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Storage time and temperature effects nutrients in spinach

21.03.2005

That seven-day-old bag of spinach in your refrigerator may not make you as strong as your grandma told you, because, according to Penn State food scientists, spinach stored for a long time loses much of its nutrient content.

Luke LaBorde, associate professor of food science, and Srilatha Pandrangi, graduate student, both at Penn State, found that spinach stored at 39 degrees Fahrenheit loses its folate and carotenoid content at a slower rate than spinach stored at 50 and 68 degrees. However, the spinach at 39 degrees still loses much of its nutrients after eight days. The average temperature of a refrigerator is 40 degrees.

"This has implications in the shipping process," said LaBorde. Their research has been published in a recent issue of the Journal of Food Science.

There is such a high demand for fresh products that it places a heavy burden on the producers. If the spinach is coming from the other side of the country, then the produce might be kept at a warm temperature in a shipping truck for an extended period of time. By the time the spinach reaches the dinner table, much of the nutrient content might already be gone, noted the Penn State researcher.

Also, an attractive appearance does not mean that the spinach is still rich in nutrients. Spinach is prized because of its high nutrient content, particularly folate and carotenoids.

Folate is a vitamin B compound, responsible for producing and maintaining new cells in the body. Folate deficiency in pregnant women can lead to birth defects such as spina bifida. Spina bifida occurs in the first month of pregnancy when the spinal column does not close completely. Carotenoids are most commonly associated with carrots and other red and orange vegetables, and they help support vision and protect eyes from UV damage. According to the FDA, spinach is high in both nutrients.

"Some people think that if the produce looks good, it has nutrients," LaBorde said. "So people will stick the spinach in some ice water to fluff it up to look nice."

The Penn State researcher noted this action is not effective because the nutrient loss is irreversible. With such a high demand for fresh foods, many people do not give a second thought to alternatives, thinking that fresh food is always more beneficial than canned or frozen foods.

"There is also a fallacy that fresh spinach is always better than canned," said LaBorde.

This belief is not always true because, despite the damage done during the heating process for canned spinach, it may retain more of its nutrients than fresh spinach kept in the refrigerator for a few days. The same holds true for frozen spinach. Frozen spinach retains more of its nutrients for a longer time than fresh spinach because of the lower temperatures at which it is kept.

The researchers found that spinach stored in a refrigerator at 39 degrees retained more nutrients than spinach kept at warmer temperatures. While they found that substantial nutrient loss occurred at all storage temperatures, the cooler temperatures retained more nutrients for a longer period of time.

Keeping spinach in the refrigerator will slow down its nutrient loss. The spinach kept at 39 degrees retained only 53 percent of its folate after eight days. When it was kept at higher temperatures, the spinach lost its nutrients at an accelerated rate. At 50 degrees it took six days for the spinach to lose 47 percent of its folate and at 68 degrees it took four days. The same holds true for carotenoid loss. As temperatures were increased, the loss of nutrients also occurred at a faster rate.

Penn State’s College of Agricultural Sciences and the Department of Food Science provided funding for this project.