Optimization of Bleaching Parameters for Soybean Oil

Dubravka Škevin¹*, Tomislav Domijan², Klara Kraljić¹, Jasenka Gajdoš Kljusurić¹, Sandra Neđeral¹ and Marko Obranović<sup>1

1</sup>Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, HR-10000 Zagreb, Croatia
²Zvijezda d.d., M. Čavića 1, HR-10000 Zagreb, Croatia

Article history:
Received June 29, 2011
Accepted December 7, 2011

Key words:
bleaching, soybean oil, oxidative stability, sterols, tocopherols

Summary:
The final stage of edible soybean oil manufacture is refining, the most delicate phase of which is bleaching. At this step, undesirable substances are removed, such as pigments, traces of metals, phospholipids and certain degradation products. However, certain valuable compounds such as tocopherols and sterols may also be removed, significant loss of oxidative stability can occur, and fatty acid content may increase. To avoid these negative oil changes, bleaching parameters such as the concentration of bleaching clay, temperature and duration should be optimized. Since bleaching conditions depend on the properties of the bleaching clay as well as on the type of crude oil, bleaching parameters should be optimized with different types of clay for each vegetable oil. Since such optimization has not yet been reported for soybean oil treated with Pure-Flo^® Supreme Pro-Active bleaching adsorbent, this study investigates the effect of bleaching parameters on bleaching efficiency, oxidative stability and the content and composition of bioactive compounds (tocopherols and sterols) using the above mentioned clay in this type of oil. Results show that the amount of clay had the greatest influence on bleaching efficiency, especially according to the Lovibond scale, on transparency, and on phosphorus content. Temperature and clay amount significantly affected oxidative stability, in particular the formation of secondary oxidation products. Increasing the amount of clay decreased tocopherol content of the bleached oil. Neutralized soybean oil bleached for 20 min at 95 °C with 1 % Pure-Flo^® Supreme Pro-Active bleaching clay showed the highest oxidative stability, best bleaching efficiency, and most favourable sterol content, although tocopherol content was reduced.

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