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Processing and Bioavailability (WG2) page 44
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really severe treatment in terms of oxidative stress, does not cause serious lycopene losses.
Some of the studies reviewed witnessed a relatively high lycopene loss and isomerisation in
heat-treated tomato products; a possible reason for these results, which are in contrast with
other data, could be the differing analytical methods and procedures were applied. Various
authors have demonstrated that lycopene is much less stable towards isomerisation and
oxidation when it is solubilised in organic solvent, and that degradation is promoted by
various factors, such as oxygen and light exposure, high temperature, or acidic pH. In order to
compare data and results from different studies, standardised analytical methods should be
defined and applied, and the use of antioxidant preservative agents (for example BHT) should
be recommended.
Other carotenoids, particularly β-carotene, are much more sensitive to oxidative and heat
damage than lycopene and are partly isomerised and lost during tomato processing. This is
probably due to the fact that different carotenoids have different bond energies and kinetics
for isomerisation and oxidation reactions. With regard to other tomato antioxidants, research
studies have shown that ascorbic acid is lost to a great extent during tomato processing, and
the degradation rate is correlated to the intensity of heat treatments. Changes in polyphenolic
compounds and tocopherols have not been sufficiently investigated; consequently, no
indications can be given about these components.
Storage of tomato products can represent a critical condition for antioxidant stability.
This is particularly true in the case of dehydrated products. Many studies have demonstrated
that lycopene is substantially stable to dehydration technologies, while other carotenoids and
ascorbic acid are degraded to a considerable extent. However, serious lycopene losses have
been observed during the storage of dried tomato products in differing conditions. Exposure
to oxygen or light, increasing temperature and very low moisture content increase the rate of
lycopene degradation. High total carotenoid and lycopene losses have also been observed
during frozen storage of quick-frozen tomato cubes; these products can be considered as lowaw
samples. The effects of oxygen, light and temperature can be easily explained considering
the mechanism of lycopene autoxidation; the effect of low moisture has not been clearly
explained. It is known that small amounts of water exhibit an important protective action and
prevent lipid oxidation in general.
However, many studies led to contradictory conclusions, relating to a presumed marked
degradatory effect of storage, probably because measurements were taken on secondtransformation
industrially processed products with high percentages of oil and/or fats