Biomedical Engineering Reference
In-Depth Information
Fig. 8.4
Staling mechanism of soft bakery products
major constituent in these products, the physical changes accompanying the starch
retrogradation is the main cause of staling (Barcenasa et al.
2003
; Karao
lu
2006a
).
Soft bakery products dries and hardens mainly due to starch retrogradation as well
as because of cross-linking between continuous protein matrix and starch granule
with hydrogen bonds (Novotni et al.
2011
).
In general, staling process is largely part of two different sub-processes. These
are the fi rming effect produced by moisture transfer from crumb to crust, and the
intrinsic fi rming of the cell wall material (i.e. starch re-crystallization during stor-
age) (Fig.
8.4
) (Pateras
2007
). In the later stages of staling, the mobility of water
decreases due to increase of re-association and re-crystallisation of amylopectin
(Curic et al.
2008
). Starch granules in their native form have a semi-crystalline
structure, which is composed of the polysaccharides (i.e. amylose and amylopectin)
(Crowther
2012
). When bakery products are baked in an oven, starch granules
absorb water, swell in size, and then transform from a crystalline to amorphous
form. This is referred to the “gelatinization” phenomenon. Immediately after the
baking process, the swollen starch granules in baked products transform from amor-
phous to a more crystalline form and these lose their elasticity causing the crumb
hard and brittle. This transformation is called starch retrogradation and is thought to
be the major cause of crumb fi rming on ageing, commonly referred to staling (Hug-
Iten et al.
1999
).
Staling of bakery products has been extensively investigated because of its
importance in determining product acceptability and shelf life. The staling process
can be controlled by maintaining appropriate product formulation, processing con-
ditions, packaging and storage. The crumb fi rming is related to starch-gluten inter-
actions of bakery products. The process of aging can be retarded by adding
anti-staling agents, such as fat, milk, whey, and enzymes. However, bakery products
rapidly lose freshness (texture and fl avour) (Karao
ğ
lu and Kotancılar
2006
; Cauvain
2004
). Emulsifi ers and similar agents have been used as anti-staling agents for
years; but they actually have a limited effect and these require special labelling
rules. However, new methods such as partial baking of the bakery products is an
effective way of delaying the staling process of the baked goods (Table
8.2
)
(Karao
ğ
lu
2006a
). Re-baking process applied to part-baked product eliminates
adverse changes in bakery products.
ğ
