Mechanism of killing of spores of Bacillus cereus and Bacillus megaterium by wet heat

Aims: To determine the mechanism of wet heat killing of spores of Bacillus cereus and Bacillus megaterium. Methods and Results: Bacillus cereus and B. megaterium spores wet heat‐killed 82–99% gave two bands on equilibrium density gradient centrifugation. The lighter band was absent from spores that were not heat‐treated and increased in intensity upon increased heating times. These spores lacked dipicolinic acid (DPA) were not viable, germinated minimally and had much denatured protein. The spores in the denser band had viabilities as low as 2% of starting spores but retained normal DPA levels and most germinated, albeit slowly. However, these largely dead spores outgrew poorly if at all and synthesized little or no ATP following germination. Conclusions: Wet heat treatment appears to kill spores of B. cereus and B. megaterium by denaturing one or more key proteins, as has been suggested for wet heat killing of Bacillus subtilis spores. Significance and Impact of the Study: This work provides further information on the mechanisms of killing of spores of Bacillus species by wet heat, the most common method for spore inactivation.     

Flash infrared radiation disinfection of fibrous filters contaminated with bioaerosols

Aims: To investigate the effectiveness of infrared (IR) radiation heating in disinfecting air filters loaded with bioaerosols. Methods and Results: An irradiation device was constructed considering the unique characteristics of IR and the physical dimensions and radiative properties of air filters. Filters loaded with test bioaerosols were irradiated with the device and flash heated to an ultra‐high temperature (UHT). A maximum of 3·77‐, 4·38‐ and 5·32‐log inactivation of B. subtilis spores, E. coli, and MS2 virus respectively was achieved within 5 s of irradiation. Inactivation efficiency could be increased by using a higher IR power. Microscopic analysis showed no visible damage from the heat treatment that would affect filtration efficiency. Conclusions: Because the disinfection was a dry heat process, a temperature greater than 200°C was found necessary to successfully inactivate the test micro‐organisms. The results demonstrate that IR is able to quickly disinfect filters given sufficient incident power. Compared to existing filter disinfection technologies, it offers a faster and more effective solution. Significance and Impact of the Study: It has been shown that IR heating is a feasible option for filter disinfection; possibly reducing fomite transmission of collected micro‐organisms and preventing bioaerosol reaerosolization.     

Modelling the influence of the incubation temperature upon the estimated heat resistance of heated bacillus spores

AIMS: In this study, the influence of the incubation temperature on the D-values was described according to a simple Bigelow-like model. METHODS: Model parameters were estimated from different sets of data from the literature and from our own data. For different Bacillus species and heat-treatment conditions, the influence of the recovery temperature was quantified and the optimal recovery temperature was determined. RESULTS: The impacts of species, bacterial strains belonging to the same species, heat-treatment temperature and composition of recovery media on the model parameters were analysed. The optimum recovery temperatures differ greatly from one species to another; however, no difference appears clearly between strains belonging to the same species. D values were significantly affected by recovery temperature. This influence of recovery temperature was dependent on the species, and affected by the composition of recovery media but not by the heating temperature. SIGNIFICANCE AND IMPACT OF THE STUDY: The developed model could be useful for determining the optimal incubation temperature and quantifying the weight of the recovery temperature influence for safe security control in the canning industry.     

微波及其联合杀菌技术在食品中的应用研究进展

微波在食品中的应用已逐渐成为研究热点，但微波作为一种新型食品杀菌技术，特别是和其他杀菌技术联合应用的综述目前还较少。本文通过分析已有的食品微波杀菌技术，包括单微波杀菌技术、微波-巴氏杀菌技术、微波-超声联合杀菌技术、微波-红外杀菌技术、微波-脉冲电场杀菌技术的特点，总结微波及其联合杀菌技术对不同类型食品的杀菌条件和效果，旨在为微波在各类食品杀菌工艺中的应用提供参考。     

Enhanced in vitro and in vivo antioxidant activity and mobilization of free phenolic compounds of soybean flour fermented with different β-glucosidase-producing fungi

Aims:  To evaluate the soybean polyphenol glucosides bioconversion to aglycone forms by different β-glucosidases-producing filamentous fungi to enhance their antioxidant activity.
Methods and Results:  Soybean defatted flour was submitted to solid-state fermentation with Aspergillus niger , Aspergillus niveus and Aspergillus awamori . The fungi studied produced approximately the same β-glucosidase activity units amount when p- nitrophenyl-β- d -glucopyranoside was used as substrate for the assay. However, electrophoretic analysis, using 4-methylumbellipheryl-β- d -glucopyranoside as substrate, showed that β-glucosidase produced by A.   niveus was more active. Fermented methanolic extracts showed an increase in polyphenol and genistein contents and antioxidant activities. The highest genistein content was found in soybean fermented by A. niveus . Methanolic extracts of the soybean fermented by the different fungi showed a similar capacity of scavenging H₂O₂ generated in vivo by the tumour promoter 12- O- tetradecanoyl phorbol-13-acetate.
Conclusions:  A.   niveus synthesized a β-glucosidase with higher specificity to hydrolyse genistin β-glycosidic bond than those produced by A .  awamori and A. niger .
Significance and Impact of the Study:  The utilization of these β-glucosidases-producing fungi in soybean fermentation processes resulted in the obtaining of methanolic extracts with different antioxidant potentials that could be used either therapeutically or as an antioxidant in nonphysiological oxidative stress conditions, as the one induced in skin by UV radiation.     

Microbiological monitoring in the biodegradation of sewage sludge and food waste

AIM: To study the microbiology of intensive, in-vessel biodegradation of a mixture of sewage sludge and vegetable food waste. METHODS AND RESULTS: The biodegradation was performed in a closed reactor with the addition of a starter culture of Bacillus thermoamylovorans SW25 under conditions of controlled aeration, stirring, pH and temperature (60 degrees C). The content of viable bacterial cells, determined by flow cytometry, increased from 5 x 108 g-1 of dry matter to 61 x 108 g-1 for 6 days of the process and then dropped to the initial value at the end of the process. The reductions of organic matter, 16S rRNA of methanogens and coenzyme F420 fluorescence during 10 days of the treatment were 67, 54 and 87% of the initial values, respectively. The biodegradability of the organic matter decreased during the 10 days of the treatment from 3.8 to 1.3 mg CO2 g-1 of organic matter per day. The treatment of sewage sludge and food waste at 60 degrees C did not remove enterobacteria, which are the agents of intestinal infections, from the material. The percentage of viable enterobacterial cells, determined by fluorescent in situ hybridization (FISH) with Enterobacteriaceae-specific oligonucleotide probe and flow cytometry, varied from 1 to 14% of the viable bacterial cells. CONCLUSIONS: The mixture of sewage sludge and food waste can be degraded by the aerobic thermophilic bacteria; the starter culture of Bacillus thermoamylovorans SW25 can be used to perform this process; and enterobacteria can survive under treatment of sewage sludge and food waste at 60 degrees C for 13 days. SIGNIFICANCE AND IMPACT OF THE STUDY: The results show that FISH with an oligonucleotide probe can be used to study not only the growth but also the degradation of biomass. Obtained results could be used to design the bioconversion of sewage sludge and food waste into organic fertilizer.     

Spore germination of the psychrotolerant, red meat spoiler, Clostridium frigidicarnis

Aims: To determine germination triggers of Clostridium frigidicarnis, an important spoilage bacterium of chilled vacuum‐packed meat. Methods and Results: Germination of Cl. frigidicarnis spores in the presence of a range of potential nutrient and non‐nutrient germinants was tested by monitoring the fall in optical density and by phase‐contrast microscopy. The amino acid l ‐valine induced strong germination when paired with l ‐lactate in sodium phosphate under anaerobic conditions. Several other amino acids promoted germination when paired with l ‐lactate in sodium phosphate and the co‐germinants NaHCO₃ and l ‐cysteine. Heat activation, while not necessary for germination, increased the rate of germination. Spore germination was not observed when spores were incubated aerobically. Conclusions: Spores of psychrotolerant Cl. frigidicarnis germinated in the presence of l ‐valine in combination with l ‐lactate in sodium phosphate buffer under anaerobic conditions. Significance and Impact of the Study: Anaerobic conditions, l ‐valine and l ‐lactate, have been identified as triggering germination in Cl. frigidicarnis, and are all present in packs of fresh, vacuum‐packaged, red meat. This new information adds to what is known about red meat spoilage by cold tolerant clostridia and can be used to develop intervention strategies to prevent meat spoilage.     

Microbial population profiles of the microflora associated with pre- and postharvest tomatoes contaminated with Salmonella typhimurium or Salmonella montevideo

Aims:  To determine the microflora profiles of pre- and postharvest tomatoes contaminated with Salmonella montevideo or S. typhimurium DT104.
Methods and Results:  Salmonella montevideo or S. typhimurium was inoculated onto the flowers of tomato plants with the microflora of the subsequent fruit examined using a combination of Source Carbon Utilization and 16S rDNA-PCR profiling. From 16S rDNA profiles it was evident that tomatoes derived from Salmonella inoculated plants harboured a different microbial population compared to nontreated controls. The same result was observed for tomatoes inoculated at postharvest and subsequently stored for 14 days at 15°C. From sequencing analysis it was found that tomatoes derived from Salmonella inoculated plants but testing negative for the enteric pathogen, frequently harboured Enterobacter and Bacillus spp. In contrast, both bacterial types were not found associated with tomatoes testing positive for Salmonella.
Conclusions:  Salmonella introduced onto tomatoes at pre- or postharvest alters the composition of the microbial community. The presence of Enterobacter and Bacillus spp negatively affects the persistence of Salmonella on preharvest tomatoes.
Significance and Impact of the Study:  Salmonella appears to modify rather than become integrated into the microbial communities associated with tomatoes. Yet, the presence of antagonistic bacteria appears to reduce the persistence of the enteric pathogen.