2009_Book_FoodChemistry

786 17 Vegetables and Vegetable Products
Table 17.6. (Continued)
17.1.2.1.3 Amines
The presence of amines has been confirmed in
various vegetables; e. g., histamine, N-acetylhistamine
and N,N-dimethylhistamine in spinach;
and tryptamine, serotonin, melatonin and tyramine
in tomatoes and eggplant (cf. 18.1.2.1.3).
17.1.2.2 Carbohydrates
17.1.2.2.1 Mono- and Oligosaccharides,
Sugar Alcohols
The predominant sugars in vegetables are
glucose and fructose (0.3–4%) as well as sucrose
(0.1–12%). Other sugars occur in small
amounts; e. g. glycosidically bound apiose in
Umbelliferae (celery and parsley); 1 F -β- and
6 G -β-fructosylsaccharose in the allium group
(onions, leeks); raffinose, stachyose and verbascose
in Fabaceae; and mannitol in Brassicaceae
and Cucurbitaceae.
17.1.2.2.2 Polysaccharides
Starch occurs widely as a storage carbohydrate
and is present in large amounts in some root and
tuber vegetables. In Compositae (e. g., artichoke,
viper’s grass, bot. Scorzonera), inulin, rather than
starch, is the storge carbohydrate.
Other polysaccharides are cellulose, hemicelluloses
and pectins. The pectin fraction has
a distinct role in the tissue firmness of vegetables.
Tomatoes become firmer as the total
pectin content and the content of some minerals
(Ca, Mg) increases, and as the degree of esterification
of the pectin decreases. In processing
cauliflower (cf. 17.2.3), 70 ◦ Cisfavorablefor
preserving tissue firmness. The reason for this
effect is the presence of pectinmethylesterase
which, in vegetables, is fully inactivated only
at temperatures above 88 ◦ C, while at 70 ◦ Cit
is active and provides a build-up of insoluble
pectates. For the conversion of protopectin to
pectin during plant tissue maturation or ripening
see 18.1.3.3.1.