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Processing and Bioavailability (WG2) page 50
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Processing and storage
Lycopene like the other carotenoids is normally present in fruits and vegetables as the all-
trans (E) form. During processing there are a number of physical and chemical changes that
need to be considered for their possible impact on bioavailability.
Giovanelli et al. (2000a) compared various tomato products (tomato pulp, tomato puree,
tomato paste and air-dried tomato halves) in terms of their antioxidant content (lycopene, β-
carotene, ascorbic acid and total phenolics) and antioxidant activity of the hydrophilic and
lipophilic fractions. Significant differences were observed in ascorbic acid content, according
to the severity of the technological process applied (ascorbic acid concentration was 2000,
621 and 400 mg/kg d.w. in tomato pulp, tomato paste and dried tomatoes respectively).
Conversely, total phenolics showed an opposite trend, with higher concentrations in tomato
paste (6720 mg/kg d.w.) and dried tomatoes (5600 mg/kg d.w.) than in tomato pulp and puree
(≅ 4000 mg/kg d.w.). Total lycopene and β-carotene concentrations were similar in tomato
pulp, puree and paste, indicating that the different processing technologies did not affect these
components.
The main conclusions of Nguyen and Schwartz work are that heat and shear stress during
typical industrial food processing operations did not produce lycopene isomerisation or loss,
whereas β-carotene readily isomerised during the processing of tomato products. This
conclusion agrees with a previous study carried out using the same analytical methods by
Lessin et al. (1995), who observed an increase in β-carotene cis isomers from 15% (raw
tomatoes) to 45% (canned tomatoes) and 48% (tomato juice).
Thermal processing is normally undertaken to render the product edible, to eliminate any
spoilage/pathogenic organisms and to inactivate enzymes. Cooking therefore softens the cell
walls so that they are easily separated or broken mechanically, all cellular membranes are
destroyed and proteins denatured. The carotenoid, stable within the original structure
(Schierle et al., 1997, Nguyen and Schwartz, 1998), is then exposed to the external
environment where it may be subject to light, atmospheric oxygen and reactive products of
other components. Lycopene appears to be quite stable in the fresh tomato and during
processing, however, once extracted it is readily oxidised. It has been shown that excessive
thermal processing may also create cis (Z) isomers, particularly 5(Z)-lycopene although
isomerisation can also occur at positions 9, 13 and 15 (Schierle et al., 1997, Nguyen and
Schwartz, 1998). Cis isomers with their kinked structure tend to be more soluble in organic