On October 27, 1999, the Food and Drug Administration, CFSAN, issued two guidance documents for the sprouting industry: 1) Reducing Microbial Food Safety Hazards for Sprouted Seeds; 2) Sampling and Microbial Testing of Spent Irrigation Water During Sprout Production. The first guidance document made specific recommendations for the sprouting industry, including the recommendation for testing of pathogens: "Because currently approved antimicrobials have not been shown to be capable of eliminating all pathogens from seed, sprout producers should conduct microbiological testing of spent irrigation water from each production lot to ensure that contaminated product is not distributed." The second guidance document described specific procedures for the testing of spent irrigation water.
The testing of spent irrigation water is viewed as a very critical control point. Following an inspection of 140 sprout growers in the United States, the FDA issued over 50 "Warning Letters". Of the 50 sprout growers receiving a "Warning Letter", a majority of those were bean sprout growers.
From the very beginning it was recognized that this guidance document described methods for sampling irrigation water in the production of "green leaf" sprouts, which uses drums and trays. Absolutely no reference is made to describe a method for collecting samples in the production of bean sprouts, which are grown primarily in bins.
According to Dr. Michelle Smith, the FDA was primarily concerned with the production of alfalfa sprouts when the guidance documents were written. All outbreaks associated with sprouts were linked to "green" leaf sprouts. With the exception of one or two outbreaks in a foreign country over a decade ago, there were no known outbreaks associated with bean sprouts. Risks associated with bean sprouts were further reduced by the fact that bean sprouts were usually cooked before consumption. Nevertheless, bean sprout growers are required to test spent irrigation water for pathogens.
The establishment of a testing program for bean sprouts is important. In the year 2000, there was only one outbreak linked to sprouts, and it was linked to bean sprouts. That particular grower was not testing spent irrigation water at that time. Another outbreak was avoided because the grower did test spent irrigation water for pathogens. A crop that tested positive and confirmed positive for Salmonella was kept off the market. This is proof that the testing program has helped the industry.
Bean Sprout Irrigation:
At one time the growing of bean sprouts varied tremendously from one grower to another. There may still be some variation. With the growth of the sprout industry came a new industry, the manufacture of sprouting equipment. By now, most bean sprout growers have changed their growing system to one of the newer generation of growing systems. It would be safe to say that over 90% of all bean sprout growing systems are of the "Calco" design. That is, bean sprouts are grown in a bin, roughly 4 feet wide, 5 feet long, by 4 feet high. The entire bottom of the bin is an open screen to allow the passage of water and air. Irrigation is supplied by an overhead spray bar that travels over bean sprout bins.
The irrigation process for bean sprouts has no similarity to the irrigation of alfalfa sprouts. Typically, alfalfa sprouts, whether on trays or drums, are irrigated by spray heads emitting water at the rate of less than 1 gallon per minute for a very short period of time (15 seconds). An irrigation cycle may begin every 30 seconds to two hours.
The irrigation of a single bin of bean sprouts may take between one to two minutes. That is, it would take one to two minutes for the irrigation spray bar to travel from one end of the bin to the other. The flow rate of the water is between 100 to 150 gallons per minute. The irrigation cycle may begin every 3 to 4 hours.
For sampling purposes, the most significant factor is the flow rate of water. For alfalfa sprouts, the entire crop lot is sprayed with a small amount of water over a short period of time. Spent irrigation water will have had an opportunity to permeate through the entire crop lot before draining out of the tray or drum. The collection of spent irrigation water is relatively simple, and the sample itself would be a good indicator of the types of microorganisms in the sprout lot.
If we were to literally take samples of spent irrigation water from bean sprout bins, the quality of the sample is far from ideal. First, the water flow rate is so high that the bacterial load in the sample will be so diluted that the detection of pathogens will be near impossible. Secondly, the sample will only represent that part of the bin above which the sample bottle is placed, and not the entire crop lot.
Sampling Procedure:
The following procedure is only a suggestion. It has not been scientifically proven to be effective, but it does overcome the two major problems described above. The FDA is currently conducting research on a sampling plan for bean sprouts, but until further study is conducted they are noncommittal.
How to Sample:
Because the irrigation rate for bean sprouts is so high, another water source is the simple alternative. All sprout growing rooms have a water hose for cleaning purposes. That water hose can be your alternative source. By adjusting your flow rate to approximately one gallon per minute, the water will have a chance to percolate through the sprouts and collect bacteria on its way down through the bin screen. As an additional precaution, make sure the water hose and spray mechanism you are using are clean and sanitary.
The second problem, sample collection, is not so easy. The ideal situation is to have one common collection point through which all the water will flow. Without requiring extensive refabrication of your growing bins, a wide-mouth sampling bottle attached to the end of a long stick is a simple alternative. As the water is sprayed over the sprouts by one person, another person can simply maneuver the wide-mouth sampling bottle underneath the entire bottom of the growing bin to collect a representative sample of the lot.
When to Sample:
The guidance document specifies that the sample should be taken at or after 48 hours from the start of the sprouting process. According to FDA research with alfalfa sprouts, microbial levels will not necessarily increase after 48 hours. Whether this theory will apply to bean sprouts is yet to be tested. The sheer volume of the irrigation water will wash away some of the bacterial load.
While 48 hours barely gives the alfalfa sprout grower enough time to complete the test before the product is ready for market, bean sprouts have a little more time. While it takes 3 to 4 days to grow alfalfa sprouts to maturity, bean sprouts take 5 to 6 days. If the goal is to get test results before the product is processed and out to market, the latest the sample can be collected and tested is at the 72 hour point after the start of the sprouting process. Therefore, until further research is completed, somewhere between the 48th hour and 72nd hour is the window of opportunity to collect water samples.
The water sample should be collected just before the beginning of a watering cycle, when the bacterial load will be at its peak. If the sample is taken just after irrigation, much of the bacterial load will have been washed away. By using this method, the actual time it takes to collect water samples will be much quicker. You no longer have to wait for the traveling spray bar.
Final Comments:
Water that has flowed over and through sprouts is a good indicator of the types of microorganisms in the sprouts themselves. In studies of irrigation water from alfalfa sprouts, the level of microorganisms recovered in irrigation water is about 1 log less than the level in sprouts. If pathogens are present in sprouts at very low levels, it is possible that they might be missed in water. For this reason pooling of samples is strongly discouraged by FDA.
The risk of having a diluted water sample is a far-gone conclusion if samples are literally taken from bean sprout irrigation. The cost of testing water for pathogens ranges from $50 to $100. That money will be wasted if proper sampling methods are not utilized. The greater risk is that consumers may get sick from the consumption of bean sprouts, notwithstanding test records showing the product negative for Salmonella and E. coli O157:H7.
While the FDA is studying methods to properly test for pathogens in the production of bean sprouts, we must use common sense in the meantime to protect consumers.
We welcome your comments and questions. Please send them to Jay Louie at louiefoods@aol.com.