Heat pretreatment of oilseeds: effect on oil quality

Abstract

We studied the effect of seed conditioning via a rapid preheating technique to destroy the activity of oil-degrading enzymes. Rape and sunflower seeds were heated via steaming, oven cooking, infrared, and microwave. After the pretreatment the oil was expelled from the seeds by a screw press and its quality was determined via the analysis of oxidative stability, peroxide value, free fatty acid content, phosphorus, and iron. From the results it was concluded that preheating of the seeds leads to the expected decreased activity of lipase, but nevertheless increased levels of phosphorus and free fatty acids were observed. However, increased levels of phenolic antioxidants markedly improved the oxidative stability of rapeseed oil. From the techniques studied for heating of the seeds, microwave and steaming appeared to be the most suitable techniques. Both methods gave markedly improved oxidative stability, whereas steaming seemed to result in less formation of free fatty acids than microwave heating. Infrared heating led to rapidly burnt seeds and off-flavours.