VIEW ARTICLE    http://dx.doi.org/10.1094/ASBCJ-2014-0320-01

Strengthening of Cell Wall Structure Enhances Stress Resistance and Fermentation Performance in Lager Yeast. Xin-er Li and Jin-jing Wang, The Key Laboratory of Industrial Biotechnology, and Lab of Brewing Science and Technology, Ministry of Education; School of Biotechnology, Jiangnan University, Wuxi 214122, China; Supatcha Phornsanthia, Biotechnology Department of Argo-Industry Faculty, 50 Ngamwongwan Road, Chatuchak, Bangkok 10900, Thailand; Xiangsheng Yin, Cargill Malt, McGinty Road West, MS 135, Wayzata, MN 55391; and Qi Li (1), The Key Laboratory of Industrial Biotechnology, and Lab of Brewing Science and Technology, Ministry of Education; School of Biotechnology, Jiangnan University, Wuxi 214122, China. (1) Corresponding author. E-mail: <liqi@jiangnan.edu.cn>; phone: +86-510-85918176; fax: +86-510-85918176. J. Am. Soc. Brew. Chem. 72(2):88-94, 2014.

Brewing condition exposes lager yeast to a continuous mix of stresses, which decreases cell viability and fermentation efficiency. Recent studies have indicated the close correlation between strain stress resistance and cell wall modification. Here, using micafungin as the selection marker, two stress-resistant mutants, MR0-8 and MR1-2, with thickened cell walls, were screened via traditional UV mutagenesis strategy. Quantitative analysis of cell wall components in MR0-8 and MR1-2 showed 64% and 52% higher glucan contents, 26% and 33% higher mannan contents, and 34% and 31% higher chitin contents, respectively, than those in the parent strain. During high-gravity brewing, the mutant strains showed efficient fermentation rates, increased cell viabilities, and increased intracellular trehalose levels compared with those of the parent strain. Meanwhile, beers fermented by the mutants had balanced flavor profiles and lower contents of diacetyl than those of the parent strain fermented beer. Moreover, levels of protease A released from mutants under nutrient limitation stress were 0.5-fold of that from the parent strain. In summary, strengthening cell wall structure improved stress resistance and the newly screened strains showed great potential in high-gravity brewing. Keywords: Cell wall mannoprotein, Cell wall structure, Fermentation performance, Lager yeast, Micafungin, Stress resistance

La levadura es expuesta a una continua mezcla de eventos estresantes por las condiciones normales cerveceras, disminuyendo la viabilidad de sus células y su eficiencia fermentativa. Estudios recientes indican que existe una correlación fuerte entre la resistencia al estrés y la modificación de la pared de la célula. Usando micafungin como el marcador selectivo, se revisaron dos mutantes resistentes al estrés con paredes celulares gruesas, MR-0-8 y MR1-2, mediante la estrategia tradicional con mutagénesis de UV. Análisis cuantitativa de los componentes de la pared celular de estos mutantes mostró que tenían 64% y 52% mayor contenido de glucano, 26% y 33% mayor contenido de manano y 34% y 31% mayor contenido de quitina, que los contenidos en las cepas parentales. Las cepas mutantes mostraron, en la elaboración de cervezas “high-gravity,” tasas eficientes de fermentación, mayor viabilidad de sus células y mayores niveles de trehalosa intracelular, en comparación con las cepas parentales. Cervezas fermentadas por los mutantes tenían un perfil sensorial balanceado y menor contenido de diacetilo que las cepas parentales. Los niveles de proteasa A liberado por los mutantes bajo estrés causado por una limitación de nutrientes fueron la mitad de las de cepas parentales. Reforzando la estructura de la pared de la célula mejoró la resistencia al estrés; los mutantes mostraron gran potencial para la fermentación tipo “high-gravity.” Palabras claves: Desempeño fermentativa, Estructura de pared celular, Levadura “lager,” Manoproteína de pared celular, Micafungin, Resistencia al estrés