Food Biochemistry and Food Processing (2 edition)

BLBS102-c34 BLBS102-Simpson March 21, 2012 14:7 Trim: 276mm X 219mm Printer Name: Yet to Come

658 Part 5: Fruits, Vegetables, and Cereals

Table 34.2.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.

water-extractable counterparts (620–1200 k) (Meuser et al.

1986). For rye bran water-unextractable arabinoxylans, how-

ever, Vinkx et al. (1995b) found that the molecular weight of

arabinoxylans solubilized with alkali were in the same range as

those reported for water-extractable arabinoxylans (Vinkx et al.

1993).

Rye arabinoxylans were reported to have an extended, rodlike

conformation (Anger et al. 1986, Girhammar and Nair 1992a).

In contrast, Dervilly-Pinel et al. (2001) stated that the water-

extractable arabinoxylans from rye have a random coil confor-

mation.

Ferulic Acid Content Ferulic acid residues can link adjacent

arabinoxylan chains through formation of diferulic acid bridges,

thereby affecting extractability of arabinoxylans.

Ferulic acid and ferulic acid dehydrodimer contents in rye

vary from 0.90 to 1.17% and from 0.24 to 0.41%, respectively,

and are significantly influenced by both rye genotype and harvest

year (Andreasen et al. 2000b). These phenolic compounds are

concentrated in the bran of the rye kernel (Andreasen et al.

2000a, Glitso and Bach Knudsen 1999).

The water-extractable arabinoxylans from rye flour contain

low levels of ferulic acid (0.03–0.15%) (Figueroa-Espinoza

et al. 2002, Vinkx et al. 1993) and ferulic acid dehydrodimers

(0.03× 10 −^2 %) (Dervilly-Pinel et al. 2001, Figueroa-Espinoza

et al. 2002).

The water-unextractable arabinoxylans from rye flour contain

higher amounts of ferulic acid (0.20–0.36%) and ferulic acid de-

hydrodimers (0.35%) than their water-extractable counterparts

(Figueroa-Espinoza et al. 2002). After alkaline extraction with

saturated barium hydroxide and 1.0 M sodium hydroxide, rye

flour arabinoxylans still contain a substantial level of ferulic acid.

Further fractionation of these arabinoxylans by ammonium sul-

fate precipitation reveals increasing levels of ferulic acid with

increasing ammonium sulfate concentration (Cyran et al. 2004).

This observation might corroborate the above-mentioned hy-

pothesis that the different arabinoxylan fractions with varying

structures obtained from rye flour may reflect contamination of

the rye flour with bran fractions.

Arabinoxylan Physicochemical Properties

Solubility of a large part of the individual arabinoxylan

molecules in water is mainly associated with the presence of

arabinose substituents attached to the xylose residues, which

prevent intermolecular aggregation of unsubstituted xylose