Food Chemistry

4.3 Oligosaccharides 293

can be written as O-β-D-Fruf( 2 → 1 )α-D-Glcp
and O-α-D-Glcp(1→4)D-Glcp, respectively.

(4.114)

Branching also occurs in oligosaccharides. It
results when one monosaccharide is bound to
two glycosyl residues. The name of the second
glycosyl residue is inserted into square brackets.
A trisaccharide which represents a building block
of the branched chain polysaccharides amy-
lopectin and glycogen is given as an example:

(4.115)

The abbreviated formula for this trisaccharide is
as follows:

(4.116)

The conformations of oligo- and polysaccharides,
like peptides, can be described by providing the
anglesΦandψ:

(4.117)

A calculation of conformational energy for all

conformers with allowedΦ,ψ pairs provides

a Φ,ψ diagram with lines corresponding to

iso-conformational energies. The low-energy

conformations calculated in this way agree with

data obtained experimentally (X-ray diffraction,

NMR, ORD) for oligo- and polysaccharides.

H-bonds fulfill a significant role in conformer sta-

bilization. Cellobiose and lactose conformations

are well stabilized by an H-bond formed between

the HO-group of C-3 in the glucose residue and

the ring oxygen of the glycosyl residue. Confor-

mations in aqueous solutions appear to be similar

to those in the crystalline state:

(4.118)

In crystalline maltose and in nonaqueous solu-

tions of this sugar, a hydrogen bond is established

between the HO-groups on C-2 of the glucosyl

and on C-3 of the glucose residues (4.119). How-

ever, in aqueous solution, a conformer partially

present is stabilized by H-bonds established

between the CH 2 OH-group of the glucosyl

residue and the HO-group of C-3 on the glucose

residue (4.120). Both conformers correspond to

the two energy minima in theΦ,ψdiagram.

(4.119)

(4.120)

Two H-bonds are possible in saccharose, the first

between the HO-groups on the C-1 of the fruc-