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Kinetics of the Thermal Degradation of β-carotene in Carrot Juice
Thesis Abstract:
The study was conducted to quantitatively define the effect of heating on the degradation of β-carotene in a natural food system. Carrot juice was heated at six temperatures: 104.4°C, 110.0°C, 115.6°C, 121.1°C, 126.7°C, and 132.2°C. The concentration of β-carotene retained after heating for a given time duration was determined using thin-layer chromatography and the absorbance of the extract was read at 451 nm. The logarithm of pro-vitamin A concentration was plotted against heating time and the thermal resistance parameters, d- and z- values, were graphically determined from the reciprocal of the slope of the graph. The reaction rate constant (k) for each temperature and the activation energy (Ea) for the degree radiation reaction were also calculated.
The destruction of β-carotene in processed carrot juice was observed to follow first-order reaction kinetics, a behavior typical of most food nutirents and other components. The reaction had an activation energy of 2.5 kcal/mole (107.2 KJ/mole) which was within the average values of Ea for vitamins and related nutrients given by Lund (1977) (i.e., 20 to 30 kca/mole). The other parameters revealed that β-carotene in carrot juice was not readily destroyed by heat and that exposure to heat temperatures is required to effect considerable degree of degradation of the molecule.
An apparent increase in β-carotene was noted during the initial stages of heating carrot juice at 104.5°C and 100°C. This may be attributed to leaching of the water-soluble constituents into the water which, in turn, increased the relative concentration of the water-insoluble components such as β-carotene; and possible reversion of cis-isomers to the more stable and more deeply colored all-trans β-carotene at the start of heating.
∝-carotene was detected in fresh carrot extracts but not in the heated samples. This indicated greater thermobility of ∝-carotene than β-carotene and was attributed to the less stable structure of the former due to the lesser number of conjugated bonds in its chromophore.