S. Orset et al., Spray-drying of the microalga Dunaliella salina: Effects on beta-carotene content and isomer composition, J AGR FOOD, 47(11), 1999, pp. 4782-4790
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.