Submitted by: Amy Simonne, Ph.D., Associate Professor, Food Safety and Quality

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A recent research publication in the December 2006 issue of Journal of Environmental Health regarding the use of microwave to sterilize cellulose sponges contaminated with raw sewage had brought up a lot of attention to consumers (1). However, it is imperative that consumers acquire additional interpretation and understanding of the experiment before applying the study to a real life situation in their own kitchen.

Researchers (2, 3, 4, 5, 6, 7, 8, 9) have definitely shown that kitchen cloths, sponges and other kitchen food contact surfaces are important factors contributing to cross-contamination of potentially harmful microbes to foods in the home kitchen and restaurants. Many methods (chemical, physical [e.g. heat]) can be used for disinfecting or sanitizing the harmful microbes from those surfaces, but in relation to the use of microwave one study was already conducted by Park and Cliver in 1997 (4)

Park and Cliver (4) clearly demonstrated that household microwave can be use for sanitizing cellulose sponges and cotton cloths. The researchers contaminated sponge and disk cloths with two strains of Escherichia coli and Staphylococcusaureus, two of the typical foodborne bacteria at levels between five hundred thousand to ten million cells and then heated the materials with microwave oven at highest setting (800W at 2450MHz). They found that after 30 seconds, no living bacterial cells were found in full size sponges and dishcloths, however, after wetting additional time required for both were 60 and 180 seconds, respectively. The result suggested that microwave heating is affective for decontamination of cellulose sponge and cotton dishcloths.

In comparison of this study (http://www.ees.ufl.edu/) and the previous work by Park and Cliver (4) in 1997 the conclusions are remarkably similar. Most bacteria are killed within two minutes of microwave heating.

What is the catch? Most scientific studies were conducted under specific conditions, and thus the results may not be necessary applicable to every situation. In both studies, cellulose sponge was the only sponge tested, and thus the effects on other type of sponges many not be the same. Furthermore, because the killing effects on the microbes in both studies come from heat generated by the vibration of water molecules by the microwave, rather than the microwave energy itself (10), changes in the mass of the material and the amount of water may affect the heating rate.

Let’s look at the definitions

Sterilization is a process to eliminate all form of microbial agents such as bacteria, fungi, viruses from a surface, food or biological culture medium. Sterilization process needs some special tools or equipments (autoclave, high dose irradiation, or some form of chemical treatment). Once sterilized, the objects can be re-contaminated again if not protected.

Disinfecting or sanitizing is to reduce the number of microorganism or to partially remove some microbes from a clean surface or clean object to a safe level.

Cleaning is a process of removing food and other type of soil from a surface or objects.

Take home message

Is it necessary to sterilize sponges and dishcloths in your kitchen?

No, per definitions, it is not necessary to sterilize sponges or dishcloths in the home kitchen, but regular cleaning (after each use) and sanitizing (every other day) is definitely necessary. Cleaning remove source of nutrient for microbial growth, and sanitizing reduce the number of bacteria and other germs so that they remain at a low number.

Steps to sanitizing or disinfecting household sponges (cellulose sponges) or cotton dishcloths

In order for sanitizing process to be effective, the sponges or cotton dishcloths must be cleaned first.

Sanitizing process can be done with household chemicals or with heat. For chemical sanitizers to work properly they must be used in a proper manner; this means that a proper combination of concentration and time must be observed. Using chemical sanitizing in home setting can be difficult for many consumers. Further, if the chemicals are not properly used it may cause some harm to the users. Therefore, using heat especially with the microwave can present a simple solution at household level.

In order to meet a minimum requirement for killing live bacterial cells, a temperature of 171ºF or 77 ºC for at least 30 seconds is necessary. This could be done by either heating cellulose sponges in hot water at 171ºF or 77 ºC for at least 30 seconds or using the microwave heating as an alternative. Things to remember: for microwave heating, cellulose sponges must be wet with water.

In the case of microwave heating, both studies (UF study and Park and Cliver) had recommended 2-3 minutes respectively; this allow enough time for the materials to reach a minimum sanitizing temperature.

Use caution when heating sponges or dishcloths in hot water or microwave! Some newer dishwashers may also have sanitizing options for operations.

References

1. D.K. Park, G. Bitton, and R. Melker. 2006. Microbial inactivation by microwave radiation in the home environment. J. Environ. Health. 69(5):17-24.
2. C. E. Enriquez, V.E. Enriquez, and C.P. Gerba. 1997. Reduction of bacterial contamination in the household kitchen environment through the use of self disinfecting sponge. Dairy, Food and Environmental Sanitation. 17(9): 550-554.
3. D. Worsfold and C. Griffith. 1997. Keeping it clean – A study of the domestic kitchen. Food-Science -&- Technology Today. 11(1):28-35.
4. P.K. Park and D. O. Cliver. 1997. Disinfection of kitchen sponges and dishcloths by microwave oven. Dairy, Food and Environmental-Sanitation. 17(3): 146-149.
5. U. Mori, T. Nakano, K. Harada, and T. Ohnishi. 1996. Various antiseptic techniques in the kitchen against Escherichia coli and Vibrio parahemolyticus J. Antibacterial and Antifungal Agents- Japan. 24(2):115-118.
6. M.S. Yepiz-Gomez, K.R. Bright, and C.P. Gerba. 2006. Identity and numbers of bacteria present on table tops and in dishcloths used to wipe down table tops in public restaurants and bars. Food Protection Trends. 26(11):786-792.
7. C. Chaidez and C.P. Gerba. 2000. Bacteriological analyses of cellulose sponges and loofahs in domestic kitchens from developing country. Dairy, Food and Environmental Sanitation. 20(11):834-837.
8. M.P. Doyle, K.L. Ruoff, M. Pierson, W. Weinberg, B. Soule and B.S. Michaels. 2000. Reducing transmission of infectious agents in the home. Control points. Dairy, Food and Environmental Sanitation. 20(6):418-425.
9. P. Rusin, P. Orosz-Coughlin, and C. Gerba. 1998. Reduction of faecal coliform and heterotrophic plate count bacteria in the household kitchen and bathroom by disinfection with hypochlorite cleaners. J. Applied Microbiology. 85(5): 819-828.
10. Anonymous. 2007. News: Microwave oven can sterilize sponges, scrub pads. Food Protection Trends. 27(3):193.

Are Commercially Manufactured Shelf-Stable, Dairy-based, Pourable Salad Dressings Potentially Hazardous Foods?

Amy Simonne, Ph.D., Associate Professor, Food Safety and Quality

Many condiments, sauces, and side items to accompany foods are available in the U.S. Despite this, the information regarding these items as far as food safety with regard to time and temperature has not been readily available. In a normal situation, most people place these items in the refrigerator for storage after opening. However, during an emergency situations such when natural disaster or power outage occurred, consumers had a hard time deciding if some of these items are safe to use or which item to keep and which item to discard.

Safe handling information for some common condiments is available from various sources. For example, according to the current USDA/FSIS emergency preparedness document, certain condiment items such as relish, taco sauce, mustard, catsup, olives, pickle, Worcestershire, soy, barbecue, and Hoisin sauces, and opened vinegar-based dressing, are considered safe even if they are opened, and at above 50ºF (10ºC) for over 8 hours. On the other hand, items such as opened fish sauces, oyster sauce, or creamy-based dressing found in that condition must be discarded (1). Still, handling information for many more condiment items are lacking.

A recent study by scientists at the University of Georgia provided additional information on commercially manufactured shelf-stable, dairy-based, pourable salad dressings (2).

The objectives: 1) to determine death rates of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in three commercially manufactured full-fat ranch salad dressings, three reduced-fat ranch salad dressings, two full-fat blue cheese salad dressings, and two reduced-fat blue cheese salad dressings, and 2) to affirm the expectation that these salad dressings do not support growth of these pathogens (disease causing organisms).

Methodology

The researchers conducted a microbial challenge study on 10 shelf-stable, dairy-based, pourable salad dressings produced by three commercial manufactures representing 70 to 75% of the retail sales of this group of dressings in the US. They conducted the experiments three times for each product in the period of 4 months. Dressings, supplied by manufacturers, were stored at 25ºC until the inoculation study. The researchers inoculated three foodborne pathogens (Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes) into salad dressings stored at 25ºC for up to 15 days. Most of the microbe strains were isolated from acid foods or from patients with illness associated with eating these foods (2).

Results

For Salmonella after 24 hours of inoculation (and storage at 25ºC) the organism was not detected in any of the 10 salad dressings regardless of the level of added organisms. For E. coli, and Listeria, overall, after 6 days of inoculation, the organisms were not detected, but there are some variations between different dressings. Overall, this study demonstrated that the death rate of Salmonella, E coli O157:H7, and L. monocytogenes in 10 commercially manufactured shelf-stable, dairy-based, pourable full-fat and reduce-fat ranch and blue cheese salad dressing stored at 25ºC is rapid. Salmonella died most rapidly, followed by E. coli and Listeria. Among these three disease-causing bacteria, L. monocytogenes exhibited the highest resistance imposed by these salad dressings. Typically, it takes at least 14 days for manufacturers to distribute these products to the food service. Results of this study show that large population of pathogens tested would die before unopened bottles of dressing reach the consumer. In case of contamination after opening, the test microorganisms would die quite rapidly at 25ºC. Results of this study showed that commercially manufactured shelf-stable, dairy-based, pourable full-fat and reduced-fat ranch and blue cheese salad dressings stored at 25ºC should not be considered as potentially hazardous foods (time-temperature control for safety of food) as defined by the FDA Food Code (4).

Take Home Message

Although these salad dressings are not potentially hazardous foods (do not support growth of disease-causing organisms), they will spoil. This is because these salad dressings only have been through mild heat treatments, thus, yeast, mold and other bacteria that are resistant to acids will survive and eventually grow to cause spoilage. Please note that this only apply to the manufactured salad dressing and not home made dressings. This is because in homemade dressing, the level of sanitation may not be the same.

During power outages or other emergencies, if these products are left without refrigeration for a few hours, they should still be safe, but they may become spoiled and eventually discarded. Consumers need to examine the product carefully for any sign of spoilage before use.

The data for this study does not apply to other foods that have pH of higher than 4.6 because inadequate refrigeration of foods that has pH higher than 4.6 (low acid foods) can increase risk of botulism. Find the estimated pH values of some foods and food products at the FDA website (3).

When in doubt, throw it out!

References

1. Keeping Food Safe During an Emergency, USDA Food Safety and Inspection Service, accessed 9/27/2006.

2. Beuchat, L.R., J.H. Ryu, B.B. Alder, and M.D. Harrison. Death of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in Shelf-Stable, Dairy-based, Pourable salad dressings. J. Food Prot. 69(4): 801-814.

3. Approximate pH of foods and food products. U.S. Food and Drug Administration. Accessed 10/2/2006.

4. U.S. Food and Drug Administration. 2005.Food code, Chapter 3. U.S. Department of Health and Human Services), Accessed September 29, 2006.

Submitted by: Amy Simonne, PhD, Assistant Professor, Food Safety and Quality

Introduction

We are in an era of excessive information. When so much information is available, consumers can find it hard to choose which guidelines to follow. When the information is also conflicting, it is even more difficult.

For example, take a case of washing of meat and poultry, according the current food safety guidelines (Chapter 10) of the new 2005 Dietary Guidelines for Americans, consumers should not wash raw meats and poultry before cooking, ¹ because it will increase chances of cross-contamination.

However, according to the leading food sanitation text book, ² the recommendation for food service operations is to wash poultry, fish, and variety meats before cooking. Washing poultry will reduce contamination of some microbes.² What would the consumer, who might also work in food service, do when facing this situation? The objective of this article is to provide research-based information regarding these two very different recommendations, so that consumers can make informed decisions about how to reduce their risk for foodborne illnesses.

In theory, the internal tissues of healthy animals should be free of bacteria. In practice this is not the case, because during the slaughtering and processing steps the meat came into contact with many sources of contamination leading to varying numbers and types of microorganisms found on raw meat products.³ Because of this, raw or improperly cooked meats are often implicated in foodborne illness outbreaks.⁴

Fresh produce is an essential part of a healthy diet. Produce is a source of vitamins, minerals, fiber, and antioxidants; it can play an important role in weight management as well.⁵ In recent years, foodborne illness traced back to fresh produce items, traditionally regarded as low risk foods, has been recognized as an emerging problem in the United States.⁶

Consumers often consume fresh produce raw without cooking or minimally processed, without a major kill step to reduce microbes. In order to reduce the risk of foodborne illnesses due to fresh produce, the FDA believes that each person in the food chain, including consumers, must take responsibility to minimize the risk of foodborne illness.⁵

Do you need to wash raw meats before cooking at home?

No, when consumers purchase raw meats or poultry from the grocery store, they do not need to wash the raw meats before cooking. Cooking is the most effective way to kill microbes that cause illness. Although research studies showed that washing raw meats may reduce numbers of bacteria; in a home setting, the washing process increases chances of cross-contamination of disease causing bacteria from raw meats/raw poultry to other ready-to-eat products and food contact surface in the home kitchens. Many studies have reveal that most consumers frequently use unsafe food-handling practices at home.⁷ When handling raw meats and poultry at home, consumers must use special care not to cross-contaminate other products.

In the food service setting, however, the recommendations may be different from the home setting regarding washing raw meats or raw poultry. If the standard procedures indicate that raw meats and poultry must be washed before the cooking process, it is perfectly acceptable. This is because:

1. The food service establishment must follow the FDA Food Code and other regulations to prevent cross-contamination of the disease causing microorganisms within their establishments and to provide safe foods to customers, and;
2. In the food service setting, the workers should receive training to handle the procedures.

Consumers need to recognize these differences between the two recommendations.

Do you need to wash raw produce before eating or cooking at home?

Yes, you definitely need to always wash your fresh produce before consumption or cooking at home. Produce needs to be washed, scrubbed, and peeled before being consumed or cooked. Because produce constitute a variety of plant parts, specific handling techniques of each of the produce are different. Consumers can find information for safe handling of produce in Fresh Produce: Safe Handling Practices for Consumers.

New research evaluating the efficacy of home washing methods for controlling microbial contamination on fresh produce⁸ suggests that consumers should wash produce under cold running tap water with rubbing and brushing where applicable. This method can reduce bacteria on the surface of produce.

Do you need to wash ready-to-eat fresh cut produce before eating or cooking?

The answer can be “Yes” or “No” depending on the situation.

No, ready-to-eat, pre-washed, bagged, produce can be used without further washing, if kept refrigerated and does not exceed the “use-by” date.

Consumers can reduce their risk of illness from fresh-cut produce by following safe handling practices such as:

1. Refrigerating the product after purchase;
2. Using only clean hands, utensils or dishes in preparing the product; and
3. Discarding the product when the "use-by" date has expired.

Yes, if consumers desire to wash the ready-to-eat fresh cut produce again. If consumers decide to wash the produce again, they should always wash the produce under running water.

Yes, if the pre-cut or pre-washed produce are sold in open bags or containers.

When washing produce, consumers should always wash the produce under running water. Washing produce under running water is recommended over soaking the produce because soaking fresh produce in water increases the potential of cross-contamination.

What about commercial produce wash? Are these products effective?

Commercial produce cleaning solutions may help remove additional dirt on some produce, but the effectiveness of these washes is not standardized. Further, do not use antibacterial soap or detergent to wash produce because the FDA does not have safety data regarding possible residue left on the produce from the products. ⁹

Take home message

1. Do not wash raw meats and poultry purchased from the store, but cook them to a proper temperature.
2. Prevent cross-contamination by following safe food handling guidelines and practices.
3. Wash your produce before consumption or cooking to reduce your risk of foodborne illness.

References

1. Dietary Guidelines for Americans 2005.
2. Marriott, G. N. and R. B. Gravani. 2006. Principles of Food Sanitation.5^th Ed. pp. 376-376.
   
3. Jay, J.M., M.J. Loessner, and D.A. Golden. 2005. Modern Food Microbiology. pp.63-145.
4. CDC.
5. FDA, 2004. Produce Safety From Production to Consumption: 2004 Action Plan to Minimize Foodborne Illness Associated with Fresh Produce Consumption.
6. Tauxe, R., H. Kruse, C. Hedberg, M. Potter, J. Madden, and K. Wachsmuth. 1997. A preliminary report to the National Advisory Committee on Microbiologic Criteria for Foods. J. Food Protection. 60:1400-1408.
7. Redmond, C.E. and Griffith, C.J. 2003. Consumer food handling in the home: A review of food safety studies. J. Food Protection. 66: 130-161
8. Kilonzo-Nthenge, A., F-C. Chen, and S. L. Godwin. 2006. Efficacy of home washing methods in controlling surface microbial contamination. J. Food Protection. 69:330-334.
9. Bruhn, C., A. Li-Cohen, L.J. Harris, 2004. Safe Handling of Fruits and Vegetables.

food safety, produce, meat, washing, Extension

Submitted by: Dr. Amy Simonne, Assistant Professor, Food Safety and Quality

Listeriosis gained its fame after the first reported outbreak associated with coleslaw in Canada in 1981. The bacterium Listeria monocytogenes, which is widespread in the environment, causes Listeriosis. The pH range for the growth of L. monocytogenes was thought to be 5.6-9.6, but new research results show that the organism can grow in laboratory media at a pH as low as 4.42. New research results further revealed that L. monocytogenes can survive and grow in refrigerated foods with pH values of approximately 4.0-5.0 and salt concentrations of 3-4%; thus home-fermented dill pickles fit this description .

Dill pickles by definition are fermented products of fresh cucumbers where the starter culture consists of the normal mixed surface flora of the cucumber surface. Cucumbers are one of the most commonly pickled foods in the US.

Home-fermented, refrigerator dill, cucumber pickles are the product of lactic acid fermentation. They are made by immersing the pickling cucumbers in brine solution and seasonings. Following this, the product typically ferments at room temperature for one week. The pickles are then stored in the refrigerator during the consumption period.

Since L. monocytogenes is widespread in the environment, contamination of this product with the organism can potentially cause serious problems because consumers do not normally heat the dill pickles prior to consumption. Newly published research by a team at the University of Georgia revealed that home-prepared dill pickles inoculated with L. monocytogenes tested presumptively positive for the organism for up to 49 days (in the internal tissue) and up to 91 days on the surface of the pickles with salt concentrations of 1.3, 3.8 or 7.6%.

Methodology
The researchers examined the fate of L. monocytogenes on the surface and in the interior of cucumbers and in brines of different salt concentrations (1.3, 3.8 and 7.6%) during a typical process of making homemade dill pickles. They measured the pH, salt (NaCl) and titratible acidity percentage, and the total population of Listeria, and other microorganisms of pickles left at room temperature storage at 2, 4, and 7 days (the fermentation period). Once the fermentation process was complete, they monitored the aforementioned parameters weekly during refrigerated storage.

Major findings:
Some of the inoculated L. monocytogenes cells in the treatment with the highest salt concentration of 7.6% remained viable.

Take home message:
Past recommendations for this type of product stated that consumption of refrigerator dill pickles, would be typically considered safe anytime after 3 days of refrigerated storage. However, from this study because L. monocytogenes may still be viable this point, there is a food safety risk.

This study recommended that home-prepared dill pickles of this type should not be distributed.

To identify at-risk population for Listeriosis, read the Research News You Can Use Summer 2005 at http://fycs.ifas.ufl.edu/newsletters/rnycufall05.pdf

References:

Schlech, W. I., P. M. Lavigne, R. A. Bortolussi, A.C. Allen, E.V. Haldane, A.J. Won, A.W. Hightower, S.E. Johnson, S.H. King, E.S. Nicholles, and C. V. Broome. 1983. Epidemic listeriosis-evidence for transmission by food. N.Engl.J. Med. 308:203-206.

Swaminathan, B. 2001. Listeria monocytogenes. In Food Microbiology Fundamentals and Frontiers, 2nd ed. Eds. M.P. Doyle, L.R. Beuchat and T.J. Montville. ASM Press.

Kim, J.K., E.M. D’SA, M.A. Harrison, J.A. Harrison, and E. L. Andress. 2005. Listeria monocytogenes survival in refrigerator dill pickles. J. Food Prot. 68(11):2005, 2356-2361.

listeriosis, food safety, foodborne illness, food poisoning, listeria, pickles