Influence of Temperature on Germination and Growth of Spores of Emetic and Diarrheal Strains of Bacillus cereus in a Broth Medium and in Rice

Germination and growth of Bacillus cereus spores from emetic and diarrheal strains were measured in Trypticase soy broth (TSB) and in autoclaved rice/beef extract from 5°– 55°C. Growth for some strains occurred from 15°– 50°C, and little difference was noted between responses of diarrheal and emetic types or between media, except a higher maximum population was achieved in rice. Germination was more extensive in rice than in TSB at <15°C and was generally more extensive for diarrheal strains in either medium.     

Germination and Heat Resistance of Bacillus cereus Spores from Strains Associated with Diarrheal and Emetic Food-Borne Illnesses

Bacillus cereus has been implicated as the cause of both diarrheal and emetic forms of food-borne illness. Spores of eight strains of B. cereus, representing diairheal, emetic and atoxigenic origins, were examined for heat resistance and germination responses. No correlation was observed between heat resistance at 85° or 90°C and origin of the strain. Germination of spores in Trypticase soy broth at 30°C, measured by loss of heat resistance, was more extensive for diarrheal strains than for emetic strains. These data should be useful in evaluating potential hazards from B. cereus in foods.     

Thermal Inactivation of Clostridium perfringens After Growth at Several Constant and Linearly Rising Temperatures

Inactivation kinetics of Clostridium perfringens strains NCTC 8238 and NCTC 8798 vegetative cells were evaluated in autoclaved ground beef after growth at constant (37, 41, 45, or 49°C) or linearly rising temperatures (4.0, 6.0, or 7.5 C°/hr) representative of long-time, low-temperature (LTLT) cooking. Inactivation temperatures of 55, 57, 59, 60, and 61°C were used. D values and z values were determined. For strain NCTC 8798 cells grown at 45°C, the average D₅₉°C was 7.2 min and the z_D was 3.8 C°. Both strains exhibited greater heat resistance after growth at higher constant temperatures. Also, NCTC 8798 was more heat resistant than NCTC 8238. With linearly rising temperature, terminal growth temperatures appeared dominant in resistance to inactivation. These data will permit predictions of growth and survival of C. perfringens during LTLT cooking of beef roasts.     

Effect of Thermal Processing on the Survival of Foot-and-Mouth Disease Virus in Ground Meat

Foot-and-mouth disease virus was examined for its stability during cooking in tissues from infected cattle. The 0₁ (CANEFA 2) serotype of foot-and-mouth disease virus survived in lymph node tissues after heating for 2 hr at 69°C, for 1 hr but not for 2 hr at 82°C, and for 15 min but not for 0.5 hr at 90°C. Incorporation of 1% NaCl into suspensions of infected lymph nodes enhanced viral survival after heating for 0.5 hr but not for 1 hr at 90°C. The virus did not survive in either ground beef or meatballs contaminated with infected lymph node tissue, when processed to internal temperatures of 93.3, 96.1 or 98.8°C using commercial thermal processing procedures. Accurate temperature measurements were achieved with a temperature sensitive indicator disc developed in this study.     

Heat Inactivation of Pectinesterase in Orange Juice Pulp

Heat inactivation of pectinesterase in juice pulp was nonlinear suggesting the presence of fractions of pectinesterase with differing heat stabilities. The residual activity rapidly decreased to 4% upon heating for 19 sec at 80°C and decreased very little upon subsequent heating for up to 180 sec at 80°C. The D values (time to inactivate 90% of the enzyme) at 90°C of the heat sensitive and heat stable fractions were estimated to be 0.225 and 32 sec, respectively. The Z values (change in temperature to achieve a 10-fold change in time of inactivation) were estimated to be 10.8°C and 6.5°C for the sensitive and stable fractions, respectively.     

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.     

Disulfide-mediated Polymerization Reactions and Physical Properties of Heated WPI-stabilized Emulsions

Heating a 19 wt% corn oil-in-water emulsion stabilized by 1 wt% whey protein isolate from 30 to 70°C and then cooling to 25°C for at least 15 hr, brought about minimal changes in droplet aggregation, apparent viscosity and susceptibility to creaming. At 75°C, droplet aggregation occurred but this decreased on heating to 90°C. The apparent viscosity and susceptibility of droplets to creaming increased as the degree of droplet aggregation increased. Inclusion of the sulfhydryl blocking agent N-ethylmaleimide to inhibit thiol/disulfide interchange reactions did not affect droplet aggregation but resulted in higher apparent viscosity values and susceptibility to creaming at 85 and 90°C and not at lower temperatures. The results suggest that droplet aggregation results from noncovalent interactions between unfolded protein molecules adsorbed on different droplets and that the interactions are strengthened by disulfide bonds.     

Protease Inactivation in Fish Muscle by High Moisture Twin-Screw Extrusion

The effects of material temperatures at the die, screw speed, and screw configurations on inactivation of protease in Arrowtooth flounder (Atheresthes stomias)muscle were studied. No inactivation occurred below a material temperature of 40°C in the extruder die. Rapid destruction of protease in Arrowtooth flounder muscle occurred in the range 50–80°C. Complete inactivation of protease occurred at 100°C irrespective of screw speed and configuration. Protease inactivation was higher at low screw speed.     

Sporulation and Heat Resistance of Spores from a Clostridium sp. RKD

A Clostridium sp. RKD isolated from the intestine of decaying fish, showing 99% sequence identity with Clostridium tetani at a 16S rRNA level, produced a neurotoxin that was neutralized by botulinum antitoxin (A+B+E). It also showed an amplification of near‐expected size when polymerase chain reaction (PCR) was performed using group‐ and type‐specific primers for botulinum neurotoxin type B. The isolate exhibited differences with both C. tetani and Clostridium botulinum with respect to phenotypic characteristics and chemotaxo‐nomic markers. Spore production was optimized with respect to media composition and stage of growth. Time‐dependant examination of sporulation revealed 2.6% to 49.0% spores in the late stationary phase culture when grown in different broth media. A simpler method for spore production and isolation from culture grown in tryptose sulfite cycloserine (TSC)/anaerobic agar sandwich resulted in >95% sporulation, which could be purified to near homogeneity by a simple 2‐step procedure. Thermal resistance of spores revealed a biphasic inactivation at lower temperatures with D values for linear inactivation varying from 26.6, 8.0, and 4.3 min at 70 °C, 80 °C, and 90 °C, respectively. The z values of 7.86 °C and 10.47 °C were obtained in the linear and tail regions, respectively. The Weibull parameter b values at 70 °C, 80 °C, and 90 °C were 27.38, 3.55, and 0.99, respectively, with a z’ value of 13.869 °C. The shape parameter n at 70 °C, 80 °C, and 90 °C were 0.63, 0.55, 0.45, respectively. Spores produced on 2 different media (cooked meat medium [CMM] and trypticase peptone yeast‐extract glucose [TPYG] agar) exhibited differences in heat resistance. The addition of lysozyme (50 jj.g/mL) before heat treatment resulted in increased thermal resistance of spores.     

Microwave heat treatment application to pasteurization of human milk

A prototype of microwave pasteurizer has been proposed as an alternative for holder pasteurization (HP) routinely used in Human Milk Bank (HMB), ensuring microbiological safety of human milk (HM). It was shown that the time of heat generation was about 15–16 min shorter by applying the microwave than in HP. Total inactivation of heat-sensitive bacteria Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis, suspended in milk, occurred in the temperature 62–72 °C in HP. In the case of heat-resistant enterococci the level of inactivation depended on the conditions of the process and the properties of the strains. The application of microwave heating allows to obtain lower D-value than those achieved during HP. The using of microwave heating at 62.5 or 66 °C for 5 or 3 min, respectively, allows to inactivation of HM microbiota. Appropriate microbiological quality of milk is critical for the effectiveness of the pasteurization process.Industrial relevanceLooking for new methods of donor human milk (HM) preservation is dictated by the necessity of providing microbiological safety and, at the same time, maintain its high nutritional and biological value. The holder pasteurization used in the Human Milk Banks (HMB) (heating at 62 °C for 30 min) leads to inactivation of all vegetative forms of microorganisms. Unfortunately, this method causes significant reduction of health benefitting properties of HM. The paper demonstrates the possibility of using the new microwave pasteurizer for preservation of HM, allowing for quick heating of milk to the appropriate temperature and maintaining it in these conditions for a required time. It was shown that the decimal reduction times (D) for strains inoculated to UHT or human milk are several times shorter by using microwave heating than in the commercial pasteurization method. The total inactivation of HM microbiota is obtained after heating at 62.5 and 66 °C for 5 and 3 min, respectively.     

Bacillus cereus emetic toxin production in cooked rice

Three mesophilic strains of Bacillus cereus known to produce emetic toxin were used to model germination, growth and emetic toxin production in boiled rice cultures at incubation temperatures ranging from 8°C to 30°C. Minimum temperatures for germination and growth in boiled rice were found to be 15°C for all strains. Toxin production at 15°C was found to be significantly greater (P<0·01; reciprocal toxin titre of 373±124) than at 20°C and 30°C (reciprocal toxin titres 112±37 and 123±41, respectively). Toxin production became detectable after 48 h incubation at 15°C, with a maximum titre reached by 96 h. At 20°C and 30°C, toxin production was detected at 24 h incubation, with a maximum titre reached by 72 h. Toxin production at 15°C was detectable at lower bacterial counts (6·2 log₁₀ cfu g⁻¹), than with incubation at 20°C and 30°C (>7·0 log₁₀ cfu g⁻¹). In this study, the lower temperature limit for germination and growth on solid laboratory medium was found to be 12°C for all strains, i.e. 3°C lower than that observed in boiled rice.     

Inactivation of Pectinesterase in Orange Juice by Supercritical Carbon Dioxide

Single strength orange juice was treated with supercritical carbon dioxide (CO₂) and the effect of process time, temperature and pressure on pectinesterase (PE) activity was determined. PE could be inactivated with supercritical CO₂ below temperatures necessary for thermal inactivation. Higher pressure, temperature and longer treatment time resulted in more inactivation. Inactivation kinetics showed activation energy was significantly reduced at SC C0₂ treatment at 31 MPa (97.4 KJ/mole), compared to identical treatments at atmospheric pressure (166.6 KJ/mole). D values ranged from 2673 min at atmospheric pressure and 40°C to 10 min at 31 MPa and 60°C. z value at atmospheric pressure was 8.8C°, and at 31 MPa 5.2C°.     

Temperature Affects Astringency Removal and Recurrence in Persimmon

Astringency was removed from‘Triumph’persimmons by immersion in water at 40°C for 5 hr or 60°C, for 1 hr. Similar treatments at 20° and 80°C, had no effect on astringency reduction. Subsequent application of 80% CO₂ for 48 hr was effective for 20°C-treated fruit but not for 80° C-treated fruit, which became nonastringent only after exposure to acetaldehyde. Extending the 60°C treatment beyond 2 hr resulted in recurrence of astringency, which was not reduced by subsequent CO₂ treatment. Astringency also recurred in CO₂-treated non-astringent fruit, when exposed to high temperatures. The disappearance and recurrence of astringency correlated with amount of methanol-soluble tannins.     

Alteration of Talaromyces flavus Heat Resistance by Growth Conditions and Heating Medium Composition

A strain of Talaromyces flavus var. macrosporus (NRRL 13641) was isolated from spoiled fruit drink and identified. It had a heat resistance (l/k) (death rate constant or decimal reduction time) of 191 min at 80°C and 6 min at 90°C with a calculated z of 6.7°C. Several strains of T. flavus were tested to determine the effects on heat resistance of environmental conditions such as pH, organic acids, brix, and type of medium. Heat resistance increased with increased brix in the heating medium. Growth on solid medium compared with liquid medium resulted in greater heat resistance. Growth at 20°C and 35°C produced ascospores with higher heat resistance than growth at 25°C while those produced at 30°C had intermediate heat resistance. Five cultures differed significantly in heat resistance.     

Viscoelastic Behavior of Commercially Processed Soy Isolate Pastes During Heating and Cooling

The viscoelastic properties of soy isolate dispersions of Prolina and Brim cultivars, commercially processed, were compared during heating and cooling utilizing small deformation rheology. All isolates formed gels upon hydration. Heating to 90 °C yielded less rigid gels, as evidenced by a decreasing G'. Holding at 90 °C induced an increase in G' for Brim isolate, possibly as a result of increased hydrophobic and/or covalent bonding. Cooling to 25 °C generated a G' increase above initial levels for both cultivars, likely due to enhanced intermolecular hydrogen bonding. Mechanical spectra at 25 °C before and after heating, and at 90 °C before and after holding, confirmed these observations. A lower G' was consistently exhibited by Prolina gels throughout testing.     

Sardine Surimi Gels as Affected by Salt Concentration, Blending, Heat Treatment and Moisture

The effects of simultaneous modification of salt concentration, blending time, moisture content and heat treatment at different setting and cooking temperatures and time on characteristics of sardine (Surdina pilchardus) surimi gels was examined using a randomized incomplete block design. Maximum gel strength (GS) was obtained at highest salt concentrations and 78% moisture. Pre-setting was required to achieve acceptable gel quality. Highest GS values were found in gels set for 30–60 min at 35°C prior to heating at 90°C for 40 min. However, GS decreased after prolonged heating at 90°C. Gels set at 25, 35 and 40°C for 90 min had lower GS values when heated at 90°C for 40 min but were stable during further heating.     

Temperature-dependent development and reproduction of the cowpea weevil,Callosobruchus maculatus F., in mungbean: Estimating a target temperature for its control using aeration cooling

The bruchid, Callosobruchus maculatus F., commonly known as the cowpea weevil, infests stored mungbean and other legumes. Aeration cooling has potential as a non-chemical means of managing this species in stored legumes. Population growth of C. maculatus in mungbean was investigated at nine constant temperatures (15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5 and 35 °C) at 60% RH so that a target temperature for cooling could be estimated. We used two laboratory strains: Strain 1 and Strain 2 that had been in culture for 16–17 years and 1–2 years respectively. The results for the two strains were very similar. Egg to adult development occurred between 20 and 35 °C for Strain 1 and 17.5 and 35 °C for Strain 2. The optimal temperature for population growth was estimated to be 32.2 and 33.7 °C for Strains 1 and 2, respectively. The estimated lower threshold for population growth, i.e. the temperature at which population growth is zero, was 17.5 °C for Strain 1 compared with 17.1 °C for Strain 2. Based on our results, we recommend a target temperature of 17 °C for aeration cooling to manage C. maculatus infestations in mungbean during storage.     

Inactivation and injury of Listeria monocytogenes as affected by heating and freezing

The effects of heating and freezing Listeria monocytogenes in tryptose phosphate broth an inactivation and injury were investigate. Four strains (Scott A, Brie-1, LCDC 81–861, and DA-3) were examined. Only slight decreases in the viable populations pf all four strains were detected after 75 min at 50°C. Populations of strains Scott A, LCDC 81–861, and DA-3 were reduced to non-detectable levels after 10 min at 60°C while viable cells of strain Brie-1 were recovered after heating at 60°C for 30 min. Viable populations of all four strains declined steadily at 52,54, and 56°C; similar inactivation rates were observed for strains Scott A, LcDC 81–861, and DA-3. Strain Brie-1 was consistently the most heat resistant. Substantial populations of viable cells of all strains heated at 52, 54, and 56°C were injured as evidenced by increased sensitivity to NaCl when plated on tryptose phosphate recover agar. Strain DA-3 was the most susceptible strain to sublethal heat injury. Viable populations of all four test strains were not appreciably reduced after 14 days at −18°C, although strain LCDC 81–861 lost viability at a more rapid rate at this temperature than did the other test strains. About 72, 82, 73, and 80% of Scott A, Brie-1, LCDC 81–861, and DA-3 cells, respectively, held at −18°C for 14 days were not receovered on tryptose phosphate agar (TPA) supplemented with 8% NaCl compared to populations recovered on TPA not supplemented with NaCl.     

Improved Tenderness of Restructured Beef Steaks by a Microbial Collagenase Derived from Vibrio B-30

To reduce connective tissue toughness Vibrio B-30 collagenase was evaluated for its ability to degrade muscle collagen in a restructured beef (RSB) product. Dissected muscles pooled from clods of 4 USDA choice chucks were made into three RSB products: untrimmed control (C), hand trimmed of epimysium (T) and untrimmed and treated with 0.01% collagenase (E). RSB products were held for 24 hr at either 2°C or 11°C and were analyzed cither raw or after heating (40°C for 1 hr). Aerobic microbial load remained low (1–2X10² cfu/g) during the 24 hr 11°C incubation. Heated samples of enzyme treated RSB had lower Lee-Kramer shear values than controls. In both raw and heated samples enzyme treatment increased hydroxyproline solubility. An enzyme treatment of 24 hr at 11°C followed by heating produced maximum tenderization. Although optimum treatment conditions need to be defined by further research, Vibrio B-30 collagenase appeared to be efficacious for the tenderization of RSB products.