On a recent NPR Science Friday episode, they explored the molecular basis of how we taste sweet things (Did you know that cats have lost the receptor sometime in their evolutionary past, and thus, cannot taste sweet?). It reminded me of the answer that Shirley Corriher did on the radio after she was asked what was the best sugar substitute: that it wasn't quite so simple. I have alluded to this in an earlier blog post, but sugar performs a lot of tasks in cooking beyond just making things sweet.
Aside from serving to tenderize baked items, sugar degradation products during heating provide properties that we take advantage of. The monosaccharides glucose and fructose are easily created, and interfere with premature crystallization, and further breakdown products, in the form of caramel, provide perhaps the most recognizable flavor of cooked foods. Substitute sweeteners are mostly targeted at just activating sweet receptors - thus, they tend to taste a lot sweeter gram for gram relative to sucrose, but don't convey the chemical advantages of sugar.
Perhaps one of the earliest sugar substitutes is the sodium cyclamate (30-50x sweeter than sucrose), but with a significant off taste, and controversial reports of causing bladder cancer, was actually banned from sale in the US. Currently, the most popular artificial sweeteners are:
Saccharin - that's the stuff in the pink packets. It's about 300x-500x sweeter than sugar, but not particularly heat stable, and does have off flavors. Still, to some, it's what's familiar.
Aspartame - that's in the blue. Aspartame is actually linked molecule of two amino acids - building blocks for proteins. Being rather unstable in elevated heat, or acid or alkalinity, it's nonetheless developed a strong use in processed foods. It's about 160x sweeter than sugar, and there's some concern that it's digestion releases a molecule of methanol per molecule of aspartame. That's not usually a problem, except the mindless consumption of diet sodas of the typical American (and arguably more of the world) results in ridiculous quantities that perhaps should concern people. One of the amino acids is phenylalanine that people with a genetic condition called phenylketonuria cannot process cleanly, hence the warning on products that are sweetened with aspartame.
Sucralose - the packets in yellow is the youngest of the compounds, a chlorinated sugar derivative that is 600x sweeter than sugar. It's main advantages are that it's biologically inert, meaning humans can't digest it, and that it's heat stable, so people can actually cook with it. It won't caramelize the same sucrose does, but it'll retain it's sweetness after baking, unlike aspartame.
So, that's a quick survey of those packets. Probably be okay for your coffee, but I don't think we'll be making taffy with them soon.