Kathleen Glass, Ph.D., Associate Director of the Food Research Institute at the University of Wisconsin-Madison, is a self-professed “preservative fanatic.” Keeping food safe is her highest priority. However, she also respects consumer demands for clean labels. Glass highlighted clean label strategies for inhibiting Listeria monocytogenes growth in foods in her presentation titled “Challenges & Solutions for “Preservative-free, Microbial-safe Foods.”
In 1985, L. monocytogenes was the “newest bug on the block.” Following an outbreak of L. monocytogenes in cheeses, and not yet knowing the organism’s infectious dose, FDA and USDA took a zero-tolerance approach to the pathogen. The ready-to-eat (RTE) meat industry realized their products were also vulnerable, leading Glass and colleagues to test a variety of RTE meat products and identify pH, moisture, nitrite and competitive microbiota as critical factors for listerial growth.
The first listeriosis outbreak in an RTE meat (frankfurters) occurred in 1998-1999. In response, USDA fast-tracked the 2004 approval of lactate and diacetate to control L. monocytogenes in processed meats. In the meantime, however, a 2002 listeria outbreak associated with turkey caused 46 illnesses and ten deaths. Lactate and diacetate, often in combination with nitrite, became the gold standard for L. monocytogenes control, with propionate and benzoate added to the anti-listerial armamentarium in 2013. Unfortunately, L. monocytogenes outbreaks have continued to occur, particularly when antimicrobials are not used, as in the devastating 2018 South African polony outbreak: an RTE sausage product killed 216 people.
Glass compared using an anti-listerial in a product to that of wearing a seat belt: you don’t expect an accident, but you wear a seat belt, just in case. Using preservatives controls microbes throughout the food chain, providing insurance against improper holding temperature and protecting susceptible consumers.
Sometimes, protection against pathogens can be achieved simply by adjusting pH (<4.6) or water activity (<0.92). Combinations of low pH and low water activity are even more effective. In the cases of moderate pH and water activity, however, additional hurdles, such as antimicrobials, are needed. The effectiveness of an antimicrobial in food depends on many factors such as fat content, salt concentration and more. Different acids may have different activities, even at the same pH; acids with higher pKas tend to be more effective against Listeria monocytogenes in cheeses. Because it is difficult to predict what will work in a particular food, validation testing in the food is essential.
Pathogens can be controlled while maintaining a clean label. Clean label substitutes with documented eﬃcacy exist for some synthetic preservatives, including cultured sugar/milk/wheat for lactate or propionate; vinegar for diacetate or acetic acid; cultured celery for nitrite; and acerola cherry powder for erythorbate or ascorbate. However, not all preservatives have suitable clean label substitutes, particularly sorbate, which is eﬀective against molds, yeast, Listeria monocytogenes, Staphylococcus aureus and Clostridium botulinum. Some clean label antimicrobials may also be required at high levels, which may impact product flavor.
Commercial fermentates (proprietary, clean label mixtures of organic acids, vinegar and bacteriocins) can be eﬀective antimicrobials but may exhibit variability between suppliers or even between lots.
Starter (protective) cultures are another clean label strategy to prevent listerial growth in some products. Glass showed how eﬀective cultured milk solids can be at controlling L. monocytogenes growth in mozzarella cheese. She also described using protective cultures to prevent L. monocytogenes growth in cottage cheese and on apples, while highlighting the need for challenge studies to identify the most eﬀective ways (temperature, application process/location) to use these antimicrobials in a specific food.
While there are no magic bullets, clean label options for pathogen control in foods exist, with ingredient companies actively developing new clean label alternatives. Clean label antimicrobials that are familiar to consumers have the potential to enhance the safety of foods while building consumer confidence.
Challenges & Solutions for ‘Preservative-free,’ Microbial-safe Foods,” Kathleen Glass, Ph.D., Associate Director of the Food Research Institute at the University of Wisconsin-Madison
This presentation was given at the 2019 Clean Label Conference. To download free presentations and the Post-conference summary of this event, go to https://globalfoodforums.com/store/clean-label-conferences/#2019
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