Spray-drying of the microalga Dunaliella salina: Effects on beta-carotene content and isomer composition

The effects of spray-drying of the unicellular microalga Dunaliella salina on its beta-carotene content and geometric isomer composition have been stu died. The efficacy of a range of synthetic and natural antioxidants in prev enting degradation of beta-carotene has been determined. Losses of beta-car otene and isomerization were minimal during processing for both the control (no exogenous antioxidants) and the samples containing butylated hydroxyto luene (BHT) and tert-butylhydroquinone (TBHQ). However, the use of tocopher ol-based antioxidants resulted in degradation of 52-72% of beta-carotene du ring the drying process. All dried powders of Dunaliella proved to be unsta ble during storage in the presence of light and air, with beta-carotene deg raded according to a first-order kinetic model. Of the antioxidants studied , only TBHQ was successful in significantly minimizing degradation (degrada tion constants of 0.03 and 0.04 days(-1), compared to 0.53 days(-1) for the respective control). For control powders and those with BHT added to the f eed, the degradation constants were reduced to values between 0.27 and 0.37 days(-1) by restricting light and flushing with nitrogen; however, storage in the dark alone had no effect. For more slowly: degrading powders having TBHQ added to the feed, it was clear that degradation of beta-carotene was influenced by both light and oxygen. During storage the 9-cis isomer of be ta-carotene was significantly more unstable than the all-transform. TBHQ wa s, however, successful in reducing relative lasses of this isomer for sampl es stored in the dark. The results suggest a dominant photodegradative mech anism for the loss of the 9-cis isomer of beta-carotene.