Chemistry Reference
In-Depth Information
assembled from these sugars are usually incompatible when their polymer chains differ in structure
and/or composition. Incompatibility between barley β-glucan and milk proteins or starch was irst
described by Burkus (1996). Further experiments by Bansema (2000) attempted to establish the
concentration-stability relationship between barley β-glucan and whey protein isolate (WPI). He
found that a mixture was stable after 2 days of holding at refrigeration temperature below critical
concentrations—β-glucan concentration was 0.25%, and that of WPI was ≤5%. A higher concen-
tration of either ingredient resulted in phase separation. However, thermal treatment may cause
instability, even at 0.25% β-glucan concentration. The incorporation of β-glucans into low-fat dairy
products may improve their mouthfeel and sensory properties to resemble those of full-fat prod-
ucts. For example, β-glucan incorporation into low-fat cheese curds has beneicial effects on their
gelation and rheological characteristics (Tudorica et al. 2004). The addition of β-glucan solutions
to milk modiies curd formation, including reducing curd cutting time and increasing curd yields
(Tudorica et al. 2004). However, when β-glucans are incorporated into a manufactured cheese sys-
tem or low-fat yogurt, the texture can be altered deleteriously (Vasiljevic et al. 2007; Vithanage
et al. 2008). It appears that the components known to be precipitated by β-glucan have a globular
structure. An important parameter in the evaluation of incompatibility is the time factor, but it has
not been studied. An increase in viscosity delays the sedimentation of a precipitated compound.
Samples stored at refrigerator temperature have increased viscosity, and consequently, the suspen-
sion of the incompatible compound is enhanced. The decrease in protein solubility and solvation
does not have to be complete. Observation of partial insolubility of protein may require times longer
than those employed in quick laboratory experiments. The longer time frame associated with shelf
life studies would provide suficient time for proper incompatibility studies. However, care must
be taken to exclude potential effects of all other factors, such as pH, temperature, and bacterial
contamination of samples. Incompatibility with other food components may be a major obstacle for
food and beverage applications of β-glucan, but this problem can be offset by the suspending ability
of β-glucan, adjusting component concentrations and proper choice of ingredients (Figure 13.3).
Barley and oat β-glucans, with other NSPs, occur in the walls of endosperm cells, which encap-
sulate starch, matrix protein, and lipid reserves of the grain, creating a few obstacles for a success-
ful extraction. The study of the physicochemical properties of isolated β-glucan fractions requires
extraction procedures that optimize yield, purity, and retained integrity of the β-glucan molecule.
β (1-3)-Linked branch
CH
2
OH
CH
2
OH
O
O
O
O
OH
β (1-6)-Branch point
HO
HO
n
OH
OH
CH
2
OH
CH
2
OH
CH
2
OH
CH
2
CH
2
OH
O
O
O
O
O
O
O
O
O
O
HO
HO
HO
HO
HO
OH
OH
OH
OH
OH
β (1-3)-Linked backbone
Figure 13.3
Structural organization of
β
-glucan.
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