RESUMEN
The pulsed light produced by xenon flash lamps was applied to 65 to 67 °Brix sugar syrups artificially contaminated with suspensions of Saccharomyces cerevisiae and with spores of Bacillus subtilis, Geobacillus stearothermophilus, Alicyclobacillus acidoterrestris, and Aspergillus niger. The emitted pulsed light contained 18.5 % UV radiation. At least 3-log reductions of S. cerevisiae, B. subtilis, G. stearothermophilus, and A. acidoterrestris suspended in 3-mm-deep volumes of sugar syrup were obtained with a fluence of the incident pulsed light equal to or less than 1.8 J/cm(2), and the same results were obtained for B. subtilis and A. acidoterrestris suspended in 10-mm-deep volumes of sugar syrup. A. niger spores would require a more intense treatment; for instance, the maximal log reduction was close to 1 with a fluence of the incident pulsed light of 1.2 J/cm(2). A flowthrough reactor with a flow rate of 320 ml/min and a flow gap of 2.15 mm was designed for pulsed light treatment of sugar syrup. Using this device, a 3-log reduction of A. acidoterrestris spores was obtained with 3 to 4 pulses of incident pulsed light at 0.91 J/cm(2) per sugar syrup volume.
Asunto(s)
Carbohidratos , Descontaminación/métodos , Conservación de Alimentos/métodos , Calor , Rayos Ultravioleta , Alicyclobacillus/efectos de la radiación , Aspergillus niger/efectos de la radiación , Bacillus subtilis/efectos de la radiación , Seguridad de Productos para el Consumidor , Relación Dosis-Respuesta en la Radiación , Contaminación de Alimentos/análisis , Contaminación de Alimentos/prevención & control , Microbiología de Alimentos , Geobacillus stearothermophilus/efectos de la radiación , Humanos , Saccharomyces cerevisiae/efectos de la radiación , Esporas Bacterianas/efectos de la radiaciónRESUMEN
Pulsed Light (PL) uses intense flashes of white light rich in ultraviolet (UV) light for decontamination. A log-reduction higher than 5 was obtained in one flash and at fluences lower than 1.8J/cm(2) on spores of a range of spore-forming bacteria, of vegetative cells of non-spore-forming bacteria and on yeasts spread on agar media. Vegetative cells were more sensitive than spores. The inactivation by PL of Bacillus subtilis, B. atrophaeus, B. cereus, Geobacillus stearothermophilus, and Aspergillus niger spores sprayed on polystyrene was similar. The inactivation by PL of B. subtilis and A. niger spores sprayed on glass was slightly lower than on polystyrene. No alteration of the spore structures was detected by scanning electron microscopy for both PL treated B. subtilis and A. niger spores. The inactivation of spores of B. subtilis, B. atrophaeus, B. cereus and B. pumilus by PL or by continuous UV-C at identical fluences was not different, and was much higher by PL for A. niger spores. The increase in the input voltage of the lamps (which also increases the UV-C %) resulted in a higher inactivation. There was no correlation between the resistance to heat and the resistance to PL. The relative effect of UV-C radiations and light thermal energy on PL inactivation was discussed.
Asunto(s)
Aspergillus niger/efectos de la radiación , Bacillus subtilis/efectos de la radiación , Bacillus/efectos de la radiación , Microbiología de Alimentos , Conservación de Alimentos/métodos , Geobacillus stearothermophilus/efectos de la radiación , Aspergillus niger/ultraestructura , Bacillus subtilis/ultraestructura , Descontaminación/métodos , Geobacillus stearothermophilus/ultraestructura , Calor , Esporas Bacterianas/efectos de la radiación , Rayos UltravioletaRESUMEN
Spores of the psychrotrophic Bacillus cereus KBAB4 strain were produced at 10 °C and 30 °C in fermentors. Spores produced at 30 °C were more resistant to wet heat at 85 °C, 1% glutaraldehyde, 5% hydrogen peroxide, 1M NaOH and pulsed light at fluences between 0.5 and 1.75 Jcm(-2) and to a lesser extent to monochromatic UV-C at 254 nm. No difference in resistance to 0.25 mM formaldehyde, 1M nitrous acid and 0.025 gl(-1) calcium hypochlorite was observed. Spores produced at 10 °C germinated more efficiently with 10 mM and 100 mM l-alanine than spores produced at 30 °C, while no difference in germination was observed with inosine. Dipicolinic acid (DPA) content in the spore was significantly higher for spores prepared at 30 °C. Composition of certain fatty acids varied significantly between spores produced at 10 °C and 30 °C.
Asunto(s)
Bacillus cereus/fisiología , Microbiología de Alimentos , Esporas Bacterianas/crecimiento & desarrollo , Temperatura , Bacillus cereus/patogenicidad , Recuento de Colonia Microbiana , Seguridad de Productos para el Consumidor , Humanos , CinéticaRESUMEN
Microbial contamination on surfaces of food processing equipment is a major concern in industries. A new method to inoculate a single-cell layer (monolayer) of microorganisms onto polystyrene was developed, using a deposition with an airbrush. A homogeneous dispersion of Bacillus subtilis DSM 402 spores sprayed on the surface was observed using both plate count and scanning electron microscopy. No clusters were found, even with high spore concentrations (10(7) spores/inoculated surface). A monolayer of microorganisms was also obtained after deposition of 10 µL droplets containing 3×10(4) spores/spot on polystyrene disks, but not with a higher spore concentration. Pulsed light (PL) applied to monolayers of B. subtilis spores allowed log reductions higher than 6. As a consequence of clusters formation in spots of 10 µL containing more than 3×10(5) spores, log reductions obtained by PL were significantly lower. The comparative advantages of spot and spray depositions were discussed.
Asunto(s)
Bacillus subtilis/aislamiento & purificación , Descontaminación/métodos , Luz , Esporas Bacterianas/aislamiento & purificación , Bacillus subtilis/efectos de la radiación , Recuento de Colonia Microbiana , Microbiología Ambiental , Contaminación de Equipos , Industria de Procesamiento de Alimentos , Microscopía Electrónica de Rastreo , Poliestirenos , Esporas Bacterianas/efectos de la radiaciónRESUMEN
Glucose reactions were conducted in hot compressed water (473-773 K, 4-40 MPa) by means of a batch-type reactor. The reactions in the heating period (about for 60s) were observed. More than 80% of the glucose was consumed in the heating period above 573 K. Gasification of glucose was promoted with increasing temperature. The effect of heating rate (from 4.2 to 15.8K/s) on glucose conversion was also examined, and gasification of glucose was enhanced with increasing the heating rate.
Asunto(s)
Glucosa/química , Calor , Agua/química , Biomasa , Dióxido de Carbono/síntesis química , Monóxido de Carbono/síntesis química , Gases , PresiónRESUMEN
The effects of the homogeneous catalysts (H(2)SO(4) and NaOH) and heterogeneous catalysts (TiO(2) and ZrO(2)) on glucose reactions were examined in hot compressed water (473 K) by a batch-type reactor. From the homogeneous catalyst studies, we confirmed that the acid catalyst promoted dehydration, while isomerization of glucose to fructose was catalyzed by alkali. Anatase TiO(2) was found to act as an acid catalyst to promote formation of 5-hydroxymethylfuraldehyde (HMF). Zirconia (ZrO(2)) was a base catalyst to promote the isomerization of glucose. The effects of the additives were also confirmed through fructose reactions.