The effects of roasting and seed moisture on the phenolic compound levels in cold‐pressed and hot‐pressed rapeseed oil

The paper looks at the levels of phenolic compounds in cold‐pressed and hot‐pressed rapeseed oils produced from seeds of various moisture levels (5, 7.5, and 10%). The paper also considers the effects of seed roasting on the levels of these compounds. The quality of the obtained oils is determined using the peroxide and acid values. The levels of phenolic compounds are analyzed using HPLC. It is demonstrated that the oils produced from rapeseeds with 5% moisture content, and in particular from cold‐pressed oils, were characterized by the lowest peroxide values. The roasting of the seeds and their level of moisture both significantly affect the quality of the obtained oil. Oils obtained by hot‐pressing the seeds with 10% moisture contained over 30% more of these compounds. The roasting process has a significant influence on the amount of phenolic compounds in the test oils. Practical applications: Depending on the environmental conditions and post‐harvesting procedures, rapeseeds are characterized by varying water contents. To obtain high‐quality cold‐pressed or hot‐pressed oil with high levels of phenolic compounds, knowledge of the effects of seed moisture content on these parameters is necessary. The paper describes the effects of moisture content, as well as of seed roasting and of the oil production methods (cold‐pressing vs. hot‐pressing). There is no doubt that such information will be useful for both small and large manufacturing operations that produce cold‐pressed oils. The rapeseeds for pressing were prepared as roasted (160°C, 15 min) or unroasted and with different moisture levels (5, 7.5, and 10%). The oils were cold‐pressed and hot‐pressed. The levels of phenolic compounds in the resulting oils differed with statistical significance. A significant increase in the level of phenolic compounds in hot‐pressed oils was seen, though this was also dependent on the moisture of the rapeseeds.