Non-invasive measurement of oxygen diffusion in model foods

- The method developed is useful to study oxygen diffusivity in foods.
- The presence of agar significantly lowers oxygen diffusivity in water.
- The addition of agar to water did not significantly alter activation energy.
- Physical models were helpful to describe oxygen diffusivity in fibrous gels.
- Oxygen content can be measured at multiple locations within a food.

In this study, we developed a non-invasive method to determine oxygen diffusivity (DO2) in food gels using an Oxydot luminescence sensor. We designed and fabricated a transparent diffusion cell in order to represent oxygen transfer into foods packaged in an 8-ounce polymeric tray. Oxydots were glued to the sides (side-dot) and bottom (bottom-dot) of the cell and filled with 1, 2, and 3% (w/v) agar gel as a model food. After deoxygenation, local oxygen concentrations in the gels were measured non-invasively at 4, 12 and 22 °C. Effective oxygen diffusivities in gels (DO2g) and water (DO2w) were obtained after fitting experimental data to the analytical solution (data from side-dot) and the numerical solution (data from bottom-dot) to Fick's second law. Temperature had significant positive influence (P < 0.05) on oxygen diffusivity estimated for different medium and analysis methods. The DO2 obtained from both methods were statistically different (P < 0.05) at 12 and 22 °C but not at 4 °C. Results show that DO2g values decreased by 72-92%, compared to DO2w. Results also show that decreasing the temperature from 22 to 4 °C reduced the DO2w and DO2g values by 55-60%. No significant difference (P > 0.05) was found between the activation energy (Ea) of water and gels (1-3% w/v) for temperatures ranging from 4 to 22 °C. We used a combined obstruction and hydrodynamic model to explain why DO2g decreased as gel concentration increased. The method developed in this study can be used to study the oxygen diffusivity in foods.

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