572 Part V: Fruits, Vegetables, and Cereals
reported. Whether the water-extractable arabinoxy-
lans from rye bran have a higher (Meuser et al.
1986) or lower (Härkönen et al. 1997) mean molec-
ular weight than those from rye flour is not clear. It
is also not clear whether extraction temperature
affects the molecular size distribution of rye flour
water-extractable arabinoxylans (Cyran et al. 2003)
or not (Härkönen et al. 1995, Meuser et al. 1986).
For water-extractable arabinoxylans isolated from
rye varieties differing in extract viscosity, increasing
molecular weights were correlated with increasing
rye extract viscosity (Ragaee et al. 2001). Rye
water-extractable arabinoxylans have higher average
molecular weights than those of wheat (Dervilly-
Pinel et al. 2001, Girhammar and Nair 1992a).
The water-unextractable arabinoxylans from rye
flour have a higher molecular weight (1500–3000 k)
than their water-extractable counterparts (620–1200 k)
(Meuser et al. 1986). For rye bran water-unex-
tractable arabinoxylans, however, Vinkx et al.
(1995b) found that the molecular weight of arabi-
noxylans solubilized with alkali were in the same
range as those reported for water-extractable arabi-
noxylans (Vinkx et al. 1993).
Rye arabinoxylans were reported to have an extend-
ed, rodlike conformation (Anger et al. 1986, Gir-
hammar and Nair 1992a). In contrast, Dervilly-Pinel
et al. (2001) stated that the water-extractable arabi-
noxylans from rye have a random coil conformation.Ferulic Acid Content Ferulic acid residues can
link adjacent arabinoxylan chains through formation
of diferulic acid bridges, thereby affecting extrac-
tability of arabinoxylans.Table 25.2.Substitution Degrees (A/X Ratios) and Xylose Substitution Levels (%) of Alkali-
Solubilized Water-Unextractable Arabinoxylans (AS-AX) from Rye Bran and Flour
AS-AX
Source Extraction Solventa A/X Unb Monob Dib Reference
Rye bran 1.1 M NaOH 0.14 88 12 0 Hromadkova et al. 1987
Rye bran 1% NH 4 OH 0.78 41 33 26 Ebringerova et al. 1990
Rye bran Saturated Ba(OH) 2 0.65 61 29 10 Vinkx et al. 1995b
H 2 O 0.55 64 24 12
1.0 M KOH 0.21 89 8 3
Delignification followed 1.10 21 46 33
by 1.0 M KOH
Rye bran Saturated Ba(OH) 2 0.54 NDc ND ND Nilsson et al. 1996
H 2 O 0.60 ND ND ND
4.0 M KOH 0.27 ND ND ND
2.0 M KOH 1.08 ND ND ND
Rye bran Saturated Ba(OH) 2 0.56 57 29 14 Nilsson et al. 1999
Rye flour Saturated Ba(OH) 2 0.68 46 40 14 Vinkx 1994
H 2 O 0.78 44 34 22
1.0 M KOH 0.72 ND ND ND
Rye flour Saturated Ba(OH) 2 0.67 ND ND ND Nilsson et al. 1996
H 2 O 0.93 ND ND ND
4.0 M KOH 0.63 ND ND ND
2.0 M KOH 1.10
Rye flour Saturated Ba(OH) 2 0.69–0.70 51 28–29 20–21 Cyran et al. 2004
H 2 O 0.79–0.84 42–44 32–34 22–26
1.0 M NaOH 0.70–0.77 45–48 33 19–22
aConsecutive extraction solvents in one reference indicate sequential alkaline extraction.
bUn, mono, and di: percentages of total xylose occurring as unsubstituted, O-2 and/or O-3 monosubstituted, and O-2, O-3
disubstituted xylose residues.
cND Not determined.