D CONTROL (sprouts)

D CONTROL (sprouts)

Summary

Significant hazards

r Salmonella. r

E. coli O157:H7.

B. cereus (home-production only).

Control measures

Initial level (H 0 ) r Good agricultural practices for production of seed used for sprouting. r Good hygienic practices in seed cleaning and storage.

Increase (ΣI) r Train food handlers on personal hygiene. r Good hygienic practices for sprout production.

Reduction (ΣR) r Seed treatments for 5D reduction. r Train food handlers on seed disinfection. r Cook sprouts prior to consumption, if possible.

Testing

r Aerobic colony counts or coliforms are not useful indicators. r Test spent irrigation water for pathogens and/or E. coli prior to harvest. r Environmental monitoring for L. monocytogenes or Listeria spp. r Monitor equipment hygiene using tests such as ATP.

Spoilage

r Control measures for pathogens control most spoilage organisms. r Strict control of sanitary conditions is also needed to prevent crop failure

due to growth of plant pathogens. r Rinse sprouted seeds in chilled water to cool quickly.

r Store at <5 ◦

C to prevent spoilage.

General considerations. Discussions of the control of mung bean sprout quality are found in Buescher and Chang (1982) and Brown and Oscroft (1989). Additionally, the NACMCF (1999) and IFT (2001) discuss controls appropriate for other types of sprouts.

Control of hazards begins with the grower, by following good agricultural practices, protecting seed crops from contamination by birds, animals, insects, etc., in maintaining clean and disinfected equipment and sampling microbiologically before shipping dried seeds (NACMCF, 1999). It is important to recognize that seeds are seldomly produced exclusively for sprouting purposes. Rather, most seed is produced for agricultural purposes. Therefore, programs that enhance seed grower and producer knowledge on potential hazards and appropriate controls are important to mitigate potential risks.

Once received, seeds should be stored in a clean, dry environment to prevent mold and bacterial growth. Foreign matter should be removed before soaking. A pre-soak in mild detergent and chlorinated (2–4 ppm free chlorine) water will remove residual foreign matter that could reduce the effectiveness of further chlorination. Since seeds are a raw agricultural commodity that may be contaminated with

MICROORGANISMS IN FOODS 6

pathogens, disinfection of water used for soaking or growing is a critical aspect of control. No matter how carefully seeds are chosen, they could be contaminated with pathogenic organisms capable of mul- tiplying during growing. Soaking presents the first opportunity to reduce pathogens; however, treatments may not reliably eliminate pathogens (NACMCF, 1999). Soaking alfalfa seeds for 45 min in a solution of 0.5% sodium hypochlorite in a commercial facility was insufficient for preventing an outbreak of salmonellosis in Finland (P¨onk¨a et al., 1995). An initial soak in water with a total chlorine level of

20 000 ppm has been proposed to reduce microbial loads (NACMCF, 1999). Treatment of mung bean seed with buffered 3.0% (wt/vol) Ca(OCl) 2 reduced Salmonella spp. and E.coli O157:H7 4–5 logs (Fett, 2002). Excess chlorine should be removed by washing in regular chlorinated tap water until the rinse is clear. Chlorine treatments are not allowed in some regions (e.g. Europe), therefore other decontamination methods should be used when appropriate. Irradiation of seeds has been approved in the United States (FDA, 2000). Fumigation of alfalfa seeds and mung bean seeds with ammonia gas has been shown to cause a 2–3 log destruction of E. coli O157:H7 and Salmonella Typhimurium (Himathongakham et al., 2001). Salmonellae may also be inactivated by heating seeds in water at 57–60 ◦

C for 5 min. However, since only a narrow range of times and temperatures are able to kill S. Stanley without serious reduction in seed germination rates, decontamination of seeds by heat may have limited commercial practicality (Jaquette et al., 1996). However, the combination of dry heat and irradiation has been found to be an effective means of reducing or eliminating E. coli O157:H7 from alfalfa, radish, and mung bean seeds (Bari et al., 2003).

For seed germination, total chlorine levels of 100–200 ppm are recommended (Brown and Oscroft, 1989) in disinfected containers, for times dependent on the temperature (longer times are required when cool). Water for irrigation during germination (at 20–30 ◦

C for 4–7 days) should contain at least 2–4 ppm free chlorine, preferably maintained by an automatic system. Chlorine is preferred over ultraviolet treatment of irrigation water because it disinfects the whole system. All equipment and rooms should

be easily cleaned and disinfected, and have adequate drainage for rinse waters which frequently contain high levels of microorganisms. Water for initial washing of harvested sprouts should be chilled, and should contain 100–200 ppm total chlorine; final washing stages (5 ± 2 ◦

C) should contain 2–4 ppm free chlorine. If water is recirculated, seed coats, roots, etc. should be filtered out. The rapid respiration rate of sprouts must be slowed to prevent rapid wilting and decay in storage. They are best washed in cold water to chill them quickly, and held at 0.6–4.4 ◦

C (Buescher and Chang, 1982). Freshness can be prolonged in polyethylene, cellophane, or PVDC film bags. At 0–5 ◦

C, the shelf life is 10–11 days and storage life decreases by 50% after even only 1 h at 20 ◦

C (Tajiri, 1979a,b). Exposure to light should be minimized. Visual checks should be made for wilting, browning, or rot, and samples should be tested for off-flavors. During transport, film-wrapped cartons should be maintained cool, and must be transferred gently. Re-usable trays or boxes should be cleaned and disinfected after every use.

Finally, consumers can reduce the risk of enteric pathogens, if necessary, by pasteurizing sprouts using a brief dip in boiling water. In 1988, concerns about the safety of seed sprouts led the UK Department of Health and Social Security to advise the public to boil bean sprouts for 15 s before consumption. Dipping green sprouts such as alfalfa for 10 s in boiling water just prior to use reduces pathogen levels with minimal impact on quality (R. Buchanan, personal communication).

Testing. Since extensive microbial growth occurs during germination and sprouting, high aerobic plate counts and Enterobacteriaceae are expected. Thus, tests of this nature are of little or no value for assessing hygiene or the microbial quality of the product. Furthermore, this information does not help in predicting the rate of spoilage.

Microbiological testing of the seeds has not reliably rejected lots contaminated with salmonellae. Test- ing the sprouted seeds (P¨onk¨a et al., 1995) or spent irrigation water (Fu, 2001; Howard and Hutcheson,

311 2003) has been more effective for detecting positive lots. Other means for controlling the presence of

VEGETABLES AND VEGETABLE PRODUCTS

pathogens, particularly enteric pathogens, are necessary. Manufacturing environmental monitoring for L. monocytogenes or Listeria spp. is appropriate to identify potential harborage sites to minimize the potential for contamination.

Spoilage. Control measures for pathogens will generally control most spoilage organisms. Strict con- trol of sanitary conditions is also needed to prevent crop failure due to growth of plant pathogens. Rinsing of sprouted seeds in chilled water to cool quickly will reduce product temperature, which re- duces spoilage. It is important to remove as much water as possible without damaging the sprouts to prevent spoilage. Product should be stored at <5 ◦

C to prevent spoilage.