Direct observation of the surface structure of French fries by UV–VIS confocal laser scanning microscopy

Observations of raw, fried and air-dried potato parenchyma samples were made with a UV–VIS confocal laser scanning microscope in reflective and fluorescence modes. Distinction between oil and cells was made possible by the addition of a fluorescent probe in the frying oil and the use of the natural fluorescence of cells. Observations were recorded at different depths and were treated to make volumetric reconstructions at different product scales. The results showed that after frying, the cellular structures were well conserved in terms of shape and size. Oil was shown to be mainly located in the first cell layer occupying around 50% of its volume. Oil remained in the cut cells emptied during the washing or the frying operation or in the damaged cells partially filled with starch. Cell detachment, because of starch swelling and dehydration, seemed to be the preferential connection between cell layers. The positive effect of air-drying toward oil uptake reduction could be the restriction of these connections.