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 studied. The efficacy of a range of synthetic and natural antioxidants in preventing degradation of beta-carotene has been determined. Losses of beta-carotene and isomerization were minimal during processing for both the control (no exogenous antioxidants) and the samples containing butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ). However, the use of tocopherol-based antioxidants resulted in degradation of 52-72% of beta-carotene during the drying process. All dried powders of Dunaliella proved to be unstable during storage in the presence of light and air, with beta-carotene degraded according to a first-order kinetic model. Of the antioxidants studied, only TBHQ was successful in significantly minimizing degradation (degradation 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 feed, 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 beta-carotene was significantly more unstable than the all-trans form. TBHQ was, however, successful in reducing relative losses of this isomer for samples stored in the dark. The results suggest a dominant photodegradative mechanism for the loss of the 9-cis isomer of beta-carotene.
Orset
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School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, United Kingdom.
Leach
G C
GC
Morais
R
R
Young
A J
AJ
D002851:Chromatography, High Pressure Liquid; D056890:Eukaryota / Q000737:chemistry*; D006873:Hydroquinones / Q000032:analysis; D007536:Isomerism; D008027:Light; D019207:beta Carotene / Q000032:analysis*
D006873:Hydroquinones; D019207:beta Carotene; C018855:2-tert-butylhydroquinone