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%.
A Canadian study mentioned in CBC News revealed that calories from sugar are reduced during cooking or baking, more so with invert sugar than sucrose. Molasses is a cooked product already and additional cooking when used as a food ingredient will further reduce some of the calories. Charring molasses is going to be what you are looking for to distill the essence of its flavor, and then grinding the result into a powder. Remember the conservation of energy law. The charring process was used by the Imperial Sugar mill in Sugar Land Texas before it shut down, for good, and the charring aroma was a delight to experience. The charring process for animal fat, like when grilling steak, reveals the sweet flavor of glycogen stored in the tissues as well as the seamfat and backfat. Early man discovered this flavor enhancing process. So caramelizing, charring, or slightly burning sugars will reduce caloric content but not eliminate them. The resultant concentrate might be what you are looking for so that the dilution rate when added as an ingredient may work. Also, when people are fat adapted, a few carbs occasionally don't matter, good luck.
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.