Biomedical Engineering Reference
In-Depth Information
the two isomers are 95:5 in favor of attachment at the terminal, alpha-position, but
at 200°C, the ratio changes to 82:18.
88
In diglycerides, the fatty acids can attach to
any two of the three positions.
Mono- and diglycerides can be solid or liquid materials depending on the nature
of fatty acids composing the molecule. Monoglycerides composed of mainly oleic
acid or unsaturated fatty acids are liquid and more sensitive to oxidation and deg-
radation while monoglycerides composed of saturated fatty acids are solid powders
or waxy materials. The melting point of the product depends on the origin, structure,
and composition of the fatty acids.
Since mono- and diglycerides are both hydrophilic (containing hydroxyl groups)
and lipophilic (containing fatty acids), they are partially soluble in both water and
fat. They are strongly adsorbed at the triglyceride/water interface and they readily
form a liquid crystal phase in association with water.
89
Hence they are excellent
emulsifiers. As in the case of other emulsifiers, MG are found at the O/W interface
with the polar groups (hydroxyls) of the molecule in the aqueous phase and the
nonpolar group (the fatty acid) in the lipid phase. In this manner, monoglycerides
act to reduce the interfacial tension and to stabilize emulsions.
90
Their lipophilic
character causes them to be excellent W/O emulsifiers, as in margarine.
91
The major uses of MG and DG are in bakery products, prepared cake mixes,
margarine, convenience foods, coffee whiteners, and frozen desserts. Normally they
are used along with a fat system, and frequently in conjunction with other emulsifiers.
MGs containing oleic acid are used as an emulsifier in ice cream. Those prepared
from lard, tallow, cottonseed, soybean, and peanut oils (usually partially hydroge-
nated) have been used as emulsifiers in cake and icing shortenings. Fully hydroge-
nated MG from meat fats and vegetable oils have been used as emulsifiers in yeast-
raised baked goods, cake shortenings, ice cream, confections, and many other food
products.
87
Compounds that contain esters of fatty acids and free hydroxylic or alcoholic
groups are used as emulsifiers in bakery products. Of these compounds, MG and
DG of saturated fatty acids and mostly those composed of stearic acids (MGS and
MDGS) are most frequently used because their functions are ideally suited to those
required for a shortening. To enhance MGS activity as an emulsifier, other com-
pounds and/or modified MG are added. These include sorbitan and polyoxyethylene
sorbitan esters of fatty acids, propylene glycol esterified with fatty acids, lecithin,
or lactylated, acetylated, and succinylated monoglycerides.
87
MGs and MDGs and
their modified forms greatly improve bakery products by functioning as dough
conditioners and strengtheners, and bread and crumb softeners. They also increase
the shelf life and softness, ensure good fat distribution, stabilize icing, and improve
slicing, volume, aeration, and moisture retention. In baked products and other cereal-
based products, the primary functions of emulsifiers are emulsification of fatty acid
components in bread, complexation of starch (amylose), strengthening of protein
(gluten/gluten interaction), and aeration improvement by reducing the surface ten-
sion of the aqueous phase in the batter. Emulsification is often the secondary func-
tion.
92-95
Complexation with GMS is essential for improving the shelf life of bread.
Starch present in the wheat granule will swell once water is added and as the mixture
is stirred amylose is released. After baking, once cooled and stored, the amylose
Search WWH ::
Custom Search