Effect of novel bottle inner surface coatings made with polylactic acid and plant extracts on the physiological status of Pseudomonas aeruginosa in real liquid foods using flow cytometry

Abstract

Polylactic acid (PLA) was used, together with a novel optimized mixture (OM) of Thymus fontanesii essential oil (EO d ) and the ethyl acetate (EA) fraction from Scirpus holoschoenus extract, to develop antimicrobial coatings for the inner surface of bottles for the preservation of food liquids against the pathogenic bacterium Pseudomonas aeruginosa. The effect of these coatings on the physiological status of P. aeruginosa was tested by flow cytometry (FC), filling coated bottles with previously contaminated fish soup or egg whites. As was expected, the release of phenolic compounds (PCs) from the inner coatings of the bottles to the liquid was temperature dependent. Although their antimicrobial activity in contaminated egg whites was negligible, probably due to the neutralization of bioactive substances by ovalbumin, the PLA-OM-coated bottles had a high antimicrobial effect when they were filled with fish soup. In this latter case, the percentage of viable cells greatly decreased, and the percentage of dead cells, killed by membrane damage, increased.