Amy Simonne, Ph.D., Associate Professor, Food Safety and Quality, reports that 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).
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).
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!