pH modulates antibacterial activity of hydroxybenzaldehyde derivatives immobilized in chitosan films via reversible Schiff bases and its application to preserve freshly-squeezed juice

Antimicrobial food grade hydroxybenzaldehyde derivatives were immobilized on the surface of chitosan films by means of reversible Schiff bases. Spectroscopy and elemental analysis evidenced the different ability of the aldehydes to form Schiff bases with chitosan. Chitosan films modified with Schiff bases of aldehydes exerted antimicrobial properties against E. coli under mild acidic environments. The efficacy of the films lied on the reversibility of synthetized imine bonds and release of the aldehydes which was promoted in mildly acid aqueous solutions. Besides acidity, imine bond reversibility depended on the chemical structure of the aldehyde covalently bonded. Films carrying salicylaldehyde presented the highest in vitro antimicrobial performance and thus, they were chosen to evaluate their effectivity in inhibiting E. coli proliferation in freshly-squeezed carrot-orange juice. Films were successfully activated by the acid environment of the juice and reduced the population of the inoculated pathogen. Salicylaldehyde migrated to the juice did not exert toxic effects on Caco-2 cells.

The authors acknowledge the financial support of the Spanish Ministry of Science and Innovation (Grants RTI2018-093452-B-I00, MAT2017-83014-C2-2P and BES-2016-077380 funded by MCIN/AEI/ 10.13039/501100011033 and by ERDF A way of making Europe). PHM, RH and RG are members of the Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy (SusPlast) from the Spanish National Research Council (CSIC) (CSIC program for the Spanish Recovery, Transformation and Resilience Plan funded by the Recovery and Resilience Facility of the European Union, established by the Regulation (EU) 2020/2094).