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Processing and Bioavailability (WG2) page 35
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method (HPLC analysis using a specially developed C30 column) allowed for the separation
and identification of 8 different lycopene isomers. In this research study, several commercial
products were analysed for their carotenoid profile. In addition, a number of tomato products
were produced at the University production centre to further investigate the formation of cis
isomers as a result of thermal processing. Data collected both on commercial products and on
home-cooked tomato products showed that cis lycopene levels were not significantly
different, despite the different technological processes applied. For commercial tomato
products, such as tomato juice, tomato sauce, tomato soup, tomato paste, pizza sauce, spraydried
and drum-dried tomato powder, and sun-dried tomatoes in oil, the total cis lycopene
percentage varied between 2.5% and 10.1%, with no relationship with the intensity of heat
treatment applied to the products (Table 4).
Table 4 - Relative abundance of lycopene isomers in various thermally-processed tomato
products prepared at the Food Industry Centre
lycopene,
mg /100 g d.w.
lycopene
cis-isomer, %
Tomato (fresh) 152.98 4.16 21.77
Peeled tomato 148.89 5.37 23.83
Tomato juice (hot-break) 161.23 5.98 57.55
Tomato juice (retorted) 161.23 3.56 78.28
Tomato (whole, retorted) 183.49 3.67 62.03
Tomato paste (concentrated) 174.79 5.07 57.82
Tomato paste (retorted) 189.26 4.07 85.85
Tomato soup (retorted) 136.76 4.34 55.57
Tomato sauce (retorted) 73.33 5.13 56.14
From Nguyen and Schwartz, 1998.
β-carotene
cis-isomer, %
Even the tomato soup and sauce, which were made from tomato paste and processed at
104°C for 50 min, and the presence of olive oil at 2% and 15% in the tomato soup and sauce,
did not affect the isomer content. Although lycopene did not isomerise under any of the
processing conditions, significant levels of β-carotene cis isomers were formed. The authors
found that the formation of cis lycopene was induced by severe heat treatments, such as
heating a thin film of tomato puree at 200°C for a few seconds to remove water (cis lycopene
level increased from 4.2 to 19.1%), as well as incubation in organic solvents. For example, 3
hours' incubation of pure lycopene in 1:1 methanol and methyl-t-butyl ether in the dark at
27°C resulted in a cis isomer content of 50% compared to 4.5% in the initial solution.
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