Bulking and Fat-Replacing Agents - Sweeteners: Nutritional Aspects, Applications, and Production Technology - page 408

Tsai 1995), in contrast to another study with a greater supplementation but no effect observed on
cholesterol levels over a 2-month period (Liu and Tsai 1995). However, the observed effects were
contributed to a soluble iber action similar to pectins or β-glucan through the production of SCFAs.
These acids have a beneicial inluence on the gut mucosa and may inhibit cholesterol synthesis in
the liver. Other reports have shown that the hypoglycemic effect of certain ibers reduces elevated
blood glucose levels (Zeng and Tan 2010).
13.8 β -GLUCaN
The health-promoting properties of β-glucan have been extensively reviewed (Murphy et al.
2010; Sirtori et al. 2009; Anderson et al. 2009). The major boost for β-glucan application in foods
was the U.S. FDA's approval of the oat health claim (FDA 1997) for food products containing
β-glucan from an oat source (bran, groats, or rolled oats), which guarantees ≥0.75 g of β-glucan
per serving. This claim was approved for oat products rather than for individual components. Oats
also contain very potent antioxidants such as avenanthramides and oat saponins, which, in min-
ute amounts, have a hypocholesterolemic effect that equals that of β-glucan (Collins 1998). The
oat health claim was iled by Quaker Oats (Chicago, IL). Besides the widely elaborated choles-
terol-lowering and blood glucose-regulating effects, a number of studies examined the immuno-
stimulating effects of β-glucan. Oat β-glucan showed the immunostimulating effect in vitro and in
vivo in mice after intraperitoneal administration and increased the survival of mice infected with
Staphylococcus aureus (Estrada et al. 1997). Causey et al. (1998) showed in vitro that even hydro-
lyzed barley β-glucan had an immunostimulating effect on human macrophages. When applied at
a concentration of 100 μg/mL, β-glucan increased the production of white blood cells sixfold. In
addition, the anticarcinogenic effect of barley bran (13% total dietary iber [TDF]) on the incidence
and development of certain tumor types was described by McIntosh et al. (1996).
The molecular structure of β-glucan has been determined to be 90% composed of cellotriosyl
and cellotetraosyl regions connected with β-(1→3) bonds (Wood 1984; MacGregor and Fincher
1993), with the rest being longer cellulosic regions. The coniguration of the molecule in three-
dimensional space is not yet known with certainty. Some intrinsic viscosity measurements suggest
that it is probably a partially stiffened worm-like cylinder (Gomez et al. 1997a,c). Straight (1 → 4)
cellulosic regions are extremely rigid sequences resistant to mechanical and chemical action. In
addition, they may align to form microcrystalline cellulosic regions with strong hydrogen bonds,
which provide additional resistance to mechanical and chemical degradation. The β-(1 → 3) linkage
is responsible for a kink in the β-glucan structure (Woodward et al. 1983). When present in a con-
secutive sequence, this bond creates a regularly shaped helical structure that can form aggregates
and gel (Zhang et al. 1997).
Due to the length of their cellulosic regions, β-glucan molecules are able to associate with each
other and create micelles (Varum et al. 1992; Grim et al. 1995) or gel (Burkus and Temelli 1999).
β-Glucan from Poria cocos (a kind of mushroom used in traditional Chinese herbal medicine),
which is entirely composed of β-(1→3)-d-glucan, was also able to create molecular aggregates that
dissolved completely in cadoxen (saturated CdO solution in 29% ethylenediamine; Zhang et al.
1997). The mechanism of aggregation was probably the formation of hydrogen bonds between regu-
larly shaped random coil regions of β-glucan chains. When heated above 60°C, micelles dissociate,
and individual molecules require greater amounts of water for solvation, providing an explanation
of the increased viscosity of β-glucan at low shear rates and elevated temperatures (70°C; Gomez et
al. 1997b). Another important property of all polysaccharides to be considered is their compatibil-
ity with other biopolymers. Incompatibility is typical for biopolymers because of the large size of
macromolecules and very low entropy that accompanies the mixing of biopolymers. Even when the
corresponding monomer sugars are cosoluble in aqueous media in all proportions, polysaccharides