic survival curve was observed, with calculated reductions of 1.1 log CFU/month from days 0 to 59 and no significant reduction from days 59 to 171. At 23°C. reductions of 0.18 and 0.30 log CFU/month were calculated fur 171 and 550 days of storage, respectively. When combined with data from the study of inoculum levels, an overall average calculated reduction at 23°C was 0.25 ± 0.05 log CFU/month. Significantly greater reductions were observed during the 24-h drying period when broth-collected cells were used as the inoculum, suggesting that cells collected from agar lawns were more resistant to drying. However, after initial drying, the rates of reduction at 23°C did not differ significantly between the inoculum preparation methods. Salmonella Enteritidis PT 30 survives for long periods on almond kernels under a variety of common storage conditions. [ABSTRACT FROM AUTHOR]

Recent outbreaks of salmonellosis associated with raw almonds have raised awareness of this food as a vector for foodborne illness. We performed a quantitative assessment of the risk of contracting salmonellosis from consumption of raw almonds, accounting for factors that become important after almonds reach the processor. We estimated the risk associated with the consumption of raw almonds and the risk reduction associated with almonds treated with a theoretical 5-log reduction process or treated with propylene oxide using a standard commercial process. Probability distributions were chosen to describe the chance of almond contamination and the effects of storage time, storage temperature, and processing from currently available data. A β-Poisson model for the dose-response relationship for Salmonella was obtained from published literature. The simulation estimated a 78% chance of one or more cases of salmonellosis per year from consumption of raw almonds. The application of a commercial propylene oxide treatment reduced this risk to 0.01%. Hypothetical 5-log reduction treatments with different standard deviations (±1, ±0.5, ±0.1, and ±0) reduced the predicted yearly risk of salmonellosis to 0.69, 0.35, 0.30, and 0.21%, respectively. These results suggest that the risk of one or more U.S. cases of salmonellosis per year from consumption of raw almonds can be reduced from 78% to less than 1% by using a process achieving a 5-log reduction in Salmonella with a process standard deviation as large as 1 log unit or by using a commercial propylene oxide treatment. [ABSTRACT FROM AUTHOR]