Are the molecular gastronomy additives kosher?
Most gelling agents are derived from flora of some kind - usually plants or algae. Since they aren't derived from any animal, they are kosher and also vegan.
The primary exception is gelatin, which is derived from animal bones. Gelatin is as kosher as the animal it came from and the conditions under which it was prepared; genuine kosher gelatin does exist (usually produced from fish bones) but it is somewhat difficult to find in most areas. If you see it, you'll know, because it will be labeled as kosher. Beware of "KoJel" and other kosher gelatin "substitutes", as they are usually some other additive or combination of additives, such as agar and/or carrageenan.
Here's a quick (incomplete) list of where some of the additives come from:
As you can see, there's nothing in there to make it unkosher.
Of course in practice it depends how strict you are. Some of these things may be prepared in facilities where they may come into contact with unkosher foods - so if you're orthodox, you might have to seek out products that have the K stamp. Good luck finding them.