This document discusses the causes of bread staling. It identifies the main causes as starch retrogradation, water migration and redistribution, protein-starch interaction, and gluten transformations. Starch retrogradation occurs as amylose and amylopectin realign themselves, causing the crumb to harden. Water migrates from the crumb to the crust, reducing moisture in the crumb and leading to firming. Protein and starch interact, shifting water from gluten to starch. The role of gluten transformations in staling is still uncertain. Understanding these staling mechanisms can help bakeries prevent staling and reduce losses from stale bread.

1. Causes of Bread Staling
Mwove, Johnson Kyalo,
M.Sc. Food Science
Egerton University
Dairy and Food Science and Technology Department
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Food Science Seminars 13th April 2014

2. INTRODUCTION
Bread staling is a complicated process that
involves loss of aroma, changes in mouth
feel, loss of crumb softness and development
of crumbliness.
It is a term which indicates decreasing
consumer acceptance of bakery products
caused by changes in crumb other than those
resulting from spoilage organisms
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3. INTRODUCTION
Bread staling is a complex phenomenon that
originates from multiple physico-chemical
events (amylopectin retrogradation, water loss
and redistribution and gluten-starch
interactions and gluten transformations) that
are not yet completely elucidated.
(Curti, et al, 2011)
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4. INTRODUCTION
It is usually characterized by
loss of aroma,
changes in mouth feel,
development of crumbliness.
toughening of the crust,
firming of the crumb,
loss of moisture and flavor,
loss in product freshness
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5. Theories explaining bread staling
The main causes of bread staling are thought
to be:
starch retrogradation
water migration and redistribution
Protein-starch interaction
Gluten transformations *
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6. Starch retrogradation
Retrogradation is a reaction that takes place in
gelatinized starch when the amylose and
amylopectin chains realign themselves causing
the dissolved starch difficult to re-dissolve.
Starch undergoes swelling or gelatinization
when heated in the presence of water
– Starch gelatinization
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7. Starch retrogradation
Starch paste consists of amylose and
amylopectin. Amylose has greater tendencies
to gelatinize faster than amylopectin.
Amylose thus retrogrades faster.
When cooling begins, starch reorganizes itself
to achieve the crystalline structure it had
before.
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8. Starch retrogradation
Due to this realignment, crumb firming
occurs.
When staling is measured as hardness
increase and increase in starch retrogradation,
it increases along the storage period.
(Barcenas and Rosell 2006)
Incorporation of water in the starch crystalline
structure occurs further reducing the moisture
content of the crumb.
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9. Water migration and Redistribution
The migration of water in cellular solid
foods during storage has been found to
cause loss of crispness.
Migration of water occurs within bread and
from bread to the environment causing
bread to firm.
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10. Water migration and Redistribution
When bread is stored with crust;
Water migrates from crumb to the crust
The crumb firms
Loss of crispiness
The crumb moisture content and water
activity decreased
Decrease in freezable water
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11. Water migration and Redistribution
When bread is stored without crust;
Moisture content remain relatively the same
No water migration occurs when crust is
absent
Less firming occurs
No change in total and freezable
water
(Baik & Chinachoti, 2000).
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12. Water migration and Redistribution
Decrease in crumb moisture is caused by
Incorporation of water into the starch crystalline
structure
Loss of water to the surrounding environment
Moisture migration from crumb to crust reduces
the level of plasticizing water of the biopolymer
networks and contributes to crumb firmness at
longer storage times.
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13. Water migration and Redistribution
Why the moisture migrates to the crust
from the crumb remains unexplained!
The crust undergoes retro gradation to a larger
extend than the crumb.
Increasing moisture content of bread does not
always result in softer breads (Piazza & Masi,
1995)
It is better to prevent bread staling by preventing
moisture loss from the bread than increasing the
moisture content of bread.
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14. Protein-starch interaction
Bread firmness is thought to result from glucan chains
of partially leached amylose and amylopectin attached
to swollen starch granules forming hydrogen bonds with
other starch granules and, to a smaller extent, with
gluten fibrils.
The distribution of water is shifted from gluten to
starch, thereby changing the nature of the gluten
network during starch retro gradation.
(Gray & Bemiller, 2003)
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15. Gluten transformation
Gluten is the composite of a gliadin and a glutenin,
which is conjoined with starch in the endosperm of
various grass-related grains.
There is considerable uncertainty about the role of
protein in bread staling.
One of the main problems with gluten-free breads is
their texture and their rapid staling.
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16. Gluten transformation
High protein breads shows lower extent of retro
gradation and hence staling.
Waxy wheat flour blends have been also found with
the ability to retard staling of breads.
Protein is thought to retarded bread staling by diluting
starch and hence reducing starch retrogradation.
Addition of bacterial protease to sourdough has been
found to increase bread firmness and staling
indicating that proteins actually are important in
retarding bread staling.
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17. Prevention of staling
Enzymes – Heat stable Alpha Amylases
Shortenings
Emulsifiers- Surface active agents
Reheating - Temperature 70-80 Degrees C
Packaging
Soy addition
Malting and Fermentation
Incorporation of high fiber flour
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18. CONCLUSION
Minimal gelatinization takes place in the oven
and thus minimal retrogradation would be
expected to occur in bread.
Water moves from the crumb to the crust
when the crust is present and it does not move
at all when the crust is removed.
The effect of gluten in bread staling needs
further clarification.
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19. CONCLUSION
Proofing- the final dough rise contributes to the
structure of the crumb and therefore it has some
contribution on bread staling.
Staling of baked products is always unacceptable to
the consumer
It adds losses to the bakery since stale bread is not
fit for sale.
For this reason, a solution to the bread staling
problem is of urgent importance.
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20. Thanks for listening
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