Graduate Thesis Or Dissertation
 

Relation of color in cooked carrots to carotene content as determined by chromatographic and spectrophotometric methods

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  • Carrots were cooked to the just tender stage in a saucepan and in a pressure saucepan for appropriate lengths of time to make them approximately equal in tenderness as determined by a panel of judges and the Kramer Shear Press. A third lot of carrots was cooked in a pressure saucepan for approximately twice as long to represent overcooked carrots. Judges and the Hunter Color Meter indicated that the carrots cooked in the saucepan were more typically red-orange and bright and the carrots overcooked in the pressure saucepan were more yellow and dull. Pigments extracted from the carrots from the three cooking treatments were chromatographed on a magnesia column and the principle fractions, α-carotene and β-carotene, eluted. The β-carotene was rechromatographed on an alumina column to separate it into all-trans-β-carotene and neo-β-carotene B. In absolute amounts, carrots cooked in the saucepan had the highest concentration of all-trans-β-carotene and the highest total of all-trans-β-carotene, neo-β-carotene B and α-carotene, followed by those carrots cooked in the pressure saucepan for 50 seconds, with those cooked in the pressure saucepan for two minutes being lowest in both all-trans-β-carotene and total carotenes. However, when the a-carotene, the neo-pcarotene B and the all-trans-β-carotene were considered as percentages of the total, the percentage of α-carotene remained constant in the three treatments. Carrots cooked in the pressure saucepan for two minutes had a lower percentage of all-trans-β-carotene and a higher percentage of neo-β-carotene B than did carrots from the other two treatments. Thus, longer cooking in the pressure saucepan caused greater conversion of the more vivid all-trans-β-carotene to the paler cis-isomer, neo-β-carotene B. This isomerization plus loss of total pigment accounts for the differences in color of the cooked carrots from the three treatments.
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