During fermentation, yeast makes thousands of different molecules. When we engineer strains to produce a molecule not usually made by yeast, we make sure to choose molecules that we know are safe. For example, we know that the molecules made by a strain engineered to make the compounds in passion fruit that gives it its delicious tropical flavor are safe because people have been consuming those same compounds at similar levels for centuries. All of the molecules made by our engineered strains have been approved by the U.S. Food and Drug Administration for safe consumption at the relevant concentrations. Berkeley Yeast fully complies with all FDA regulations and has gone above and beyond strict compliance.
For each commercial strain, we perform whole genome sequencing to confirm that no major genetic alteration occurred during the engineering process. By comparing the genome of an engineered strain to the genome of the parent strain, we can verify that any intended changes occurred at the correct location in the genome, and that no unintended genetic changes have arisen. We also confirm that the changes we introduce do not affect fermentation characteristics, like rate of sugar consumption, pH of fermentation, and cell morphology.
We use mass spectrometry methods to measure thousands of molecules made by yeast during fermentation. By comparing the levels of these molecules, we can verify that the only new molecules made by the engineered strains are the ones we intended. This test lets us confirm that there are no major unintended differences between our engineered yeast and the un-engineered parental yeast. We emphasize that the methods used to measure the different molecules are “untargeted” in that mass spectrometry methods agnostically capture metabolite levels present in the fermented product, instead of focusing on the ones we expect to be there. That way, we can be confident that we are taking an unbiased approach to our safety assessment.
To do this, we make beer or wine with the engineered yeast and the parental yeast. At the end of fermentation, we analyze the beer or wine using mass spectrometry, which can detect molecules at concentrations as low as parts per trillion.