Lemon juice contains citric acid, which is an ingredient that is used as a preservative to extend or improve the shelf life of various foods. Citric acid can be used in liquid form, but it is usually dried into a powder when used as a preservative. Citric acid is found in many types of fruits, but lemon and lime juice contain the most citric acid.
Citric acid is used as a preservative in cosmetics, pharmaceuticals, beverages and foods. It improves the shelf life of these items by preventing bacteria growth, preventing rancidity and stabilising colour, taste and ingredients. Lemon juice is a natural, food-grade preservative that can be used in food products that are labelled as being made without preservatives.
Citric acid can double as a preservative and as a flavouring agent. Sour candies are often coated in a blend of citric acid and sugar, adding flavour while improving shelf life. Citric acid is also used in sourdough bread and soft drinks to increase the sour flavour.
Citric acid helps balance the pH in some foods and some household cleaning products. Because it is an acid, it can help lower the alkalinity of some products, while preserving their shelf life.
Some fruits and vegetables, such as apples and artichokes, are prone to turning brown after they are cut up and exposed to the air. A few spoonfuls of lemon juice added to chopped apples prevents browning, and placing artichokes in a bowl of water with a few spoonfuls of lemon juice can prevent them from turning colour.