Influence of the vacuum break conditions on oil uptake during potato post-frying cooling

Reduced pressure frying is an alternative to conventional frying that enables products to be obtained at lower processing temperatures with lower fat content. The oil uptake in frying mainly occurs during the subsequent cooling stage. With vacuum frying, this stage necessarily includes a period of vacuum break when the system recovers the initial pressure. The different conditions under which this pressurisation occurs can influence the final oil content of the product. To study this effect, potatoes of the "Monalisa" variety, with different geometries, were fried at 140 degrees C and moderate vacuum (24.9 kPa). Various combinations of draining times (30, 60, and 90s) and vacuum break velocity, VBV (0.75, 2.21, 4.43 and 12.43 kPa s(-1)), were tested for this stage, and the final oil content of the product determined by comparison with the dry weight. The results showed that both parameters have a significant influence (alpha < 0.05) on oil uptake. A short draining time and a low vacuum break velocity result in greater final fat content. There is a linear relationship between the oil uptake and the inverse of VBV, following the Washburn equation. The influence of VBV is such that differences of up to 70% in the final fat content can be obtained in the range tested. (C) 2009 Elsevier Ltd. All rights reserved.