Presence and growth of Bacillus cereus in dehydrated potato flakes and hot-held, ready-to-eat potato products purchased in New Zealand

Potato products prepared from dehydrated potato flakes have been implicated in foodborne illness incidents involving Bacillus cereus intoxications. B. cereus can survive as spores in potato flakes and can germinate and multiply in the rehydrated product. This study assessed the frequency and concentration of B. cereus in dehydrated potato flakes and hot-held, ready-to-eat mashed potato products. Of 50 packets of potato flakes tested, eight contained greater than 100 CFU/g B. cereus (maximum 370 CFU/g). The temperature of the potato portion of 44 hot-held food products was measured immediately after purchase, and 86% were below the safe hot-holding temperature of 60 degrees C. The potato portions were subsequently tested for B. cereus. Only two of the potato portions contained B. cereus at greater than 100 CFU/g, a potato-topped pastry (1000 CFU/g) and a container of potato and gravy (120 CFU/g). To assess multiplication of B. cereus in this food, we held rehydrated potato flakes with naturally occurring B. cereus at 37, 42, and 50 degrees C and tested them over 6 h. By 6 h, the number of B. cereus in potato stored at 37 degrees C had exceeded 10(3) CFU/g, was greater than 10(4) CFU/g at 50 degrees C, and was close to 10(6) CFU/g at 42 degrees C. Growth data were compared to predictions from the U.S. Department of Agriculture Pathogen Modeling Program (PMP 7.0). The PMP predictions were found to simulate the measured growth better at 42 degrees C than at 37 degrees C. Hot-held potato products should be safe for consumption if held at 60 degrees C or above or discarded within 2 h.     

Prevalence and characterisation of Bacillus cereus in vacuum packed potato puree

Refrigerated processed foods of extended durability (REPFED) potato puree was analysed for Bacillus cereus contamination along the production line and during the product shelf‐life. Isolated B. cereus strains were tested for their psychrotrophic character and the ability to produce enterotoxins. Bacillus cereus contamination during four subsequent productions was in the range of 2.3–4.0 log cfu g^?1. Productions five and six were significantly less contaminated with B. cereus (≤1 log cfu g ^?1). All B. cereus isolates from the first four productions were able to grow at 7 ° and 10 °C, whereas the majority of the isolates from productions five and six did not. No B. cereus isolates grew at 4 °C. randomly amplified polymorphic DNA (RAPD) fingerprinting showed that the most of B. cereus contamination originated from one source. In total, 30.4% of isolates expressed enterotoxic character. The present study points out the necessity to prevent an ‘in house’ colonisation and contamination during food processing in order to accomplish the safety of REPFED throughout the shelf‐life. It also indicates the most critical steps in the production line of ready‐to‐eat potato puree and impact of failures regarding the food safety. The data provided can be used for risk assessment studies regarding B. cereus in REPFED.     

Presence of Bacillus cereus in street foods in Gaborone, Botswana

The purpose of this study was to evaluate the microbiological safety and quality of street foods sold in Gaborone, Botswana. A total of 148 point-of-sale composite street food samples were bought and analyzed between June 2001 and May 2002. The analysis focused on the level of contamination of various street foods with Bacillus cereus. The B. cereus (vegetative and spores), total spore, and total viable counts were determined on all the samples. Also B. cereus isolates from 444 individual point-of-sale food samples were characterized with respect to their biochemical profiles and enterotoxigenic properties. The B. cereus contamination rate for point-of-sale foods was 65%. The B. cereus counts ranged from not detectable to levels as high as 9.1 log CFU/g. Despite the high rate of contamination of some samples, generally, most samples had B. cereus counts of less than 4 log CFU/g; hence, they were of acceptable microbiological quality. Bacillus diarrheal enterotoxin was detected from 52 isolates from individual portions of meals using the B. cereus enterotoxin reversed passive latex agglutination kit. Results of the assay revealed that 59.6% of the B. cereus isolates were enterotoxigenic. Most of the enterotoxigenic isolates were obtained from vegetable samples.     

Detection of Bacillus cereus on selected retail chicken products

Samples from five chicken meat products, obtained at retail stores, were evaluated for the presence of Bacillus cereus. The products tested were as follows: breaded, fully cooked, frozen nuggets (NUGGETS); breaded, fully cooked, frozen tenders (TENDERS); fully cooked, frozen, white-meat fajita-style strips (STRIPS); raw, refrigerated, boneless, skinless, marinated breast fillets (FILLETS); and raw, refrigerated, cut-up, tray-pack bone-in parts (PARTS), either split breasts or thighs. Four packages of each item were obtained on three different days (n = 60). Frozen and refrigerated products were held overnight in their respective environments as appropriate; then packages were opened aseptically, and a total of 25 g of tissue was excised from multiple pieces within a package. The 25-g samples were enriched in 225 ml of Trypticase soy-polymixin broth for 18 to 24 h at 30 degrees C and then plated on mannitol-egg yolk-polymixin agar and incubated for 18 to 24 h at 30 degrees C. Colonies characteristic of B. cereus were chosen and replated for isolation on mannitol-egg yolk-polymixin agar. Suspect colonies were confirmed as Bacillus spp. by Gram stain, hemolysis on blood agar, and a biochemical test strip. Isolates were further confirmed as B. cereus using Bacteriological Analytical Manual procedures, including tests for motility, rhizoid growth, hemolysis, and protein toxin crystal production. B. cereus was detected in 27 of 60 total samples. By product, the prevalence levels were as follows: NUGGETS, 11 of 12 positive; TENDERS, 8 of 12 positive; STRIPS, 6 of 12 positive; FILLETS, 0 of 12 positive; and PARTS, 2 of 12 positive. Isolates were tested by PCR for presence of the toxin-encoding genes bceT, nheABC, hblACD, and cytK. Results indicate that B. cereus organisms were present on four of the five retail poultry products tested in this study, with the highest rates reported for the three fully cooked items, especially the two breaded products. All strains isolated contained the gene(s) for at least one of the toxins, although none of the strains contained the cytK gene.     

Prevalence and characterization of toxigenic Bacillus cereus group isolated from low-moisture food products

Food Science and Biotechnology - The present study was conducted to determine the occurrence of B. cereus group members in low-moisture food products by phenotypic and genetic assessment and to...     

Aroma of dehydrated pear products

Pear purees and cubes were dehydrated with sugars (sucrose and trehalose) addition. Freeze drying and foam-mat drying were used. Manual solid-phase microextraction (SPME) coupled with gas chromatography (GC-flame ionization detector (FID) and GC-MS) was applied to determine the changes in retention of aroma compounds in dehydrated pear purees and cubes. The best retention of aroma compounds in dehydrated pear purees was noticed in the case when freeze drying and trehalose addition were combined. In dehydrated pear cubes, previously dipped in trehalose solution, the highest aroma retention was also determined. This study showed possible application of trehalose as potentially beneficial food ingredient, with the aim to improve the quality of dehydrated fruit products, especially their aroma, and to produce superior dried fruit products or ingredients, which are widely used in food formulation.     

Bacillus cereus in free-stall bedding

To increase the understanding of how different factors affect the bacterial growth in deep sawdust beds for dairy cattle, the microbiological status of Bacillus cereus and coliforms in deep sawdust-bedded free stalls was investigated over two 14-d periods on one farm. High counts of B. cereus and coliforms were found in the entire beds. On average, 4.1 log₁₀B. cereus spores, 5.5 log₁₀B. cereus, and 6.7 log₁₀ coliforms per gram of bedding could be found in the upper layers of the sawdust likely to be in contact with the cows’ udders. The highest counts of B. cereus spores, B. cereus, and coliforms were found in the bedding before fresh bedding was added, and the lowest immediately afterwards. Different factors of importance for the growth of B. cereus in the bedding material were explored in laboratory tests. These were found to be the type of bedding, pH, and the type and availability of nutrients. Alternative bedding material such as peat and mixtures of peat and sawdust inhibited the bacterial growth of B. cereus. The extent of growth of B. cereus in the sawdust was increased in a dose-dependent manner by the availability of feces. Urine added to different bedding material raised the pH and also led to bacterial growth of B. cereus in the peat. In sawdust, a dry matter content greater than 70% was needed to lower the water activity to 0.95, which is needed to inhibit the growth of B. cereus. In an attempt to reduce the bacterial growth of B. cereus and coliforms in deep sawdust beds on the farm, the effect of giving bedding daily or a full replacement of the beds was studied. The spore count of B. cereus in the back part of the free stalls before fresh bedding was added was 0.9 log units lower in stalls given daily bedding than in stalls given bedding twice weekly. No effect on coliform counts was found. Replacement of the entire sawdust bedding had an effect for a short period, but by 1 to 2 mo after replacement, the counts of B. cereus spores in the beds had increased about 2 log units and were as high as they were before bed replacement. Therefore, free-stall management could, to a limited extent, reduce the content of B. cereus spores in the beds by daily bedding and entire bed replacement.     

Prevalence of Bacillus cereus in dried milk products used by Chilean School Feeding Program

The prevalence of Bacillus cereus, in a total of 381 samples of dried milk products (milk with rice, milk substitute, milk powder, milk-cereal-rice, pudding milk, flan, and mousse) used by the Chilean School Feeding Program, was investigated. The potential of 94 selected isolates of B. cereus to produce diarrhoeal enterotoxin (by the BCET-RPLA test) in BHI culture, as well as the ability of enterotoxigenic-strains to grow at psychrotrophic temperatures were also verified. B. cereus was found in 175 of 381 of the samples analysed (45.9%), reaching levels from 3.0 to 10(4) spores g(-1). As expected, the higher prevalence and counts were observed in those products that contained whole rice, cereals and pulses extruded, and food additives. Of the 94 isolates of B. cereus tested for diarrhoeal enterotoxin production, 28 (29.8%) were positive, and none of these was able to grow at < or = 7 degrees C. The prevalence of B. cereus in dried milk products analysed was fairly high, although it was present in low number. However, as they were composed to a large extent of enterotoxigenic mesophilic strains, the potential risk for the safety of reconstituted products held at improper temperature should not be neglected.     

Sterilization of dehydrated potato granules with propylene oxide

Summary Results were provided for propylene oxide cold sterilization of dehydrated mashed potato granules that contained 7% moisture and 0.044% chloride. Treatment with an optimum concentration of 0.1% w/w sterilant for 6 days at 22° C gave a bacterial count reduction from 3.4 × 10⁵ to less than 5 × 10³, a low glycol residue of 29 ppm, and 12 ppm of chlorohydrin, with the 1-chloro-2-propanol isomer constituting 94% of the total. This indicated that, in spite of the granule pH of 5.62, nucleophilic attack in dehydrated granules involves nonprotonated propylene oxide. Based on NMR analysis, evidence was given that such sterilization does not result in detectable etherification of starch, even though its content of 83% on a dry basis places it as the major potentially reactive constituent.

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Sterilisation von getrocknetem Kartoffelpulver mit Propylenoxyd

Zusammenfassung Propylenoxyd wurde zur Kaltsterilisation von Kartoffelpulver mit 7% Feuchtigkeit und einen Chloridgehalt von 0,044% verwendet. Bei einem optimalen Gehalt des Sterilisationsmittels von 0,1% wurde die Behandlung während 6 Tagen bei 22° C durchgeführt, was eine Reduktion des Keimgehaltes von 3,4 × 10⁵ auf weniger als 5 × 10³ bewirkte. Der Glykolrückstand war mit 29 ppm niedrig, ebenfalls das Chlorohydrin mit 12 ppm, wobei das 1-Chlor-2-propanol 94% der beiden Isomere ausmachte. Dies ergab einen Hinweis, daß im Pulver trotz des pH-Wertes 5,62 nicht protoniertes Propylenoxyd als Acceptor nucleophiler Übergänge dient. Aufgrund von NMR-Untersuchungen wurde gefunden, daß die obengenannte Behandlung keine nachweisbare Ätherbildung der Stärke bewirkte, obwohl ihr Gehalt 83% des Trockengewichtes beträgt und damit als potentieller Hauptreaktionspartner anzusehen wäre.

     

蜡样芽胞杆菌生长特性及大蒜精油对其抑菌活性的研究

主要研究了37℃条件下3种蜡样芽胞杆菌在营养肉汤中的生长状况,建立了37℃下蜡样芽胞杆菌在营养肉汤中的Boltzmann牛长模犁,3条牛长曲线相关系数鼯均大于0．97;检测了不同培养时间蜡样芽胞杆菌的产芽胞情况,结果表明1号菌株和14号菌株较早产芽胞,培养相同时间,产芽胞数：1号菌株,4号菌株〉标准菌株;采用牛沣杯法和平板计数法研究了大蒜精油对蜡样芽胞杆菌的抑制效果,结果表明浓度为lO。的人蒜精油对3种蜡样芽胞杆菌都有很好的抑制效果,3种菌株中l号菌株最难抑制。     

Emetic toxin-producing strains of Bacillus cereus show distinct characteristics within the Bacillus cereus group

One hundred representative strains of Bacillus cereus were selected from a total collection of 372 B. cereus strains using two typing methods (RAPD and FT-IR) to investigate if emetic toxin-producing hazardous B. cereus strains possess characteristic growth and heat resistance profiles. The strains were classified into three groups: emetic toxin (cereulide)-producing strains (n=17), strains connected to diarrheal foodborne outbreaks (n=40) and food-environment strains (n=43), these latter not producing the emetic toxin. Our study revealed a shift in growth limits towards higher temperatures for the emetic strains, regardless of their origin. None of the emetic toxin-producing strains were able to grow below 10 degrees Celsius. In contrast, 11% (9 food-environment strains) out of the 83 non-emetic toxin-producing strains were able to grow at 4 degrees Celsius and 49% at 7 degrees Celsius (28 diarrheal and 13 food-environment strains). non-emetic toxin-producing strains. All emetic toxin-producing strains were able to grow at 48 degrees Celsius, but only 39% (16 diarrheal and 16 food-environment strains) of the non-emetic toxin-producing strains grew at this temperature. Spores from the emetic toxin-producing strains showed, on average, a higher heat resistance at 90 degrees Celsius and a lower germination, particularly at 7 degrees Celsius, than spores from the other strains. No difference between the three groups in their growth kinetics at 24 degrees Celsius, 37 degrees Celsius, and pH 5.0, 7.0, and 8.0 was observed. Our survey shows that emetic toxin-producing strains of B. cereus have distinct characteristics, which could have important implication for the risk assessment of the emetic type of B. cereus caused food poisoning. For instance, emetic strains still represent a special risk in heat-processed foods or preheated foods that are kept warm (in restaurants and cafeterias), but should not pose a risk in refrigerated foods.     

Analytical methods for Bacillus cereus and other Bacillus species

Bacillus cereus can give rise to two distinct forms of foodborne disease, the emetic and the diarrhoeal syndromes. The emetic syndrome is believed to be associated with an emetic toxin pre-formed in food. Cooked rice is the most common vehicle, and the symptoms are similar to those of Staphylococcus aureus intoxication. The diarrhoeal type is caused by an enterotoxin and the symptoms generally parallel those of the Clostridium perfringens food poisoning. The heat resistance of B. cereus spores and the non-fastidious nature of the organism facilitates its survival and/or growth in a wide variety of foods. This review describes analytical methods available for the isolation, identification, and enumeration of the organism, in addition to details about biological and immunological methods for toxin assay. Data are also presented concerning the incidence and epidemiology of B. cereus food poisoning around the world, and especially in Japan.     

Organic pathomorphological changes in animals with dietary infection by food products contaminated by Bacillus cereus

The authors noticed marked vascular disorders in the capillary system, focal hemorrhages, and inflammatory, largely proliferative reactions in the stroma coupled with dystrophic and necrotic changes in parenchymal elements. The changes were found to be the most pronounced in the intestine, liver, myocardium, and in brain tissue. The degree of the lesions depended on the microorganism dosage. Provided the food contained 10(9)/g Bac. cereus, the injuring action was recorded to be more powerful, which manifested in the increased extent of vascular disorders with the hemorrhagic manifestations, thrombus formation in the vessels of the brain, heart, lungs, stomach and intestine, augmentation of dystrophic changes in organ parenchymal elements.     

Viscoelastic behaviour of dehydrated products during rehydration

Viscoelastic behaviour of dehydrated products during rehydration of apple, banana, carrot and potato was examined under uniaxial compression tests. Samples were dehydrated with four different drying methods: conventional, vacuum, freeze and osmotic-freeze drying and after that they were rehydrated in an air dryer at 50°C and 80% air humidity. Compression tests were performed during rehydration for various moisture contents, ranging from 0.01 to 1.5 kg/kg dry basis. The viscoelastic behaviour of dehydrated products during rehydration were examined comparing the values of the four parameters incorporated into the stress–strain model, during rehydration with those of dehydrated products. The four examined parameters: maximum stress, maximum strain, elastic parameter and viscoelastic exponent seem to show a hysteresis phenomenon. It can be concluded that dehydrated product do not keep their viscoelastic behaviour after rehydration due to structural damages that occur during drying. More specifically, freeze dried materials present the highest hysteresis after rehydration, losing their elasticity and becoming more viscous. Osmotic pretreatment seems to help freeze dried materials to keep their elastic nature, probably due to solids gain. Air and vacuum dried materials showed the smallest hysteresis tendency, keeping their viscoelastic characteristics during rehydration close to those of dried materials.     

Structural properties of dehydrated products during rehydration

The following structural properties of dehydrated apple, banana, carrot and potato were examined during rehydration: true density, apparent density, porosity and specific volume. Samples were dehydrated using five different drying methods: conventional, vacuum, freeze, microwave and osmotic; after which they were rehydrated in an air dryer at 50 °C and 80% air humidity. Structural properties were examined during rehydration to various moisture contents, ranging from 0.01 to 3.5 kg kg^–1 (dry basis). The dehydrated products did not recover their structural properties after rehydration as a result of structural damage that occurred during drying and the hysteresis phenomenon which took place during rehydration. Porosity of the rehydrated products was higher during rehydration than during dehydration. A generalized structural model was used to describe the structural properties, and of the four parameters that were incorporated, only the shrinkage coefficient, which represents volume expansion, changed on rehydration.     

Biofilm-spore response in Bacillus cereus and Bacillus subtilis during nutrient limitation

This study aimed to trace the dynamics of biofilm formation by vegetative cells and endospores of Bacillus cereus DL5 and Bacillus subtilis 168. Counts of B. cereus DL5 and B. subtilis 168 vegetative cells and spores either attached to glass wool or, correspondingly, planktonic cells were determined by standard plate-counting methods. Results from this study highlighted the biofilm-forming potential of both spores and vegetative cells of two different Bacillus species. It was shown that once Bacillus spores had attached to a surface, the spores germinated under favorable (B. cereus DL5) and even unfavorable (B. subtilis 168) nutrient conditions, resulting in biofilms containing both spores and vegetative populations. Furthermore, it was suggested that vegetative B. cereus DL5 cells exhibited a low propensity for spore formation in attached and planktonic growth forms in nutrient-limited growth medium. By contrast, vegetative B. subtilis 168 cells readily formed spores in planktonic and attached microcosms when exposed to nutrient-limited growth conditions. Sporulation in attached Bacillus populations is an important practical consideration for many food industries, such as dairy processing, where bacilli are routinely isolated from populations attached to processing-equipment surfaces.     

Bacillus cereus food poisoning and its toxins

The genus Bacillus includes members that demonstrate a wide range of diversity from physiology and ecological niche to DNA sequence and gene regulation. The species of most interest tend to be known for their pathogenicity and are closely linked genetically. Bacillus anthracis causes anthrax, and Bacillus thuringiensis is widely used for its insecticidal properties but has also been associated with foodborne disease. Bacillus cereus causes two types of food poisoning, the emetic and diarrheal syndromes, and a variety of local and systemic infections. Although in this review we provide information on the genus and a variety of species, the primary focus is on the B. cereus strains and toxins that are involved in foodborne illness. B. cereus produces a large number of potential virulence factors, but for the majority of these factors their roles in specific infections have not been established. To date, only cereulide and the tripartite hemolysin BL have been identified specifically as emetic and diarrheal toxins, respectively. Nonhemolytic enterotoxin, a homolog of hemolysin BL, also has been associated with the diarrheal syndrome. Recent findings regarding these and other putative enterotoxins are discussed.     

Application of gaseous ozone to control populations of Escherichia coli, Bacillus cereus and Bacillus cereus spores in dried figs

The effect of ozonation as a method to reduce Escherichia coli, Bacillus cereus and Bacillus cereus spores in dried figs was investigated. Dried figs were sprinkle inoculated with E. coli, B. cereus and B. cereus spores in sterile bags at a level of 10(7)microorganism g(-1), mixed and allowed to dry for 1h at 25 degrees C prior to ozonation. Inoculated samples were exposed to gaseous ozone in a chamber at 20 degrees C and 70% relative humidity. Ozone concentrations of 0.1, 0.5 and 1.0 ppm up to 360 min were used to inactivate E. coli and B. cereus while 1.0, 5.0, 7.0 and 9.0 ppm ozone concentrations for 360 min were used to treat B. cereus spores. E. coli and B. cereus counts were decreased by 3.5 log numbers at 1.0 ppm ozone concentration for 360 min ozone treatment. Up to 2 log reductions in the number of B. cereus spores were observed above 1.0 ppm ozone concentration at the end of 360 min of ozonation. No significant changes in color, pH and moisture content values of dried figs were observed after the ozonation treatments. No significant changes were found between sweetness, rancidity, flavor, appearance and overall palatability of ozonated and non-ozonated dried figs. Ozonation was found to be effective especially in reduction of vegetative cells in dried figs and a promising method for the decontamination of dried figs.     

Pectin changes in the pre-cooking step of dehydrated mashed potato production

Some in-vivo and in-vitro characteristics of pectin methylesterase (PME) from cell wall and whole potato tuber were determined and its role was elucidated in the pre-cooking and cooling steps of commercial dehydrated mashed potato production. The isolated cell walls contained 16.3% anhydrogalacturonic acid with a degree of esterification (DE) of 56, and 25% of tuber total PME. Cell wall pre-cooking in model systems resulted in a DE of 53.2. Native cell wall pectin solubilisation was much less than that of H-cell walls devoid of metal cations. Calcium but not Mg, supplied as Ca(Mg)-starches, retarded pectin solubilisation, while Ca-uptake by retained pectin was high when cooling followed pre-cooking. Texture measurements of potato slices pre-cooked, cooled and cooked suggested a firming effect which could be attributed to Ca-release from gelatinised starch during pre-cooking, and stabilisation of Cabridges with free COO^? groups of cell wall pectin duringcooling. The role ascribed to PME in causing firming is de-emphasised.