Reference Number: 26
A review on the main aspects associated with yeast flocculation and its application in biotechnological processes is presented. This subject is addressed following three main aspects – the basics of yeast flocculation, the development of “new” flocculating yeast strains and bioreactor development. The construction of flocculating yeast strains includes not only the recombinant constitutive flocculent brewer’s yeast, but also recombinant flocculent yeast for lactose metabolisation and ethanol production. As bioreactors using flocculating yeast cells have particular properties, mainly associated with a high solid phase hold-up, a section dedicated to its operation is presented. Aspects such as bioreactor productivity and culture stability as well as bioreactor hydrodynamics and mass transfer properties of flocculating cell cultures are considered. Finally, the paper concludes describing some of the applications of high cell density flocculation bioreactors and discussing potential new uses of these systems.
SIGNIFICANCE OF THIS STUDY
Yeast flocculation is defined as the non-sexual cell aggregation of yeast cells which helps in the speeding up the fermentation process during the making of bread or alcoholic beverages. Flocculated yeast has been shown to increase productivity compared to non-flocculated yeasts and this might be responsible for a greater rate of fermentation and shorter dough rising periods when making long slow fermented breads. Minerals such as calcium and magnesium are important for yeast flocculation to occur. For this reason, the use of unrinsed salts that are naturally high in these minerals provide the most ideal environment for yeast flocculation to occur and result in shorter dough rising periods that also provide favourable sourdough breads in terms of texture.