EFFECT OF LOW TEMPERATURE ON THE STEREOISOMER COMPOSITION OF β‐CAROTENE IN THE HALOTOLERANT ALGA DUNALIELLA BARDAWIL (CHLOROPHYTA)1

Dunaliella bardawil Ben‐Amotz & Avron, a β‐carotene‐accumulating halotolerant alga, was analyzed for the effect of growth temperatures on its pigment content and on the stereoisomeric composition of β‐carotene by the use of advanced liquid chromatography and photodiode array detection. Decreasing culture temperature from 30° to 10°C increased the β‐carotene content twofold and the ratio of 9‐cis to all‐trans β‐carotene fourfold, with no significant changes in the other cell pigments. The variation of total β‐carotene content by temperature was correlated with the integral irradiance received by the algal culture during a cell division cycle, whereas the 9‐cis stereoisomer increased over the amount expected by that integration. The massive accumulation of 9‐cisβ‐carotene within the β‐carotene globules is interpreted as indicating that the oily 9‐cis stereoisomer protects against the crystallization of all‐trans β‐carotene at low temperatures.