Agriculture Reference
In-Depth Information
nonstarch fl our lipids (in addition to lipid addi-
tives) that interact with fl our proteins during
dough mixing, with proven technical value in
baking processing.
which glycolipids are bound to the gliadin pro-
teins hydrophilically and to the glutenin proteins
hydrophobically. Simultaneous binding of polar
lipids to both protein groups may contribute
structurally to the gas-retaining complex in gluten
(Hoseney et al., 1970). Glycolipids may also likely
be involved within the starch-glycolipid-gluten
complex. It has been proposed that phospholipids
interact with lipid-binding proteins to form bio-
molecular layers, with protein chains bound to
the outer edges of a phospholipid leafl et array,
probably via salt-type linkages between acidic
groups of the phospholipids and the basic protein
groups (Marion et al., 2003). This model is
capable of providing gluten with the plasticity
necessary for optimum baking characteristics
(Marion et al., 2003).
Interaction with gluten proteins
Lipids become bound or associated with gluten
protein to form protein-lipid complexes during
dough mixing (Chung 1986). Gluten that has
been water-washed from fl our contains much
higher lipid content than fl our. The lipid in gluten
cannot be readily extracted using nonpolar sol-
vents. However, the association of lipids with
proteins in gluten often depends on the condi-
tions used to isolate the gliadin and glutenin frac-
tions. By dissolving gluten in dilute acetic acid,
then fractionating it with 70% ethanol, more
lipid, particularly polar lipids, are found in the
gliadin protein fraction than in the glutenin
protein fraction; but when gliadin and glutenin
are fractionated in acid media by pH precipita-
tion, more than 80% of gluten lipid is found to
be associated with the glutenin protein and very
little with the gliadin (Chung 1986).
Gluten is not composed of discrete molecules.
It is a water-insoluble aggregated network in
which protein-protein, lipid-lipid, and protein-
lipid interactions can occur (Frazier et al., 1981).
Therefore, physical techniques are more desirable
to probe these interactions for the whole gluten
system. These studies have shown that lipids are
retained with the gluten network in a fairly non-
specifi c way through a combination of forces,
involving the physical entrapment of lipids and
also by polar and/or ionic bonding between
protein and the surfaces of the lipid phases
(Marion et al., 1987).
Our study (McCann et al., 2008) suggests that
nonpolar lipids (primarily triglycerides), glyco-
lipids, and phospholipids have different interac-
tive mechanisms with gluten proteins. Nonpolar
lipids are likely embedded within the gluten
protein matrix as lipid vesicles, therefore provid-
ing a lubricating or plasticizing effect to gluten
and dough rheology. Glycolipids may be involved
in a gliadin-glycolipid-glutenin complex, in
The role of fl our lipids in baking
One way of elucidating the role of lipids in baking
is to remove the lipids from fl our and to reconsti-
tute the lipid fractions back to the defatted fl our
(MacRitchie and Gras 1973; MacRitchie 1981).
Fractions of polar and nonpolar lipid affect loaf
volume and crumb texture in opposite ways. Polar
lipids, such as phospholipids and glycolipids,
decrease the loaf volume until a threshold concen-
tration is attained. Above this concentration, the
loaf volume increases. These observations were
interpreted as competition between the surface-
active soluble proteins and polar lipids for the
gas-water interface, followed by the progressive
replacement of the interfaces by polar lipids (Gan
et al., 1995). On the contrary, increasing the non-
polar lipid content of triglycerides and free fatty
acids leads to a continuous decrease of bread loaf
volume, because these lipids provide a new inter-
face for surface-active components dispersed in
the aqueous phase of dough and are also capable
of destabilizing the interfacial protein fi lms. Tri-
glycerides present in the gluten matrix as vesicles
may interfere with protein-protein interaction or
complexation in the gluten matrix.
When the ratio of polar to nonpolar lipids is
increased, the minimum of the loaf volume versus
lipid content curve is shifted to lower lipid con-
