According to Fatima Hachem, a senior nutrition officer at the United Nations Food and Agriculture Organization (FAO), food has the highest nutritional value at harvest. Fresh produce begins to lose nutrients as soon as it is picked because it loses its source of nutrients and energy.
Hachem explains that fresh vegetables cooked after being stored for a while may lose some nutritional value. After being picked, fruits and vegetables use their own nutrients to maintain cell life. Some nutrients are particularly prone to loss, such as vitamin C, which helps the body absorb iron, lower cholesterol, and combat free radicals. Vitamin C is especially likely to degrade when exposed to air and light.
Refrigerating fresh fruits and vegetables can slow the rate of nutrient loss, but different vegetables and fruits lose their nutrients at different rates.
There has been extensive research on the nutritional value of canned fruits and vegetables. In 2007, Diane Barrett, a food science researcher at the University of California, Davis, reviewed multiple studies. She found that spinach stored at 20°C (68°F) room temperature for seven days loses 100% of its vitamin C, whereas if refrigerated, it loses 75%. However, carrots stored under the same conditions for seven days only lose 27% of their vitamin C. Barrett concluded that vegetables and fruits containing water-soluble nutrients like vitamin C and vitamin B, such as spinach, are better consumed fresh and are less suitable for canning.
Vegetables and fruits containing fat-soluble nutrients like vitamins A and E, such as carrots and tomatoes, are more suitable for canning. Canned foods also have unique advantages, particularly in terms of safety, as they are less prone to bacterial contamination.
Barrett noted that the advantage of canned foods is that they undergo a sterilization process, killing all microorganisms, making the contents safe to eat once sealed in the can.
