Preservatives affect the shelf life of bread. When less preservatives are added, mould grew on the bread faster and the shelf life decreased. However, if more preservatives are added, mould grew slower and the shelf life increased. This shows that the shelf life of bread is affected by the amount of preservatives in the bread.
As for why this is so, it is mainly due to the fact that preservatives are meant to prolong shelf life by making sure the food does not rot or spoil too soon. So, when less preservatives are added, the shelf life will not be prolonged as much and the food (bread in this case) will not spoil as soon.Vice versa, when more preservatives are added, the shelf life will be prolonged and the bread will last longer.