Natural hop extracts for prolonging the shelf-life of sausage products and cooked ham

RESEARCH PROJECT (IGF projects)

Hop cones with leafs
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Microbes limit the shelf-life of sausage products and are a risk for food safety

The microbial spoiling of cured and sliced cooked sausage products, packaged under a vacuum or modified gas atmosphere, is chiefly caused by psychrotrophic lactic acid bacteria (Borch et al. 1996). The spoiling is manifested by off-odors/off-tastes, discoloration, and slime formation. It is known that nitrite curing salts have a marked antimicrobial effect against anaerobic clostridia. In contrast, they have only a slight effect on the growth of various other microorganisms that cause food spoiling belonging to the Lactobacillus, Leuconostoc, Weissella, and Carnobacterium genera (Kroeckel 2008).

In addition, there is a risk to consumers due to the possible contamination with zoonotic agents such as Listeria monocytogenes. Listeria are a particular risk for ready-to-eat sausage products due to their specific nature as psychrotrophic, facultative anaerobic bacteria, their relatively high tolerance to external influences, and their ubiquitous presence. Listeria are known to be able to readily propagate on packaged ready-to-eat sliced meats having a relatively long shelf-life. The consequence is recall of contaminated products due to the presence of Listeria monocytogenes. Alternative approaches are needed to guarantee satisfactory shelf-life and safety for ready-to-eat sausage products.

Beta acids from hop plants have a powerful antimicrobial effect

The beta acids in hop plants possess antimicrobial activity against gram-positive bacteria such as lactic acid bacteria, listeria, and clostridia. In contrast to the alpha acids used in beer manufacture, beta acids are essentially a byproduct of hops processing. The antimicrobial effect of beta acids is higher than that of the alpha acids and the bitter taste is less pronounced. Our own studies have shown that listeria growth is suppressed by concentrations of less than 10 µg/ml of a commercially available hop extract. It is also known that the antimicrobial effect of beta acids is intensified in slightly acidic media and when cooled (Kramer et al. 2015) and this is beneficial for use in foods such as sausage products.

Hop extracts suppress listeria growth in sausage products

The IGF project entitled Stabilization of sausage products and cooked ham using hop extracts (reference 20795 N) is studying the use of beta acid rich extracts in cooked sausage and ham to provide microbiological stabilization and potentially also chemical stabilization of the products. Specific processes for incorporating the hop extracts during meat manufacture are being trialed. Microbiological tests and storage tests to evaluate the quality of packaged sliced meat products under typical retail conditions are providing the required knowledge for subsequent industrial implementation.

Initial results have shown that hop extracts significantly reduce the growth of listeria on vacuum-packed Lyon type sausage with no significant sensory impairment of the taste or color. The growth of L. sakei that is known to spoil sausage products was reduced by more than a factor of 100 by the use of 0.8 g hop extract per kg sausage over the storage period.

The use of hop extract for cooked ham is also being investigated. Various practical aspects are being looked at such as the effect of the formulation/recipe, the storage temperature, and the packaging to ultimately enable the economical and beneficial use of hop extracts in industrial production processes.

Hop extracts as preservatives for clean labeling

Hop extracts are a natural way of increasing the microbiological safety of foods such as sausage products. As a natural preservative, hop extracts are suitable for clean labeling and also as a sustainable natural ingredient to replace chemical preservatives. Their high effectiveness in relatively low concentrations is promising for industrial application.

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Borch, E., Kant-Muermans, M. L., & Blixt, Y. (1996). Bacterial spoilage of meat and cured meat products. International journal of food microbiology, 33(1), 103-120.

Kramer, B., Thielmann, J., Hickisch, A., Muranyi, P., Wunderlich, J., & Hauser, C. (2015). Antimicrobial activity of hop extracts against foodborne pathogens for meat applications. Journal of applied microbiology, 118(3), 648-657.

Lothar Kroeckel (2008). Microbiological quality of prepackaged sliced deli meats - Current studies, Fleischwirtschaft -Frankfurt- 88(11):112-116.

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Project term: 2019 to 2021
Project management/ funding: Arbeitsgemeinschaft industrieller Forschung AiF (via Industrievereinigung für Lebensmitteltechnologie und Verpackung e. V. - IVLV) / Federal Ministry of Economics and Energy BMWi
IGF funding code: 20795 N