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

42 Volker Böhm
The substrate system is another factor investigated on its influence on tomato
ingredients. Four hydroponic systems, based on rock wool and expanded clay as
substrates with and without recirculating nutrient solution, were compared to a
soil culture system. All tomatoes were cultivated in greenhouses. Tomatoes grown
on the soil system contained significantly lower amounts of ascorbic acid and
carbohydrates compared to the hydroponic systems (Lippert, 1993). Another study
used the sugar/acid ratio to compare tomatoes grown on soil to those grown on
rock wool or on expanded clay. The results did not significantly differ between
the three substrates (sugar/acid ratios: 6.18–8.46) (Schnitzler et al., 1994). Regarding
the contents of 18 major and trace elements of tomatoes grown on soil (target
electrical conductivity (EC): 3–4 mS/cm), rock wool (EC: 3–4 mS/cm) and rock
wool (EC: 5–6 mS/cm) the concentrations of 9 elements were significantly different
depending on the substrate. The concentration of cadmium was 15–30 times
higher and that of calcium 50–115% higher in soil-grown fruits than in rock woolgrown
fruits (Gundersen et al., 2001).
Carbon dioxide enrichment (700–900 ppm CO 2) during the maturation in a
greenhouse affected some quality parameters of tomatoes. Compared to tomatoes
grown under control conditions (250–400 ppm CO 2), those grown under CO 2enriched
conditions had lower amounts of vitamin C as well as those of glucose
and fructose (Islam et al., 1996).
7. EFFECTS OF STORAGE PERIOD AND TEMPERATURE
Micra RS tomatoes, frozen in the form of cubes, were stored during 12 months at
–20 °C and –30 °C. The storage did not affect the level of dry matter, soluble
solids, sugars, dietary fibre, total nitrogen, nitrates, nitrites, pH, ash or its
alkalinity. In contrast, contents of vitamin C and carotenoids changed significantly.
During the 12 months’ storage vitamin C decreased to 29% (–20 °C) or 55%
(–30 °C) of its basal value. β-carotene significantly decreased to 49% or 68% of
its initial value while lycopene losses were 48% and 26%. Figure 4 shows the
contents of these three ingredients before and after 12 month storage (Lisiewska and
Kmiecik, 2000).
Own storage experiments for 4 months at –30 °C showed a 35% decrease for
β-carotene while lycopene was reduced by 50% (Böhm and Bitsch, 1995).
Another study (Sharma and Le Maguer, 1996) investigated the three storage
temperatures –20/5/25 °C, varying the storage conditions from vacuum + dark
over dark + air to air + light. The largest loss of lycopene (77.6%) resulted after
storage for 60 days at 25 °C with air + light. Storage of freeze-dried samples for
4 months at room temperature led to 97% loss of lycopene compared to 73–79%
for oven-dried samples (Sharma and Le Maguer, 1996).
Mature green tomatoes were stored at 5/7/12 or 19 °C for 0/3/9/12 or 21 days,
then ripened at 19 °C for 3 or 6 days before analysis. The contents of citric acid
increased after storage at 5 or 7 °C while they decreased at 19 °C. Malic acid
decreased at all temperatures with the greatest decrease occurring at 19 °C (Thorne
and Efiuvwevwere, 1988).