I had read about guar gum which can be used as a thickener and is much more effective than corn flour. It is a dietary fibre and I can only find good things about it from my research, although due to it being fibre it may make you go! It can be used in cold preparations, as I have done here.
You do have to be cautious about how much you use as it really does thicken stuff quickly and thickly!
In this recipe, I used 1/4 of a tsp and it made a perfect vinaigrette with no oil and gave exactly the right viscosity.
1/2 cup Nut Vinegar (i used Walnut vinegar that I picked up in France ages ago)
1/4 cup Water
1-2 Cloves of Garlic, peeled
2-3 Tsp Maple Syrup
1/2 Tsp Salt or Herbamare
1/4 Tsp Black Pepper
3 Tsp of Dijon Mustard
1/4 Tsp of Guar Gum Powder
Add all ingredients to a blender or food processor and whiz until thoroughly blended. Leave to thicken for a few mins and taste. Adjust seasoning and flavour balance and adjust if needed.
I have to say that this was utterly splendid and tasted as good if not better an oil based dressing.