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1.
Characterisation of spore formers associated with extended shelf life milk was performed by analysing the bacteriological quality of milk samples collected at various processing stages and during storage. Isolates were identified with MALDI‐TOF‐MS. Milk had spore counts <2 log10 cfu/mL and 4 log10 cfu/mL during processing and storage, respectively. Bacillus pumilus dominated the bacterial population. Bacterial species were inoculated into sterile milk for a shelf life study, and the population change was observed over 42 days at 7 °C. Although the extended shelf life milk process was effective in reducing bacterial counts and species diversity, the presence of Bacillus cereus shows a potential safety problem in extended shelf life milk.  相似文献   
2.
Bacillus sporothermodurans produces highly resistant endospores that can survive ultra-high-temperature treatment in milk. The induction of endospore germination before a heat treatment could be an efficient method to inactivate these bacteria and ensure milk sterility. In this work, the rate of spore germination of B. sporothermodurans LTIS27 was measured in distilled water after high-pressure treatments with varying pressure (50–600 MPa), treatment temperature (20–50 °C), pressure-holding time (5–30 min) and post-pressurization incubation time (30–120 min) at 37 °C or 4 °C. The results showed that pressure-induced germination was maximal (62%) after a treatment at 200 MPa and 20 °C and increased with pressure-holding time and post-pressurization incubation time. Treatment temperature had no significant effect on germination. A central composite experimental design with three factors (pressure, pressure-holding time, and post-pressurization incubation time) using response surface methodology was used to optimize the germination rate in distilled water and in skim milk. No factor interaction was observed. Germination was induced at lower pressure and was faster in milk than in distilled water, but complete germination was not reached. The optimum germination obtained with experimental data was 5.0 log cfu/mL in distilled water and 5.2 log cfu/mL in milk from 5.7 log cfu/mL of spores initially present in the suspension. This study shows the potential of using high hydrostatic pressure to induce the germination of B. sporothermodurans spores in milk before a heat treatment.  相似文献   
3.
Numerous studies examined the antimicrobial effects of spice and herb extracts, whereas little is known about the effects of dry condiments on the survival of microorganisms. This study investigated the impact of dried condiments on the survival of Bacillus cereus and B. thuringiensis spores as well as Staphylococcus aureus cells. In addition, the survival variability between different strains was evaluated. Condiments (allspice, basil, cinnamon, nutmeg, oregano, paprika, parsley and pepper) were artificially contaminated by a dry spiking method using sand as carrier matrix and as control. The results show that counts of B. cereus and B. thuringiensis spores (initial spore count 5.6 ± 0.2 log10 cfu/g and 6.7 ± 0.1 log10 cfu/g, respectively) did not decline significantly in all condiments over a period of 50 weeks. In contrast, in some of the spiked test materials, cell counts of S. aureus (initial cell count 8.1 ± 0.5 log10 cfu/g) were reduced below the detection limit of 10 cfu/g within 10 weeks of storage. D values for S. aureus ranged between 5 and 31 days depending on the strain, condiment and initial contamination level. In conclusion, dried condiments may not affect the survival of spores but can significantly affect the survival of non-spore forming bacteria. As strain variability can occur, tenacity studies should be conducted including a variety of strains.  相似文献   
4.
Spores of Bacillus sporothermodurans are known to be contaminant of dairy products and to be extremely heat-resistant. The induction of endospore germination before a heat treatment could be an efficient method to inactivate these bacteria and ensure milk stability. In this study, the nutrient-induced germination of B. sporothermodurans LTIS27 spores was studied. Testing the effect of 23 nutrient elements to trigger an important germination rate of B. sporothermodurans spores, only d-glucose, l-alanine, and inosine were considered as strong independent germinants. Both inosine and l-alanine play major roles as co-germinants with several other amino acids. A central composite experimental design with three factors (l-alanine, d-glucose, and temperature) using response surface methodology was used to optimize the nutrient-induced germination. The optimal rate of nutrient-induced germination (100%) of B. sporothermodurans spores was obtained after incubation of spore for 60 min at 35 °C in presence of 9 and 60 mM of d-glucose and l-alanine, respectively. The results in this study can help to predict the effect of environmental factors and nutrients on spore germination, which will be beneficial for screening of B. sporothermodurans in milk after induction their germination. Moreover, the chosen method of optimization of the nutrient-induced germination was efficient in finding the optimum values of three factors.  相似文献   
5.
The assessment and optimization of food heating processes require knowledge of the thermal resistance of target spores. Although the concept of spore resistance may seem simple, the establishment of a reliable quantification system for characterizing the heat resistance of spores has proven far more complex than imagined by early researchers. This paper points out the main difficulties encountered by reviewing the historical works on the subject.  相似文献   
6.
This study was designed to evaluate how conditions encountered by spores during cleaning-in-place (CIP) procedures affected their surface properties, their viability and ability to contaminate materials. Spores from five Bacillus cereus strains were treated with NaOH at high temperature. Results revealed that high temperatures (exceeding 60 °C) and NaOH concentrations (over 0.5%) were required to significantly decrease spore viability (3–5 log decrease). In these conditions, modifications were also clearly observed by microscopy to various surface structures of spores (appendages, exosporium, and especially to the hair-like nap) but also to their coat. Therefore, the ability of culturable spores to adhere decreased for the majority of strains tested. We then demonstrated that spores in suspension in NaOH could adhere to surfaces of a CIP rig and that the contamination level was controlled by flow pattern. Consequently, re-adhesion along the processing line might occur during CIP procedures and this phenomenon must be taken into account when defining cleaning strategies.  相似文献   
7.
The effect of ozone on Aspergillus niger causing black rot disease in onion was studied in culture. Ozone induced the spore germination in all treatments and few spores showed rapid swelling, resulting in the production of 2-3 germ tubes per spore compared to control. Although all the ozone treated spores germinated, all of them did not produce uniform colony morphology. Some colonies which developed from ozone treated spores failed to produce spores and such colonies appeared as grey patches of mycelia without spores amidst surrounding black sporulating colonies. Further work is in progress to study the mechanism involved in formation of sterile mycelia by ozone.  相似文献   
8.
Bacilli and clostridia share the characteristic of forming metabolically inactive endospores. Spores are highly resistant to adverse environmental conditions including heat, and their ubiquitous presence in nature makes them inevitable contaminants of foods and food ingredients. Spores can germinate under favourable conditions, and the following outgrowth can lead to food spoilage and foodborne illness. Germination of spores has been best studied in Bacillus species, but the process of spore germination is less well understood in anaerobic clostridia. This paper describes a genome mining approach focusing on the genes related to spore germination of clostridia. To this end, 12 representative sequenced Bacillus genomes and 24 Clostridium genomes were analyzed for the distribution of known and putative germination-related genes and their homologues. Overall, the number of ger operons encoding germinant receptors is lower in clostridia than in bacilli, and some Clostridium species are predicted to produce cortex-lytic enzymes that are different from the ones encountered in bacilli. The in silico germination model constructed for clostridia was linked to recently obtained experimental data for selected germination determinants, mainly in Clostridium perfringens. Similarities and differences between germination mechanisms of bacilli and clostridia will be discussed.  相似文献   
9.
The microbiological criteria of commercial cocoa powder are defined in guidelines instituted by the cocoa industry. Twenty-five commercial samples were collected with the aim of assessing the compliance with the microbiological quality guidelines and investigating the occurrence and properties of aerobic Thermoresistant Spores (ThrS). Seventeen samples complied with the guidelines, but one was positive for Salmonella, five for Enterobacteriaceae and two had mould levels just exceeding the maximum admissible level. The treatment of the cocoa powder suspensions from 100 °C to 170 °C for 10 min, revealed the presence of ThrS in 36% of the samples. In total 61 ThrS strains were isolated, of which the majority belonged to the Bacillus subtilis complex (65.6%).Strains resporulation and spore crops inactivation at 110 °C for 5 min showed a wide diversity of heat-resistance capacities. Amplified fragment length polymorphism analysis revealed not only a large intraspecies diversity, but also different clusters of heat-resistant spore-forming strains. The heat-resistance of spores of six B. subtilis complex strains was further examined by determination of their D and z-values.We concluded that B. subtilis complex spores, in particular those from strain M112, were the most heat-resistant and these may survive subsequent preservation treatments, being potentially problematic in food products, such as chocolate milk.  相似文献   
10.
Inhibitory effects of pulsed electric fields (PEF) on Penicillum expansum inoculated into sour cherry juice, apricot and peach nectars were determined based on germination tube elongation, spore germination rate, and light and scanning electron microscopy (SEM) observations in this study. After inoculation of juice/nectar samples with P. expansum spores at the level of 10(5)-10(6)cfu/mL, the samples were processed by bench scale PEF pulse generator as a function of differing electric field strengths (0, 13, 17, 20, 23, 27, 30 and 34kV/cm) and processing times (0, 62, 94, 123, 163, 198 and 218mus). Results revealed that with an increase in electric field strength and processing time, germination tube elongation and spore germination rate were completely inhibited. Light and SEM observations revealed considerable morphological alterations in fungal conidia such as cytoplasmic coagulation, vacuolations, shrinkage and protoplast leakage. PEF processing of juice/nectars was demonstrated to be effective in inactivating P. expansum. To our knowledge, this is the first study confirming the inhibitory effects of PEF on germination tube elongation and spore germination rate of P. expansum in fruit juice/nectars.  相似文献   
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