Experimental evidence of water loss and oil uptake during simulated deep-fat frying using glass micromodels

Abstract

Different studies have emphasized the importance of cooling in oil absorption after frying, suggesting that the largest proportion of oil is sucked into the crust after the product is removed from the oil. Microscopy has been a powerful tool to support these determinations, but, direct observation of fluxes has not yet been possible. The aim of this research was to develop an experimental procedure based on the use of glass micromodels to get direct evidence of transport phenomena during oil immersion for the first time. To do so, micromodels were saturated with water and immersed in oil at 190 °C. Fluids displacements were monitored using video-microscopy as well as fluorescence microscopy. Results showed that only a small fraction of oil penetrated during the immersion period, due to the vigorous escape of bubbles. Once the release of steam stopped, after some initial cooling, oil-uptake began abruptly and oil movement into the pores could be clearly identified. Oil absorption ended as soon as the oil film lost continuity, due to air penetration. Overall, the developed technique illustrates how glass micromodels may be used to visualize and provide valuable information to understand key transport phenomena during processing.