Reviewed May 2006

General Information

David Shafer

For those concerned about the risks of consuming produce in Mexico versus the US, I suggest reading this study from Cornell University which indicates there is no evidence that produce grown outside the US is any less safe.

For general information (English and Spanish) about all types of food safety, try the American Dietetic Association site

Food Safety – Fruits & Vegetables

It would seem that the best advice is simply to wash your vegetables as directed below in potable water. This conclusion is based on the simple steps outlined by the U. S. Food & Drug Administration (FDA) and the considerable research review conducted by the World Health Organization (WHO), the FDA, and the US Dept of Agriculture (see below).

If you are going to use a sanitizer (chlorine seems most effective), the research shows the effect of the sanitizer takes place in just a few seconds, so soaking only increases the likelihood of chemical absorption into the produce. Even commercial use time is limited to under 2 minutes.

While information from 3 of the world’s largest food safety organizations has been cited, I would suggest that anyone with interest do additional research.

Latest Guidelines From The US Food & Drug Administration

1. Wash hands with warm water and soap for at least 20 seconds before and after handling fresh fruits and vegetables.
2. Clean all surfaces and utensils with hot water and soap, including cutting boards, counter tops, peelers and knives that will touch fresh fruits or vegetables before and after food preparation.
3. Rinse fresh fruits and vegetables under running tap water (do not soak), including those with skins and rinds that are not eaten (avoids cross contamination). Rub firm-skin fruits and vegetables under running tap water or scrub with a clean vegetable brush while rinsing with running tap water.
4. Dry fruits and vegetables with a clean cloth towel or paper towel.
5. Never use detergent or bleach (chlorine) to wash fresh fruits or vegetables. These products are not intended for consumption.

More information can be found here An excellent scientific review can be found here . Most of the conclusions and recommendations in this FDA review are in agreement with those found by the WHO. An excerpt is as follows:

“Effects of chlorine on bacterial pathogens inoculated onto produce have been investigated with mixed results. Studies indicate those chlorine concentrations traditionally used with produce (<200 ppm) are not particularly effective at reducing microbial populations on lettuce. Survival of E. coli O157:H7 on cut lettuce pieces after submersion for 90 s in a solution of 20 ppm chlorine at 20 or 50 °C (68 or 122 °F) was not significantly different from the non chlorine treatment (Li and others 2001). Spray treatment of lettuce with 200 ppm chlorine was no more effective at removing E. coli O157:H7 than treatment with deionized water (Beuchat 1999). Increasing the exposure time from 1 to 5 min did not result in an increased kill. Likewise, Adams and others (1989) indicated that a standardized washing procedure for lettuce leaves was only slightly improved with inclusion of 100 ppm chlorine over tap water alone. Although a reduction of p H of the chlorine solution to between 4.5 and 5.0 increased lethality up to 4-fold, longer wash times (from 5 to 30 min) did not result in increased removal of microorganisms.”

Survey By The World Health Organization

The WHO conducted an extensive review of the literature on food decontamination studies. The full article is rather lengthy, however the conclusions (page 27) are as follows:

• Efficacy of disinfectants varies with different fruits and vegetables, characteristics of their surfaces, temperature and type of pathogen.
• Little is known about the efficacy of disinfectants in killing parasites and viruses on fruits and vegetables.
• Washing fruits and vegetables in potable water removes a portion of microbial cells. In some instances, vigorous washing can be as effective as treatment with water containing 200 ppm chlorine, which generally reduces populations by 10-100-fold.
• Heavily contaminated fruits and vegetables should be subjected to a double wash treatment.
• Success in removing soil or faecal matter, and the contaminants therein, is more likely to be achieved by first washing in potable water and then washing or rinsing in water containing a disinfectant.
• The temperature of wash-water should be higher than that of the fruits or vegetables in order to minimize uptake of microorganisms by tissues.
• The lethal effect of chlorine occurs within the first few seconds of treatment (soaking doesn’t improve lethality). The population of microorganisms decreases as the concentration of chlorine increases to about 300 ppm, above which effectiveness is not proportional to increased concentration.
• Leaving fruits and vegetables wet after disinfecting or washing can negate any beneficial effect of treatment.
• Chlorine dioxide is useful in controlling populations of microorganisms in wash-water but varies in efficacy in killing microorganisms on the surface of fruits and vegetables.
• Bromine and iodine may have limited potential as disinfectants for fruits and vegetables, partly because of their adverse effect on sensory quality.
• Trisodium phosphate has good potential as a disinfectant for whole fruits and vegetables in a commercial setting. Use in households may be limited, however, because the high alkalinity of TSP may cause skin irritation.
• Although disinfectants have variable effects on pathogen control on fresh fruits and vegetables, they are certainly useful for sanitizing wash-water to prevent contamination of the produce that could result from using waters that are not microbiologically safe.
• Organic acids (e.g. acetic, lactic, citric and peroxyacetic acids) have good potential as disinfectants for fruits and vegetables, but conditions under which they are most effective have not been defined.
• Ozonation of wash-water reduces numbers of microorganisms, thus resulting in reduced numbers on the surfaces of fruits and vegetables.
• Faecal matter or water containing faeces should never come into contact with fruits and vegetables, as even the most powerful treatment (e.g. irradiation) cannot be relied on to eliminate some of the pathogens they may contain.
• Prevention of contamination of fruits and vegetables with pathogens at all points from the field to the plate, through application of good agricultural practices (GAP), good manufacturing practices (GMP) and HACCP programs, is preferred to application of chemical disinfectants after contamination has occurred.
• There is a lack of information on the extent and type of microbial contamination of raw fruits and vegetables on an international scale. Nevertheless, observations support these conclusions, and can serve as a basis for developing recommendations and plans of action.

“Microdyn” – Confusing And Possibly Ineffective.

(Information reprinted with permission of Ed T. from a Mex Connect Post in March, 2004)

The real problem is that

• there's multiple products which have some variation of the "microdyn" (microdyne, microdine) product name, each of these products have very different active ingredients, and few people have any idea what active ingredient might have any effect, they're simply grabbing for bottles with the "microdyn" (microdyne, microdine) name. Active ingredients-wise your choices include metallic or inorganic silver compounds, quaternary ammonium chloride compounds, and iodine or an iodophor. Each will have its own bacteriological as well as toxicological profile. Here's some quick thoughts, I'd suggest anybody who's interested should spend some time doing their own homework.
• Silver- high (percentage-range) concentrations of metallic silver, inorganic silver compounds such as silver nitrate, and organic silver compounds such as silver sulfadiazine are used medically as topical (direct contact treatment) antimicrobial treatments. At one time activated charcoal used to strip organic compounds from water were treated with silver compounds to inhibit bacterial and algal growth, but this application appears to died out, at least in the US. Similarly, a colloidal silver and copper compound ("Microdyn", in the US, EPA-registered by a Movidyn Corporation) was once sold to suppress bacterial and fungal build-up in recirculated industrial water such as used in the pulp and paper industry; Movidyn cancelled its registration for Microdyn in the mid-80's. I can find no legitimate references to the use of metallic, inorganic, or organic silver compounds as a sanitizer, disinfectant, or sterilizing agent.
• Wuaternary ammonium chloride compounds - Mixtures of compounds such as alkyl dimethyl benzyl ammonium chloride, didecyl dimethyl ammonium chloride, dioctyl dimethyl ammonium chloride, and octyl decyl dimethyl ammonium chloride are very commonly used as surface sanitizer; if you look at your household cleaners that claim disinfecting properties, there's a high percentage chance that you'll find a "quat". Eurochem International has what's in the US an EPA-registered product under the Microdyne Extra tradename for use as an industrial and institutional sanitizer. Although the quats are commonly used as food-service sanitizing agents, in my limited poking around I can find no reference to their use disinfecting foodstuffs like produce (my initial reaction is yuck....).
• Iodine - Iodine solutions such as tincture of iodine (2% iodine, 2.4% sodium iodide in ethanol) and povidone-iodine are commonly used medically as topical antimicrobial treatments; in this application there's a considerably greater breadth of use than with silver compounds. Falling into the same chemical class as chlorine, iodine also has uses as a disinfectant, albeit a lesser one, possibly because of its lower reactivity (the halogens function as disinfectants through the simple means of oxidizing whatever they come into contact with), as well as an poorly-characterized concern about excess iodine-induced thyroid disorders. Although more commonly recognized in the US as "Betadine", povidone-iodine solutions (typically 10%, which would yield about 1% available iodine) are sold worldwide under the name "Microdine". Targeted to the food services industry Rochester-Midland Corporation also sells what's in the US an EPA-registered germicide/sanitizer under the "Microdyne" tradename which contains 3.5% available iodine and phosphoric acid - (see the WHO’s take on Iodine above).

It should be noted that there's also a food and institutional deodorizing product sold by Misco International under the Microdyne name which contains "enzymatic odor eliminators".

Now my overall take on the subject is that the "microdyn" that people originally suggested for use on produce was an iodine compound. Iodine compounds have been one of the traditional compounds used for purifying water while camping or traveling, and by extension for sanitizing washable foods and utensils. In at least the early (1988) edition of Carl Franz's classic The People's Guide to Mexico I've got kicking around, Franz recommended purchasing Yodo para lavar veduras in drugstores, and using 1-2 drops per quart of water to sanitize vegetables.

Please note that none of the above should be taken to be me advocating or refuting the need for the disinfection of produce, which could be the subject of an entirely separate discussion, which I'm not particularly interested in taking on for the time being.

Additional Notes:

Quantities of iodine required for disinfection will vary depending on the actual product used. The 1-2 drops/quart of water does, however appear to be somewhat low, noting that 0.25-0.5 m L of a standard tincture of iodine is recommended for treating water for drinking, while 0.35-0.7 m L of a 10% povidone-iodine solution is normally used. If this sounds low, calculate how much of a colloidal silver compound would be needed to achieve the 5-10 ppm concentration recommended by Movidyn for bacteriostatic use in what's a markedly non-critical application. 0 With regards to the recommendation for the use of Grapefruit Seed Extract (GSE), there's at least two articles (a, b) published in peer-reviewed journals indicating that commercial [GSEs] tested contained all contained significant concentrations of synthetic anti-microbial agents including benzethonium chloride, methyl-p-hydroxybenzoate and 2,4,4'-trichloro-2'-hydroxydiphenylether (triclosan). A third publication (c) went further to identify that 5 of 6 tested commercial GSE products contained measurable anti-microbial agents, and neither the 6th compound, nor several in-house prepared [GSEs] exhibited any kind of anti-microbial activities. Try:

a. Sakamoto, S.; Sato, K.; Maitani, T.; Yamada, T. Analysis of components in natural food additive 'grapefruit seed extract' by HPLC and LCIMS. Bull. Nat. Inst. Health Sci. 1996, 114,38-42. b. Takeoka, G.; Dao, L.; Wong, R.; Lundin, R.; Mahoney, N.; Identification of Benzethonium Chloride in Commercial Grapefruit Seed Extracts. J. Agric. Food Chem. 2001, 49, 3316-3320. c. Von WoedTke, T.; Schluter, B.; Pfiegel, P.: Lindequist, U.; Jiilich, W. -D. Aspects of the anti-microbial efficacy of grapefruit seed extract and its relation to preservative substances contained. Pharmazie 1999, 54.452-456.

Mexican Secretary Of Tourism Advice

One of our own local food experts, Lani Wooll , utilizes SECTUR recommendations, under the prestigious Distintivo H Program and she states, “All fruits and vegetables must be first scrubbed and washed with detergent, then rinsed and soaked in iodine. … most everything has to be soaked for at least 15 minutes and 20 is better. “

Additional general information on this program can be found here The actual Distintivo H Check List has specific instructions for handling fruits and vegetables as follows:

1. Wash with potable water and soap in small batches or individually.
2. Rinse thoroughly to remove any residual detergent.
3. Submerge in an SSA approved disinfectant and follow the product specific instructions.

Both of the above SECTUR methods are contradictory to the advice given by the FDA and the WHO. The FDA recommends not using any soap or detergent and both the FDA & WHO question the use of Iodine as a disinfectant other than for surfaces. Further, the WHO suggests that prolonged contact by soaking with chemicals increases the likelihood of absorption. There were no studies found which suggest prolonged contact of a chemical sanitizer with produce.