- Edible sprouts such as alfalfa, broccoli, mung bean, and radish sprouts, are excellent sources of antioxidants, essential amino acids, and a handful of nourishing vitamins and minerals. As such, sprouts have been labeled as functional foods that have health-promoting benefits and lower the risk of many diseases.
- Despite their nutritional advantages, sprouts carry a serious risk of foodborne illness. Seeds and beans need warm and humid conditions to sprout and grow. These conditions are also ideal for the growth of bacteria, including Salmonella, Listeria,and coli.
- Raw or lightly cooked sprouts have been implicated in 58 reported foodborne outbreaks within the United States every year since 1998. The majority of these outbreaks were caused by Salmonella and E. coli.
- Sprout-related outbreaks in the U.S. have led to over 1900 reported illnesses since 1998. However, studies have shown that for every reported case, 28 go unreported, meaning that could mean that there have been as many as 53,000 or more sprout related illnesses in the U.S. in the past 19 years.
- The FDA recommends that everyone cook their sprouts thoroughly to reduce the risk of illness from possible contamination.
Sprouts are the premature growth of a plant from a germinated seed. Every vegetable becomes a sprout at some point in its journey from seed to bloom. Only some seeds, however, form sprouts that are edible and palatable.
Sprouts were first cultivated by humans in ancient India and Southeast Asia. Sprouts have long been valued in the East for their density of micronutrients, rapid growth, and resilience in adverse weather. It was not until the second half of the 20th century, however, that sprouts began to gain popularity in the West. Since their debut on the Western palate in the 1970s, sprout production has exploded, and sprouts of all kinds are now regulars in many grocery stores, sandwich shops, and local markets across the country.
Due to the relative ease and thrift of growing sprouts, many sprouts are grown for personal use directly in people’s homes, others by local small market “sprouters”, and others by large-scale nationally distributing sprouting facilities. Because of the high-risk of microbial contamination inherent in sprout production, along with the complex landscape of their production and distribution, sprouts are considered high risk foods by the FDA. The following will be an overview of the different varieties of popularly consumed sprouts, the steps involved in sprout production, and the risks of microbial contamination encountered along the way. This article is intended as a tool for investigators of foodborne outbreaks to assist them with possible sprout-related outbreaks.
The most commonly consumed sprout varieties are alfalfa, mung bean, red clover, radish, broccoli and wheat grass.
Alfalfa sprouts are among the most common sprout varieties consumed in the U.S. They are sprouted from the tiny brown seeds of the common alfalfa plant, Medicago sativa. The alfalfa plant is a legume, which in its full form, is commonly used as a forage crop for cattle. If left to grow, the alfalfa plant could reach a height of three feet, with small purple flowers spiraling upward.
Approximately 80 million pounds of alfalfa seed are produced each year in the United States. Eighty-five percent of this production comes from the states of California, Idaho, Oregon, Washington and Nevada. While only a small fraction of these seeds will be sold for use in sprouting facilities, the seeds used for sprouting are not typically distinguished or handled differently than seeds sold for agricultural production.
Depending on the variety of seed, sprouts will germinate and grow approximately 3-7 days after seeds have been placed in a warm, humid environment. Certain seed types can take up to 14 days to produce sprouts, while other varieties can produce slightly sprouted product within 48 hours.
Once ready to consume, alfalfa sprouts feature thin and tangled white stalks with deep green leaves. Despite public health warnings, they are typically eaten raw and have a mild flavor and a crunchy texture, which make alfalfa sprouts popular additions to sandwiches and salads on the American lunch plate. Alfalfa sprouts are a rich source of vitamins A and C, iron, calcium, protein and dietary fiber.
Mung Bean Sprouts
Mung bean sprouts are the most widely consumed sprouts in the world. The sprouts emerge from common mung beans, which develop inside long seed pods produced by the legume Vigna radiata.
In the U.S., 15-20 million pounds of mung beans are consumed annually, nearly all of which are consumed as sprouts. Seventy-five percent of mung beans consumed in the U.S. are imported, many coming from China and Japan, and nearly all the domestically produced mung beans are grown in Oklahoma. Mung bean seeds are sprouted and packed for fresh use or canned for shipment to restaurants and grocery stores around the world.
The sprouts are typically 2-4 inches long and have thick white stalks and tapered yellow ends. Like alfalfa sprouts, mung bean sprouts are an excellent source of vitamin C, iron, calcium, protein and dietary fiber.
Red Clover Sprouts
Red clover sprouts are very similar to alfalfa sprouts in taste and appearance. They are sprouted from the seeds of the commonly used forage legume Trifolium pratense and have a characteristic purple flower when fully grown. The sprouts of the red clover are long and thin with a white base giving way to a light green top.
They have a mild flavor and mild crunch. Because of their fragility, they do not maintain their form when cooked and, and a result, are often eaten raw on salads and in sandwiches. Like other sprout varieties, red clover sprouts are rich in vitamins A and C, iron, calcium and protein.
Radish sprouts come in several different varieties and are edible root vegetables of the Brassicaceae family, Raphanus sativus. They are sometimes referred to as “daikon.” The radish can have many different skin colors, including red, purple, black, yellow and pink, but its flesh is usually white. Its root varies in flavor, size, and length depending on which part of the world it was produced in.
They have a spicy bite and crunch to them, much like the root vegetables into which they later grow. Radish sprouts are usually found raw or lightly cooked, and are often found in salads and sushi, or used as a garnish. They are high in vitamins B and C, folate and manganese.
Broccoli sprouts are heralded for the health benefits by sprout growers and are the most famous sprout in the U.S. They are grown from the seeds of the common broccoli plant (Brassica oleracea). The sprouts are composed of thin white stalks and light green leaves.
The flavor of broccoli sprouts is mild with a small crunch. Like other thin sprouts, they do not maintain their structural integrity when cooked, and are typically eaten raw as part of a salad or on sandwiches. Broccoli sprouts are a good source of vitamins A, C, and K, folic acid, and soluble fiber and are particularly sought-after for their high concentration of antioxidants.
Wheatgrass has gained popularity in recent years as a healthy superfood which enthusiasts claim is full of immune boosting enzymes, cancer-fighting agents, and a host of important vitamins and minerals.
Wheat grass is simply the early sprouted growth of the common wheat plant (Triticum aestivum), and while it is not often thought of in the same family as other edible sprouts, it is, in fact, a sprout. Wheatgrass is different from other edible sprouts in that the seed are typically sprouted in a shallow bed of soil, rather than warm water like other sprouts.
Despite its nearly unpalatable composition, wheatgrass has found a niche as a “health-boosting” addition to fresh smoothies in its raw and a powder form, and, in capsule form, as a supplement for people who do not like its flavor. While the cancer-fighting properties and many other alleged health benefits of wheatgrass have not been substantiated by the FDA or research studies, wheatgrass is known to be a good source of vitamins A, C, and E, and minerals such as calcium, iron, and magnesium, and amino acids and chlorophyll.
From 1998 to 2018, there have been 57 foodborne outbreaks, including 30 multi-state outbreaks, and 1,940 illnesses reported in association with various types of sprouts. The following pathogens were associated with these outbreaks: Salmonella (40 outbreaks), E. coli (10 outbreaks), Listeria monocytogenes (3 outbreaks), norovirus (1 outbreak), and unknown etiology (3 outbreaks).
Sprouts are generally served raw on items such as sandwiches and salads. They require warm and humid conditions to grow, which is also ideal for bacterial pathogens such as Salmonella and E. coli. Consumption of contaminated raw sprouts can cause foodborne illness, especially in children, the elderly, pregnant women, and persons with weakened immune systems.
In 1999, a total of 157 cases of Salmonella Muenchen were identified in eight states. A contaminated alfalfa seed lot was distributed to 33 sprout growers in 10 states. An FDA Class I recall was enacted and involved 32,900 pounds of alfalfa seeds. Soon after the outbreak had subsided, FDA released a guidance document to improve food safety laws for raw sprouts.
Also in 1999, an outbreak of Salmonella Mbandaka occurred in Oregon, Washington, and Idaho from alfalfa seed grown in the Imperial Valley of California. Of the five sprout growers involved, only the two growers who had not utilized chemical disinfection were linked to the Salmonella cases.
Sprouts have been a controversial menu item at Jimmy John’s in recent years. After an E. coli O26 outbreak sickened 29 customers beginning in December 2011, Jimmy Johns decided to remove clover sprouts from store menus. Jimmy John’s had been using clover sprouts as a “safer alternative” to alfalfa sprouts, a menu item associated with Salmonella illnesses in 2010. In late 2012, Jimmy John’s announced it would add sprouts back to the menu; around the same time Kroger announced it would remove sprouts from its 2,400 store locations. Currently, sprouts are offered, and when ordered online, a warning appears stating “The consumption of raw sprouts may result in an increased risk of food borne illness and poses a health risk to everyone. Click ‘Yes’ if you understand the potential risks, or ‘Cancel’ if you’d like to continue without adding sprouts”.
In 2014, raw sprouts were found to be the implicated food item in an outbreak of Shiga toxin-producing E. coli O121 (STEC O121). Nineteen people were infected across six states, seven of which were hospitalized. Epidemiology and traceback investigations conducted by local, state, and federal officials indicated that contaminated raw clover sprouts produced by Evergreen Fresh Sprouts, LLC of Idaho was the likely source of this outbreak. Contaminated sprouts were served at restaurants such as Jimmy Johns, the Pita Pit, and Daanen’s Deli. An FDA inspection revealed several unsanitary working conditions in the facility. The contaminated seed lot was discontinued.
Seed Production, Distribution and Storage
The initial risk for disease from sprouts has its genesis in the potential contamination during seed production and distribution and is magnified by the sprouting process itself. Seeds may be reared, harvested, milled, and sprouted locally, or shipped globally to sprout growers; in which bacterial contamination may occur at any point in this chain.
- Plants for seed production are grown in typical agricultural environments and seeds are generally treated as a raw agricultural product. Potential sources of contamination in the field include agricultural water, improperly managed animal manure, contact with wild animals, and inadequate worker hygiene. In addition, domestic animals may be allowed to graze on alfalfa fields. While such contact is not likely to be a significant problem for the primary use of seed, i.e., seed for forage production, even low level, sporadic contamination of seed for food use may result in significant public health concerns because the sprouting process amplifies pathogen levels.
- Harvesting procedures expose the seed to dirt and debris and likely spread localized contamination throughout the harvested seeds.
- Seeds may also encounter pathogens during storage and transportation to sprouting facilities. The FDA recommends storing seeds in air-tight containers and positioned off the floor and away from walls to reduce the possibility of contamination by rodents and other pests.
- Processing techniques such as scarification of the seed can create a rough surface with pores and gashes in which pathogens can reside and even penetrate the seed, making decontamination efforts more difficult.
- Salmonella can survive for months under the dry conditions used for seed storage.
Below is a diagram of the steps involved in seed production:
The key aspect of sprouts that increases the risk of foodborne disease compared to other fresh produce is the exponential growth of bacteria during sprouting. Microorganisms on seeds can grow quickly under the favorable conditions of the sprouting process (e.g. water activity, temperature, pH, time, and nutrients). An overnight soak of seeds in tap water caused a 10-fold increase in aerobic plate counts. Overall, the presence of even a few salmonellae on, or inside of, a seed may increase bacterial contamination by 3-5 orders of magnitude per gram.
Although seeds are almost always the primary source of contamination in sprout–associated outbreaks, certain practices at the sprouting facilities increase the extent of microbial hazards, such as the following:
- Poor sanitation of sprouting equipment and inadequate worker hygiene at sprouting facilities can cause primary contamination or help spread contamination from infected seeds.
- Contamination of water used during sprouting could be the source of initial contamination, or a vehicle for subsequent cross-contamination.
In an exhaustive review by the FDA in 1999 following a rash of sprout-related outbreaks, several sanitation lapses were found in sprouting facilities. While industry standards have improved since the report, contamination and foodborne illness remain a continual challenge. Some of these problems noted by the FDA in their 1999 report included:
- Less than half of facilities applied disinfection treatment to seeds before sprouting
- 22% of facilities used untreated well water for sprout irrigation
- Half of the facilities did not test water for microbial quality
- Many facilities did not have hot water for cleaning equipment and hand-washing
- Equipment at many facilities was not easily cleaned and was improperly stored
- Half of the facilities reported that employees had not received basic hygiene or sanitation training
- Five facilities had no coolers to hold finished products
- None of the facilities surveyed had sufficient records to facilitate a complete traceback from finished product to the field where the seeds were grown
Below is a diagram of the steps in sprout production:
Due to the high risk of microbial seed contamination and subsequent amplification of bacteria during the spouting process, the FDA recommends sprouters take several steps to minimize the risk of future sprout-related foodborne illnesses. The most effective procedure shown to reduce microbial concentrations has been soaking the seeds in 20,000 ppm solution of Calcium hypochlorite. Sprouters often avoid these decontamination steps, because high concentrations of these antimicrobial solutions can affect germination rates and yield. In a 2004 publication on sprout safety, the FDA stressed the following:
“There is no single treatment so far that has been shown to completely eliminate pathogens on seeds or sprouts that cause foodborne illness without affecting germination or yield.”
Other sprout safety recommendations are listed in the table below. They include inspecting incoming seed bags for tears and feces using UV light, testing runoff water from sprouting tanks multiple times, and holding sprout shipments until test results come back negative.
Retail Sprouting Industry Best Practices
|PROCESS STEP||SOURCE OF CONTAMINATION||CONTROL MEASURES|
|Receiving (Seeds or Sprouts)||
|Seed Storage at Retail||
|Seed Treatment (Soaking & Rinsing)||
|Post-Germination (Harvesting/Packaging or Repackaging)||
|Storage & Display||
Source: FDA 2004
Many sprout enthusiasts enjoy growing sprouts in their home. The FDA warns eating raw home-grown sprouts may be no less injurious than eating raw sprouts from the grocery store. Since most outbreaks have been attributed to contaminated seed, pathogenic bacteria present in or on the seed could multiply to high levels during sprouting even in one’s own home. Furthermore, trays, flats and domes used to sprout seeds may become contaminated, and, unless disinfected properly, could continue to infect fresh batches of sprouts at home.
In a 2009 letter sent to seed suppliers, distributors, and sprout growers, Stephen Sundlof, the Director of the National Center for Food Safety and Applied Nutrition at the FDA, wrote the following:
This letter is intended to make you aware of the Food and Drug Administration’s (FDA’s) serious concern with the continuing outbreaks of foodborne illness associated with the consumption of raw and lightly cooked sprouts…Sprouts are often consumed raw (or lightly cooked in the case of bean sprouts) without processing to reduce pathogens that may be present. Therefore, the manner in which they are produced, packed, and distributed is crucial to minimizing microbial contamination, thereby reducing the risk of illness to consumers.
Foodborne illness outbreaks attributed to sprouts are continuing to appear at an alarming rate. Contamination of sprouts by pathogens like Salmonella, E. coli and Listeria can occur at any point on the journey from seed to stomach. It is necessary that producers, consumers, and investigators of foodborne illness outbreaks be knowledgeable about the current procedures used in sprouting facilities, and the food safety risks inherent in sprout production.
Due to the high risk of foodborne illness, the FDA recommends that children, elderly, pregnant women, and immunocompromised individuals do not consume raw sprouts. There are a variety of steps that can be taken to encourage a safer consumption of sprouts and lessen the risk of foodborne illness. These include:
- Wash raw sprouts thoroughly before consuming.
- Look for International Sprout Growers Association seal on sprout packages, especially when buying sprouts in bulk.
- Do not purchase sprouts if past the sell-by date.
- Physically examine sprouts before purchasing. The sprout roots should be clean, buds should not be dark color or have a musty smell, and sprouts should not have a slimy appearance.
- Sprouts should smell fresh and clean.
- Sprouts should be stored at 40ºF or below, in a clean refrigerator.
- Cooking sprouts or adding them to dishes near the end of the cooking process will reduce the risk of ingesting foodborne pathogens.
Although sprouts have been a diet staple in Chinese culture for over 5,000 years, they remained relatively unpopular in the United States until WWII. Growing concerns of wartime food shortages brought Dr. Clive McKay’s work with soybean sprouts into the forefront. Dr. McKay recognized the great benefits of soybean sprout cultivation and consumption, highlighting their nutritious properties, rapid growth period, easy preparation, and ability to be grown all year round.
In the 2006-2007 FoodNet Population Survey of Exposures, 4.4% of the survey cohort reported eating alfalfa sprouts within the past 7 days. Roughly 6% of the cohort (n=17,372) reported eating bean sprouts within the past 7 days, and 8% of the cohort reported eating “other sprouts” which included clover, mixed, and broccoli sprouts.
California reported the largest consumption of alfalfa sprouts, followed by Colorado and New Mexico. California also reported the largest consumption of bean and other (clover, mixed, broccoli) sprouts, followed by Colorado. California and Colorado were also above the nationwide average for consuming “any sandwich with sprouts on it” in the past 7 days.
Sprouts began gaining popularity in Western countries in the 1980s due to the focus on healthy and exotic eating. Within the last few years, they have continued gaining popularity due to a shifting focus on low-processing and additive-free foods. As discussed by variety above, sprouts are a source of protein, iron, calcium, and vitamin C. One serving of sprouts typically will have between 10 and 25 calories and approximately 2 grams of protein depending on the variety.
While many sprouts enthusiasts claim they are good for treating, curing, mitigating, or preventing diseases such as autism, Alzheimer’s cancer, dementia, diabetes and others, advertising product with such benefits is illegal. The FDA has determined that sprouts are not recognized as safe and effective for these uses. Overall, the only valid claims about sprouts can state the nutrients provided by them and not what medicinal value these nutrients may have until the FDA verifies it, which has not yet occurred. The nutrient profiles of each sprout type are discussed in the corresponding section about that sprout.
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**All photos courtesy of William Keene