E456 (Potassium polyaspartate) is a chemical compound, the potassium salt of polyaspartic acid to which it is a homopolymer and is produced by the reaction of l-aspartic acid with potassium hydroxide.
It comes in different forms: white or yellowish powder, easily mixed with other ingredients or dissolved in water to obtain a solution or granular.

What it is used for and where
Food
Ingredient included in the list of European food additives as E456, stabiliser.
Potassium polyaspartate A-5D K/SD is effective as a stabiliser in wines with a maximum utilisation level of 300 mg/L and typical levels in the range of 100-200 mg/L (1) and also stabilises potassium bitartrate by preventing its precipitation (2). It is also effective in preventing crystal formation in red wine. Approved for use in wine for the tartaric stabilisation of white wine.

Chelating agent. It has the function of preventing unstable reactions and improving the bioavailability of chemical components within a product, and removes calcium and magnesium cations that can cause cloudiness in clear liquids.
Corrosion inhibitor. Potassium polyaspartate has been studied for its potential as a corrosion inhibitor. It can help protect metal surfaces from corrosion.
Potassium polyaspartate is used in agriculture as a foliar fertiliser to improve nutrient uptake, plant growth and crop yield.
References_____________________________________________________________________
(1) Bosso A, Motta S, Panero L, Lucini S, Guaita M. Use of potassium polyaspartate for stabilization of potassium bitartrate in wines: influence on colloidal stability and interactions with other additives and enological practices. J Food Sci. 2020 Aug;85(8):2406-2415. doi: 10.1111/1750-3841.15342.
(2) Bosso A, Motta S, Panero L, Lucini S, Guaita M. Use of potassium polyaspartate for stabilization of potassium bitartrate in wines: influence on colloidal stability and interactions with other additives and enological practices. J Food Sci. 2020 Aug;85(8):2406-2415. doi: 10.1111/1750-3841.15342