Which process is NOT caused by microorganisms in post-mortem changes?

Rigor mortis is a post-mortem change that occurs as a result of biochemical processes in the body after death, specifically the depletion of adenosine triphosphate (ATP) in muscle tissues. This process leads to the stiffening of muscles, which is primarily caused by the biochemical changes rather than by the activity of microorganisms.

In contrast, mortis (which encompasses both algor mortis and livor mortis), decomposition, and fermentation are all processes influenced significantly by the action of microorganisms. Mortis refers to the physical changes in the body temperature and blood pooling after death, while decomposition involves the breakdown of body tissues through the action of bacteria and other microorganisms. Fermentation can also be linked to microbial activity, as it involves the breakdown of sugars and organic matter by bacteria and yeasts, processes that may occur in the body after death.

Thus, since rigor mortis is a result of internal biochemical processes rather than direct microbial action, it is the process that is not caused by microorganisms in post-mortem changes.