Biological control of postharvest spoilage caused by Penicillium expansum and Botrytis cinerea in apple by using the bacterium Rahnella aquatilis.

The epiphytic bacterium Rahnella aquatilis, isolated from fruit and leaves of apples, was tested for antagonistic properties against Penicillium expansum and Botrytis cinerea on Red Delicious apple fruit. In "in vitro" assays, this bacterium inhibited completely the germination of P. expansum and B. cinerea spores, but it needed direct contact with the spores to do it. However the putative mechanism seemed be different for the two pathogens. The bacterium did not produce extracellular antibiotic substances and when the acute toxicity test was performed no mortality, toxicity symptoms or organ alterations of the test animals (Wistar rats) were observed. Assays of biological control of P. expansum and B. cinerea on apple fruit were carried out at different temperatures. At 15 degrees C and 90% RH, the incidence of disease caused by P. expansum on apples stored for 20 days, was reduced by nearly 100% by R. aquatilis (10(6) cells/ml), while in the case of B. cinerea, the reduction of decay severity was nearly 64% but there was no reduction in the incidence of disease. At 4 degrees C and 90% RH the treatment with the bacterium significantly inhibited the development of B. cinerea on apples stored for 40 days and the incidence of disease was reduced by nearly 100%, while the incidence of disease caused by P. expansum at 4 degrees C was 60%. The results obtained show that R. aquatilis would be an interesting microorganism to be used as a biocontrol agent.

Multienzymatic-rotating biosensor for total cholesterol determination in a FIA system.

Fabrication of an amperometric-rotating biosensor for the enzymatic determination of cholesterol is reported. The assay utilizes a combination of three enzymes: cholesterol esterase (ChE), cholesterol oxidase (ChOx) and peroxidase (HRP); which were co-immobilizing on a rotatory disk. The method is developed by the use of a glassy carbon electrode as detector versus Ag/AgCl/3M NaCl in conjunction with a soluble-redox mediator 4-tert-butylcatechol (TBC). ChE converts esterified cholesterol to free cholesterol, which is then oxidized by ChOx with hydrogen peroxide as product. TBC is converted to 4-tert-butylbenzoquinone (TBB) by hydrogen peroxide, catalyzed by HRP, and the glassy carbon electrode responds to the TBB concentration. The system has integrated a micro packed-column with immobilized ascorbate oxidase (AAOx) that works as prereactor to eliminate l-ascorbic acid (AA) interference. This method could be used to determine total cholesterol concentration in the range 1.2muM-1mM (r=0.999). A fast response time of 2min has been observed with this amperometric-rotating biosensor. Lifetime is up to 25 days of use. The calculated detection limits was 11.9nM. Reproducibility assays were made using repetitive standards solutions (n=5) and the percentage standard error was less than 4%.

Estudio sobre la preselección de cepas de Aspergillus niger destinada a la producción de acido citrico / Preselection of aspergillus niger strains in citric acid production

El objetivo del presente trabajo fue establecer parámetros que permitan en forma rápida y sencilla, predecir la habilidad de distintas cepas de Aspergillus niger, para producir ácido cítrico. Se logró establecer una relación entre morfología y productividad. Así mismo se diseñó un medio sólido de facil manejo, que evidencia rápidamente la producción de un buen nivel de ácido cítrico, por la cepa en estudios. La efectividad de la selección fue luego confirmada mediante la productividad en un cultivo sumergido