Monday, April 30, 2007

Yeast biomass production in brewery's spent grains hemicellulosic hydrolysate

L. C. Duarte, Florbela Carvalheiro, S. Lopes, I. Neves, and Francisco M. Gírio. Departamento de Biotecnologia, INETI, Estrada do Paço do Lumiar, 22, Lisboa, 1649-038, Portugal

Yeast single cell protein and yeast extract (YE) in particular, are two products, which have many feed, food, pharmaceutical and biotechnological applications. Many of these applications are limited by its market price. Specifically, YE requirement is one of the major technical hurdles to be overcome for the development of low cost fermentation routes for several top value chemicals in the biorefinery framework. A possible solution is the exploitation of yeast biomass derived or produced from the hemicellulosic fraction stream.

Three pentose-assimilating yeast cell factories, Debaryomyces hansenii, Kluyveromyces marxianus and Pichia stipitis were compared when grown in shake flasks, using non-detoxified brewery’s spent grains hemicellulosic hydrolyzates supplemented with mineral nutrients. The yeasts exhibited different specific growth rate, biomass productivity and yield, with D. hansenii being the one that presented the best performance, assimilating all sugars and also consuming most of the inhibitors present. This yeast has also a potential GRAS status.

Under optimized conditions D. hansenii displayed a maximum specific growth rate, biomass yield and productivity of 0.34 h-1, 0.61 g g-1 and 0.56 g l-1 h-1, respectively. The nutritional profile of D. hansenii was thoroughly evaluated and it compares favorably to others reported in literature. It contains considerable amounts of some essential amino acids and a high ratio of unsaturated over saturated fatty acids.