Simulation of Microwave Assisted Finish Drying and Inactivation of Escherichia Coli, Bacillus Cereus and Staphylococcus Aureus of Onion Powder

Abstract

The onion powder with initial moisture content of 10% (db) in form of thin infinite layer of thickness 5mm was dried using a laboratory microwave oven at 50W/g microwave power density to final moisture content of 2% (db).The temperature, moisture change pattern of the experimental process was monitored. Computer simulation of the predicted temperature pattern with drying time was obtained by using the mathematical model governed by energy balance equation and using data of the thermo-physical properties of the onion powder obtained either experimentally or through literature review. The usage of high microwave power to mass ratio results in raised temperature with reduced drying time. The decrease in drying rate is due to initial moisture content. Effective moisture diffusivity increases with decreasing moisture content due to the application of high power density. Lethality values for Escherichia coli, Bacillus cereus spores and Staphylococcus aureus, which are more prominent in onion powder, were then evaluated from the simulated temperature curve. DT and z values were used to estimate the sterilization values for each individual microorganism. It was observed that significant sterilization of E.coli and S.aureus start after 35 s at a minimum temperature of 89oC with 0.047 and 0.044 log reduction while, for B.cereus it starts after 75 s at 117oC with 0.431 log reduction. The maximum temperature of 117ᵒC was limited due to unacceptable sensory quality of end product.