Well, there are a few possibilities.
There's Mycoplasma Fermentans which is thought to have a role in fermenting sugars,
Many biofilmic bacteria store sugars in the form of sacchyrides (literally a tough mat of sugars that the bacteria can reside in, like in the mother in a kombucha or apple cider vinegar ferment), though biofilms usually come out as gelatinous.
Candida Albicans and its' related bacteria (ones that are involved in the maturation of fruit) have a role in breaking down fibers into sugars.
Diet would be the first place I'd look for clues, since seeds and the like are quite resilient in the gut. I'd say isolate some of the trapezoidal objects, keep track of your foods, and consider if any changes are in order. I've had quite a few occurances where I've had a false alarm on the toilet due to very resistant fibers looking a bit like worms.
Though I'm NOT saying it's a sign you should ignore. Just work down the list of possibilities.
There are reports of folks with C. Difficile infections giving sickly-sweet smelling poo odor, though I would not immediately suspect a Clostridium bowel infecion unless all the other symptoms of it are showing up.
Is the smell only accompanying those trapezoidal chunks? If you're not taking in a food that has a similar (even if faint) odor, there is always the possibility of some parasites being eliminated.
Keep in mind that parasites have their own digestive bacteria, which help them survive and digest their food. There'd be a big difference between them smelling like a pathogenic bacteria, and that bacteria taking to colonizing you.
There are a good many bacterial metabolites that generate odor. One of them is butyric acid, which is the precursor to GABA (relaxant neurotransmitter in the brain), a necessary nutrient for the gut to move normally and make a protective barrier against infection, a trigger for the pancreas to produce new beta cells.. just to name a few functions.
Butyric acid is used in fish bait. It smells a lot like vomit (bile) and has a pineapple-like sweet tang.
Plant fibers (resistant fibers) are the food for bacteria that generate butyric acid. Butyric acid combats pathogenic candida by stopping it from forming biofilms (which happens when the cell walls of candida are attacked, like in Antibiotics ).