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June 30, 2009
Consider the onion. This humble vegetable adds layers of color, texture, nutrition and flavor to many prepared foods, from soups and stews to onion rings and pizzas.
According to Wayne Mininger, executive vice president, National Onion Association, Greeley, CO, "Nearly 20% of U.S. bulb onions are utilized in some sort of value-added, processor-managed food product."
Following is an overview of the humble, yet essential, vegetable.
Onions constitute the third largest fresh vegetable industry in the United States and are grown in 20 states from coast to coast. Idaho, eastern Oregon, Washington and California are the leading production areas. The National Onion Association estimates that fewer than 1,000 U.S. farmers plant more than 142,000 acres of onions each year.
Per capita consumption of onions in the United States has more than doubled in the past 25 years, with Americans consuming nearly 20 pounds of onions annually.
Onion types and colors
A domestic supply of onions is available yearround. Their flavor is determined by many factors, including genetics, planting location, soil and temperature.
Onions come in different colors and sizes, but are from the same species. On average, dry bulb onions are 89% water and 8% to 9% soluble sugars (this amount varies based on the time of year). Minerals, proteins and sulfur compounds make up the remaining composition.
The distinctive flavor and aroma of onions and other allium family members (like garlic) come from the sulfur compounds. These compounds are also responsible for the tear response created when cutting an onion. In raw or partially cooked onions, these compounds can mask sugars and dominate the flavor profile.
Fresh onions, available from March to August, have thin, light-colored skins. They have more water content and typically taste mild to sweet. The term sweet onion is used to describe fresh onions. Fresh onions have a mild flavor and are ideal for raw and lightly cooked dishes.
Storage onions, available August to April, have multiple layers of thick, dark-colored, papery skin. Being low in water content, storage onions have higher amounts of solids. They are the best choice for soups, stews, and caramelized or roasted applications.
Long cook times will dampen the flavor of all onions, so it is important to use stronger-flavored onions for caramelizing, roasting and in soups or other dishes that have lengthy cook times. Avoid high heat, as this will cause the onion to develop a bitter flavor. Low heat over a long time will diminish an onions strong flavor and enhance its natural sweetness.
Both fresh and storage onions are available in yellow, red and white. Yellow onions are all-purpose and popular. In fact, 87% of the U.S. onion crop is comprised of yellow varieties. Most of the sweet varieties that carry a trade name are yellow.
Red onions are a favorite for salads and sandwiches. Their color comes from the common plant pigment anthocyanidin. Mostly used for raw applications or for grilling, red onions tend to be a bit coarse in texture. About 8% of the U.S. onion crop is red. Demand for red onions in foodservice has grown in recent years. White onions are commonly associated with Mexican or Southwest cuisine.
Onions range in size from less than 1 inch in diameter (creamers and boilers) to more than 4.5 inches in diameter (super colossal). The most common sizes of onions sold in the United States are medium (2 to 3.25 inches in diameter) and jumbo (3 to 3.75 inches in diameter).
Onion nutrition and health benefits
Onions not only provide flavor, they also provide health-promoting phytochemicals and nutrients, The flavonoid quercetin, a plant-based phytochemical, is found in generous amounts in onions. Quercetin appears to have anti-inflammatory and antioxidant properties. Some research shows that quercetin can help protect the body against many chronic diseases, including cataracts, cardiovascular disease and some cancers. Good sources of quercetin include apple skin, onion, tea, red wine and other foods. Scientists have shown the absorption of quercetin from onions is twice that from tea and more than three times that from apples.
Another naturally occurring chemical in onion is known as organosulfur compound, which is linked to lowering blood pressure and cholesterol.
Onions are an important source of vitamin C, potassium, dietary fiber and folic acid (see the nutrition chart below). They also contain calcium, iron and have a high protein quality (ratio of mg amino acid per gram protein). Onions are free of sodium, cholesterol and fat. A serving of onion has 45 calories. One medium onion, or 148 grams, is considered to be one serving.
Serving Size 1 Medium Onion (148 g)
Amount Per Serving
Calories 45 Calories from Fat 0
% Daily Value*
Total Fat 0g 0%
Saturated Fat 0g 0%
Trans Fat 0g
Total Carbohydrate 11g 4%
Dietary Fiber 3g 12%
Vitamin A 0% * Vitamin C 20%
Calcium 4% * Iron 4%
Potassium 190 g
* Percent Daily Values are based on a 2,000 calorie diet.
Your Daily Values may be higher or lower depending on your
Calories: 2,000 2,500
Source: Food and Drug Administration (FDA) 2008
Packaging and precut and processed formats
Dry bulb onions are commonly packaged in:
Bags (2, 3, 5 lb pre-packs, 10, 25 and 50 lb.)
Cartons (40 and 50 lb.)
Processed fresh onions are available in a variety of cuts, including:
Custom cuts and various packaging sizes are also available.
Processed frozen onions (IQF) are commonly available in the following cuts:
Onion handling and storage tips
The following are tips for receiving and storing onions:
Onions should feel firm and dry, but may have loose outer skins.
Onions should be free of gray or black mold and should not have any visible sprouting.
Always make sure the number of bags or cartons delivered matches the delivery invoice, and the onions are the correct color and size ordered.
Always handle onions with care. Do not drop onions, as this can cause bruising.
Store onions in a cool, dry, well-ventilated area.
Bagged or boxed onions should be stored at least one foot away from walls and other pallets to allow proper air movement. Do not wrap onions in plastic or store in plastic bags. A lack of circulation will reduce shelf life.
Do not store onions with potatoes or other produce items that release moisture.
Keep onions out of direct sunlight.
Cut onions will keep for several days if sealed in plastic bags or containers and refrigerated.
Tips to avoid tearing
When an onion is pierced, a series of rapid chemical reactions takes place. In technical terms, the enzyme alliinase begins to react with the substrates known as Alk(en)yl-L-Cysteine Sulfoxides (ACSO). One of these ACSOs is called 1-propenyl L cysteine sulfoxide. When it reacts with alliinase, the reaction produces 1-propenesulfenic acid, pyruvic acid, and ammonia. The 1-propensulfenic acid then reacts with an enzyme called lachrymatory factor synthase, which generates propanethial sulfoxide. This compound reacts with the nerve cell membrane of the eye to form sulfuric acid, and causes tearing.
To reduce tearing: Chill onions for about 30 minutes before cutting. Always use a sharp knife and use quick, precise movements. Begin cutting at top. Leave the root end intact as long as possible as it contains the highest concentration of sulfur.
Kimberly Reddin is Director of Public and Industry Relations for the National Onion Association. In this role, Kim coordinates consumer, retail and foodservice promotion activities for the third largest fresh vegetable industry in the United States. The National Onion Association is the official organization representing growers, shippers, brokers and commercial representatives of the U.S. onion industry. In the last two decades, the association has played a role in increasing per capita onion consumption by 63 percent.
As a fourth generation agriculturalist, Kim is passionate about her roots. In her youth, she was actively involved in a purebred cattle operation as well as her familys grain and hay crops. She earned a bachelors degree in Animal Science/Agribusiness. She has worked in human resources, sales and marketing for several organizations. Kim is now combining her layers of experience to develop promotional and educational materials that encourage consumption of onions.
For more information about onions, visit www.onions-usa.org .
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