Mixing stretches the molecules and breaks the relatively weak bonds. It is gluten which has the strength to physically entrap gas within the loaf, giving bread its desirable texture. Too little protein in the flour or too little mixing results in a weak and sticky dough which is easily stretched but does not retain much gas. Likewise, dough can be overworked, resulting in few intramolecular bonds, and a dough which is strong but inelastic. Some processes use high speed, high energy mixing to speed up the gluten development.
Dough conditioners can offer similar results with more traditional equipment.
Often dough conditioners and high speed mixing are combined. The mechanism of dough strengthening by oxidizers has been found, in fact, to be quite different. In addition to disulfide bonding, which strengthens gluten, sulfur atoms on the protein molecules can bind with hydrogen atoms. Sulfur bound to hydrogen cannot form a disulfide linkage. Early oxidizers like potassium bromate and iodate are effective but less in favor today as they produce bromide and iodide compounds in bread which can have toxic effects.