The effect of rapeseed treatment by microwave and radio-frequency application on oil extraction and oil quality. Part II: Influence on oil quality

The aim of our research was to investigate the influence of microwave and radio-frequency (RF) pretreatments of rapeseed on oil quality. Oil was extracted from the seeds through mechanical pressing. Few quality parameters of the gained oil as well as special enzymatic activities of the seeds were analyzed. Microwave application at temperatures ranging from 80 to 100°C (surface temperature of the seed) reduced the acid and peroxide values in oil, whilst the intensity of the oil colour increased. On the other hand, there was no effect noted on iodine value. Thiobarbituric acid value (TBA) and lipid acid composition of oil were not affected either. The peroxidase and methylumbelliferyl-palmitic-acid-esterhydrolase (MUPase) activities in the seeds decreased, which is very important in relation to the storability and the later processing of seeds or oils. The advantage of radio frequency (RF) compared to microwaves in this research was that no burning aroma was emitted by treating rapeseeds at 120°C so that the oil yield of the seeds by pressing could be further improved. Despite this high temperature, some parameters of oil quality (acid, peroxide, and TBA values) of treated seeds have not so much changed in general in comparison to untreated control. Like microwaves, RF-waves did not affect lipid acid composition of the oil.