Factors That Affect the Rate of Staling During Storage
Generally, there are two types of bread staling which are crust staling and crumb staling. Crust staling is cause by the transfer of moisture from crumb to the crust, thus results in a firm and soft texture and is less undesirable than the crumb staling. The factors that may affect staling of bread during storage are storage temperature, processing, packaging, moisture migration, moisture redistribution between crumb and crust and moisture redistribution among components (Hui 2006).
For the first factor which is the storage temperature, bread staling will occur at a faster rate when it is stored at lower temperature between -1ºC to 21ºC whereas at high temperature between 32ºC to 43ºC, the role of starch crystallization will be less effective. However, at low temperature which is between -6.7ºC to 10ºC, the texture of the crumb tends to firm faster but in high temperature, which is above 35ºC, it will affect the colour, texture as well as the flavour of the bread. Thus, the optimum temperature for storage of bread is between 21ºC to 35ºC. Bread staling may affect starch recrystallization if it is being stored at maximal rate of 4ºC (Bread Staling 1996).
Processing is one of the factors that may affect the crumb softness through loaf volume. Particularly, fermentation and mixing that contribute to dough development for given flour will maximize the volume and crumb softness. Water absorption and baking procedures might alter the moisture levels of the crumb. As for packaging, it has been found that it can affect the crust texture, moisture changes and flavour of the bread. For instance, unwrapped bread tends to lose the moisture and flavour faster as it is being exposed to the environment, but it helps in retaining the crumb texture better. Whereas wrapped bread will remain softer and firmer especially when wrapped warm and taste better when wrapped cool, but the crust will softens faster (Bread Staling 1996).
On the other hand, moisture migration may be one of the factors that affect the staling of bread. Water is the main concern that causes changes in bread system which includes drying out, moisture equilibrium between the crumb and crust as well as the moisture distribution between and among bread components. Drying out of the bread does not have much correlation in bread staling, it just that it may speed up the reactions that lead to staling. There are inverse relationship between moisture content and rate of staling, even though it is found that the rate of starch retrogradation in bread will increase with the increase of moisture content. It has been reported that the moisture content of bread is optimal for amylopectin retrogradation and any addition of either monoglycerides or shortening will not alter the available moisture content (Gray & Bemiller 2003).
As for the crumb-crust redistribution moisture, when baked bread started to cool, the moisture gradient will formed in the loaf. The differences in vapour pressure between the internal region and the crust of the loaf causing the moisture to migrate from the crumb to the crust. After a period of time, the internal region will have lower moisture content compared to the external region of the loaf. Studies have found that bread that is stored with its crust will have significantly firmer texture than the bread stored without its crust. Besides that, bread that is stored with its crust will have more recrystallized amylopectin as a result from the loss of freezable water in the crumb of the bread which correlated with changes in the thermomechanical profile. By using Nuclear Magnetic Resonance (NMR) technique, it has been found that the water in the bread become less mobile as the staling process proceeds (Gray & Bemiller 2003).
The next factor is the moisture redistribution among components. Water acts as plasticizer that makes the bread components more flexible. Thus, as water being removed, the crumb firmness will increase. During staling, moisture was released from starch and taken up by gluten. Some studies claimed that it was the gluten that hardened as a result of moisture loss to starch. Free and bound water has been reported to be the factors that lead to the alteration of rate of staling in bread. By the helps of NMR and few studies being conducted by the experts, they had come into conclusion that starch taken up water from gluten upon aging of bread. When starch started to change to a more crystalline state, more water molecules become immobilized as they have been incorporated into the crystals structure (Hui 2006).
For the first factor which is the storage temperature, bread staling will occur at a faster rate when it is stored at lower temperature between -1ºC to 21ºC whereas at high temperature between 32ºC to 43ºC, the role of starch crystallization will be less effective. However, at low temperature which is between -6.7ºC to 10ºC, the texture of the crumb tends to firm faster but in high temperature, which is above 35ºC, it will affect the colour, texture as well as the flavour of the bread. Thus, the optimum temperature for storage of bread is between 21ºC to 35ºC. Bread staling may affect starch recrystallization if it is being stored at maximal rate of 4ºC (Bread Staling 1996).
Processing is one of the factors that may affect the crumb softness through loaf volume. Particularly, fermentation and mixing that contribute to dough development for given flour will maximize the volume and crumb softness. Water absorption and baking procedures might alter the moisture levels of the crumb. As for packaging, it has been found that it can affect the crust texture, moisture changes and flavour of the bread. For instance, unwrapped bread tends to lose the moisture and flavour faster as it is being exposed to the environment, but it helps in retaining the crumb texture better. Whereas wrapped bread will remain softer and firmer especially when wrapped warm and taste better when wrapped cool, but the crust will softens faster (Bread Staling 1996).
On the other hand, moisture migration may be one of the factors that affect the staling of bread. Water is the main concern that causes changes in bread system which includes drying out, moisture equilibrium between the crumb and crust as well as the moisture distribution between and among bread components. Drying out of the bread does not have much correlation in bread staling, it just that it may speed up the reactions that lead to staling. There are inverse relationship between moisture content and rate of staling, even though it is found that the rate of starch retrogradation in bread will increase with the increase of moisture content. It has been reported that the moisture content of bread is optimal for amylopectin retrogradation and any addition of either monoglycerides or shortening will not alter the available moisture content (Gray & Bemiller 2003).
As for the crumb-crust redistribution moisture, when baked bread started to cool, the moisture gradient will formed in the loaf. The differences in vapour pressure between the internal region and the crust of the loaf causing the moisture to migrate from the crumb to the crust. After a period of time, the internal region will have lower moisture content compared to the external region of the loaf. Studies have found that bread that is stored with its crust will have significantly firmer texture than the bread stored without its crust. Besides that, bread that is stored with its crust will have more recrystallized amylopectin as a result from the loss of freezable water in the crumb of the bread which correlated with changes in the thermomechanical profile. By using Nuclear Magnetic Resonance (NMR) technique, it has been found that the water in the bread become less mobile as the staling process proceeds (Gray & Bemiller 2003).
The next factor is the moisture redistribution among components. Water acts as plasticizer that makes the bread components more flexible. Thus, as water being removed, the crumb firmness will increase. During staling, moisture was released from starch and taken up by gluten. Some studies claimed that it was the gluten that hardened as a result of moisture loss to starch. Free and bound water has been reported to be the factors that lead to the alteration of rate of staling in bread. By the helps of NMR and few studies being conducted by the experts, they had come into conclusion that starch taken up water from gluten upon aging of bread. When starch started to change to a more crystalline state, more water molecules become immobilized as they have been incorporated into the crystals structure (Hui 2006).