Browsing by Author "Peltomäki, Katja"

The literature part of the study dealt with frying methods, frying fats and oils, chemical and physical changes of frying fats and oils during the frying and analyse methods of frying fats and oils. The aim of the experimental part was to study changes in rapeseed oil quality during continuous frying process during three different frying periods. Especially the effect of day without production during the frying period was studied. Samples, frying oils, were taken every day during the different frying periods. In period one and two there was one day without production. Oils were stored in storage tanks during that time. In third period, there was production on every day. All samples were inspected for colour, odour, viscosity and clearness by visual methods. Also viscosity by rotation viscometer, smoking point, free fatty acids by titration method, fatty acid content and water content of samples was analysed. Based on sensory evaluation, the quality of oil deteriorated over thedays of use. Colour was darker, viscosity was higher and off-odours were sensed. Instrumental analyses indicate same kind of changes; viscosity and free fatty acid were increased and smoking point and amount of unsaturated fatty acid were decreased while frying time was increasing. In literature, also same changes were mentioned. There was changes in fatty acid content during the frying periods. More fatty acids characteristic to meat was detected in oils at the end of period than in fresh oils. Based on these results, oil quality remained acceptable in everyday use for a typical frying period of one week. Difference between fresh oil and used oils was clear but still acceptable. The amount of free fatty acids, and the level of viscosity and smoking points were under the limits applied in Finland. The day without production deteriorated oils quality substantially Reducing the amount of oil in process and having shorter frying periods or more efficient filtering of oils can help to keep the quality of frying oil better.