Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
stable to changes in pH and salts. 20 The gum has a molecular weight between 50,000
and 100,000, probably due to aggregate formation between smaller chains, 21 and the
main components galactose and arabinose are present in a variable ratio between
8:1 and 23:1 as an α(1-3)-linked galactan backbone with (α-6)- linked arabinose
and galactose substituents. 22 The gum has achieved only limited use in the food
market since its introduction as a stabilizer in sweeteners. The advantage of the gum
is that it can be produced as a by-product from the wood milling industry, but the
main disadvantage compared with other gums is that it has to be added at high levels
to exert an effect.
15.2.4 PECTINS (RHAMNOGALACTURONANS)
Pectins are a major class of wall-related plant polysaccharides that are used in food
and are considered in more detail in Chapter 12. Pectins are charged, acidic polysaccharides
with a variety of structures based on a rhamnogalacturonan. Unlike other
plant gums, they can exhibit gelling properties which are of considerable value to
the food industry. Here we discuss only those water-soluble rhamnogalacturonans
that are not considered as traditional pectins in the food industry.
15.3 SOLUBLE MUCILAGE POLYSACCHARIDES
15.3.1 YELLOW MUSTARD SEED GUM
Yellow mustard seed gum (YMG) is obtained from the seeds of yellow mustard
(Sinapsis alba), which release a mucilage from the seeds when wet. Commercially,
the gum can be prepared from ground seeds by cold-water extraction 23 and the seed
bran can also be used as raw material for hot-water extraction, 24 which is economically
advantageous as bran is a by-product of mustard processing. YMG is a mixture
of several polysaccharides containing two major water-soluble components, one an
acidic rhamnogalacturonan and the other β(1-4)-glucans with varying degrees of
ether substitution. 25
YMG exhibits some useful functional properties. Emulsifiant action has been
reported, with crude mucilage showing an emulsion capacity similar to that of
xanthan gum. 26 Dilute solutions of YMG show shear-thinning behavior, 27 a viscosity
decrease with increase in temperature, reasonable stability with changing ionic
concentration, and a minimum of shear thinning at pH 7. The rheology of YMG
shows synergistic effects with galactomannans. Mixtures of LBG and YBG give
large increases in viscosity, and YMG–LBG mixtures in the ratio 9:1 show gel-like
properties. 28 Synergy is also observed with guar and fenugreek galactomannans, but
the effect is strongest with LBG.
YMG can act as a useful complement to other hydrocolloids as a stabilizer and
has been tested in a salad cream, giving equivalent performance to that by commercial
xanthan-stabilized products. 29 YMG is not digested, acts as soluble dietary fiber,
and has shown some beneficial effects of reducing glycemic index when added to
the diet. 30