Chemical preservatives are used to keep food fresh and slow the growth of bacteria, moulds and yeasts.
But which preservatives do what, and how do they actually work? An article published in the Chemical and Engineering News offers some answers.
Chemical preservatives fall under three general groups: antimicrobials that block the growth of bacteria, moulds or yeasts; antioxidants that slow oxidation of fats and lipids that cause food to become rancid; and a third group that combats enzymes that cause ripening of fruits and vegetables after they're harvested.
Sulphites are a group of preservatives found in many foods, including vinegar, fruit juices and dried fruits. Sulphites block the growth of microbes by interrupting their normal cell function. Some people are allergic to sulphites.
Bakery products are kept fresh by antimicrobials called propionates, which occur naturally in apples, strawberries, grains and cheese. These propionates combat bread moulds and the spores of bacterium that cause a condition called "rope," which makes bread inedible.
Benzoates, found naturally in cranberries, fight fungi.
Nitrates and nitrites preserve meat and counter deadly botulism bacteria. They give a fresh pink colour to cured meat, which would turn brown without nitrates or nitrites.
Antioxidant preservatives halt the chemical breakdown of food caused by exposure to air. Unsaturated fatty acids in oils and lipids are particularly prone to oxidisation, which can cause them to become rancid.
Ascorbic acid and citric acid attack enzymes that cause fruits and vegetables to over-ripen after they're picked. – (HealthDayNews)