I am guessing it refers to potassium bromate. The substance use in baking.
In shortest terms, it is a dough enhancer and bleach. Oh! I should have said whitening agent instead. The word “bleach” sounds unhealthy.
Why omit from bread? Study found it cancerous in rat and mice. Its use is banned in many countries around the world after series of research studies. However, USFDA limit it to less than 20 parts per billion. Potassium bromate is a processing aid. During baking, it is converted to harmless substance potassium bromide.
If health awareness in you kicks in, you’ll patronize this brand including similar brands with same slogan. Then avoid the rest.
Absence of potassium bromate on ingredient listing does not mean it has none. As far as I remember, processing aid may not be listed as ingredient.