Light-activated antimicrobial activity of turmeric residue edible coatings against cross-contamination of Listeria innocua on sausages

The high number of foodborne outbreaks in ready-to-eat (RTE) food such as cooked sausages illustrate the importance of controlling microbial safety during post-processing stages of food products. Edible antimicrobial coatings can be applied to food after processing and sanitation with the goal of preventing microbial cross-contamination, decreasing the risk of foodborne illness and increasing the product shelf life. In this study, edible hydrogel coatings that can present strong antimicrobial activity when combined with UV-A light were prepared. The hydrogels coatings were prepared using either turmeric residue and gelatin hydrogels (TGH) or cassava starch and gelatin hydrogels with added purified curcumin (CGH). The coatings were characterized regarding their thickness, encapsulated curcumin concentration and water swelling, in addition to their light-activated antimicrobial activity against different initial loads of Listeria innocua at different incubation temperature. Additionally, the coatings were applied to the surface of cooked sausages and evaluated for their ability to prevent bacterial cross-contamination. It was observed that UV-A light-exposed hydrogels coatings could inactivate more than 5 log CFU/mL of L innocua after light treatments as short as 5 min. In addition, the light-activated antimicrobial activity of the hydrogel coatings were not affected by the incubation temperature. Hydrogel-coated sausages exposed to UV-A light experienced a reduction from 4 log CFU/mL of incubated bacteria to levels below the detection limit of 1 log CFU/mL after 5 and 15 min of light exposure, for CGH and TGH, respectively. Further mechanistic studies suggested that L innocua inactivation was due to the photo-irradiation of low levels of curcumin released from the coatings to solution. Lastly, it was shown that the combination of curcumin-loaded hydrogels coatings and UV-A light have great potential as antimicrobial coatings to prevent cross-contamination of L. innocua in refrigerated sausages. (C) 2017 Elsevier Ltd. All rights reserved.