Fresh fruit in an array of colors is visually appealing and full of nutrients that are essential to human health. But when fruit is stored improperly, or when it is processed, it can lose much of its nutritional value. One natural chemical process that is harmful to many nutrients is oxidation, the same process that turns an apple brown when bruised or exposed to air.
Oxidation is a natural chemical process that occurs in living cells. When the skin of a fruit is broken, cell walls and membranes are ruptured, allowing oxygen in. The compounds in the fruit react with the oxygen, incorporating it into their molecular structure. The process is facilitated by the enzyme polyphenoloxidase, which oxidizes the phenolic compounds found in fruits, resulting in brown spots.
The way in which fruit is harvested, shipped and stored, and the time it remains at room temperature once off the tree determines the rate at which oxidation and the loss of nutrients takes place. When stored at 70 degrees Fahrenheit, most fruits will spoil within one to seven days, according to the Food and Agriculture Organization of the United Nations, or FAO. It is best to store fruit in a cool place for as short a time as possible between harvesting and shipping. Temperature and light intensity strongly affect the nutritional quality of fruits and vegetables and the rate of oxidation, according to a report by the United States Department of Agriculture.
Nutrients Effected by Oxidation
Heat, water and oxidation are the three primary enemies of vitamins and minerals, according Patrick Holford, author of "The New Optimum Nutrition Bible," who also notes that vitamin C and the fat-soluble vitamins A and E are particularly prone to oxidation, and are lost over a relatively short period of time. The longer a fruit is exposed to air and light, the less vitamins it will have. Low temperatures delay the oxidation of vitamins. Keeping fruits refrigerated protects them from exposure to light and slows the rate of nutrient loss, but oxidation still occurs.
Other Harmful Processes
Besides oxidation due to exposure to heat and light, other processes can rob fruits of their nutrients. Cooking and deep frying are highly destructive to nutrients. Canned fruits and fruit juices are often heated during processing. Frozen fruits retain their nutrient content much longer than fresh, according to Holford. If you buy fresh fruit, it is best to consume it within a few days of purchase to realize the most nutritional value, or freeze it for later use.
- "Scientific American"; Why Does Bruised Fruit Turn Brown?; July 21, 1997
- Food and Agriculture Organization of the United Nations; Fruit and Vegetable Processing
- United States Department of Agriculture; Nutritional Quality of Fruits, Nuts, and Vegetables and their Importance in Human Health; Adel A. Kader, et.al.
- "The New Optimum Nutrition Bible"; Patrick Holford, 2005