A study by 1H nuclear magnetic resonance of the influence on the frying medium composition of some soybean oil-food combinations in deep-frying

- Soybean oil is submitted to heating and three series of deep-frying experiments.
- The evolution of the oil and the frying media composition is monitored by 1H NMR.
- Acyl groups, aldehydes, alcohols and 1,2-diglycerides are determined.
- Migration from food lipids to the frying media occurs.
- Influence of the food in the soybean oil-frying media composition is noticeable.

A study of the evolution of the composition of both soybean oil submitted to heating at frying temperature for a prolonged period of time, as well as of soybean oil-frying media used in three different series of deep-frying experiments is carried out by means of 1H nuclear magnetic resonance. The foods involved in the deep-frying processes have very different lipid contents and their lipid composition is also very different. The results obtained allow one to clarify how the nature of the food being fried influences the changes observed in the composition of the soybean oil-frying media throughout the deep-frying process. The study refers both to the evolution of the molar percentage of the different kinds of acyl groups in the frying-media as well as to the nature of the aldehydes formed and the evolution of their concentrations. It is noteworthy that the main aldehydes detected, in both soybean oil and soybean oil-frying media, are the reactive (E,E)-2,4-alkadienals; likewise the genotoxic and cytotoxic 4-hydroxy-(E)-2-alkenals and 4,5-epoxy-2-alkenals are also present. The considerable influence of the food being fried on the occurrence of these reactive and toxic aldehydes in the frying media is shown. Furthermore, the occurrence and evolution of other oxygenated compounds such as alcohols are also addressed, as is the extent of hydrolytic processes. In addition, the evolution of Iodine Value and of the percentage in weight of Polar Compounds is also considered. The influence of the oil nature on all the above mentioned compositional characteristics is also given attention by comparison of these results with those previously obtained using extra virgin olive oil; it is noteworthy that from the toxic aldehyde content point of view the results obtained indicate that the extra virgin olive oil-frying media are much safer than the soybean oil-frying media.