Method development and validation for the efficient detection of super-attenuating (Over-Fermenting) yeast contaminants (Saccharomyces cerevisiae var. Diastaticus) in the brewery industry

• Autor(a) principal: Tchonkouang, Rose Daphnee Ngameni
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/17791
• topic: Saccharomyces cerevisiae var; Diastaticus; Beer; Spoilage; Super-attenuation; Quality control; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

Saccharomyces cerevisiae var. diastaticus is the most dangerous spoilage yeast of fermented beverages in the brewery industry. In contrast to conventional brewing yeast, diastaticus yeast causes super-attenuation due to its ability to degrade residual dextrin and starch in beers, thereby causing degraded mouthfeel, over-carbonation, high alcohol levels, and package explosion. Usually, a diastaticus contamination can remain unnoticed several months after packaging. Diastaticus yeast is particularly difficult to detect with traditional microbiological analyses due to the common characteristics shared with brewing yeast. The objective of the present study was to optimize/develop the detection and growth control of diastaticus yeasts using three different assays: a) the modified Durham test, b) the dextrin agar test and, c) a novel test developed during this project, called the ‘attenuation test’. Strain DSM 70487 and Strain-Y were used as positive and negative controls, respectively. The attenuation test was the most reliable assay because all the investigated diastaticus strains were detected by monitoring the reduction in density (°P) associated with residual saccharides consumption in fully attenuated beer medium. Although the spoilage yeast strain TUM 1-B-8 demonstrated mild super-attenuating activity in the attenuation test, this strain did not show spoilage potential when assayed for growth on dextrin agar plates and did not demonstrate gas production potential in the Durham test. The positive control DSM 70487 showed spoilage potential in all assays, with the fastest detection time of 2 days recorded in the Durham test. Growth on dextrin agar at pH 5.2 and 6.2 revealed faster growth and more rapid detection at pH 5.2. The lowest detection limit (5x100 cells/ml) was noted in the agar tests. This research demonstrated clear variations in the super-attenuating strength of S. cerevisiae var. diastaticus yeast strains and highlighted the necessity to combine multiple assays for reliable detection of diastaticus activity in investigated samples.