Xanthan gum is a thickening agent used in pastry fillings, pie crusts and other baked goods and sauces. It is created through the introduction of bacteria during the fermentation of corn sugar. Substitutes for this ingredient include several older ingredients that xanthan gum was actually created to replace. These substitute ingredients may be more expensive.
Cornstarch makes an ideal thickening substitute for xanthan gum when used in baked goods, gravies and sauces. It is gluten-free and imparts no added flavours to food. Cornstarch may also be kept for indefinite periods of time as long as it is stored in an airtight container in a dry environment. A problem with cornstarch occurs when products made with it are frozen as this can cause separation of ingredients. Foods that are inherently acidic like fruit pie filling generally require a larger amount of cornstarch to thicken them.
Arrowroot has a similar consistency and look to cornstarch and works as a thickening agent substitute for xanathan gum. The plant is native to countries in South America where native peoples used it to draw out poisons from the skin according to the website for the Culinary Cafe. When arrowroot is used as a thickening agent for fruit pie fillings and other baked goods, it thickens at a lower temperature than cornstarch, however, more arrowroot powder is needed to produce the same effect.
Gelatin is made from boiled animal bones and other tissues. Kosher gelatin can be produced from fish bones. As a thickening agent this product is most often seen in commercial "Jello-O" products and commercially produced pastry fillings. While this substance can be used as a substitute for xanathan gum, certain portions of the population like vegetarians and vegans tend to avoid it because of its animal components. Gelatin cannot be produced in a vegan-friendly format according to the International Vegetarian Union.
Agar agar is a seaweed gathered from the East Indian shore and produced chiefly in China. The plant contains glose, which is a powerful thickening agent on par with xanthan gum and other commercial thickeners. It is seen most often in Eastern countries as a thickener in jellies and soups. Agar agar makes an ideal vegan or vegetarian alternative thickening agent as it contains no animal byproducts.