Influence of airflow intensity on phytase production by solid-state fermentation.

Phytase production by Aspergillus niger F3 by solid state fermentation (SSF) on citrus peel was evaluated at pilot scale under different aeration conditions. The best airflow intensity was 1 VkgM (Lair kg medium(-1) min(-1)), which allowed to produce 65 units of phytases per gram in dry basis (65 Ug(-1) d.b.) as it removed the metabolic heat generated by the microorganism, Agitation did not improve heat removal. Airflow intensity was considered as scale-up criterion. When the airflow intensity was maintained at 1 VkgM for SSF with 2 and 20 kg of medium, the kinetics parameters for biomass and enzyme concentration at the end of fermentation differed by less than 2. The air flow intensity was required to maintain the temperature and cool the SSF and to provide oxygen for microbial growth. Air flow intensity is a key a factor that must be considered when scale-up of SSF is attempted.

[Stability of Lactococcus lactis phages treated with sodium hypochlorite and during storage]. / Estabilidad de fagos de Lactococcus lactis frente al hipoclorito de sodio y durante el almacenamiento.

Survival of lytic bacteriophages active against Lactococcus lactis ssp. lactis and ssp. cremoris was determined after treatment with sodium hypochlorite and during storage at 4 degrees C. Three phages were isolated from dairy plants in Argentina (ARG) and the other phages were isolated in the United States of America (US). All of them represent phages that infected cheese manufacture industries and belong to different morphological or serological groups. These phages showed higher survival in M17 broth, buffered with sodium glycerophosphate, than in trypteine soy broth (TSB). Phage populations did not decrease significantly during 14 weeks in M17 broth, whereas in TSB the titers of phage suspensions began to decline around 9 days. In addition, the effect of sodium hypochlorite was more marked in broth than in milk. A higher surviving fraction was obtained in milk, even when tenfold higher concentrations of chlorine were used. The effect of hypochlorite on phages of the same serological group was quite similar and independent of phage morphology. However, phage 137-1, which belongs to other serological group, showed lower resistance to sodium hypochlorite. Comparing the hypochlorite inactivation for ARG and US phages, it was observed that they have their own inactivation values, independently of their origin and morphological group. Long periods of time and high concentrations of chlorine were necessary to reduce the surviving fraction in milk. This indicates that hypochlorite concentrations and times of contact can be critical for the efficiency of the operative sanitization processes.

Estabilidad de fagos de Lactococcus lactis frente al hipoclorito de sodio y durante el almacenamiento / Stability of Lactococcus lactis phages treated with sodium hypochlorite and during storage

Survival of lytic bacteriophages active against Lactococcus lactis ssp. lactis and ssp. cremoris was determined after treatment with sodium hypochlorite and during storage at 4 degrees C. Three phages were isolated from dairy plants in Argentina (ARG) and the other phages were isolated in the United States of America (US). All of them represent phages that infected cheese manufacture industries and belong to different morphological or serological groups. These phages showed higher survival in M17 broth, buffered with sodium glycerophosphate, than in trypteine soy broth (TSB). Phage populations did not decrease significantly during 14 weeks in M17 broth, whereas in TSB the titers of phage suspensions began to decline around 9 days. In addition, the effect of sodium hypochlorite was more marked in broth than in milk. A higher surviving fraction was obtained in milk, even when tenfold higher concentrations of chlorine were used. The effect of hypochlorite on phages of the same serological group was quite similar and independent of phage morphology. However, phage 137-1, which belongs to other serological group, showed lower resistance to sodium hypochlorite. Comparing the hypochlorite inactivation for ARG and US phages, it was observed that they have their own inactivation values, independently of their origin and morphological group. Long periods of time and high concentrations of chlorine were necessary to reduce the surviving fraction in milk. This indicates that hypochlorite concentrations and times of contact can be critical for the efficiency of the operative sanitization processes.

Estabilidad de fagos de Lactococcus lactis frente al hipoclorito de sodio y durante el almacenamiento / Stability of Lactococcus lactis phages treated with sodium hypochlorite and during storage

Survival of lytic bacteriophages active against Lactococcus lactis ssp. lactis and ssp. cremoris was determined after treatment with sodium hypochlorite and during storage at 4 degrees C. Three phages were isolated from dairy plants in Argentina (ARG) and the other phages were isolated in the United States of America (US). All of them represent phages that infected cheese manufacture industries and belong to different morphological or serological groups. These phages showed higher survival in M17 broth, buffered with sodium glycerophosphate, than in trypteine soy broth (TSB). Phage populations did not decrease significantly during 14 weeks in M17 broth, whereas in TSB the titers of phage suspensions began to decline around 9 days. In addition, the effect of sodium hypochlorite was more marked in broth than in milk. A higher surviving fraction was obtained in milk, even when tenfold higher concentrations of chlorine were used. The effect of hypochlorite on phages of the same serological group was quite similar and independent of phage morphology. However, phage 137-1, which belongs to other serological group, showed lower resistance to sodium hypochlorite. Comparing the hypochlorite inactivation for ARG and US phages, it was observed that they have their own inactivation values, independently of their origin and morphological group. Long periods of time and high concentrations of chlorine were necessary to reduce the surviving fraction in milk. This indicates that hypochlorite concentrations and times of contact can be critical for the efficiency of the operative sanitization processes.(AU)

Estabilidad de fagos de Lactococcus lactis frente al hipoclorito de sodio y durante el almacenamiento. / [Stability of Lactococcus lactis phages treated with sodium hypochlorite and during storage]

Survival of lytic bacteriophages active against Lactococcus lactis ssp. lactis and ssp. cremoris was determined after treatment with sodium hypochlorite and during storage at 4 degrees C. Three phages were isolated from dairy plants in Argentina (ARG) and the other phages were isolated in the United States of America (US). All of them represent phages that infected cheese manufacture industries and belong to different morphological or serological groups. These phages showed higher survival in M17 broth, buffered with sodium glycerophosphate, than in trypteine soy broth (TSB). Phage populations did not decrease significantly during 14 weeks in M17 broth, whereas in TSB the titers of phage suspensions began to decline around 9 days. In addition, the effect of sodium hypochlorite was more marked in broth than in milk. A higher surviving fraction was obtained in milk, even when tenfold higher concentrations of chlorine were used. The effect of hypochlorite on phages of the same serological group was quite similar and independent of phage morphology. However, phage 137-1, which belongs to other serological group, showed lower resistance to sodium hypochlorite. Comparing the hypochlorite inactivation for ARG and US phages, it was observed that they have their own inactivation values, independently of their origin and morphological group. Long periods of time and high concentrations of chlorine were necessary to reduce the surviving fraction in milk. This indicates that hypochlorite concentrations and times of contact can be critical for the efficiency of the operative sanitization processes.

Yersinia enterocolitica biogroup 1A, serotype O:5 in chicken carcasses.

To evaluate the presence of Yersinia enterocolitica in raw chicken, 70 samples of chicken carcasses were obtained from a Buenos Aires, Argentina, processing plant. The detection of this psychotropic microorganism was carried out using the whole carcass rinse method and enrichment in phosphate-buffered saline, 0.067 M, pH 7.6, at 4 degrees C, followed by alkaline treatment and isolation on cefsulodin-irgasan-novobiocin nutrient agar. Y. enterocolitica or related species were detected in 7 of 70 samples. From them, 4.3% were identified as Y. enterocolitica, 1.4% as Yersinia intermedia, and 4.3% as Yersinia frederiksenii. The serotype and phagotype of Y. intermedia isolates were O:5(2), 5(3), and Xz and those of Y. frederiksenii were O:4.16 and Xo. All Y. enterocolitica isolates belong to the biogroup 1A, serotype O:5, phagotype Xz, which presents uncertain pathogenic potential. These findings reinforce the worldwide concern on the microbiological quality of food products. Quality assurance programs on the whole poultry process are increasingly being adopted in Argentina.

[Relationship between food habits and serum cholesterol levels in a suburban population in Argentina]. / Relación entre hábitos alimentarios y niveles de colesterol sérico en una población suburbana de Argentina.

Studies of cholesterol levels in a population of Gran Buenos Aires was made in 1983, 1988, 1993 and 1996, and the Argentinian alimentary habits in this period were analyzed. It was noticed a change in food consumption, with reduction in the intake of fatty foods, such as meat, butter, milk, and other dairy products, with the concomitant increment in fiber rich products and oil, meat and dairy products reduced in fats. Changes in serum cholesterol level were analysed in 3051 persons along 1983-1996. They were grouped according their age and sex: A) 1-6 years old, B) 6-12, C) 12-17, D) 17-30, E) 30-60, F) 60-80. It was observed an increment in cholesterol level with age. For each group during the first 10 years of study was noticed a constant decrease in total cholesterol being higher in women than in men and according with the alimentary changes. Group D in 1983 became group E in 1993, maintained their cholesterol level along 10 years of life, being lower than the corresponding E group of 1983, while the older ones did not present differences. Values of cholesterol/cholesterol-HDL index over 6.5 correlate with a high incidence in cardiovascular diseases. The 40% of the population studied during 1993 and 1996 was evaluated, and the maximum average value found was 4.90. These results suggest that reduction in fat intake and diversification in food consumption during this period has contributed to decrease cholesterol levels and cholesterol/cholesterol-HDL index, particularly in younger than 30 years old and women, contributing to reduce metabolical cardiovascular diseases.

Lactic acid bacteria growth promoters from Spirulina platensis.

Spirulina has been used for many years as human food because of its high protein content and nutritional value. Some strains also produce bioactive substances that may inhibit or promote microbial growth. Lactococcus lactis, Streptococcus thermophilus, Lactobacillus casei, Lactobacillus acidophilus, and Lactobacillus bulgaricus were grown in rich media, MRS and RM, as well as in minimal saline medium with and without addition of extracellular products obtained from a late log phase culture of Spirulina platensis in Zarrouk medium. In both MRS and RM media, the extracellular products significantly promote the growth of the lactic acid bacteria assayed. This stimulatory effect was observed in media with pH adjusted to 5.3, 6.3 and 7.0. No effect was observed in minimal saline medium.

Microbiological and technological aspects of cassava-starch fermentation.

The major genera found in the microflora of fermented, sour, cassava-starch were Streptococcus, Bacillus, Lactobacillus and Saccharomyces with amylase activity. Lactic acid bacteria predominated whereas the presence of moulds was not significant. No coliforms were detected. Electron microscopy showed bacteria and yeasts in contact with the starch granules and signs of erosion on the granule surface. Lactic acid was the main metabolite; no oligosaccharides, maltose or glucose were detected, indicating their rapid utilization. The degree of acidification, which correlated with the decrease in viscosity and the final quality of the product, was influenced by the variable microbial ecology.

Comparison of lactococcal bacteriophage isolated in the United States and Argentina.

Bacteriophage of Lactococcus lactis ssp. lactis and ssp. cremoris, isolated in the United States and Argentina, were compared with respect to host range, adsorption, latent period, burst size and immunological cross-reactivity. Only 1 out of 13 U.S. culture isolates was sensitive to Argentinian phage. Argentinian L. lactis ssp. lactis C2 mutants were resistant to 13 U.S. phage isolates (4 prolate and 9 isometric). While Argentinian phage Stl-3 multiplied on U.S. culture isolate 59-1, low adsorption (38%) and insignificant burst size and latent period data were evident. Antisera prepared against U.S. phage D59-1 (prolate) and F4-1 (isometric) neutralized the lytic activities of all Argentinian prolate phage although the F4-1 antiserum was less effective. The data suggest homology especially between U.S. phage D59-1 and the Argentinian phage.

Crecimiento de Staphylococcus aureus en medios sólidos de actividad acuosa inferior a 0,86 / Growth of Staphylococcus aureus in solid media with a water activity less than 0,86

El propósito de este estudio fue determinar si distintas cepas de S. aureus podían desarrollar en sustratos sólidos con actividad acuosa 0,843 equilibrados por adsorción acuosa. Los medios sólidos usados incluían polvos deshidratados de carne de vaca, carne de cerdo y leche como sustratos básicos a los que se les agregó una fuente adicional de nutrientes para compensar las eventuales deficiencias producidas en el proceso de cocción y deshidratación. Las cepas analizadas fueron: ATCC6538P, FDA-C243, NAI y FM1. Se observó que ninguna de ellas desarrolló a 30 -C en dichos medios con actividad acuosa 0,843. Estos datos se compararon con otros donde se observó que S. aureus desarrolla en niveles de actividad acuosa comprendido entre 0,83 y 0,84 y discutidas las diferencias en el valor mínimo informado para el desarrollo de S. aureus

Crecimiento de Staphylococcus aureus en medios sólidos de actividad acuosa inferior a 0,86 / Growth of Staphylococcus aureus in solid media with a water activity less than 0,86

El propósito de este estudio fue determinar si distintas cepas de S. aureus podían desarrollar en sustratos sólidos con actividad acuosa 0,843 equilibrados por adsorción acuosa. Los medios sólidos usados incluían polvos deshidratados de carne de vaca, carne de cerdo y leche como sustratos básicos a los que se les agregó una fuente adicional de nutrientes para compensar las eventuales deficiencias producidas en el proceso de cocción y deshidratación. Las cepas analizadas fueron: ATCC6538P, FDA-C243, NAI y FM1. Se observó que ninguna de ellas desarrolló a 30 -C en dichos medios con actividad acuosa 0,843. Estos datos se compararon con otros donde se observó que S. aureus desarrolla en niveles de actividad acuosa comprendido entre 0,83 y 0,84 y discutidas las diferencias en el valor mínimo informado para el desarrollo de S. aureus (AU)

[Growth of Staphylococcus aureus in solid media with a water activity less than 0.86]. / Crecimiento de Staphylococcus aureus en medios sólidos de actividad acuosa inferior a 0.86.

The purpose of this study was to determine whether S. aureus could grow in solid substrates with aw 0.843 adjusted by water adsorption. The media used included dehydrated powder of pork, beef and milk as basic substrates in order to compensate an eventual deficiency; additional source of nutrients was added. The tested strains were ATCC 6538 P, FDA-C243, NA1 and FM1. It was observed that no strain grew at 30 degrees C in those media at aw 0.843. These data were compared with others which indicate that S. aureus could grow al aw 0.83-0.84. The possible reasons for the difference in the minimal aw value reported to be required for the growth of S. aureus are discussed.

Crecimiento de Staphylococcus aureus en medios sólidos de actividad acuosa inferior a 0.86. / [Growth of Staphylococcus aureus in solid media with a water activity less than 0.86]

The purpose of this study was to determine whether S. aureus could grow in solid substrates with aw 0.843 adjusted by water adsorption. The media used included dehydrated powder of pork, beef and milk as basic substrates in order to compensate an eventual deficiency; additional source of nutrients was added. The tested strains were ATCC 6538 P, FDA-C243, NA1 and FM1. It was observed that no strain grew at 30 degrees C in those media at aw 0.843. These data were compared with others which indicate that S. aureus could grow al aw 0.83-0.84. The possible reasons for the difference in the minimal aw value reported to be required for the growth of S. aureus are discussed.

Mutante de Streptococcus lactis con resistencia a bacteriófagos aislados en Argentina y Estados Unidos de América / A mutant of Streptococcus lactis with resistance to bacteriophages isolated in Argentina and the United States of America

Streptococcuslactis y S. cremoris, bacterias lácticas utilizadas para la producción de quesos, pueden reesultar infectadas por bacteriófago específicos, lo que ocasiona alteraciones en la calidad, disminución de la productividad económicas significativas. Los métodos de desinfección y control más usuales no siempre resultan en una completa protección contra la proliferación de los fagos, por los que se ha recurrido al empleo de cepas resistentes a los mismos. En el presente trabajo se ha empleado un método simple y directo para obtener mutantes espontáneas de S. lactis con resistencia a fagos. La mutante S.lacts C26 obtenida a partir de la cepa S. lactis C2 sensible a fagos exhibe propiedades bioquímicas y microbiológicas similares a las de la cepa original C2, diferenciándose de ella por una clara resistencia al fago St15, de morfología alargada, utilizado para la selección. Las curvas de la cinética de crecimiento de la mutante en ausencia y en presencia del fago resultaron semejantes. La cepa C26 fue controlada con otros dos fagos aislados en Argentina y con seis fagos de dos tipos morfológicos, aislados en la Universidad de Cornell en EE.UU. La cepa C26 que fuera aislada como mutante resistente al fafo St15, resultó también resistente a todos ellos. Por otra parte, ha sido de interés verficar que los fagos no siempre observan una especificidad estricta con respecto a la especie de la célula huésped. El fago D59-1, aislado utilizando una cepa S. cremoris, también provoca una lisis significativa en la cepa S. lactis C2, suiriendo que ambas poseen sitios receptores semejantes. La mutante C26 fue empleada con éxito en Buenos Aires, en la planta elaborada de quesos donde fuera aislado el fago St15, lo que alienta la posibilidad de emplear esta metodología en el desarrollo de fermentos lácticos

Mutante de Streptococcus lactis con resistencia a bacteriófagos aislados en Argentina y Estados Unidos de América / A mutant of Streptococcus lactis with resistance to bacteriophages isolated in Argentina and the United States of America

Streptococcuslactis y S. cremoris, bacterias lácticas utilizadas para la producción de quesos, pueden reesultar infectadas por bacteriófago específicos, lo que ocasiona alteraciones en la calidad, disminución de la productividad económicas significativas. Los métodos de desinfección y control más usuales no siempre resultan en una completa protección contra la proliferación de los fagos, por los que se ha recurrido al empleo de cepas resistentes a los mismos. En el presente trabajo se ha empleado un método simple y directo para obtener mutantes espontáneas de S. lactis con resistencia a fagos. La mutante S.lacts C26 obtenida a partir de la cepa S. lactis C2 sensible a fagos exhibe propiedades bioquímicas y microbiológicas similares a las de la cepa original C2, diferenciándose de ella por una clara resistencia al fago St15, de morfología alargada, utilizado para la selección. Las curvas de la cinética de crecimiento de la mutante en ausencia y en presencia del fago resultaron semejantes. La cepa C26 fue controlada con otros dos fagos aislados en Argentina y con seis fagos de dos tipos morfológicos, aislados en la Universidad de Cornell en EE.UU. La cepa C26 que fuera aislada como mutante resistente al fafo St15, resultó también resistente a todos ellos. Por otra parte, ha sido de interés verficar que los fagos no siempre observan una especificidad estricta con respecto a la especie de la célula huésped. El fago D59-1, aislado utilizando una cepa S. cremoris, también provoca una lisis significativa en la cepa S. lactis C2, suiriendo que ambas poseen sitios receptores semejantes. La mutante C26 fue empleada con éxito en Buenos Aires, en la planta elaborada de quesos donde fuera aislado el fago St15, lo que alienta la posibilidad de emplear esta metodología en el desarrollo de fermentos lácticos (AU)