Surface-engineered Saccharomyces cerevisiae displaying α-acetolactate decarboxylase from Acetobacter aceti ssp xylinum.

Abstract

To convert α-acetolactate into acetoin by an α-acetolactate decarboxylase (ALDC) to prevent its conversion into diacetyl that gives beer an unfavourable buttery flavour. We constructed a whole Saccharomyces cerevisiae cell catalyst with a truncated active ALDC from Acetobacter aceti ssp xylinum attached to the cell wall using the C-terminal anchoring domain of α-agglutinin. ALDC variants in which 43 and 69 N-terminal residues were absent performed equally well and had significantly decreased amounts of diacetyl during fermentation. With these cells, the highest concentrations of diacetyl observed during fermentation were 30% less than those in wort fermented with control yeasts displaying only the anchoring domain and, unlike the control, virtually no diacetyl was present in wort after 7days of fermentation. Since modification of yeasts with ALDC variants did not affect their fermentation performance, the display of α-acetolactate decarboxylase activity is an effective approach to decrease the formation of diacetyl during beer fermentation.