Low--Water Activity Foods: Increased Concern as Vehicles of Foodborne Pathogens

Abstract

Foods and food ingredients with low water activity (a(w)) have been implicated with increased frequency in recent years as vehicles for pathogens that have caused outbreaks of illnesses. Some of these foodborne pathogens can survive for several months, even years, in low-a(w) foods and in dry food processing and preparation environments. Foodborne pathogens in low-a(w) foods often exhibit an increased tolerance to heat and other treatments that are lethal to cells in high-a(w) environments. It is virtually impossible to eliminate these pathogens in many dry foods or dry food ingredients without impairing organoleptic quality. Control measures should therefore focus on preventing contamination, which is often a much greater challenge than designing efficient control measures for high-a(w) foods. The most efficient approaches to prevent contamination are based on hygienic design, zoning, and implementation of efficient cleaning and sanitation procedures in the food processing environment. Methodologies to improve the sensitivity and speed of assays to resuscitate desiccated cells of foodborne pathogens and to detect them when present in dry foods in very low numbers should be developed. The goal should be to advance our knowledge of the behavior of foodborne pathogens in low-a(w) foods and food ingredients, with the ultimate aim of developing and implementing interventions that will reduce foodborne illness associated with this food category. Presented here are some observations on survival and persistence of foodborne pathogens in low-a(w) foods, selected outbreaks of illnesses associated with consumption of these foods, and approaches to minimize safety risks.

Microbial Safety of Low Water Activity Foods: Study of Simulated and Durban Household Samples

“…Infant cereal (0,352), adult cereal (0,381), and milk powder (0,284) values also corresponded with values in the literature by [1,17].…”

“…This could be due to poor hygiene practices in industry and prolonged exposure to air. Furthermore, spices and nuts originate from natural sources and could also have been contaminated from the natural environment as mentioned in the literature [1,3]. There was no growth detected for aerobic and anaerobic spore-formers counts in adult cereal, indicating that these samples were well kept at household level and were not exposed to the air for prolonged periods of time.…”

“…Recently over the years, a number of incidences relating to outbreaks caused by the presence of food-borne pathogens in low water activity ( ) foods have increased [1]. According to Byrd-Bredbenner et al [2], households were ranked as the most common setting and primary location in which food-borne illnesses took place in the United States.…”

“…However, many studies done by researchers in literature have found that microorganisms have the capability of surviving in low foods [1,5]. The increased number of food-borne related illness outbreaks recently, associated with low foods, has portrayed that even though microorganisms cannot proliferate in such foods, there is a likelihood for them to be persistent for extended periods of time [1,5,6].…”

“…The main pathogens of concern in literature were those of Salmonella spp., Escherichia coli O157:H7, Listeria monocytogenes, Cronobacter sakazakii, Staphylococcus aureus, and Clostridium botulinum [1,8]. A crucial step that is often omitted is an additional heating step which has the ability to control or kill potentially contaminated food-borne bacteria.…”