As already noted – in practical application the preservatives for breads and similar baked goods are often in pill format, for easier dosage in the bakery.
Most preservatives in bread the usage is based on ‘Good Manufacturing Practices’ (GMPs), as excessive amounts would product poor quality product. Others that may have regulated dosage, are based on the amount in the finished baked product. This would be for a chemical or ingredient that might have adverse effects on human health if the levels are too high, and otherwise not have any effect on product quality. This is pretty rare from my experience, and I cannot think of one at the moment as an example.
In the US as an example of calcium propionate commonly used in breads – CFR 21 184.1221
(c) In accordance with 184.1(b)(1), the ingredient is used in food with no limitation other than current good manufacturing practice. The affirmation of this ingredient as generally recognized as safe (GRAS) as a direct human food ingredient is based upon the following current good manufacturing practice conditions of use:
(1) The ingredient is used as an antimicrobial agent as defined in 170.3(o)(2) of this chapter.