Lycopene degradation

Only 6% of the iifitial total lycopene prepared as a thin film on the surface of each vial remained after 144 hr under fluorescent light (2000 to 3000 lux) at 25°C under N2. Lycopene degradation occurred as a first-order reaction at 2.93 x 10" /min, and the concentration of aU lycopene mono-c isomers already present in the sample, 5-cis-, 9-cis-, l3-cis- and 15-d5 -, showed an inconsistent change in this period. Nevertheless, formation of lycopene di-c isomers was observed after 32 hr of light exposure and when considering relative percentage, loss of 13% of all-trani-lycopene occurred while an increase of 11% for total cis isomers was found after 144 hr. ... 

Sharma, S.K. and Le Maguer, M., Kinetics of lycopene degradation in tomato pulp solids under different processing and storage conditions. Food Res. Int, 29,309, 1996. 

Saponification is often used to extract xanthophylls as well as remove chlorophylls and lipids from samples prior to analysis, as these compounds can interfere with the chromatographic detection. Although saponification with methanol and potassium hydroxide is routinely used to facilitate carotenoid extraction, numerous studies indicate that saponification can also result in losses of carotenoids. For example, Khachik et al.60 demonstrated that saponification actually caused the loss of total carotenoids in samples. Alternatively, enzymatic saponification using lipase can be used to help prevent the loss and isomerization of some carotenoids. Fang et al.32 suggested that saponification of plasma samples should be avoided to prevent unnecessary lycopene degradation. 

FIGURE 4.3 Schematic of lycopene degradation pathway. [Modified from Karrer and Jucker... 

FIGURE 4.6 The effect of heat treatment on total lycopene degradation (Shi and Le Maguer, 1999b). 

Lycopene isomerization increases as a function of processing time using heat. The results in Table 4.7 show that food processing can enhance d,v-isomerization in tomato-based foods. Heating tomato-based foods in oil caused increased lycopene isomerization vs. heating in water. This would indicate that not only the duration and temperature of heat treatment, but also the food matrix components (such as oil or fat) further influence the lycopene isomerization. An outline of the lycopene degradation pathway has been proposed by Boskovic (1979) (Figure 4.11). 

Kanasawud, P. and Crouzet, J.C. 1990. Mechanism of formation of volatile compounds by thermal degradation of carotenoids in aqueous medium. 2. Lycopene degradation. J. Agric. Food Chem. 38 1238-1242. 

Shi and Le Maguer (2000) recently showed that the main causes of tomato lycopene degradation during processing are isomerization and oxidation. Thermal processing generally causes some loss of lycopene in tomato-based foods. In general, dehydrated and powdered tomatoes have poor lycopene... 

Bioactivity potency of lycopene is dependent on the extent of degradation due to isomerization and oxidation. The main causes of lycopene degradation during food processing are oxidation and isomerization. Determination of the extent of lycopene isomerization would provide better insights into the potential health benefits of processed food products. In processed foods, oxidation is a complex process and depends upon many factors, such as processing conditions, moisture, temperature, and the presence of pro- or antioxidants and of lipids. The characterization and quantification of isomers would be desirable to more accurately assess the bioactivity than just the total lycopene content with no knowledge of its isomeric composition. 

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