Analysis of Commercially Available Active Dry Yeast Used for Industrial Fuel Ethanol Production

摘要

Siete levaduras activas secas industriales (ADY) que se venden específicamente para la producción de alcohol combustible, pero que podrán tener linaje de cerveza, vino, o pan (debido a la indisponibilidad de cepas especialmente seleccionadas para uso de alcohol combustible), fueron obtenidas de diferentes proveedores. Todas fueron sujetadas a métodos de investigación tradicionales para determinar viabilidad, niveles de contaminante, velocidad de fermentación, tiempos de generación, temperatura óptima de fermentación, y funcionamiento fermentante en macerados de maíz normales y de muy alta gravedad. También se compararon usando dos técnicas moleculares, cariotipo y análisis ADN mitocondrial. Se observo que de las siete muestras, una tenía una viabilidad perceptiblemente más baja comparada a la norma industrial prevista de aproximadamente 2.2 x 10~(10) células/g. Una muestra tenía altos niveles de contaminantes (0.1% bacteria anaerobia), sugiriendo que esta ADY no se utilice debido al riesgo de contaminación bacteriana y pérdida subsecuente de producción de etanol durante fermentación. De más importancia, el examen molecular de las siete ADY reveló solamente cuatro patrones cariotipicos distintos. El análisis ADN mitocondrial confirmó los resultados ca- riotipicos, pero solamente se podían observar tres patrones distintos.%Seven industrial active dry yeasts (ADY) that are sold specifically for fuel alcohol production, but which may have brewing, winery, or bakery lineage (due to unavailability of specially selected strains for fuel alcohol use), were obtained from different suppliers. All were subjected to traditional screening methods to assess viability, contaminant levels, fermentation rates, generation times, optimal fermentation temperature, and fermentative performance in normal and very-high-gravity corn mashes. They were also compared by using two molecular techniques, karyotyp-ing and mitochondrial DNA analysis. It was observed that of the seven samples, one had a significantly lower viability compared with the expected industrial norm of approximately 2.2 x 10~(10) cells/g. One sample had high levels of contaminants (0.1% anaerobic bacteria), suggesting that this ADY should not be used because of the risk of bacterial contamination and subsequent loss of ethanol yield during fermentation. More importantly, of the seven ADY, molecular examination revealed only four distinct karyotypic patterns. Mitochondrial DNA analysis confirmed the karyotypic results, but only three distinct patterns could be seen. These results demonstrated that of the seven ADY, only three unique yeast profiles were present. These results strongly suggest that many of the industrially available ADY are similar and indicate that yeasts may have been purchased by contract for resale or that some companies may have procured, grown, and sold the yeasts of their competitors.