Listeria monocytogenes is inhibited on fillets of cold-smoked sunshine bass, Morone chrysops x M. saxatilis, with an edible corn zein-based coating incorporated with lemongrass essential oil or nisin

Authors: HAGAR, JANELLE - Kentucky State University; Rawles, Steven - Steve; XIONG, YOULING - University Of Kentucky; NEWMAN, MELISSA - University Of Kentucky; THOMPSON, KENNETH - Kentucky State University; Webster, Carl

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2018
Publication Date: 6/1/2019
Citation: Hagar, J., Rawles, S.D., Xiong, Y., Newman, M., Thompson, K., Webster, C.D. 2019. Listeria monocytogenes is inhibited on fillets of cold-smoked sunshine bass, Morone chrysops x M. saxatilis, with an edible corn zein-based coating incorporated with lemongrass essential oil or nisin. Journal of the World Aquaculture Society. 50(3):575-592. https://doi.org/10.1111/jwas.12573.
DOI: https://doi.org/10.1111/jwas.12573

Interpretive Summary: Aquaculture has been the most rapidly growing global agriculture industry for the past four decades and now accounts for >50% of all fish consumed. Unfortunately, fish is a highly-perishable product and has a short shelf-life of between 6-10 d. Listeria monocytogenes has a high prevalence on fish fillets and is a serious health concern to humans. Essential oils (EOs), one of many secondary metabolites derived from the distillation of plant materials, are also generally recognized as safe (GRAS) compounds that have been shown to be effective against food pathogens and spoilage bacteria in both laboratory media and in food. The EO of lemongrass (Cymbopogon flexuosus; or LEO) has been identified as particularly effective against gram-positive bacteria. By introducing EO flavors that are complementary to the food product, a secondary safety step could be created to reduce the occurrence of L. monocytogenes in refrigerated RTE food products. A particularly high-risk food group is ready-to-eat (RTE) foods which do not require cooking or processing before consumption. RTE foods are often identified in outbreaks of foodborne illness that include vegetables, pre-packaged salads, fruit, deli meats, soft cheeses, and meats. Smoked fishery products, particularly those from aquaculture sources, have been implicated in a number of listeriosis cases. From 15-18% of all smoked fish is contaminated with L. monocytogenes. With demand for fishery products on the rise, L. monocytogenes poses a serious threat to consumer safety. This study evaluated the effect of GRAS compounds, LEO and nisin, for reducing L. monocytogenes and spoilage bacteria on cold-smoked HSTB fillets when incorporated into an edible zeinbased coating. This study shows that LEO was only able to decrease spoilage bacteria by 0.5log in PVC packaging, though similar effects were not seen in vacuum-packaged samples. While the difference is significant, it is improbable that LEO in a corn-zein coating could extend the shelf-life of smoked fillets. However, the use of GRAS compounds to alleviate risk of illness resulting from food pathogens on RTE product has great potential. Exploring the use of natural, readily-available compounds, like LEO, is becoming an attractive alternative. Future work in this field should focus on the physiochemical properties of a LEO coating, potential chemical or sensory changes to the food product, verifying the safe use and dosage of LEO, and the likelihood of industrial application. Data from the present study indicates that application of edible coatings incorporated with EOs promotes not only food product safety, but may also satisfy the environmental conscience of the consumer.

Technical Abstract: Ready-to-eat (RTE) foods have been identified as a high-risk food group due to the number of outbreaks caused by food-borne pathogens isolated from these products. As these items receive no further processing or heat treatment prior to consumption, bacterial pathogens such as Salmonella, Staphylococcus aureus, Escherichia coli, and Listeria monocytogenes present a serious threat to consumer safety. Of particular concern, L. monocytogenes is resistant to various food storage techniques including reduced or modified atmosphere packaging, refrigerated storage, and increased salt concentration. Cold-smoked fishery products have been implicated in a number of listeriosis cases, where it is estimated that between 6-36 percent of cold-smoked fish is contaminated with L. monocytogenes. Edible coatings incorporated with natural antimicrobials have been suggested to control pathogenic and spoilage bacteria on a variety of meat products. In this study, edible zein-based coatings incorporated with nisin and lemongrass essential oil (LEO) (8%) were evaluated for antibacterial action against L. monocytogenes and spoilage organisms on cold-smoked, cultured hybrid striped bass, Morone saxatilis x M. chrysops, under polyvinyl chlorine (PVC) and vacuum-packaging. In this study, corn zein-based edible coatings were found to be an effective carrier for nisin and LEO. Nisin-treated samples were most effective against L. monocytogenes in both PVC and vacuum-packaged fillets, with a total reduction of 3.5log and 3.7log, respectively over the length of the storage time. LEO-treated samples reduced L. monocytogenes cell counts by 2.5log in PVC and 1.7log in vacuum-packaged samples. Only LEO-treated samples packaged in PVC were found to inhibit the growth of spoilage organisms. Because nisin- and LEO-treated fillets reduced L. monocytogenes, they may be useful methods to improve food safety in smoked seafood.