How squeezing fruit can give a boost to its antioxidant levels

New evidence that a century-old food preservation technique can double the levels of certain antioxidants in fruit was reported at a recent meeting of the American Chemical Society.

The technology, known as high pressure processing, involves subjecting food to a pressure of 40,000–80,000 pounds per square inch for about 15 minutes. Despite this huge pressure, the food is not squashed, but the pressure apparently changes its molecular structure in ways that enhance the biosynthesis of antioxidants, such as carotenoids.

The technique is also known as pascalisation after the 17th century French scientist Blaise Pascal, who was famous for his research involving application of pressure on liquids, but high pressure processing differs from the more familiar thermal pasteurisation processes used to kill bacteria in milk.

Preliminary work has shown that high pressure processing of fruit such as avocado and papaya can increase overall carotenoid content by 50 per cent, with increases in some individual carotenoids of up to 500 per cent.

The researchers speculate that these changes could result from a type of self-defence mechanism in the fruit tissue which causes the fruit to synthesise more antioxidants to cope with the stress from the high pressure processing. Such technology could find application in the production of fruit extracts with enhanced antioxidant content.