Factors determining the steradiene formation in bleaching and deodorisation

Steradienes are steroidal hydrocarbons formed by a sterol dehydration reaction during the vegetable oil refining process. The influence of the bleaching and deodorisation process conditions on the formation of steradienes was studied by use of mathematical model equations. During the bleaching process steradienes are formed due to a dehydration catalysed by the acid-activated bleaching earth. By increasing the bleaching temperature from 90 to 110 °C a gradual increase in the steradiene concentration from 5.1 to 22.3 ppm was observed. The steradiene content linearly increased with increasing bleaching earth concentration and increasing degree of acid activation. Steradiene formation was also observed at elevated temperatures applied during the deodorisation. Steradienes were distilled during deodorisation and recovered in the deodoriser distillate. Depending on the deodorisation temperature 0.046—1.06% of the free sterols were dehydrated, resulting in the formation of steradienes.