Background: Enteral formulas can be stored for up to 2 years. Fat oxidation during storage can lead to the loss of nutritive value and generation of toxic products such as lipid peroxides.
Methods: Two standard enteral formulas were stored for short periods at high temperatures (1-4 weeks at 32-55 degrees C) or for long periods at low temperatures (12-36 weeks at 4 degrees C, 20 degrees C, or 30 degrees C). The present study included the assessment of lipid oxidation by measuring related fluorescent compounds and the evolution of fatty acids profile.
Results: Enteral formula fat was oxidized under all assayed conditions, including storage at 4 degrees C. The loss of essential fatty acids (linoleic and linolenic acids) was always higher when time and temperature were increased. The omega6/omega3 ratio was increased by storage from 5.6 to 7.8, which could exacerbate the inflammatory response in critically ill patients. Fluorescence intensity increased with time and temperature of storage and was correlated with the decrease in essential fatty acids (lineal correlation between -0.9416 and -0.9996).
Conclusions: Enteral formula fat was oxidized during storage, leading to a loss of nutritional value. These formulas should be stored under refrigeration to minimize this loss. Finally, fluorescence measurement proved to be a fast and easy method to assess fat oxidation status.