Exploring the use of natural antimicrobial agents and pulsed electric fields to control spoilage bacteria during a beer production process / Exploración del uso de agentes antimicrobianos naturales y de campos eléctricos pulsantes para el control de bacterias contaminantes durante el proceso de elaboración de cerveza

Different natural antimicrobials affected viability of bacterial contaminants isolated at critical steps during a beer production process. In the presence of 1 mg/ml chitosan and 0.3 mg/ml hops, the viability of Escherichia coli in an all malt barley extract wort could be reduced to 0.7 and 0.1% respectively after 2 hour- incubation at 4 °C. The addition of 0.0002 mg/ml nisin, 0.1 mg/ml chitosan or 0.3 mg/ml hops, selectively inhibited growth of Pediococcus sp. in more than 10,000 times with respect to brewing yeast in a mixed culture. In the presence of 0.1mg ml chitosan in beer, no viable cells of the thermoresistant strain Bacillus megaterium were detected. Nisin, chitosan and hops increased microbiological stability during storage of a local commercial beer inoculated with Lactobacillus plantarum or Pediococcus sp. isolated from wort. Pulsed Electric Field (PEF) (8 kV/cm, 3 pulses) application enhanced antibacterial activity of nisin and hops but not that of chitosan. The results herein obtained suggest that the use of these antimicrobial compounds in isolation or in combination with PEF would be effective to control bacterial contamination during beer production and storage.

Diferentes antimicrobianos naturales disminuyeron la viabilidad de bacterias contaminantes aisladas en etapas críticas del proceso de producción de cerveza. En un extracto de malta, el agregado de 1 mg/ml de quitosano y de 0,3 mg ml de lúpulo permitió reducir la viabilidad de Escherichia coli a 0,7 y 0,1%, respectivamente, al cabo de 2 horas de incubación a 4 °C. El agregado de 0,0002 mg/ml de nisina, 0,1 mg/ml de quitosano o de 0,3 mg/ml de lúpulo inhibió selectivamente (10.000 veces más) el crecimiento de Pediococcus sp. respecto de la levadura de cerveza en un cultivo mixto. El agregado de 0,1 mg/ml de quitosano permitió disminuir la viabilidad de una cepa bacteriana termorresistente, Bacillus megaterium, hasta niveles no detectables. Por otra parte, el agregado de nisina, quitosano y lúpulo aumentó la estabilidad microbiológica durante el almacenamiento de cervezas inoculadas con Lactobacillus plantarum y Pediococcus sp. aislados de mosto de cerveza. La aplicación de campos eléctricos pulsantes (CEP) (3 pulsos de 8kV/cm) aumentó el efecto antimicrobiano de la nisina y del lúpulo, pero no el del quitosano. Los resultados obtenidos indicarían que el uso de antimicrobianos naturales en forma individual o en combinación con CEP puede constituir un procedimiento efectivo para el control de la contaminación bacteriana durante el proceso de elaboración y almacenamiento de la cerveza.

Aumento de la actividad panificante de levaduras comerciales por aplicación de condiciones de estrés durante su propagación / Increase of baking activity of commercial yeasts by application of stress conditions during their propagation

La actividad panificante valorada como producción de CO2 de dos cepas comerciales de Saccharomyces cerevisiae pudo ser incrementada, principalmente en amasijos azucarados, por la aplicación de un esquema de “hambreado/ pulso¼ de melaza de caña de azúcar durante su propagación bajo la forma de lote alimentado. Dicho incremento fue dependiente de la cepa utilizada. Otras características relacionadas con el comportamiento industrial de las levaduras no se vieron afectadas, con excepción de la concentración intracelular de trehalosa.Se discute la aplicabilidad del método para la producción industrial de levaduras de panificación.

Baking activity determined as CO2 production of two commercial strains of Saccharomyces cerevisiae could be increased mainly in sweet bread doughs by introducing a “starvation/ pulse feeding” schedule of sugar cane molasses during a fed-batch propagation . Such increase was strain dependent. Except for the trehalose intracellular level, other traits related to the yeast industrial performance were unaffected. Applicability of method for baker‘s yeast industrial production is discussed.

Optimización de las condiciones de electroporación y agregado de nisina en la inhibición de Pseudomonas aeruginosa / [Optimization of the conditions for electroporation and the addition nisin for Pseudomonas aeruginosa inhibition]

A mathematical approach was applied in order to optimize the effect of electroporation by application of pulsed electric fields (PEF) and nisin addition on the inhibition of a strain of Pseudomonas aeruginosa isolated from river sediments. This strain showed to be highly resistant to nisin as only two log cycles reduction of viable cells were obtained in the presence of 84,000 IU/ml nisin. But when a combination of bacteriocin and selected PEF treatment conditions were applied, 4.4-decimal log cycle reduction could be achieved. PEF and nisin interaction seems to be complex, as at lower electric field intensities (i.e., 5 kV/cm) an increment in the number of pulses applied clearly induced a lower inhibitory effect of nisin. At higher PEF intensities (i.e., 11 kV/cm), the inhibitory effect of nisin increased with the number of pulses applied. Results overall, the obtained indicate the possibility of combining PEF and nisin treatments in order to improve the inhibition of resistant microorganisms. The Doehlert experimental design and surface response methodology was an interesting tool to obtain or predict the optimal combination of the stress factors applied.

Inhibición del desarrollo de Bacillus coagulans en medios de laboratorio y en puré de frutas / Inhibition of Bacillus coagulans growth in laboratory media and in fruit purees

The growth of two strains of B. coagulans was inhibited in laboratory media at pH < or = 4.5, and at water activity (aw) levels of 0.96 for B. coagulans NRS 609 and 0.95 for B. coagulans ATCC 803. The growth of both strains was also inhibited in apple and strawberry purees (pH = 3.5) stored at 37 degrees C for over two months. B. coagulans was able to grow in banana puree (pH approximately equal to 5.0) but acidification of the puree at pH = 3.5 was enough to prevent growth. The addition of up to 3,000 ppm vainillin ("natural" preservative) or 1,000 ppm potassium sorbate (traditional preservative) at pH higher than the inhibitory level previously determined could not prevent growth of B. coagulans in laboratory or in fruits, but 100 ppm lysozyme retarded growth in laboratory media at different pH levels (from 4.5 to 6.7) and in banana puree. As lysozyme showed to be effective at pH < or = 6.7, it might be used to prevent growth of B. coagulans at an eventual increment of pH during storage.

Modificaçöes na morfologia dos nódulos hemolinfóides de bovinos esplenectomizados / Morphological alterations in hemal nodes in splenectomized cattle

Pelo estudo das alteraçöes morfológicas nos nódulos hemolinfóides, averiguou-se a compensaçäo da deficiência imunológica transitória em bovinos esplenectomizados. Houve aumento acentuado de tamanho dos nódulos hemolinfóides dois meses após a esplenectomia. Além disso, ocorreu aumento significativo na espessura da zona intermediária dos nódulos hemolinfóides, bem como hiperplasia celular porém sem modificaçäo na populaçäo e distribuiçäo das células. As células B foram detectadas na zona central dos folículos, enquanto que as CD4+ se assentaram no córtex, na área interfolicular e nos cordöes da zona intermediária. As células M2+ estavam dispersas no tecido cordonal e as CD8+ coraram-se de modo similar às células CD4+