Elsevier

Current Research in Food Science

Volume 3, November 2020, Pages 158-165
Current Research in Food Science

Research Paper
Understanding water activity change in oil with temperature

https://doi.org/10.1016/j.crfs.2020.04.001Get rights and content
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Highlights

  • A method is presented for the measurement of water activity of oil at temperatures up to 85 °C.

  • The water activity of peanut oil is found to decrease exponentially as the temperature increases.

  • A model is derived to predict the water activity of oil as a function of temperature.

  • Desiccation may happen to bacteria in oil during thermal processing, which explains the protective effect of oil.

Abstract

Our recent studies and several publications suggest that the low water activity (aw) of oil in thermal processing might be a major contributing factor towards the increased thermal resistance of bacteria in oils. In this study, we developed a reliable method to measure the water activity of oil by measuring the equilibrium relative humidity in a small headspace. Using this method, water activity of peanut oil was found to decrease exponentially with increasing temperature. A model derived from excess Gibbs free energy was fitted to the observations with an R2 = 99.6% and RMSE = 0.01 (aw). Our results suggest that the sharply reduced water activity of oil resulting from a rise in temperature could cause desiccation of bacteria. This is a possible explanation for the protective effect of oil in thermal processing.

Keywords

Water activity
Peanut oil
Thermal processing
Excess gibbs free energy
Low-moisture food

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