Figure 5.3 shows the functional correlation between the lutein con-
tent on one hand and PPFD and daily mean temperature on the other
hand. The lutein concentration in broccoli reached a maximum at a daily
mean temperature of nearly 15°C. These results indicate that -carotene
and lutein biosynthesis is strongly dependent on temperature. Previous
investigations support the present results: Carotenoids have been re-
ported to be synthesized in darkness in carrot roots or harvested toma-
toes (Gross, 1991).
Another group of bioactive substances are the glucosinolates that
mainly occur in cruciferous plants like broccoli (Fenwick and Heany,
1983; Zhang et al., 1992). Glucoraphanin is a main glucosinolate in broc-
coli, which is a precursor of sulforaphane and described as a protection
compound for carcinogenesis (Fahey et al., 1997). Consumers show an
increased demand for health benefits in broccoli (Schonhof et al., 1998).
Effect of Preharvest Climatic Conditions on Bioactive Substances 89FIGURE 5.4Correlation between PPFD, temperature and glucoraphanin of broccoli
‘Emperor.’