I'm curious why there isn't a zero-calorie molasses substitute. The USDA nutrient database lists a bunch of minerals, but what is it that gives it the "taste" of molasses?
There is no single "molasses molecule". It's a complex flavor from a complex combination of chemicals. There is no "caramel molecule" either. It also contains several different types of sugar (mono- and disaccharides), which impart their own flavor and calories.
It will include residual sugars, all the types of molecules produced during caramelization, along with a wide varieties of proteins and miscellaneous not-sugar-things that are found in sugar cane juice. McGee lists a breakdown of 35% sucrose, 20% invert sugars, and 10% minerals (for blackstrap). There's also some water and other organic material, as that obviously does not add up to 100%.
There's no zero-calorie substitute because Molasses is made directly from sugar cane. However, Blackstrap molasses has fewer calories than other versions as most of the sucrose is removed during processing.
As for the minerals, the sugar cane is not refined prior to processing for Molasses, therefore it retains many of its original minerals.
The taste comes from the repeated concentration of the juice from the sugar cane.
More info available on wikipedia.
Maillard reaction research proves that much of the flavor is indeed a bunch of different molecules created from high heat, low water, combination of amino acids and sugars