Effect of external pressure on the magnetic properties of RRCoAsO (RR = La, Pr, Sm): a μ\muSR study

We report on a detailed investigation of the itinerant ferromagnets LaCoAsO, PrCoAsO and SmCoAsO performed by means of muon spin spectroscopy upon the application of external hydrostatic pressures $p$ up to $2.4$ GPa. These materials are shown to be magnetically hard in view of the weak dependence of both critical temperatures $T_{C}$ and internal fields at the muon site on $p$. In the cases $R$ = La and Sm, the behaviour of the internal field is substantially unaltered up to $p = 2.4$ GPa. A much richer phenomenology is detected in PrCoAsO instead, possibly associated with a strong $p$ dependence of the statistical population of the two different crystallographic sites for the muon. Surprisingly, results are notably different from what is observed in the case of the isostructural compounds $R$CoPO, where the full As/P substitution is already inducing a strong chemical pressure within the lattice but $p$ is still very effective in further affecting the magnetic properties.Comment: 8 pages, 9 figure

Common effect of chemical and external pressures on the magnetic properties of RECoPO (RE = La, Pr)

We report a detailed investigation of RECoPO (RE = La, Pr) and LaCoAsO materials performed by means of muon spin spectroscopy. Zero-field measurements show that the electrons localized on the Pr$^{3+}$ ions do not play any role in the static magnetic properties of the compounds. Magnetism at the local level is indeed fully dominated by the weakly-itinerant ferromagnetism from the Co sublattice only. The increase of the chemical pressure triggered by the different ionic radii of La$^{3+}$ and Pr$^{3+}$, on the other hand, plays a crucial role in enhancing the value of the magnetic critical temperature and can be mimicked by the application of external hydrostatic pressure up to 24 kbar. A sharp discontinuity in the local magnetic field at the muon site in LaCoPO at around 5 kbar suggests a sizeable modification in the band structure of the material upon increasing pressure. This scenario is qualitatively supported by \emph{ab-initio} density-functional theory calculations.Comment: 13 pages, 10 figure

Mohos toxigénicos y micotoxinas en maíz y otros cultivos en Venezuela

Desde su formación en la planta hasta que son procesados los granos están expuestos a la acción de factores abióticos y bióticos que determinan su calidad. Los mohos han recibido especial atención por sus implicaciones tanto en salud pública como animal y por los enormes perjuicios económicos que pueden ocasionar. Los que han recibido mayor atención son especies de los géneros Aspergillus, Fusarium y Penicillium. En regiones tropicales y subtropicales las especies y las micotoxinas más importantes son Aspergillus flavus y las aflatoxinas, Fusarium verticilloides y las fumonisinas, y Aspergillus ochraceus y las ocratoxinas. Dependiendo de la micotoxina, su concentración y el tiempo de exposición, sus efectos sobre animales y humanos son variables; pueden ser carcinogénicas, mutagénicas, teratogénicas, inmunosupresivas, neurotóxicas, hepatotóxicas y nefrotóxicas, entre otros. La magnitud de la colonización y el contenido de micotoxinas dependen de muchos factores que actúan durante el proceso productivo y en ese sentido la prevención se basa en minimizar el mayor número de estos. En Venezuela prevalecen condiciones altamente favorables para el crecimiento de los mohos y la síntesis de micotoxinas en granos de cereales y otros cultivos; sin embargo, la magnitud del problema y sus posibles implicaciones en salud pública y animal son hasta ahora desconocidos. Un considerable número de investigaciones, a lo largo de los últimos cuarenta años, demostraron su importancia en maíz, arroz, sorgo, maní, leguminosas de grano, café y almendras de cacao, entre otros cultivos. Destaca el hecho de que no se realiza la capacitación de los productores del campo (agricultores) para prevenir el problema desde el inicio de la cadena productiva.   Toxigenic molds and mycotoxins in maize and other crops in Venezuela ABSTRACT From their formation in the plant until they are processed, grains are exposed to the action of abiotic and biotic factors that determine their quality. Molds have received special attention because of their implications for public and animal health and because of the enormous economic damage they can cause. Those that have received most attention are species of the genera Aspergillus, Fusarium and Penicillium. In tropical and subtropical regions the most important species and mycotoxins are Aspergillus flavus and aflatoxins, Fusarium verticilloides and fumonisins, and Aspergillus ochraceus and ochratoxins. Depending on the mycotoxin, its concentration and exposure time, their effects on animals and humans are variable; they can be carcinogenic, mutagenic, teratogenic, immunosuppressive, neurotoxic, hepatotoxic and nephrotoxic, among others. The magnitude of colonization and the content of mycotoxins depend on many factors that act during the production process and in this sense, prevention is based on minimizing the greatest number of these factors. In Venezuela, highly favorable conditions prevail for the growth of molds and the synthesis of mycotoxins in cereal grains and other crops; however, the magnitude of the problem and its possible implications in public and animal health are so far unknown. A considerable amount of research over the last forty years has demonstrated its importance in maize, rice, sorghum, peanuts, grain legumes, coffee and cocoa beans, among other crops. It is important to highlight the fact that there is no training of farmers to prevent the problem from the beginning of the production chain.

CARACTERIZACIÓN DE ADITIVOS ENZIMÁTICOS OBTENIDOS POR MONOCULTIVO (Aspergillus niger) Y COCULTIVO (Aspergillus niger-Saccharomyces cerevisiae) Y SU EFECTO SOBRE EL COMPORTAMIENTO PRODUCTIVO DE POLLOS DE ENGORDE

Se obtuvieron y caracterizaron las propiedades nutricionales, enzimáticas y ocratoxigénicas de aditivos enzimáticos obtenidos de residuos húmedos del procesamiento de la pasta alimenticia, fermentados mediante el monocultivo de Aspergillus niger (A1) y el cocultivo de Aspergillus niger - Saccharomyces cerevisiae (A2). Se utilizaron 150 pollitos raza Cobb-500 para evaluar el efecto de la inclusión de los aditivos A1 y A2 en 30 ppm y 3000 ppm, respectivamente, durante 21 d sobre los parámetros productivos, utilizando un diseño completamente aleatorizado. Los resultados demuestran que las actividades de lasa-amilasas y glucoamilasas en el A2 fueron superiores en 42% y 69% a las del A1, respectivamente. La composición fisicoquímica y las propiedades enzimáticas de los aditivos, revelaron que éstos están compuestos principalmente por almidón y proteína, con una actividad amilolítica similar 16020 y 15540 (FAU/g), respectivamente. Sin embargo, el A2 presentó actividad de glucoamilasa (U/g) y de fitasas (U/g) superior en 58%, respecto al A1. Los niveles de ocratoxina A de 2.10-4 y 2.10-2 ppb para A1 y A2, respectivamente, fueron inferiores a la dosis letales medias (DL50) para pollos y a los límites establecidos por la FAO/OMS. Adicionalmente, la viabilidad de Aspergillus niger  en A1 y A2 fue de 3.103 UFC/mL y de 2.102 UFC/mL en las células de levadura, respectivamente. La inclusión de 3000 ppm de A1 y de 30 ppm de A2, mejoró significativamente (P<0,05) la conversión alimenticia (11-13%) y el consumo de alimento (6-8%), al compararse con el grupo control. La ganancia de peso no fue afectada significativamente por los tratamientos.   (Palabras clave: Pollos de engorde; Aspergillus niger; Saccharomyces cerevisiae; aditivos alimentarios; dieta; fermentación)     Abstract   A study was conducted to obtain and characterize the nutritional, enzymatic, and ocratoxigenic properties of enzyme additives obtained from fermentation of moist residues of commercial production of pasta, of both a monoculture of Aspergillus niger (A1) and a mixed culture (coculture) of Aspergillus niger-Saccharomyces cerevisiae (A2). The effects on productive performance parameters were assessed, during 21 d. A total of 150 broilers (Cobb-500) were used and fed with diets which included the additives A1 and A2 in the amount of 30 and 3000 ppm, respectively, using a completely randomized design. The results show that both a-amylase and glucoamylase activities in A2 were 42 and 69% higher than those of A1, respectively. The physicochemical composition of additives revealed that they are mainly composed of starch and protein. Both A1 and A2 showed a similar amylase activity (15540 and 16020 FAU/g, respectively). However, the A2 exhibited higher glucoamylase and phytase activities (U/g) 58% than the A1. The ocratoxin A levels for A1 (2.10-4 ppb) and A2 (2.10-2 ppb), respectively, were below the median lethal dose (LD50) for chickens and for the limits established by FAO/WHO. Additionally, the viability of Aspergillus niger in A1 and A2 was 3.103 UFC/mL and of 2.102 CFU/mL in yeast cells, respectively. The inclusion of 30 ppm of A1 and 3000 ppm of A2, respectively significantly (P<0.05) improved feed conversion (11-13%) and feed intake (6-8%), when compared to control animals. The treatments did not significantly affect weight gain.   (Key words: Broiler chickens; Aspergillus niger; Saccharomyces cerevisiae; food additives; diet; enzyme; fermentation

Effect of external pressure on the magnetic properties of RCoAsO (R=La, Pr, Sm): A μSR study

We report on a detailed investigation of the itinerant ferromagnets LaCoAsO, PrCoAsO and SmCoAsO performed by means of muon spin spectroscopy upon the application of external hydrostatic pressures p up to 2.4 GPa. These materials are shown to be magnetically hard in view of the weak dependence of both critical temperatures TC and internal fields at the muon site on p. In the cases R=La and Sm, the behaviour of the internal field is substantially unaltered up to p=2.4 GPa. A much richer phenomenology is detected in PrCoAsO instead, possibly associated with a strong p dependence of the statistical population of the two different crystallographic sites for the muon. Surprisingly, results are notably different from what is observed in the case of the isostructural compounds RCoPO, where the full As/P substitution is leading to smaller values of unit cell volume already at ambient pressure but p is still very effective in further affecting the magnetic properties

Effect of external pressure on the magnetic properties of RCoAsO (R=La, Pr, Sm): a μSR study

We report on a detailed investigation of the itinerant ferromagnets LaCoAsO, PrCoAsO and SmCoAsO performed by means of muon spin spectroscopy upon the application of external hydrostatic pressures p up to 2.4 GPa. These materials are shown to be magnetically hard in view of the weak dependence of both critical temperatures TC and internal fields at the muon site on p. In the cases R=La and Sm, the behaviour of the internal field is substantially unaltered up to p=2.4 GPa. A much richer phenomenology is detected in PrCoAsO instead, possibly associated with a strong p dependence of the statistical population of the two different crystallographic sites for the muon. Surprisingly, results are notably different from what is observed in the case of the isostructural compounds RCoPO, where the full As/P substitution is leading to smaller values of unit cell volume already at ambient pressure but p is still very effective in further affecting the magnetic properties