Nanoencapsulation Strategies for Antimicrobial Controlled Release to Enhance Fresh and Fresh-Cut Produce Safety

Abstract

Spice essential oils and their constituents are powerful antimicrobials against foodborne pathogens. However, their low sensory threshold and low aqueous solubility make their application to fresh produce a challenge. Encapsulation within a biocompatible material has the potential to mask sensory attributes and increase aqueous solubility of the oils, thereby improving their applicability as antimicrobials onto fresh produce. Cinnamon bark extract (CBE), trans-cinnamaldehyde, clove bud extract, and eugenol were encapsulated in β-cyclodextrin (BCD), poly(DL-lactide-co-glycolide) (PLGA), alginate, chitosan, and poly(N-isopropylacrylamide) (PNIPAAM) singly and in combination. All essential oil capsules were characterized for particle size and morphology, polydispersity index, entrapment efficiency, phase-solubility, and controlled release profile. Following physical and chemical characterization, the oils and their nanocapsules were analyzed for their antimicrobial activity against Salmonella enterica serovar Typhymirium LT2 and Listeria spp. using a microbroth dilution assay to determine minimum inhibitory and bactericidal concentrations at 35°C. The most efficacious antimicrobial nanocapsules during in vitro testing were BCD-CBE, PLGACBE, and chitosan-PNIPAAM-CBE, which were applied to fresh-cut romaine lettuce, along with free CBE, to determine their efficiency against L. monocytogenes in a food system. The chitosan-PNIPAAM-CBE yielded the greatest bacterial inhibition (P<0.05); therefore, it was subjected to a shelf-life study to determine if there were any effects of the particles on fresh-cut romaine lettuce quality over the course of storage. The antimicrobial nanoparticles did not significantly affect (P>0.05) overall product quality, making encapsulated essential oils a viable treatment for improving food safety without negatively impacting the product’s key attributes. This research project developed several natural antimicrobial delivery systems that each exhibited unique release properties and mechanisms, which improved the antimicrobial efficacy (P<0.05) of essential oils and their active compounds. This study sought to characterize and compare different nanoencapsulation systems based on their performance as controlled delivery systems for natural antimicrobials against foodborne pathogens, which has not been previously reported.