There are not many approved thickening agents that meet USDA organic certification guidelines, but sodium alginate is one ingredient that is on the NOP approved list (see guideline rule § 205.60). Moreover, for every formulation we've tested it in, it works great as a terrific gelling/thickening agent.
In the presence of calcium and acid mediums, it forms stable gels. It is a cold gelling agent that does not rely on heat to be activated, in fact its best agitated into room temperature or cold aquatic soluble ingredients.
This product is food grade and can also be used in the kitchen as a stabilizer for ice cream, yogurt, cream, and cheese. It acts as a thickener and emulsifier for salad dressing, puddings, and jams. It is most commonly used with calcium lactate or calcium chloride in the (food) spherification process.
To use, simply add a ratio of 0.3 to 3% (a little goes a long ways) and agitate into cold or room temp liquids. Allow to set for 15 minutes, it will be fully hydrated at the 15 minute marker. The base may appear to be white, but the color generally settles to clear, depending upon the color of the liquids you are emulsifying.
Though this product is not certified organic, it is naturally derived from brown seaweed.