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Reducing the Unique Risks in Sprouts
by Stephen Grove, PhD
Sprouts are considered a healthy and highly nutritious food, often eaten raw in the U.S. on salads and in sandwiches. However, sprouts have also been linked to a number of outbreaks of foodborne illness in the past two decades. According to the Center for Science in the Public Interest (CSPI, 2011), 46 outbreaks related to consumption of sprouts were recorded between 1990 and 2011, causing at least 2,500 illnesses. Salmonella and pathogenic E. coli were responsible for the majority of outbreaks, and Listeria monocytogenes the cause of one.
These bacterial pathogens thrive under the same conditions that are used to sprout seeds. The warm, moist and nutrient-rich conditions will promote the growth of even a small number of cells to a high level.
In the second half of the 1990s, a number of large outbreaks resulting in more than 1,000 cases of illness prompted the FDA to issue two guidance documents to the industry in 1999. The first, entitled “Guidance for Industry – Reducing Microbial Food Safety Hazards For Sprouted Seeds,” outlined preventive controls that sprout producers should undertake to minimize the risk of sprouts being a vehicle of foodborne illness (FDA, 1999 a ). The guidelines were largely based on recommendations provided by the National Advisory Committee on Microbiological Criteria for Foods (NACMCF, 1999), including that seeds should be grown under good agricultural practices (GAPs), sprout producers should employ good sanitation practices, seeds should be treated with an approved sanitizer to reduce the number of pathogens that may be present on the seed surface, and that spent irrigation water during sprouting should be tested from each production lot.
The second guidance document, entitled “Guidance for Industry: Sampling and Microbial Testing of Spent Irrigation Water During Sprout Production,” was written specifically to guide sprout producers through the steps necessary to test the spent irrigation water for the two major pathogens of concern in raw sprouts, Salmonella and E. coli O157:H7 (FDA, 1999b).
Spent irrigation water is water that has flowed over and through sprouting seeds and then drained off. The array of microorganisms in this water is a good indicator of the types of microorganisms present in the sprouts. It’s generally recommended that sprouters test spent irrigation water for pathogenic bacteria rather than testing the sprouts themselves, for several reasons. First, bacteria are often distributed sporadically in sprout seeds, but are generally distributed uniformly throughout spent irrigation water. Second, testing spent irrigation water is easier than sprouts because no additional steps to release microorganisms into the liquid are needed. Therefore, proper sampling and testing of spent irrigation water is important to detect bacterial pathogens that may be present in sprouts.
Many varieties of sprouts are grown around the world and in the U.S., requiring various growing times and conditions. The FDA guidance document on spent irrigation water testing was written with a focus on alfalfa and mung bean sprouts, where pathogenic bacteria, if present, are likely to be at their highest levels at or after 48 hours from the start of the sprouting process. Collection of samples for testing was therefore recommended to be performed at least 48 hours after sprouting, including any length of time that seeds are presoaked prior to irrigation.
Testing should be performed at an appropriate time that ensures the sprouter will obtain test results before product is shipped. A number of rapid test kits are listed in the FDA guidance and these screening tests can provide a presence or absence result for Salmonella and E. coli O157:H7 within 48 hours. Therefore, by collecting samples at least 48 hours prior to shipping product, the test result can be known to the company prior to making a decision on whether or not to ship the product.
The FDA guidance document recommends that spent irrigation water be sampled from each production lot or batch, described as “sprouts from a single lot of seed that were started at the same time in a single growing unit (i.e., a single drum or rack of trays).” Generally, 1 liter of water is recommended for sampling spent irrigation water, collected as the water leaves a drum or trays during the irrigation cycle. Pooling from different production batches is discouraged since any pathogens present may be diluted with samples that are not contaminated. In addition, if a presumptive positive is found in a pooled sample, the sprouter would need to either discard all batches represented by the pooled sample or retest each individual batch in order to determine which is/are contaminated.
Testing spent irrigation water is easier than sprouts because no additional steps to release microorganisms into the liquid are needed.
Hurdles and Solutions
Other types of sprouts present a challenge in recommending a best practice for testing. Some types of sprouts are commonly irrigated for less than 48 hours, and if microbiological testing is performed, results may not be reported to the sprout producer prior to the product entering the food supply. In such a case, a sprout producer may instead sample the sprouts themselves, rather than the spent irrigation water. The concern in this case is that detecting a low level of contamination present in the sprouts is challenging.
The recommendations in the two FDA guidance documents, along with other resources, including documents from international scientific bodies, international regulations, training material, etc., relating to best practices for sprout safety are currently being evaluated and used to develop a core curriculum by the Sprout Safety Alliance (SSA), a public-private alliance between stakeholders from the food industry, academia, and federal, state, and local food protection agencies. The SSA was created by the FDA in cooperation with Illinois Institute of Technology’s Institute for Food Safety and Health in 2012 to enhance the sprout industry’s understanding and implementation of best practices for improving sprout safety. The SSA aims to develop a core curriculum and training program for stakeholders in the sprout production community for improving sprout safety and understanding the requirements outlined in the FDA Proposed Rule on Standards for Produce Safety.
Sprout producers will likely need to adhere to the appropriate requirements in the Proposed Rule covering fresh produce safety under the FDA’s Food Safety Modernization Act (FSMA), and in particular, in the specific section on sprouts (FDA, 2013). The proposed requirements include using a scientifically valid method to treat seeds immediately prior to sprouting in order to reduce pathogens that may be present on the seeds. The FDA also proposes that sprout producers perform environmental testing for Listeria spp. or L. monocytogenes, and test spent irrigation water or sprouts for Salmonella and E. coli O157:H7. In each case, a written sampling plan must be prepared and include considerations of when, how, where, and what to sample, and for spent irrigation water testing, how much sample to collect.
The SSA is working with sprout producers, academic researchers, and other stakeholders to develop best practices for sampling so sprout producers large and small can benchmark their current practices, and strive to improve their practices surrounding sprout safety. Mock sampling and testing plans are expected to be part of the SSA training program, in order to assist the sprout industry, and particularly the small sprout producers, with developing their own individual plans.
Raw sprouts will continue to have safety concerns due to the inherent issues surrounding their growth, which also promote the growth of any pathogenic bacteria that may be present. Testing sprout spent irrigation water for bacterial pathogens has long been known to be an effective tool, amongst others, that can be used to improve the safety of sprouts.
Dr. Grove is manager, industry projects/research assistant professor for the Institute for Food Safety and Health, Illinois Institute of Technology. He is also the coordinator for the Sprout Safety Alliance, www.iit.edu/ifsh/sprout_safety. Dr. Grove can be reached at firstname.lastname@example.org.
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