Elsevier

Food Microbiology

Volume 92, December 2020, 103571
Food Microbiology

Microbial safety of oily, low water activity food products: A review

https://doi.org/10.1016/j.fm.2020.103571Get rights and content

Highlights

  • Many foodborne outbreaks and recalls have been linked to oily, low (OL) aw foods.

  • Adequate heat treatment during processing of OL aw foods eliminated pathogens.

  • Irradiation and natural antimicrobials inhibited pathogens in OL aw foods.

  • Post-processing contamination allowed pathogen survival in these foods.

  • Sanitation and good hygiene were the best ways to control pathogens in OL aw foods.

Abstract

Oily, low water activity (OL aw) products including tahini (sesame seed paste), halva (tahini halva), peanut butter, and chocolate, have been recently linked to numerous foodborne illness outbreaks and recalls. This review discusses the ingredients used and processing of OL aw products with a view to provide greater understanding of the routes of their contamination with foodborne pathogens and factors influencing pathogen persistence in these foods. Adequate heat treatment during processing may eliminate bacterial pathogens from OL aw foods; however, post-processing contamination commonly occurs. Once these products are contaminated, their high fat and sugar content can enhance pathogen survival for long periods. The physiological basis and survival mechanisms used by pathogens in these products are comprehensively discussed here. Foodborne outbreaks and recalls linked to OL aw foods are summarized and it was observed that serotypes of Salmonella enterica were the predominant pathogens causing illnesses. Further, intervention strategies available to control foodborne pathogens such as thermal inactivation, use of natural antimicrobials, irradiation and hydrostatic pressure are assessed for their usefulness to achieve pathogen control and enhance the safety of OL aw foods. Sanitation, hygienic design of manufacturing facilities, good hygienic practices, and environmental monitoring of OL aw food industries were also discussed.

Section snippets

Fatty or oily, low water activity (OL aw) foods

Foods with low water activity (aw) (<0.70) have a long shelf life and can be shelf stable for years. The number of food items and food ingredients considered to be or that can contribute to the low aw of a food are almost limitless. Examples of products in this category include soup mixes, spices, herbs, nuts, dried fruits and vegetables, dried meats, chocolate, cocoa, pasta, breakfast cereals, cake mixes, powdered milk and infant formula, egg powder, hydrolyzed vegetable protein, snacks,

Manufacture of tahini and halva

Tahini and halva-making technologies are based on traditional methods and have been described in the literature in detail (QUALEB, 2015; Mureşan et al., 2013). The technological features of tahini and halva manufacture are presented schematically in Fig. 1, Fig. 2, respectively.

Tahini is mainly manufactured by milling roasted and dehulled sesame seeds (QUALEB, 2015). The first stage of the process involves washing and drying sesame seeds using special machines to remove the sand and other

Contamination of OL aw foods with foodborne pathogens

The contamination of OL aw products foods with foodborne pathogens may occur during growth, storage or processing (Podolak et al., 2010; Sheth et al., 2011). Pathogens which were isolated from the major raw component (eg. cacao beans, sesame seeds and peanuts) of OL aw foods have also been found at the processing stage of the food chain which means that these pathogens may originate from the production environment and survive until processing (Frank, 2014). Pathogenic bacteria may contaminate

Illness outbreaks and recalls linked to OL aw foods

In recent years, low aw foods or food ingredients have been associated with foodborne illness outbreaks due to contamination with foodborne pathogens. Unfortunately, several pathogens can persist in low aw foods for months, or years, in concert with static health hazard (Beuchat et al., 2013).

The persistence of pathogens in the foods increases with decreasing aw and increasing fat content (Santillana Farakos et al., 2013). Foodborne pathogens that survive in low aw foods showed higher

Survival of pathogenic bacteria in OL aw foods

The growth or survival of pathogenic bacteria in food products is affected by various factors including the chemical and physical properties of foods (intrinsic features), storage conditions or extrinsic features, implicit features which include the physiological properties of microorganisms, as well as processing features such as heating, canning, and irradiation (Jay, 2000; Yousef and Courtney, 2003). The major intrinsic factors affecting behavior of pathogens in OL aw foods are the low aw

Bacterial responses and mechanism of survival in OL aw foods

Although there are some suggested methods by which bacteria present in an OL aw food can survive such harsh conditions, the exact mechanisms of survival are not well understood (Finn et al., 2013a). Upon exposure to the osmotic stress of low aw foods, bacteria try to overcome the stress by increasing intracellular concentrations of compatible solutes, which balance the osmolarity of the intracellular environment with that externally and thus prevent water loss. Osmoprotectants are accumulated

Control of bacterial pathogens in OL aw foods

Contamination of OL aw products with foodborne pathogens may occur during pre-processing, processing or post-processing steps (Olaimat and Holley, 2012). Therefore, control of pathogens in these products is necessary at each step of potential contamination: in the field, during harvesting, processing, distribution, retail markets, foodservice facilities, or at home to improve the safety of these products (Beuchat et al., 2013; Frank, 2014). However, preservation treatments still need to be

Sanitation, hygienic design of manufacturing facilities, good hygienic practices, environmental monitoring

OL aw producers are required to find means to prevent the occurrence of pathogenic organisms in their finished products. The potential hazards and risks throughout the manufacturing stages of these products could be eliminated through implementation of planned approaches of food safety management systems such as the International Organization for Standardization (ISO) 22000, good manufacturing practices (GMP), Good Hygienic Practices (GHP), and Hazard Analysis Critical Control Points (HACCP)

Conclusions

OL aw products have been routinely associated with large illness outbreaks and recalls, particularly involving Salmonella spp. The remarkable ability of some foodborne pathogens to survive in OL aw food products for long periods is commonly observed and is due to the high levels of fat in these foods. Although these low aw products are usually exposed to heat treatment during processing, which is sufficient to eliminate pathogens from the seed or seed coat, post-processing contamination may

Further studies

The general strategy for contamination prevention is to understand the mechanism well enough by which contamination and disease transmission can occur to interrupt them. Therefore, the effective application of control requires coordinated effort among those responsible for harvesting, processing and distribution activities. It is evident that study is required to more fully characterize the main routes by which pathogen contamination occurs in these products during production in the field and

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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