Chemical and Functional Properties of Food Saccharides

1-SST
Sucrose
G 1 - 2 F
© 2004 by CRC Press LLC
6-SFT or
6-SST
1- Kestose
G-F 1- 2F
6- Kestose
G 1 - 2 F 6 - 2 F
Neo-kestose
F 2 - 6 G 1 - 2 F
6-FFT
1-FFT
Bifurcose
1-FFT
β(2-1)
6-SFT or 6-FFT β(2-6)
1-FFT
β(2-1)
β(2-6)
6-SFT or 6-FFT
β(2-1)
1-FFT
6-FFT
β(2-6)
Inulin
Mixed-type
and / or
branched
fructans
Levan
Inulin
neo-series
levan
Mixed-type
fructans
FIGURE 13.2 Biosynthesis of kestoses and fructans in crops. 1-SST: sucrose:sucrose fructosyltransferase;
1-FFT, 6-FFT: fructan:fructan fructosyltransferases; 6-SFT: sucrose:fructan
fructosyltransferase.
chains and branches generates rather complex molecules, which contribute significantly
to the broad-band functional properties of these fructans. 21
Three categories need to be distinguished in fructan metabolism of crops: synthesis/two-step-mechanism
polymerization, utilization/depolymerization, and mobilization
to respond on environmental stress. For instance, in tubers of Helianthus tuberosus
(Jerusalem artichoke), high SST activities are observed at high photosynthetic activities
and fast transformation of initial carbohydrates to fructans. SST activity decreases and
finally vanishes in the course of the vegetation period with increasing amounts of
stored reserve fructans, whereas FFT activities stay even in the final vegetation states.
FFT activity in tubers increases in stress conditions such as frost and causes depolymerization
to support osmoregulatory mechanisms. At the state of expelling after the
winter frost period, fructosyl exohydrolase (FEH) activity appears additionally and
increases to mobilize depolymerized fructosyl residues in the cytosolic pathway forming
sucrose by transfer to a glycosyl residue. Obviously, fructan-forming and transforming
enzymes are closely correlated with sucrose metabolism. 22
Fructans are obtained from crop raw materials by hot-water extraction and
different processing drying steps as a white powder. Depending on their content of
mono- and disaccharides, low-molecular-weight fructans (fructooligosacchaides) are
more or less sweet in taste, whereas high-molecular-weight fructans are more or
less of neutral taste.