61B-19 |
Potent aromas from the thermal degradation of b-carotene as detected by GC-Olfactometry |
K. MAHATTANATAWEE and R. L. Rouseff. Food Science and Human Nutrition, University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850 Carotenoids, are large, non-volatile molecules which produce color in orange juice. Enzyme or chemical cleavage of carotenoids will generate C9-C13 fragments (norisoprenoids). Some norisoprenoids may have aroma activity. Juice carotenoids may be the source of some aromas due to thermal degradation during processing. One of the carotenoids found in orange juice, b-carotene, was studied in model aqueous solution to determine which aroma active compounds were produced from thermal degradation. Beta-carotene was chosen because it should be the most unstable as it cannot be esterified to improve thermal stability. One milligram of b-carotene (99% purity) was first dissolved in a few drops of tetrahydrofuran (THF) and diluted to 100 ml citric acid buffered to pH 3.8. Ten milliliters of the model solution was added to a 40 ml vial and heated at 98±2oC for 0.5,1,2 and 3 h in a water bath. Headspace volatiles were collected using SPME (Carboxen/PDMS) at 40oC with agitation. Separation was accomplished with a HP-5890 GC using either a DB-Wax or DB-5 column. The effluent was split between an olfactometer or flame ionization detector, FID. Column oven temperature was 40 to 240oC at 7oC /min with a 5 min hold. Degradation products were tentatively identified from their aroma description and retention characteristics on two column types and by comparison with standards. Four to eight aroma peaks were observed in air. More aroma peaks were detected at longer heating times. b-ionone, b-damascone and b-cyclocitral were identified. Helium sparged samples produced only the above three compounds. The additional aroma active compounds produced in air remain to be identified. Fewer b-carotene aromatic degradation products are produced when oxygen is excluded. Some b-carotene aroma active compounds can be found in commercial orange juice thus suggesting that b-carotene may contribute to the aroma of pasteurized orange juice.
Session 61B, Food Chemistry: Flavor and aroma chemistry
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