Graduate Thesis Or Dissertation
 

Oxidative degradation of Beta-carotene

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  • The role of beta-carotene degradations in the development of off-flavors in milk and milk products has not been established. The purpose of this investigation was to study the oxidation of beta-carotene and to identify volatile compounds arising from autoxidizing beta-carotene. Pure cyrstalline beta-carotene, mixed with Celite to accelerate oxidation, was oxidized at 50°C by molecular oxygen in two different systems. The peroxide value and loss of beta-carotene were measured after controlled oxidation periods. In one system the maximum peroxide value, 295 milliequivalents per 1,000 grams, occurred after three hours of oxidation. In the other system the maximum peroxide value, 586 milliequivalents per 1,000 grams, was observed after six hours of oxidation. Approximately 80 percent of the beta-carotene was decomposed within the first ten hours of oxidation. Volatile compounds from autoxidizing beta-carotene were collected by a cold-trap gas-entrainment technique. The collected compounds were subjected to gas-liquid chromatography and rapidscan mass spectrometry, and the following compounds were identified: n-pentane, ethyl ether, acetaldehyde, acetone, propanal, methyl vinyl ketone, toluene, isobutanal, 2-octanone and acetic acid. Compounds tentatively identified included diacetyl, 3-methyl- 2-pentanone, 4-methyl-3-pentan-2-one, 2-methylfuran, 1,3,3-trimethylcyclohexene, rnethyl formate, butanone, 2-methyl-2-heptenal, 1, 3-dimethyl-2-ethylcyclohexane, 2-ethyl-2-hexenal, 2-formyl-3, 3- dimethylcyclohexene, 1, 1, 3-trimethyl-2-n-propylcyclohexane, 2- methyl-3-nonene and 3, 5, 5-trimethyl-4-(4'-butyl-3'-en-2'-onyl) cyclohexa-1, 3-diene. A fraction possessing a strong "nutty" aroma was tentatively identified as 2-methyl-2-heptenal. The volatile compounds identified can be predicted as degradation products of beta-carotene oxidation.
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