Group: E500–E599 (acidity regulators, anti-caking agents)
Sodium carbonates (E500) can be derived from a number or sources:
E500 (i) - Sodium carbonate,
E500 (ii) - Sodium hydrogen carbonate / Sodium bicarbonate,
E500 (iii) - Sodium sesquicarbonate.
Sodium carbonate (also known as washing soda or soda ash), Na2CO3 is a sodium salt of carbonic acid.
Functions performed by the food additive when used in cooking:
Acidity regulator - Regulates the acidity or alkalinity of a food,
Anticaking agent - Helps prevent food particles from sticking together,
Raising agent - A substance which increases dough volume by producing gas,
Stabiliser - A substance that maintains the uniform dispersal of substances in a food.

E500i Sodium carbonate, Na2CO3, (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na₂CO₃ and its various hydrates. All forms are white, water-soluble salts. All forms have a strongly alkaline taste and give moderately alkaline solutions in water. Historically it was extracted from the ashes of plants growing in sodium-rich soils. Because the ashes of these sodium-rich plants were noticeably different from ashes of wood (once used to produce potash), sodium carbonate became known as "soda ash". It is produced in large quantities from sodium chloride and limestone by the Solvay process.
Sodium carbonate is a food additive (E500) used as an acidity regulator, anticaking agent, raising agent, and stabilizer. It is one of the components of kansui, a solution of alkaline salts used to give ramen noodles their characteristic flavor and texture. It is used in the production of snus to stabilize the pH of the final product. Sodium carbonate is used in the production of sherbet powder. The cooling and fizzing sensation results from the endothermic reaction between sodium carbonate and a weak acid, commonly citric acid, releasing carbon dioxide gas, which occurs when the sherbet is moistened by saliva. In China, it is used to replace lye-water in the crust of traditional Cantonese moon cakes, and in many other Chinese steamed buns and noodles. In cooking, it is sometimes used in place of sodium hydroxide for lyeing, especially with German pretzels and lye rolls. These dishes are treated with a solution of an alkaline substance to change the pH of the surface of the food and improve browning.

E500ii Sodium bicarbonate (IUPAC name: sodium hydrogen carbonate), commonly known as baking soda, is a chemical compound with the formula NaHCO₃. It is a salt composed of a sodium cation (Na+) and a bicarbonate anion (HCO3−). Sodium bicarbonate is a white solid that is crystalline, but often appears as a fine powder. It has a slightly salty, alkaline taste resembling that of washing soda (sodium carbonate). The natural mineral form is nahcolite. It is a component of the mineral natron and is found dissolved in many mineral springs.
In cooking, baking soda is primarily used in baking as a leavening agent. When it reacts with acid, carbon dioxide is released, which causes expansion of the batter and forms the characteristic texture and grain in pancakes, cakes, quick breads, soda bread, and other baked and fried foods.
Acidic materials that induce this reaction include hydrogen phosphates, cream of tartar, lemon juice, yogurt, buttermilk, cocoa, and vinegar. Baking soda may be used together with sourdough, which is acidic, making a lighter product with a less acidic taste. Heat can also by itself cause sodium bicarbonate to act as a raising agent in baking because of thermal decomposition, releasing carbon dioxide at temperatures above 80°C (180°F)
When used this way on its own, without the presence of an acidic component (whether in the batter or by the use of a baking powder containing acid), only half the available CO2 is released (one CO2 molecule is formed for every two equivalents of NaHCO3). Additionally, in the absence of acid, thermal decomposition of sodium bicarbonate also produces sodium carbonate, which is strongly alkaline and gives the baked product a bitter, "soapy" taste and a yellow color. Since the reaction occurs slowly at room temperature, mixtures (cake batter, etc.) can be allowed to stand without rising until they are heated in the oven.
When adding acid, alkaline ingredients such as whole milk or Dutch-processed cocoa are often added to baked foods to avoid an over-acidic taste from the added acid.
Baking powder, also sold for cooking, contains around 30 % of bicarbonate, and various acidic ingredients which are activated by the addition of water, without the need for additional acids in the cooking medium. Many forms of baking powder contain sodium bicarbonate combined with calcium acid phosphate, sodium aluminium phosphate, or cream of tartar. Baking soda is alkaline; the acid used in baking powder avoids a metallic taste when the chemical change during baking creates sodium carbonate.
Sodium bicarbonate was sometimes used in cooking green vegetables, as it gives them a bright green colour which has been described as artificial-looking—due to its reacting with chlorophyll to produce chlorophyllin. However, this tends to affect taste, texture and nutritional content, and is no longer common.
Baking soda is still used to soften pulses (peas, beans) before and during cooking, as in the traditional British mushy peas recipe for soaking the peas. The main effect of sodium bicarbonate is to modify the pH of the soaking solution and cooking water, that in turn softens the hard external shell, reduces cooking times and may alter the percentage of nutrients in the dish, its flavour and consistence.
Baking soda may react with acids in food, including vitamin C (L-ascorbic acid).
It is used in Asian and Latin American cuisine to tenderize meats. It is also used in breading, such as for fried foods, to enhance crispness and allow passages for steam to escape, so the breading is not blown off during cooking.
Toothpaste containing sodium bicarbonate has in several studies been shown to have a better whitening and plaque removal effect than toothpastes without it.
Sodium bicarbonate is also used as an ingredient in some mouthwashes. It has anticaries and abrasive properties. It works as a mechanical cleanser on the teeth and gums, neutralizes the production of acid in the mouth, and also acts as an antiseptic to help prevent infections. Sodium bicarbonate in combination with other ingredients can be used to make a dry or wet deodorant. Sodium bicarbonate may be used as a buffering agent, combined with table salt, when creating a solution for nasal irrigation.
It is used in eye hygiene to treat blepharitis. This is done by addition of a teaspoon of sodium bicarbonate to cool water that was recently boiled, followed by gentle scrubbing of the eyelash base with a cotton swab dipped in the solution.