Glucosinolates

CH2OH

CH2OH

Figure 3. Basic structure of glucosinolates (Schnug 1990).

Figure 3. Basic structure of glucosinolates (Schnug 1990).

Glucosinolates affect the flavour of spicy crops such as mustard and radish (Fenwick et al. 1983) and cause their pungency. Glucosinolates are antinutritive because of their goitrogenic effect (Berdanier 2002), which restricted for instance the use of extracted rape meal from single low oilseed rape cultivars in animal feeding. In human nutrition, glucosinolates are studied for their anticarcinogenic and antimicrobial potential (Watzl and Leitzmann 1999). In animal experimentation an anticarcinogenic effect could be attributed to isothiocyanates (phenethylisothiocyanate, bencylisothiocyanate, sulphoraphane), thiocyanates (bencylthiocyanate) and indoles (Watzl and Leitzmann 1999). Another beneficial effect of glucosinolates is their antimicrobial action, particularly that of bencylisothiocyanate (Watzl and Leitzmann 1999).

Secondary metabolites are often synthesised during maturation of crops. With a better degree of maturity, a higher concentration is expected in foods grown in organic farming systems (Molgaard, 2000, Brandt et al. 2001). Broccoli is rich in sulphoraphane which, in animal feeding experimentation has shown a protective effect against chemically induced breast cancer (Zhang et al. 1994). Adam (2002) found sulphoraphane contents in broccoli that were two to six-fold higher in market products that were organically grown.

Generally, N fertilisation tended to result in lower glucosinolate contents (Rosa et al. 1997). Under field conditions the effect of N fertilisation on the glucosinolate content varied substantially between seasons (Asare and Scarisbrick 1995). Schnug (1989) found a distinct interaction between N and S fertilisation in the range of an insufficient N supply, whereby the alkenyl, but not the indole glucosinolate content in seeds of rapeseed increased with higher N and S rates. Kim et al. (2002) showed that N fertilisation increased particularly the alkenyl-glucosinolates, gluconapin and glucobrassicanapin, in Brassica rapa.

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