Citric acid is a common component of many foods. It occurs naturally in fruits and fruit juices and serves as an additive in processed foods. Sodium citrate is simply another form of citric acid; the two act the same in the human body. They e safe for consumption in food.

Citric acid is a small carbon-based molecule that is ubiquitous in living cells, because its part of how most living cells generate energy from nutrient compounds. You yourself make citric acid in your cells when you burn carbohydrates, proteins and fats for energy. Like all acids, citric acid has a sour flavor and occurs naturally in many fruits, contributing to their tangy taste. Unlike most acids, however, its safe to eat, so its often added to foods.

Sodium citrate is the sodium salt of citric acid. This means that its the citric acid molecule with one fewer hydrogen atom. This leaves citric acid -- now called citrate -- with a negative charge. Sodium has a positive charge, and is attracted to citrate. Like table salt, sodium citrate is a solid thats often called "sour salt" to distinguish it from the much more common salt you use on your food, which is sodium chloride.

In fruits and fruit juices, citric acid occurs naturally. The compound is in the form of citric acid rather than sodium citrate because fruits are naturally acidic, which leaves citric acids hydrogen in place. In foods, manufacturers add citric acid to acidic foods, like soda, while adding sodium citrate to dry foods or those that aren acidic. Both citric acid and sodium citrate act as preservatives and flavoring agents.

When you consume food, you absorb the citric acid or sodium citrate into your bloodstream, explains Dr. A. Pajor in a 1999 article in the journal "Seminars in Nephrology." Because your bloodstream is near neutral in acidity, all citric acid takes the form of citrate in the blood. You excrete most of this citrate in the urine. Some, however, your liver cells can take up, explain Drs. K. Inoue and colleagues in a 2002 article in "Biochemical and Biophysical Research Communications," and convert into a very small amount of fat.