Thermal and Photochemical Degradation of Carotenoids - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 233

TABLE 12.2
Observed Rate Constant ( k obs ) and Activation Energy ( E a ) Values Found for Carotenoid
Thermal Degradation in Model Systems

Model Systems Carotenoid T (°C) k obs (min −1 ) E a (kcal/mol) Reference

Crystal All- trans - α -carotene 150 4.3 × 10 −2 n.r. Chen et al. (1994)

Crystal 100 9.3 Chen and Huang (1998)

All- trans -β-carotene 2.0 × 10 −3

Crystal 150 n.r. Chen et al. (1994)

All- trans -β-carotene 1.7 × 10 −2

Dry thin layer Lycopene 100

150

14.6 Lee and Chen (2002)

12.4 × 10 −3
16.5 × 10 −2

Safl ower seed oil 95

95
95
95

26.2
25.1
19.8
24.9

Henry et al. (1998)

All- trans -β-carotene
9- cis -β-carotene
Lycopene lutein

5.4 × 10 −3
5.9 × 10 −3
8.6 × 10 −3
4.5 × 10 −3

Chlorophyll a +
methyl stearate
(hexane)

All- trans - β -carotene 60

120

2.2 × 10 −2 n.r. Liu and Chen (1998)

8.2 × 10 −2

Chlorophyll a +
methyl oleate

60
120

n.r. Liu and Chen (1998)

All- trans -β-carotene 1.3 × 10 −2

4.2 × 10 −2

Chlorophyll a +
methyl linoleate

60
120

n.r. Liu and Chen (1998)

All- trans -β-carotene 6.0 × 10 −3

1.9 × 10 −2

Ethanol/water (2:8) Bixin 98 36.9 Rios et al. (2005)

2.0 × 10 −2

Amorphous powder Norbixin n.r. n.r. 36.8 Silva et al. (2007)

Note: n.r., not reported.

whereas the rates of formation of two di- cis lycopene isomers showed increasing trends during
heating. At 150°C lycopene degraded almost ten-times faster than

β -carotene crystals (Chen et al.

1994), as compared in Table 12.2.
The thermal degradation of all- trans - -carotene, lycopene, and lutein was

studied in an oil model system, safl ower seed oil, at 75°C, 85°C, and 95°C (Henry et al. 1998).
The kinetic data was i tted as i rst-order reaction for all carotenoids; and the k obs value calculated
for lycopene was about twice as high as those found for the other carotenoids, whereas no signii -
cant difference was found between the stability of

β -carotene, 9- cis - β

β -carotene isomers (Table 12.2). The calculated

E a values were similar for all- trans - -carotene, and lutein, while lycopene with

lower E a was found to be less affected by temperature. Heating

β -carotene, 9- cis - β

β -carotene at several temperatures

formed 13- cis -carotene in higher amounts, followed by 9- cis - -carotene and an unidentii ed cis

isomer. Although several degradation products were formed during lycopene heating and lutein
heating, they were not identii ed (Henry et al. 1998).
In toluene solution, 84.7% and 83.4% of the initial contents of

β

-carotene and lutein were, respec-
tively, retained after heating at 98°C for 60 min. In chloroplast preparations, a similar degradation
rate of

β

-carotene (83.2%) was observed, whereas 72.0% of lutein remained (Aman et al. 2005a).
The addition of fat to chloroplast did not affect the retention of total

β

-carotene (82.0%), whereas an
enhancement of lutein stability was found (93.0%). In these systems, apart from degradation, all- trans -
β

β

-carotene and all- trans -lutein were partially converted into its cis - isomers. After heat treatment at
98°C for 1 h, the predominant cis - isomers were 13- cis - β -carotene, 13- cis -lutein, and 13 ′ - cis -lutein

in toluene, whereas 9- cis - - cis -lutein were found as the major cis - iso-

mers in chloroplasts. The different isomeric proi le after heating may result from the interactions of
chlorophylls in the chloroplast enhancing the formation of the 9- cis isomers. It is remarkable that
these effects, occurring in well-organized chlorophyll-protein complexes, were still observed after

β -carotene, 9- cis -lutein, and 9 ′