Retrogradation starch

Longer carbon chains can also be added, such as carboxyethyl groups, or carboxypropyl groups. Adding bulky functional components like carboxymethyl and carboxyethyl groups reduces the tendency of the starch to recrystallize. When the starch stays as a gel, a product is softer, and we refer to it as fresh. When the starch regains its crystalline form, the product becomes firmer, and we refer to it as stale. The technical term for this recrystallization is starch retrogradation. 

This recrystallisation releases water. This is probably why, although deep freezing prevents starch retrogradation, refrigeration at temperatures above zero causes bread to stale faster than storage at ambient temperature. 

Emulsifiers are used in a range of bakery products. Their use in bread is covered in Section 3.8.2. In general, emulsifiers can substitute for some egg in sponge cakes. Emulsifiers soften the crumb of baked products and retard staling by impeding starch retrogradation. 

These solve the shelf life problem by having a very low water activity aided by the quantity of dried fruit that they contain. The fat content and the low water activity inhibit starch retrogradation. 

The problem of starch retrogradation is tackled by using a starch complexing emulsifier. When all these problems have been attended to the shelf life can be measured in months rather than days. 

Starch retrogradation has been used to describe changes in physical behavior following gela-tinization. It is the process that occurs when starch molecules reassociate and form an ordered stmcture. Under favorable conditions, a crystalline order appears and physical phase separation occurs. 

DSC can also be used to determine starch retrogradation. After heating potato starch (30% (w/w)) to 180°C, samples are cooled to 5°C. Once the temperature reaches 5°C, the sample is immediately removed from the DSC and stored at low temperature. After a certain number of days, the sample pan is placed into the sample holder of the DSC, and heated from 5 to 180°C at 10°C /min. The instrument is calibrated using indium and an empty pan as a reference. The enthalpy (AH) of phase transitions is measured from the endotherm of DSC thermograms based on the mass of dry solid. Transition temperatures such as onset, peak, and completion temperature are also measured. 

Although starch oxidation was still deemed worthy of investigation due to its ability to deter aqueous starch retrogradation, no starch oxidizing agent approved for food use was apparently specific enough for the production of the desired dialdehyde... 

Figure 8.4 DSC thermal curves of aqueous suspensions ofwaxy maize starch (a, b, c) and resistant starch (retrograded amylose) (d).

Fig. 33.—Effect of lipid on starch retrogradation, measured as changes in the degree of gelatinization during the storage of cooked rice. Solid points, native rice open points, defatted rice solid squares, refatted rice. (Reprinted with permission from Y. Hibi, S. Kitamura, and T. Kuge, Cereal Chem., 67 (1990) 7-10.)...

Starch is a polysaccharide formed by two polymers of glucose linear amylose and branched amylopectin. The gelatinization process can be regarded as a fusion of fhe crystalline starch regions in the presence of enough wafer and heafing. Starch retrogradation is a recrystallization process that is controlled by diffusion and depends on solute mobility in the system. 

Differential scanning calorimetry Samples of gels (8 to 11 mg) were placed in hermetically sealed stainless steal pans and analyzed with a DSC QlOO (TA Instruments, New Castle, DE, USA). An empty pan was used as reference. Samples were heated at 10°C/min from -40 to 120°C. At least triplicate samples were analyzed for each gel. The endothermic melting peak around 0°C was taken as an evidence of ice melting. Endothermic peaks in the 50 to 70°C range were taken as evidence of starch retrogradation (stored samples). 

One practical effect of starch retrogradation is on bakery products recrystallization of amylopectin has a great role in staling of baked products during storage. As amylopectin... 

Perdon, A. A., T. J. Siebenmorgen, R. W. Buescher, and E. E. GUurr. 1999. Starch retrogradation and texture of cooked milled rice during storage. Journal of Pood Science 64 828-831. 

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