STALING

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STALING
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Staling

• increase in crumb firmness
• reduction in crispness
• aroma loss

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Mechanisms

• retrogradation of starch
• amylopectin recrystallization
• interaction between gluten and starch
• partial drying
• glassy-rubbery transition
• moisture redistribution

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• Amylopectin partially crystalline
• after gelatinization
• retrogradation
• amylopectin recrystallization (slow)
• must be concentrated but also dilute to have
  enough mobility
• Amylose present in amorphous region

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• During storage
• T storage gt Tg
• due to increase in storage T
• due to decrease in Tg, water sorption
• critical moisture content (TTg)
• crystallization occur
• rate of crystallization T-Tg

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• Storage temperature
• Moisture content
• rate of crystallization at same T-Tg
• decrease with increase in moisture content
• type of starch, lipids, surfactants, sugar,
  enzymes, pentosans

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• highest rate of retrogradation
• 5 C
• gluten interacts with amylose and amylopectin
• gluten-rich crumbs stale slow
• during aging aw decreases as water moves from
  less-bound to more-bound state
• from amorphous to crystalline parts

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Piazza and Masi (1995)

• moisture movement from crumb to crust
• dehydration rate staling
• additives delay dehydration
• delay staling

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Baik and Chinachoti (2000)

• Crumb with crust
• aw0.954-0.961 first 3 days
• aw0.936 at day 14
• Crumb without crust
• no change in aw

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• Firmness
• both increased
• crumb with crust continously increased
• crumb without crust leveled off after 1 wk
• at constant moisture
• amylopectin recrystallization
• moisture loss
• moisture redistribution
• not only amylopectin recrystallization
• decrease in freezable water

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Hallberg and Chinachoti (2002)

• compared white bread with meal-ready-to-eat bread
• moisture permeable and hermetic package
• SWB after 3 mo became very firm
• MRE 3-15 mo soft, after 4-7 y very firm
• moisture loss
• glycerol
• changes in non-crystalline regions
• more amylopectin crystallization in MRE bread but
  longer time

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