Asparagus has some dietary fiber, vitamin A, and vitamin C. It is an excellent source of the B vitamin folate. A serving of six cooked fresh asparagus spears has 1 g dietary fiber, 490 IU vitamin A, 10 mg vitamin C and 131 mcg folate. Besides, it is also low in fat, sodium and practically no cholesterol.
The most nutritious way to serve asparagus is by serving it fresh, boiled and drained. Canned asparagus may have less than half the nutrients found in freshly cooked spears. As such it is encouraged to take asparagus when it is fresh.
Look for bright green stalks when buying asparagus. The tips should be purplish and tightly closed and the stalks should be firm. Asparagus is in season from March through August. Always avoid wilted stalks and asparagus whose buds have opened. When storing, keep it fresh in the refrigerator.
To keep it as crisp as possible, wrap it in a damp paper towel and then put the whole package into a plastic bag. Keeping asparagus cool helps it to hold onto its vitamins. At 32 degrees F, asparagus will retain all its folic acid for at least two weeks and nearly 90 percent of its vitamin C for up to five days. At room temperature, it would lose up to 75 percent of its folic acid in three days and 50 percent of the vitamin C in 24 hours.
The adverse effects associated with asparagus is that after eating, we will excrete the sulfur compound methyl mercaptan, a smelly waste product, in our urine. Eating asparagus may also interfere with the effectiveness of anticoagulants whose job is to thin blood and dissolve clots because asparagus is high in vitamin K, a vitamin produced naturally by bacteria in our intestines, an adequate supply of which enables blood to clot normally.
The white part of the fresh green asparagus stalk is woody and tasteless, so you can bend the stalk and snap it right at the line where the green begins to turn white. If the skin is very thick, peel it, but save the parings for soup stock.
What happens when we cook asparagus? Chlorophyll, the pigment that makes green vegetables green, is sensitive to acids. When we heat asparagus, its chlorophyll will react chemically with acids in the asparagus or in the cooking water to form pheophytin, which is brown. As a result, cooked asparagus is olive-drab. We can prevent this chemical reaction by cooking the asparagus so quickly that there is no time for the chlorophyll to react with acids, or by cooking it in lots of water which will dilute the acids, or by leaving the lid off the pot so that the volatile acids can float off into the air.
Cooking also changes the texture of asparagus. Water escapes from its cells and they collapse. Adding salt to the cooking liquid slows the loss of moisture.