Construction of Baker’s Yeast Strains with Enhanced Tolerance to Baking-Associated Stresses

Abstract

In dough fermentation and baker’s yeast production, yeast cells are exposed to numerous stresses, including freeze-thaw, high-sucrose, and air-drying, collectively referred to as baking-associated stresses. These conditions can also induce oxidative stress in yeast, leading to increases in reactive oxygen species levels probably due to damage to the mitochondrial membrane and respiratory chain components and denaturation of antioxidant enzymes. To prevent lethal damage, baker’s yeast employs a number of stress tolerance mechanisms, such as the expression of stress proteins, accumulation of stress protectants and compatible solutes, changing the composition of the membrane, and repression of translation via stress-associated signal transduction pathways to regulate the expression of particular genes. As proline and trehalose play important roles in stress tolerance in baker’s yeast, altering their metabolism via genetic engineering is a promising approach for the development of more stress-tolerant strains. So-called “omics” approaches, such as comprehensive phenomics and functional genomics, can be used to identify novel genes that affect stress tolerance. Further improvements in the fermentation capability and production efficiency of yeast strains, however, will require elucidation of the mechanisms underlying the stress response, adaptation, and tolerance. We believe that the engineering of not only baker’s yeasts but also other important industrial yeasts exhibiting greater stress tolerance would enhance the production of yeast-based products such as bread doughs and alcoholic beverages and facilitate breakthroughs in bioethanol production.