176
reported use of aqueous extraction for isolating water soluble arabinoxylans from
rye flour. Michniewicz et al. (1990) reported centrifugation of flour-water suspensions resulting in a sludge layer which is further purified with hydrolytic enzymes
like protease and amylase to remove proteins and starch. Praznik et al. (2009)
reported use of hot water extraction in combination with α-amylase for extraction of
water soluble pentosans from rye flour. After cellite filtration, the clear filtrate was
precipitated in ethanol—acetone solution. Revanappa et al. (2010) reported extraction of pentosans from hemicellulose of wheat varieties by glucoamylase digestion
for 4 h. The polysaccharide was then precipitated in ethanol followed by centrifugation and freeze drying. Izydorczyk and Biliaderis (1993) obtained nearly protein
free pentosan extracts from wheat flour after adsorption of contaminating proteins
in the water extracts on various clays. Chemical, physical and enzymatic methods
have been reported to extract arabinoxylans from wheat and rye bran (FigueroaEspinoza et al. 2004). The extraction of pentosans from rye bran and flour was carried by alkaline method followed by addition of enzymes (α-amylase,
amyloglucosidase, and protease). Furthermore, the pentosan was purified by ultradia-filtration through a ceramic membrane with a cut-off-level of 8 kDa (Mansberger
et al. 2014). Tran and Nordin (1977) reported following methods for extraction of
pentosans from wheat flour: (a) Flour extracted with water; (b) Flour extracted with
0.01 M sodium dodecyl sulfate in 0.1 M phosphate buffer pH 7.6; and (c) Flour
extracted by stirring in about two volumes of 15% trichloroacetic acid.
Physicochemical Properties of Arabinoxylans
Viscosity
Arabinoxylan exhibit high viscosity in aqueous solution. The factors affecting the
viscosity of arabinoxylans includes molecular weight, chain length, degree of substitution and substitution patterns, and ferulic acid cross-links (Izydorczyk and
Biliaderis 1995; Dervilly-Pinel et al. 2001). Arabinoxylans with high ferulic acid
content, high xylose/arabinose ratio, and low content of doubly substituted xylose
on the backbone chain have high intrinsic viscosity (Izydorczyk and Bilideris 2000).
The intrinsic viscosity of arabinoxylans was reported in the range of 2.5–3.1 dL/g
(Medcalf et al. 1968), 0.8–3.1 dL/g (D'Appolonia and Macarthur 1975), and
2.75–5.48 dL/g (Izydorczyk et al. 1991). Fincher and Stone (1986) reported viscosity of 0.214 dL/g for dextran, and 0.195 dL/g for beet arabinan. Izydorczyk et al.
(1991) reported viscosity of guar gum in the range of 2.3–6.75 dL/g and pectin with
a low degree of esterification in the range of 3.38 dL/g. Izydorczyk and Biliaderis
(1992) reported the intrinsic viscosity to vary between 3.4 and 8.5 dL/g for the different fractions of wheat arabinoxylans obtained by preparative gel permeation
chromatography.
A. Shah et al.
reported use of aqueous extraction for isolating water soluble arabinoxylans from
rye flour. Michniewicz et al. (1990) reported centrifugation of flour-water suspensions resulting in a sludge layer which is further purified with hydrolytic enzymes
like protease and amylase to remove proteins and starch. Praznik et al. (2009)
reported use of hot water extraction in combination with α-amylase for extraction of
water soluble pentosans from rye flour. After cellite filtration, the clear filtrate was
precipitated in ethanol—acetone solution. Revanappa et al. (2010) reported extraction of pentosans from hemicellulose of wheat varieties by glucoamylase digestion
for 4 h. The polysaccharide was then precipitated in ethanol followed by centrifugation and freeze drying. Izydorczyk and Biliaderis (1993) obtained nearly protein
free pentosan extracts from wheat flour after adsorption of contaminating proteins
in the water extracts on various clays. Chemical, physical and enzymatic methods
have been reported to extract arabinoxylans from wheat and rye bran (FigueroaEspinoza et al. 2004). The extraction of pentosans from rye bran and flour was carried by alkaline method followed by addition of enzymes (α-amylase,
amyloglucosidase, and protease). Furthermore, the pentosan was purified by ultradia-filtration through a ceramic membrane with a cut-off-level of 8 kDa (Mansberger
et al. 2014). Tran and Nordin (1977) reported following methods for extraction of
pentosans from wheat flour: (a) Flour extracted with water; (b) Flour extracted with
0.01 M sodium dodecyl sulfate in 0.1 M phosphate buffer pH 7.6; and (c) Flour
extracted by stirring in about two volumes of 15% trichloroacetic acid.
Physicochemical Properties of Arabinoxylans
Viscosity
Arabinoxylan exhibit high viscosity in aqueous solution. The factors affecting the
viscosity of arabinoxylans includes molecular weight, chain length, degree of substitution and substitution patterns, and ferulic acid cross-links (Izydorczyk and
Biliaderis 1995; Dervilly-Pinel et al. 2001). Arabinoxylans with high ferulic acid
content, high xylose/arabinose ratio, and low content of doubly substituted xylose
on the backbone chain have high intrinsic viscosity (Izydorczyk and Bilideris 2000).
The intrinsic viscosity of arabinoxylans was reported in the range of 2.5–3.1 dL/g
(Medcalf et al. 1968), 0.8–3.1 dL/g (D'Appolonia and Macarthur 1975), and
2.75–5.48 dL/g (Izydorczyk et al. 1991). Fincher and Stone (1986) reported viscosity of 0.214 dL/g for dextran, and 0.195 dL/g for beet arabinan. Izydorczyk et al.
(1991) reported viscosity of guar gum in the range of 2.3–6.75 dL/g and pectin with
a low degree of esterification in the range of 3.38 dL/g. Izydorczyk and Biliaderis
(1992) reported the intrinsic viscosity to vary between 3.4 and 8.5 dL/g for the different fractions of wheat arabinoxylans obtained by preparative gel permeation
chromatography.
A. Shah et al.