Pressure-driven infiltration of water and bacteria into plant leaves during vacuum cooling: A mechanistic model

Abstract

Vacuum cooling of leafy greens can quickly lower their temperature, thus efficiently extending their shelf-life. However, passive bacterial infiltration into the leaf through openings such as stomata or wounds during this process presents a risk. This study develops a mechanistic model of stomatal infiltration and elaborates controlling parameters. Water and vapor phases transport in the leaf tissue as a porous medium, with convective flow driven by pressure changes outside the leaf, capillary diffusion of water and molecular diffusion of vapor. Water exchange between symplast and apoplast in the leaf is driven by pressure changes. Bacteria are convected with intercellular water, along with their motility. Heat transfer includes evaporation that varies with pressure. Increased water and bacterial infiltration are primarily caused by longer re-pressurization time, lower initial moisture content of the leaf and larger stomatal pores, and less so by increased vacuum level. Findings should help make vacuum cooling processes microbiologically safer.