Bulking and Fat-Replacing Agents - Sweeteners: Nutritional Aspects, Applications, and Production Technology - page 410

At the same time, the process should be simple enough to ensure reproducibility. The cost effec-
tiveness of the product, so that it can compete with other food hydrocolloids, is obviously a major
concern. The extraction of β-glucans from cereal grains generally involves three basic steps: (1)
inactivation of endogenous enzymes; (2) extraction; and (3) precipitation of the β-glucans. A high
yield of β-glucan can be achieved with one-step aqueous alkali extraction (Wood et al. 1977, 1978).
The yield and hydrolytic stability of β-glucan may also be inluenced by a pretreatment of barley
grains or lour, which is usually applied to stabilize the β-glucan extract by inactivating β-glucanase
enzymes. Beer et al. (1996) and Burkus and Temelli (1998) found that the ethanol reluxing of
lour lowered the yield of β-glucan, respectively, and did not deactivate β-glucanase. A high-purity
product is always a goal of every extraction process. Further puriication following extraction is
always costly. The amount of impurities is primarily inluenced by the extraction process param-
eters (Burkus 1996). Protein is considered to be the main impurity imparting a beige to brown color
to β-glucan powders. Protein easily becomes incompatible with a hydrocolloid in the same solution
and undergoes phase separation (Tolstoguzov 1991, 1997). When the gum is dissolved in water,
proteins cause opalescence, which limits gum applications in certain products such as clear drinks.
However, the lack of solution transparency may not be a problem in cloudy fruit beverages.
If β-glucan is to be competitive in the hydrocolloid market, it should be of the high-viscosity
type. At least, that is the current thinking based on demonstrated health beneits, which are mostly
linked to viscosity. Dawkins and Nnanna (1995) found that from the standpoint of viscosity, oat
β-glucan is comparable to locust bean gum and better than guar gum whereas xanthan had much
higher viscosity. Highly viscous β-glucan can be obtained from both oats and barley, although
oats routinely outperforms barley (Wood 1991; Wood et al. 1991; Beer et al. 1997). The stability of
β-glucan, in this case, is deined as constant viscosity over time, which is a desirable trait for a typi-
cal hydrocolloid. The main reason for the loss of viscosity is enzyme activity on the β-glucan chain,
although viscosity loss due to agglomeration and precipitation was observed. The latter type of
instability may be dealt with by reheating the β-glucan solution. Viscosity instability due to enzyme
activity is a much harder problem for several reasons. Historically, barley has been selected for high
enzymatic activity, and as such, it contains a great deal of β-glucanase enzymes to germinate the
kernel quickly and transform it into malt or, actually, a new plant. These native enzymes work in the
pH range of 5-7, with optimal temperatures of <40°C. Native β-glucanases are thermolabile, and a
thermal process above 60°C degrades them relatively easily (Ballance and Meredith 1976).
Being a hydrocolloid, β-glucan may form highly viscous pseudoplastic solutions with a low
behavior index n ≪ 1 if it is of the high-viscosity type (Autio et al. 1987; Autio 1996; Bhatty 1995;
Burkus and Temelli 1998; Temelli et al. 2004), but even high-viscosity β-glucan at concentrations
≤0.25% behaves as a Newtonian luid (Autio et al. 1987; Burkus and Temelli 1998). In the presence
of other solutes, such as salt and sugar, β-glucan solutions may have increased viscosity (Autio et al.
1987; Dawkins and Nnanna 1995; Bansema 2000), but the increase is concentration dependent, and
the order of hydration may affect the inal solution viscosity (Burkus 1996). Gelation of low-viscos-
ity β-glucan was described by Burkus and Temelli (1999) and Morgan and Ofman (1998). The irm-
ness of the network and the rate of network formation were concentration and viscosity dependent.
Although extracted on a commercial scale, neither barley nor oat β-glucan gum is used as an
ingredient in food products, mainly due to the high price of high-purity preparations (Wood and
Beer 1998). Oatrim ® , an extract of hydrolyzed oat lour containing 1%-10% β-glucan, is used as a fat
replacer in some types of low-fat milk products (Pszczola 1996). Oatrim is used in several ConAgra
Healthy Choice products: hot dogs, bologna, cheese, and 96% fat-free ground beef. Smaller compa-
nies are using the fat replacer in baked products such as mufins and cookies and in chocolate candy
(Inglet and Grisamore 1991). Morgan and Ofman (1998) developed a hot water extraction procedure
with the recovery of the β-glucan by freezing and thawing of the extract. The resulting product
(Glucagel TM ) contained between 89% and 94% β-glucan, depending on the duration of the initial
extraction, and is one β-glucan preparation commercially available as a food ingredient.