NO - Besoin d'assistance

Composition of tomatoes and tomato products in antioxidants (WG1) page 77
__________________________________________________________________________________________
When 0.1% of the antioxidant BHT was added in the stock solution, the % of lycopene
degradation was limited to 7-11%. When diluted in the mobile phase (working solution),
lycopene concentration remained unchanged over 20 days. At 27°C, lycopene isomerized
readily in organic solvent and the content of cis-lycopene reached 50% after 3h of incubation.
Lowering the temperature to 4°C or addition of BHT limited the isomerization rate but did not
modify the final equilibrium distribution of lycopene isomers (Nguyen and Schwartz 1998).
The BHT effect suggested that free radicals might be involved in the isomerization process of
lycopene (Gao et al. 1996). Because of the lycopene instability, it has been proposed to
evaporate lycopene solution under nitrogen before storing at –20°C , to prepare daily working
solution and to inject it separately on the chromatographic system (Hart and Scott 1995,
Porrini et al. 1998).
8.4 Extraction
In a comparative study of extraction procedure on 2 g tomato juice, Taungbodhitham
et al. (1998) reported that the methods validated by the Association of Official Analytical
Chemists (AOAC) were 2 fold more efficient for lycopene than the other methods based on
chlorinated solvents, which were usually applied to extract total lipids (Table 26, Fig 17).
Methods
Table 26. Extraction methods for comparative study using canned tomato juice.
1 Association of Official 2-5 g extracted 5 min with
Analytical Chemists,
1984, Section 43.015
100 ml acetone:hexane (4:6)
2 Folch et al.., 1957 2 g sample extracted with 34ml
chloroform:methanol (2:1)
3 Hara and Radin, 1978 2 g sample extracted with 36 ml
hexane:isopropanol (3:2)
4 Hsieh and Karel, 1983 2-5 g sample extracted with
acetone:petroleum ether (50:50)
(Solvent ratios in the parentheses are by volume ratio)