This is an interesting question! I am not sure what is going on here. Green usually indicates the presence of chlorophyll, which is more indicative of immature plant tissue.

Sliming of carrots would not be expected in such a short time frame unless (one possibility) they have been treated with a highly acidified "finishing agent" and/or been subjected to uniform contam

We have done some work on pectin methyl esterase which does indeed occur in carrots. Here is a link to a manuscript on this topic from our group.

In the absence of performing forensic microbiology; an educated guess leads me to suggest that the core issue is sub-optimal cleaning and process sanitation.