Inactivation Kinetics of Yeast Cells during Infrared Drying

Abstract

In this study, aqueous yeast suspensions were used to investigate the effects of drying (in an infrared heating environment) on the survival of yeast. The processes were modeled mathematically using a range of kinetics rate equations. The model parameters for each kinetic rate expression were obtained using a Matlab optimization procedure and the more suitable models describing the inactivation processes were identified. In order to provide the data for model validation, experiments were conducted using freshly prepared yeast suspensions. Additional experiments were also performed that further demonstrate the protective effects of sucrose and skim milk solids on yeast survival during drying. The simple Arrhenius equation was found to be a good model for predicting yeast survival during the control experiments, when heat was applied without dehydration occurring. Models incorporating both temperature and moisture content were more effective in describing yeast inactivation during drying. The model that gave the best predictions included the drying rate and the rate of temperature change as variables; the predicted activation energy for yeast deactivation was closest to that obtained from heating-only experiments in comparison with the other models examined. The results from this work are discussed and future prospects are suggested.

Keywords:

• Drying
• Inactivation kinetics
• Mathematical modeling
• Yeast

Notes

^a The X here is the moisture content based on the wet basis (i.e., X = 1 when the water content is 100 wt%). k _d is the inactivation rate constant, k _o is the preexponential factor, E _d is the activation energy, and a and b are fitting coefficients.

^a f _min is the minimum value for Eq. (10) attained for the model fit; the smaller the f _min , the better the model fits.