Staling of bread is a complex process that is mostly thought to be associated with retrogradation of starch to make the bread get firmer over time, although some researchers have also been able to show that protein and arabinoxylans play a role. Emulsifiers are typically used to complex with the starch to prevent it from retrograding and thereby slow the staling process. Different emulsifiers impact the staling process in different ways. Not all emulsifiers will keep bread softer for longer time. Typically mono and di glycerides and sodium stearoyl lactylate (SSL) are the common emulsifiers used by bakes to delay staling. The bread will still stale, but their use may delay it 3-5 days.
For even longer shelf-life extension, most bakers use a blend of enzymes to slow staling. The chief enzyme that is used is alpha amylase that breaks down the starch to make it into smaller fragments. There are many different sources of alpha amylase: fungal, cereal, maltogenic, and bacterial. Most crumb softening enzyme blends rely on a maltogenic amylase along with other enzymes such as hemicellulases or xylnases to delay crumb firming and staling.