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Understanding water activity change in oil with temperature.
Ren Yang1, Jiewen Guan1, Sicheng Sun1
1Department of Biological Systems Engineering, Washington State University, P.O. Box 646120, Pullman, WA, 99164, USA.
Current Research in Food Science
|September 11, 2020
Summary
Low water activity (aw) in oil during thermal processing increases bacterial resistance. This study developed a method to measure oil aw, finding it decreases with temperature, potentially desiccating bacteria.
Area of Science:
- Food Science
- Microbiology
- Chemical Engineering
Background:
- Bacterial thermal resistance in oils is a significant concern in food processing.
- Low water activity (aw) in oils is hypothesized to contribute to increased bacterial heat resistance.
Purpose of the Study:
- To develop a reliable method for measuring the water activity of oils.
- To investigate the relationship between oil temperature and water activity.
- To explore the implications of temperature-dependent water activity on bacterial desiccation.
Main Methods:
- Development of a novel method to measure oil water activity by assessing equilibrium relative humidity in a sealed headspace.
- Experimental determination of peanut oil water activity across a range of temperatures.
- Application of a model derived from excess Gibbs free energy to describe the observed data.
Main Results:
- A reliable method for measuring oil water activity was successfully developed.
- Peanut oil water activity exhibited an exponential decrease with increasing temperature.
- The developed model accurately fitted the experimental data (R² = 99.6%, RMSE = 0.01 aw).
Conclusions:
- Elevated temperatures significantly reduce oil water activity.
- The desiccation of bacteria due to sharply reduced water activity at higher temperatures is a plausible explanation for the protective effect of oil during thermal processing.
- This research provides a mechanistic understanding of bacterial behavior in heated oils.
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