Production Practices and Quality Assessment of Food Crops. Vol. 1

Effects of Agronomic Practices 43
Figure 4. Contents of vitamin C, β-carotene and lycopene in raw tomato cubes and in tomato cubes
after 12 months’ storage at –20 °C and at –30 °C (modified from Lisiewska and Kmiecik, 2000).
8. EFFECTS OF HEATING
Heating tomato pulp at 100 °C for 120 min at atmospheric pressure led to a decrease
in lycopene concentration from 185.5 to 141.5 mg/100 g total solids (24%
reduction) (Sharma and Le Maguer, 1996). In another study, thermal treatment at
100 °C for 30 min in water increased the (Z)-isomer percentages by an average of
21 and 27% for β-carotene and lutein. In contrast, lycopene remained stable to
isomerisation. Heating trials in 80:20 water/olive oil mixtures led to comparable
results (Nguyen et al., 2001).
Cooking tomatoes for 4/8/16 min at 100 °C did not significantly affect the
lycopene contents of different varieties (Thompson et al., 2000). Microwave heating
(850 W, 3 min) reduced β-carotene by 35% and lycopene by 15% (Böhm and Bitsch,
1995). Regarding the flavonoid quercetin, boiling in simmering water for 15 min
resulted in greater reduction (82%) compared to heating in a microwave oven for
1.3 min with 800 W (65%). These reductions in ingredients are mainly due to
their extraction from tomato by hot water. In contrast, frying in sunflower oil for
3 min led to a reduction of 35% quercetin (Crozier et al., 1997).
Heat-based processing of tomatoes to tomato paste showed a different behaviour
for ascorbic acid, tocopherols, and carotenoids. The ascorbic acid content was
reduced by 54.6% while the losses of α-tocopherol (–20.3%) and γ-tocopherol
(–32.7%) were lower. In contrast, the concentration of (E)-lycopene significantly
increased by 36.9% (all results are based on dry matter). This remarkable increase
was mainly explained by the removal of seeds and peels (both without lycopene)
and the loss of soluble volatile compounds during water evaporation steps (Abushita
et al., 2000). In another study, losses of (E)-lycopene during tomato paste produc-