Development of an antimicrobial sachet containing encapsulated allyl isothiocyanate to inactivate Escherichia coli O157:H7 on spinach leaves

A sachet releasing allyl isothiocyanate (AIT) vapor was developed and its effectiveness as an antimicrobial packaging system for fresh spinach was evaluated. AIT was encapsulated in calcium alginate beads (AIT beads) and the release of AIT as affected by temperature and relative humidity (RH) was determined. The release rate of AIT from beads increased with increased temperature, but was not significantly affected by RH. A low-density polyethylene (LDPE) sachet containing AIT beads (AIT sachet) was prepared and the rate of release of AIT as affected by film thickness and temperature was studied. The release of AIT from sachets increased significantly with decreased LDPE thickness and increased temperature. Finally, antimicrobial effects of the AIT sachet against Escherichia coli O157:H7 and molds and yeasts (MY) on fresh spinach leaves were determined. E. coli O157:H7 and MY had similar sensitivities to AIT vapor. The number of E. coli O157:H7 on spinach leaves (5.6 log CFU/leaf) decreased by 1.6–2.6 log CFU/leaf at 4 °C and 2.1–5.7 log CFU/leaf at 25 °C within 5 days. The reduction of E. coli O157:H7 was significantly greater at 85% RH than at 43% RH. Reductions on control leaves (no AIT sachet) did not exceed 1.2 log CFU/leaf under any of the test conditions. Results of the study will be useful when developing antimicrobial packaging systems to increase the microbiological safety and extend the shelf life of spinach and possibly other fresh produces.