Effects of heating and bleaching on formation of stigmastadienes in olive oil

Extra virgin olive oil was heated at various temperatures in the range 187–253 °C. The stigmastadiene content was shown to increase linearly with time, and the energy of activation for sitosterol dehydration was calculated as 191.0 ± 9.0 kJ mol−1. The effect on stigmastadiene formation of bleaching extra virgin olive oil was studied using three bleaching earths at temperatures in the range 80–120 °C. The earth that was most active for pigment removal was also most active for sitosterol dehydration. The bleaching earths had a major catalytic effect on stigmastadiene formation, with the activation energy for the dehydration of β‐sitosterol being reduced to 70.8–80.6 kJ mol−1 in their presence. It was concluded that a common catalytic effect was exerted by all bleaching earths, but the number of active sites for sterol dehydration per unit surface area was greater for the Premiere bleaching earth than for the other bleaching earths, and this was the main cause of the greater catalytic activity of this earth.