So adding pure O2 before pitching is good. And adding excessive o2 before pitching will negatively affect the flavor. And aerating after pitching can be ok in certain situations like starters and high gravity beer or mead. But pure o2 after pitching is always bad. Is that right?
Adding pure O2 before pitching is good.
You can't add excessive O2 before pitching, it is not possible due to saturation.
Adding O2 to beer
(not wort) negatively affects flavor.
Aerating after pitching in starters is fine because although that can affect the flavor stability in a negative way, you are not drinking your starter.
Pure O2 after pitching is not always bad, as long as it is done in a controlled, measured manner and you don't add so much that it is toxic to the yeast, and as long as it is done before fermentation has progressed too far (because then it can affect the flavor and stability).
Essentially, oxygen toxicity can be caused by oxygen radicals like superoxide (O2-) that are generated in and can damage the cell. Superoxide is grabbed by superoxide dismutase, which alternately converts it to either hydrogen peroxide (H2O2) or molecular oxygen (O2). Since the H2O2 can also damage the cell it is further degraded to water and oxygen (2 H2O2 -> 2 H2O + 2 O2). This is the same reaction that happens during respiration in our bodies all of the time, and dealing with it is important enough that we have superoxide dismutase all over our bodies, circulating and in every cell.
Your google search may not have led to anything that the authors directly relate to brewing, but the yeast strains that are used in labs are derived from beer/bread strains and share nearly all of their genetics with our brewing strains.
You should at least be able to read the abstracts of some papers here:http://onlinelibrary.wiley.com.offcampus.lib.washington.edu/doi/10.1002/yea.320070203/abstracthttp://www.ncbi.nlm.nih.gov/pmc/articles/PMC3380282/