Efficacy of acidified water-in-oil emulsions against desiccated as a function of acid carbon chain-length and membrane viscosity.

Sanitizing low-moisture food (LMF) processing equipment is challenging due to the increased heat resistance of spp. in low-water activity (a) environments. Food-grade oils mixed with acetic acid have been shown effective against desiccated . In this study, different hydrocarbon chain-length (C) organic acids were tested against desiccated by using 1% v/v water-in-oil (W/O) emulsion as the delivery system for 200 mM acid. Fluorescence lifetime imaging microscopy (FLIM) was utilized with a BODIPY-based molecular rotor to evaluate membrane viscosity under environmental conditions such as desiccation and temperature elevation. Drying hydrated cells to 75% equilibrium relative humidity (ERH) increased the membrane viscosity from 1,199 to 1,309 mPa·s (cP) at 22°C. Heating to 45°C decreased the membrane viscosity of hydrated cells from 1,199 to 1,082 mPa·s, and decreased that of the desiccated cells from 1,309 to 1,245 mPa·s. At both 22°C and 45°C, desiccated was highly susceptible (>6.5 microbial log reduction (MLR) per stainless-steel coupon) to a 30-min treatment with the W/O emulsions formulated with short carbon chain acids (C). By comparison, the emulsion formulations with longer carbon chain acids (C) showed little to no MLR at 22°C, but achieved >6.5 MLR at 45°C. Based upon the decreased membrane viscosity and the increased antimicrobial efficacy of C W/O emulsions with increasing temperature, we propose that heating can make the membrane more fluid which may allow the longer carbon chain acids (C) to permeate or disrupt membrane structures.