Current Research in Food Science (Nov 2020)

Understanding water activity change in oil with temperature

  • Ren Yang,
  • Jiewen Guan,
  • Sicheng Sun,
  • Shyam S. Sablani,
  • Juming Tang

Journal volume & issue
Vol. 3
pp. 158 – 165

Abstract

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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.

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