Do foods with preservatives stay digestible for longer in the gut by not rotting as much (producing less toxins)?
Do foods with preservatives take longer to digest?
Food preservatives are either antimicrobials (e.g. sorbate, sulfite) or antioxidants (free radical scavengers such as butylated hydroxyanisole).
Digestion is initiated in the stomach by hydrochloric acid and pepsin. It continues in the small intestine with the action of numerous other enzymes including amylases, lipases and proteases. There is no obvious way that these digestive processes would be inhibited by preservatives.
I've done some more research and it was believed that food in the gut putrefied and became toxic up until early 20th century when advances in science showed no evidence of such. source: http://www.ncbi.nlm.nih.gov/pubmed/2668399
So given that food doesn't become toxic in the first place preservatives don't have an effect on something that doesn't happen.