High pressure carbon dioxide based liquid food preservation: experiments and modeling

Abstract

High pressure Carbon Dioxide (HPCD) treatment of food products is evolving as a novel technique that has potential to compliment or even replace traditional processing methods to enhance shelf life without hampering food quality. The effect of CO2 pressure (40-70 bar), number of pressure cycles (1-4 Cycles) and treatment time (15-60 minutes) on Tomato puree was studied in a high pressure vessel to check the efficacy of the HPCD treatment. Among all pressures, 70 bar pressure showed the least colony forming units (cfu)/ml and highest % inactivation for both bacteria (94%) and fungi (87%). Among all cycles, 4- Cycles experiment showed the least cfu/ml and highest % inactivation for both bacteria (67%) and fungi (74%). Also, 60 minutes of treatment time showed the least cfu/ml and highest % inactivation for both bacteria (77%) and fungi (51%). The pre- and post-treatment pH values of tomato puree stayed almost constant at ~4 for all experiments. Viscosity changes in the treated tomato puree become pronounced at very high pressures (60 and 70 bar giving 67 and 97% drop from untreated sample viscosity respectively) where a significant decrease in viscosity upon depressurization was obtained. Mathematical modeling of diffusion of CO2 inside a grampositive bacterial cell was done using 1-D transient diffusion-reaction model. Simulation results reveal instantaneous nature of CO2 diffusion process inside a gram positive bacterial cell where steady state in CO2 concentration was observed after 0.0003 seconds and almost 99% CO2 equilibrium concentration was achieved. SEM analysis of treated samples showed the evidences of physical damage to the cell structure upon violent depressurization for samples treated 60 and 70 bar pressure.