Ascorbic acid is used primarily as an antioxidant, which can provide multiple benefits to food products.
Slowing the oxidation preserves color (think about how cut apples and avocados brown when they come into contact with oxygen) and it preserves the freshness. The low pH of ascorbic acid can help prevent microbial growth, thereby preventing spoilage and preserving freshness. For these reasons, ascorbic acid is a popular natural ingredient preservative.
It can be used as a preservative in a vast array of food products, including bread, cured meats, jams and jellies, and other sauces and spreads.
The Vitamin C properties of ascorbic acid make it an excellent ingredient for vitamin supplementation. Simply adding ascorbic acid to food increases the Vitamin C content. Since naturally occurring Vitamin C is easily destroyed, many foods are fortified with ascorbic acid to replenish the Vitamin C content. Ascorbic acid is often added to fruit juices, dried fruit, cereal, and other snack foods for this purpose.
The flavor of ascorbic acid shouldn't be overlooked. Like any acid, it provides a nice tart flavor that enhances many food products. Candies, jams, jellies, and fruit juices often benefit from this burst of acidity that gives the consumer the distinct impression of fresh fruit.